hot-dip galvanized steel sheet and production method

专利摘要:
GALVANIZED STEEL SHEET BY HOT IMMERSION AND THE SAME PRODUCTION METHOD. The present invention provides a hot dip galvanized steel sheet which is excellent in coating wetting capacity and coating adhesion capacity even when the base steel plate contains Si and Mn and a method of producing it. The hot dip galvanized steel sheet according to the present invention includes a base steel sheet containing Si, Mn, and other predetermined components, and a hot dip galvanizing layer formed on at least one surface of the base steel sheet. In the base steel sheet, an HA value representing the average hardness in a surface layer ranging from the interface between the base steel sheet and the hot dip galvanizing layer up to 50 (?) M deep and a value of HB representing the average hardness in a deep portion varying from the interface to more than 50 (?) M in depth satisfy the following three relational expressions. 50 Lesser equal HA Lesser equal 500 ... (1) 50 Lesser equal HB Lesser equal 500 ... (2) 0.5 Lesser equal HA / HB Lesser equal 0.9 ... (3)
公开号:BR112015001809B1
申请号:R112015001809-2
申请日:2013-08-02
公开日:2020-11-10
发明作者:Soshi Fujita；Shintaro Yamanaka
申请人:Nippon Steel Corporation；
IPC主号:

专利说明:

Technical Field
[001] The present invention relates to a hot-dip galvanized steel sheet and a method of producing it, and, in more detail, it refers to an excellent hot-dip galvanized steel sheet in capacity wetting of the coating and adherence capacity of the coating and applicable as a product element in the automotive field, in the field of household appliances, or in the field of construction materials and a production method thereof. Background Technique
[002] As product elements in the automotive field, in the field of household appliances, or in the field of construction materials, steel sheets with treated surface are used, which are given rust prevention property. Among them, a hot-dip galvanized steel sheet is excellent at preventing rust and is inexpensive, so it is used expressively.
[003] Generally, this hot-dip galvanized steel sheet is produced by the following general method:
[004] Initially a thin steel plate obtained by performing a hot rolling treatment, a cold rolling treatment, and a heat treatment on a plate is prepared as a base steel plate (base metal). Second, in a pre-treatment step aimed at cleaning the surface of the base steel plate, degreasing and / or pickling is carried out, or the base steel plate is introduced in a preheating oven without carrying out the pre-treatment step, and so the oil on the surface of the base steel plate in burnt to be removed. Third, the base steel sheet is heated to a high temperature in a heating furnace (an annealing furnace) to be subjected to recrystallization annealing. Fourth, the base steel sheet obtained is immersed in a hot dip galvanizing bath, in order to be subjected to a hot dip galvanizing treatment. Incidentally, the base steel plate is cooled to a suitable coating temperature before immersion in a molten zinc bath.
[005] Here, the atmosphere of the heat treatment will be explained. The treatment atmosphere where the recrystallization described above is performed is adjusted to an Fe reducing atmosphere. This makes it possible to suppress the generation of Fe oxides and prevent or inhibit iron oxides from worsening the coating's wetting capacity and adhesion capacity. of the coating in the subsequent hot dip galvanizing treatment. In addition, the treatment atmosphere of the aforementioned hot dip galvanizing treatment is also adjusted to an Fe reducing atmosphere similar to the recrystallization annealing. Thus, hot-dip galvanized steel sheet can be produced continuously without being exposed to an oxidizing atmosphere such as air.
[006] Incidentally, the heating furnace used to perform the recrystallization annealing on a continuous hot dip galvanizing equipment that allows for the continuous production described above includes types such as a DFF (type of direct firing), a NOF (type non-oxidizing), a type of radiant tube that allows the atmosphere of the entire treatment in the oven to be exchanged into an Fe reducing atmosphere (a type of total reduction), and combinations of them. At the moment, due to the point of easy operation, the point at which the reception of the cylinder does not occur easily in the heating furnace, and the point at which a high-quality coated steel sheet can be produced at a lower cost, equipment Continuous hot dip galvanizing using a radiant tube heating furnace has become widely useful.
[007] By the way, in recent years, in the automotive field in particular, among hot-dip galvanized steel sheets, a hot-dip galvanized steel sheet in which elements such as Si and Mn are contained in a material of a base steel plate and thus the base steel plate is increased in strength, it has been used increasingly. This is to satisfy the demand to achieve both an increase in the resistance of a limb for the protection of passengers at the time of the collision and a decrease in the weight of an element for fuel efficiency in the automotive field.
[008] However, Si and Mn are easily oxidizable elements compared to Fe, so the problem is that the Si and Mn contained in the base steel plate are oxidized by heating for the annealing of recrystallization in the heating furnace of radiant tubes despite the fact that the treatment atmosphere is an atmosphere of reduction of Fe. Concretely, in the process of recrystallization annealing, Si and Mn that exist on the surface of the base steel plate are oxidized with a high probability, and in addition to that , Si and Mn thermally diffused are also oxidized in the vicinity of the base steel plate surface, resulting in the fact that Si and Mn oxides are gradually concentrated in a steel plate surface layer. Then, in the case where Si and Mn oxides are concentrated in the surface layer of the base steel plate, when the base steel plate is immersed in a molten zinc bath in the subsequent hot dip galvanizing treatment, the oxides of Si and Mn oxides exposed to the surface of the base steel plate prevent the molten zinc and the base steel plate from coming into contact with each other, and thus become the cause of the wettability of the coating worsening and become the cause inhibiting the coating from adhering to the base steel plate.
[009] As documents describing a technique for suppressing the concentration of Si and Mn oxides described above, those to be described below can be cited.
[0010] Patent Document 1 describes that, before the hot dip galvanizing treatment, an oxidation treatment is carried out on a base steel plate in such a way that the thickness of the oxide film to be formed on the surface becomes 400 to 10000 Â, and subsequently the Fe is reduced in an oven atmosphere containing hydrogen. In addition, Patent Document 2 describes that, before hot dip galvanizing treatment, a portion of the surface of a base steel plate is first oxidized, and subsequently an oxygen potential that determines the treatment atmosphere in an oven reduction ratio is adjusted, so that the reduction of Fe and the oxidation of Si inside the steel plate (internal oxidation) are both controlled.
[0011] The techniques described in these two documents are done focusing on the recrystallization annealing process. Here, when the Fe reduction time period (reduction time period) is very long, the removal of an Fe oxide film can be performed, but the concentration of Si oxides in the surface layer of the plate is caused of base steel, and furthermore, when the reduction time period is very short, the Fe oxide film remains on the surface portion of the base steel plate. So, realistically, when it is considered that the thickness of the oxide film formed on the surface of the base steel plate by the oxidation treatment is non-uniform, a problem is caused that the technique of adjusting the reduction time period described above just does not it is sufficient to improve the adhesion capacity of the coating. In addition, when the thickness of the Fe oxide film formed by the oxidation treatment is very thick, a theme is caused in which the oxides are peeled from the base steel sheet to bond to the surfaces of the cylinders arranged in the oven (receiving cylinder ). In this case, a problem is also caused that the essence of the oxides attached to the surfaces of the cylinders is transferred to the surface of the next steel sheet and thus the quality is impaired (appearance of flaws).
[0012] In addition, Patent Documents 3, 4, and 5 each describe a technique in which, with the purpose of solving the problems described above caused by the oxidation of Fe and suppression of the mentioned concentration of Si and Mn oxides previously, before the hot dip galvanizing treatment, during the recrystallization annealing in all heating furnaces of the radiant tube type, an oxygen potential that determines the treatment atmosphere is increased to a point where Si and Mn are internally oxidized.
[0013] Similarly, Patent Documents 6, 7, 8 and 9 each describe a technique for adjusting the treatment atmosphere used for a heating oven.
[0014] However, in the techniques described in Patent Documents 3 to 9, when the oxygen potential is increased too much, Si and Mn can be oxidized internally, but Fe is also oxidized, resulting in the fact that the same problems are caused than those described above. On the other hand, even when the oxygen potential is increased to the point that Fe is not oxidized, the internal oxidation of Si and Mn becomes insufficient, resulting in the fact that oxides of Si and Mn are concentrated in the surface layer of the base steel plate. Thus, each case causes a problem that the oxygen potential that determines the treatment atmosphere cannot be precisely adjusted. Therefore, by these techniques, a hot-dip galvanized steel sheet that has a uniform quality cannot be safely produced.
[0015] In addition, as another example of a technique for suppressing the concentration of oxides of Si and Mn, a technique of employing a means of also increasing the steps required for a general production method of hot dip galvanizing described can be cited. above. For example, Patent Document 10 describes a technique in which annealing is performed twice before hot dip galvanizing treatment. Such a technique is considered that when Si oxides formed on the surface of the base steel plate (substances concentrated on the surface) are pickled and removed after the first annealing is carried out, the formation of substances concentrated on the surface can be suppressed at the time of the second annealing. . However, when the Si concentration in the base steel plate is high, the substances concentrated on the surface cannot be removed sufficiently by blasting, resulting in the fact that a problem is caused by the coating's wetting capacity and its adhesion capacity. of the coating cannot be improved sufficiently. In addition, to remove the Si substances concentrated on the surface, equipment to perform annealing twice and equipment to perform pickling are again required, so that the problem is also raised that the cost of the equipment is increased, and thus the production cost is also increased.
[0016] In addition, as yet another example of the technique for suppressing the concentration of Si and Mn oxides described above, a technique can be cited in which before the coating step, Si and Mn are internally oxidized in a laminating step hot. For example, Patent Document 11 describes a technique in which when a galvanized steel sheet is produced in continuous hot-dip galvanizing equipment, the oxygen potential is adjusted in the hot rolling step, so as to internally oxidize the Si on a thin steel plate (the base steel plate). However, in such a technique, when the lamination of the base steel plate is carried out in a cold rolling step after the hot rolling step, an internal oxide layer is also rolled simultaneously and the dimension of the thickness of the internal oxide layer is decreased, resulting in the fact that, in the subsequent recrystallization annealing process, Si oxides are concentrated in a surface layer of the base steel plate. Therefore, the problem arises that even with this technique, the wetting capacity of the coating and the adhesion capacity of the coating cannot be improved sufficiently. In addition, in the art, Fe oxides are formed at the same time that Si is oxidized internally in the hot rolling stage, but, as described above, there is also a problem that the quality of the steel plate to be produced is impaired due to the peeling of Fe oxides.
[0017] Incidentally, hot dip galvanized steel sheet containing Si and Mn is not limited to the problems described above (problems explained using Patent Documents 1 to 11 as examples), and has a fundamental problem that working capacity (for example, ductility) of the base steel sheet is lower than that of a hot dip galvanized steel sheet that does not contain Si and Mn because the resistance (hardness) of the base steel sheet is increased. Here, when the ductility of the base steel sheet is low, even if the contact between the hot dip galvanizing layer and the base steel sheet is well done, for example, in the case where the work (for example, forming pressing) is performed on the hot-dip galvanized steel sheet, a fracture is caused in the base steel sheet itself or at an interface between the base steel sheet and the hot-dip galvanizing layer and thus the galvanizing layer by hot immersion it can be peeled from the base steel plate. That is, the hot dip galvanized steel sheet containing Si and Mn needs to improve the coating adhesion more than the hot dip galvanized steel sheet that does not contain Si and Mn. Prior art documents Patent Documents
[0018] Patent Document 1: Japanese Patent Application Open to Public Inspection No. 55-122865
[0019] Patent Document 2: Japanese Patent Application Open to Public Inspection No. 2001-323355
[0020] Patent Document 3: Japanese Patent Application Open to Public Inspection No. 2008-007842
[0021] Patent Document 4: Japanese Patent Application Open to Public Inspection No. 2001-279412
[0022] Patent Document 5: Japanese Patent Application Open to Public Inspection No. 2009-209 = 397
[0023] Patent Document 6: Japanese Patent Application Open to Public Inspection No. 2001-111670
[0024] Patent Document 7: Japanese Patent Application Open to Public Inspection No. 2005-060743
[0025] Patent Document 8: Japanese Patent Application Open to Public Inspection No. 2006-233333
[0026] Patent Document 9: International Publication Pamphlet No. WO 2013/047804
[0027] Patent Document 10: Japanese Patent Application Open to Public Inspection No. 2010-196083
[0028] Patent Document 11: Japanese Patent Application Open to Public Inspection No. 2000-309847 Description of the invention Problems to be solved by the invention
[0029] The main objective of the present invention is to provide a hot dip galvanized steel sheet which is excellent in coating wetting capacity and coating adhesion capacity even when the base steel plate contains Si and Mn, and a method production.
[0030] Here, the term "hot dip galvanized steel sheet" is a treated surface steel sheet provided with a coating layer (hereinafter referred to as "hot dip galvanizing layer") formed for undergoing a coating treatment using a melt containing zinc as its main component (to be referred to hereinafter as "hot dip galvanizing treatment").
[0031] Furthermore, the term "coating wetting capacity" means a property in which the coating in a molten state (molten zinc) tries to spread on a surface of a base steel plate (base metal) without being repelled by same. In greater detail, this wetting capacity of the coating can be evaluated by observing the state of the liquid-solid interface (contact angle), but in the present invention it is evaluated depending on whether the peeling of the coating has occurred to a point where the plate of hot-dip galvanized steel is conformed by pressing, and then the steel sheet obtained is evaluated as a non-coating defect (appearance failure, failure of rust prevention property, or the like). When appearance failure is caused by hot dip galvanized steel sheet conformed by pressing, for example, it is assessed to be "poor coating wetting capacity".
[0032] The term "coating adherence capacity" means a property in which the coating in a solidified state (a hot dip galvanizing layer) and a base steel plate (base metal) are in a state of adhesion between while they are in superficial contact with each other, or they try to maintain that state. In more detail, this ability to adhere the coating can be evaluated by observing the state of the solid-solid interface, but in the present invention it is evaluated depending on whether when the hot-dip galvanized steel sheet is formed by pressing using a metallic mold, the action in which part of the hot-dip galvanizing layer peeled from the steel sheet is transformed into powder to adhere to the surface of the metallic mold (which is called spraying) is recognized. When spraying is recognized, for example, the failure in appearance is caused by the next steel plate to be obtained by conformation by pressing, or the worsening ability of the metallic mold to worsen, in order to be assessed as "poor in coating adherence capacity ". Incidentally, the adhesion capacity of the coating can be assessed according to "Test methods for hot dip galvanized coatings" of Japanese Industrial Standard JIS H 0401: 2007 (corresponding to International Standard ISO 1460: 1992).
[0033] Incidentally, Those skilled in the art may understand other objectives of the present invention by referring to the description in this description with their own general technical knowledge. Objectives of providing a method for producing a hot-dip galvanized steel sheet with excellent coating wetting capacity and adherence capacity of the coating and providing a hot-dip galvanized steel plate having excellent workability and containing Si and Mn, for example, are also included within the scope of the present invention. Means for solving problems
[0034] The present inventors, to solve the problems described above, focused on an effect of, in the vicinity of an interface between the hot-dip galvanized layer and the base steel plate constituting a hot-dip galvanized steel plate, the hardness in the base steel plate in the wetting capacity of the coating and in the adhesion capacity of the coating and they performed careful exams, and as a result they found that even when the base steel plate contains Si and Mn, define the hardness of the plate base steel using predetermined parameters makes it possible to provide an excellent hot-dip galvanized steel sheet in working capacity. In addition, the present inventors focused on the conditions of production of such hot-dip galvanized steel sheet and carried out careful examinations, and as a result found that the conditions that the treatment atmospheres of a radiant tube heating furnace and an oven rinses supplied in equipment for the production of hot-dip galvanized steel sheets (particularly, partial pressure ratios of carbon dioxide and carbon monoxide to be supplied to these furnaces) must satisfy are defined, thus making it possible to provide a method for continuously producing hot-dip galvanized steel sheet with excellent coating wetting capacity and uniform coating quality.
[0035] That is, the essence of the present invention is as follows.
[0036] (A1) A hot dip galvanized steel plate including a base steel plate and a hot dip galvanizing layer formed on at least one surface of the base steel plate, on which the base steel plate contains , in% by mass, C: not less than 0.05% nor more than 0.50%, Si: not less than 0.1% nor more than 3.0%, Mn: not less than 0.5% nor more than 5.0%, P: not less than 0.001% nor more than 0.5%, S: not less than 0.001% nor more than 0.03%, Al: not less than 0.005% nor more than 1.0 %, and one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B, Ca and a rare earth element REM: not less than 0% nor more than 1% each , and the balance being made up of Fe and the inevitable impurities, and in the base steel plate, the HA value that represents the average hardness in the surface layer varying from the interface between the base steel plate and the dip galvanizing layer at hot to 50 pm deep and an Ha value that represents the average hardness in one per deep interaction ranging from the interface to more than 50 pm in depth satisfy all the relational expressions (1) to (3) below.

[0037] (A2) The hot-dip galvanized steel layer as per item (A1), in which Wc (A), WSÍ (A), and WMΠ (A) which represent the percentages of the contents of C, Si and Mn in% by mass in the surface layer of the base steel plate respectively, and WC (B), WSÍ (B), θ WMΠ (B) which represent the percentages of the contents of C, Si and Mn in% by mass in deep portion of the base steel plate respectively satisfy all the relational expressions (4) to (6) below.

[0038] (A3) The hot-dip galvanized steel sheet according to item (A1) or (A2) in which the base steel sheet contains one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B and a rare earth metal (REM) in no less than 0.0001% or more than 1% each.
[0039] (A4) The hot-dip galvanized steel sheet conforming to any of the items (A1) to (A3), in which the hot-dip galvanizing layer has a thickness in the range of not less than 1 pirn no more than 30 pm, and contains no less than 4 wt% nor more than 14 wt% Fe, not less than 0.1 wt% nor more than 1 wt% Al, and the balance being composed of Zn and the inevitable impurities.
[0040] (B1) A method for producing a hot dip galvanized steel sheet by performing a hot dip galvanizing treatment on a base steel sheet, in which the base steel sheet is obtained after suffering a linning step, a hot rolling step, a pickling step, a cold rolling step, an annealing step, and a rinsing and retention step, and contains, in mass%, C: not less than 0.05% or more than 0.50%, Si: not less than 0.1% nor more than 3.0%, Mn: not less than 0.5% or more than 5.0% , P: not less than 0,001% nor more than 0,5%, S: not less than 0,001% nor more than 0,03%, Al: not less than 0,005% nor more than 1,0%, and one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B and Ca, and a rare earth element REM: not less than 0% nor more than 1% each, and the balance being composed of Fe and the inevitable impurities, the annealing step and the rinse and retention step are performed in an eq Continuous hot dip galvanizing equipment equipped with a radiant tube type heating oven as a heating oven and as a rinsing oven, the annealing step is performed in order to satisfy the following conditions in the heating oven: heating: a To plate temperature [° C] representing the maximum temperature that, when the cold rolled steel sheet obtained after undergoing the cold rolling stage is heated in the heating furnace, the cold rolled steel sheet reaches in the range of no less than the temperature Ti [° C] nor greater than the temperature T2 [° C]; heating time period: The heating time period So [seconds] in the heating furnace is in the range of no less than 0 time period Si [seconds] nor longer than a time period S2 [seconds], and gas from atmosphere: a nitrogen atmosphere containing carbon dioxide and carbon monoxide in which log (POCO2 / PCO) where the logarithmic value of the partial pressure value of carbon dioxide divided by the partial pressure value of carbon monoxide in the heating furnace presents a value in the range of no less than -2 nor more than 1, here the temperatures Ti and T2 θ θs time periods Si and S2 are defined as follows: Ti: a temperature [° C] that satisfies the relational expression (7 ) then using WSÍ (B) and WMΠ (B) which represent the percentage contents of Si and Mn in% by mass in a deep portion ranging from the surface of the cold-rolled steel sheet to a depth of more than 50 pm respectively;
T2: a temperature [° C] that satisfies the relational expression (8) below using the temperature TACS [° C] which corresponds to the transformation point AC3 of the cold rolled steel sheet;
Si: a period of time [seconds] that satisfies the relational expression (9) below using WSÍ (B) [mass%] that represents the percentage content of Si and WMΠ (B) [mass%] that represents The percentage content of Mn in the deep portion of the cold-rolled steel sheet, and
S2: a period of time [seconds] that satisfies the relational expression (10) using WC (B) [mass%] that represents the percentage C content in the deep portion of the cold-rolled steel sheet,
the rinse and retention step is performed in order to satisfy the following rinse oven conditions: rinse and retention time period: the time period during which the cold rolled steel sheet is kept in the rinse oven is in the range of not less than 100 seconds or more than 600 seconds, and gas from the atmosphere: a nitrogen atmosphere containing carbon monoxide carbon dioxide in which the log value (PCO2 / PCO) in the rinsing oven is in the range -5 or more to less than -2, and in the coating step, the hot dip galvanizing layer containing not less than 4% by weight nor more than 14% by weight of Fe, not less than 0.1% by weight mass no more than 1% by mass of Al, and the balance being composed of Zn and the inevitable impurities is formed on the surface of the base steel plate so as to have a thickness of not less than 1 pm or more than 30 pm.
[0041] (B2) The method according to item (B1) in which, when performing the hot dip galvanizing treatment, the base steel sheet obtained after undergoing the rinsing and retention stage is immersed in a galvanizing bath by hot immersion containing not less than 0.05% by weight nor more than 0.20% by weight of Al, and then it is subjected to a bonding treatment in which heating is carried out to a heating temperature in the range of no less than 450 ° C or more than 560 ° C. Effect of the invention
[0042] According to the present invention, it is possible to provide a hot dip galvanized steel sheet which is excellent in coating wetting capacity and in coating adhesion capacity even when the base steel plate contains Si and Mn, and a method of producing it. Brief description of the drawings
[0043] FIG. 1 is a graph showing the relationship between the Vickers HA hardness on the surface portion of the base steel plate and the Vickers HB hardness on a deep portion of the hot-dip galvanized steel sheets produced by a steel plate production method hot dip galvanized according to the present invention, (Examples A1 to A72 and B1 to B36) and hot dip galvanized steel sheets produced by another production method (Comparative Examples C1 to C7, C11, C29 a C35, C38, C40 to C50, C52, C53 and C56);
[0044] FIG. 2 is a graph showing the relationship between the Vickers HA hardness in the surface portion of the base steel plate and the ratio of the Vickers HA hardness in the surface portion to the Vickers HB hardness in the deep (HA / HB) portion of the galvanized steel sheets hot-dip galvanized steel sheet production methods (Examples A1 to A72 and B1 to B36) and hot-dip galvanized steel sheets produced by another production method (Comparative Examples C1 to C56);
[0045] FIG. 3 is a graph showing the relationship between the ratio of the percentage of the C content in the surface portion to the percentage of the C content in the deep portion (WC (A) / WC (B)) and the value of the percentage ratio from the Si content in the surface portion of the base steel sheet to the percentage of Si content in the deep portion (Wsi (A) ZWsi (B)) of the galvanized steel sheets produced by the dip galvanized steel sheet production method hot according to the present invention (Examples A1 to A72 and B1 to B36);
[0046] FIG. 4 is a graph showing the relationship between the ratio value of the percentage of the C content in the surface portion of the base steel plate to the percentage of the C content in the deep portion (Wc (A) / Wc (B)) and the value of the ratio of the percentage of the Mn content of the base steel sheet to the percentage of the Mn content in the deep portion (WMΠ (A) / WMΠ (B)) of the hot-dip galvanized steel sheets produced by the production method of hot-dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36);
[0047] FIG. 5 is a graph showing the relationship between the thickness of a hot dip galvanizing layer [m] and the percentage of the Fe content in the hot dip galvanizing layer [mass%] of the galvanized steel sheets by immersion at hot produced by the production method of hot dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36);
[0048] FIG. 6 is a graph showing the relationship between the thickness of the hot dip galvanizing layer [m] and the percentage of the Al content in the hot dip galvanizing layer [mass%] of the hot dip galvanized steel sheets produced by the method of production of hot-dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36);
[0049] FIG. 7 is a graph showing the relationship between the value of the difference between the temperature of the To [° C] sheet which represents the maximum temperature that, when the base steel sheet for a hot dip galvanized steel sheet is heated in an oven heating method according to the production method of hot dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36) and another production method (Comparative Examples C1 to C8 and C17 to C24), the base steel sheet reaches and the temperature Ti [° C] associated with WSÍ (B) [mass%] which represents the percentage of Si content and WMΠ (B) [mass%] which represents the percentage of Si content Mn contained in the base steel plate (To a Ti) and the value of the difference between the temperature T2 [° C] associated with the temperature TAC3 [° C] corresponding to the transformation point AC3 of the base steel plate and the aforementioned plate temperature To [° C] (T2- To);
[0050] FIG. 8 is a graph showing the relationship between the value of the difference between the heating time period So [seconds] when the base steel plate for a hot dip galvanized steel plate is heated in the heating oven according to the method of production of hot-dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36) and another production method (Comparative Examples C11 to C24) and the time period Si (seconds) associated with WSÍ ( B) [% by mass] which represents the percentage of Si and WMΠ content (B) [% by mass] which represents the percentage of Mn content in the base steel plate (So - Si) and the value of the difference between the time period S2 [seconds] associated with WC (B) [% by mass] which represents the percentage of C content in the base steel plate and the heating period mentioned above So [seconds] (S2-So).
[0051] FIG. 9 is a graph showing the relationship between the logarithmic value of the partial pressure ratio of CO2 to CO in an atmosphere gas when the base steel plate for a hot dip galvanized steel plate is heated in the heating furnace and the value logarithmic ratio of the partial pressure of CO2 to CO in an atmosphere gas when it is rinsed and kept in the rinsing oven according to the production method of hot dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36) and another production method (Comparative Examples C9, C10 and C41 to C56);
[0052] FIG. 10 is a graph showing the relationship between the heating time period [seconds] when the base steel plate for a hot dip galvanized steel plate is heated in the heating furnace and the rinse and hold time period [seconds ] when it is rinsed and kept in the rinsing oven according to the production method of hot dip galvanized steel sheet according to the present invention (Examples A1 to A72 and B1 to B36) and another production method (Comparative Examples C17 to C49); and
[0053] FIG. 11 is a graph showing the relationship between the percentage of Al content [mass%] in a hot dip galvanizing bath when a hot dip galvanizing treatment is performed on the base steel sheet for a galvanized steel sheet by hot dip and the heating temperature [° C] when heating is performed to perform a bonding treatment after hot dip galvanizing treatment according to the hot dip galvanized steel sheet production method as the present invention (Examples A1 to A72 and B1 to B36). Mode for carrying out the invention
[0054] Hereinafter, modalities for implementing the present invention will be explained in detail.
[0055] A hot-dip galvanized steel sheet according to a first embodiment of the present invention includes a base steel sheet and a hot-dip galvanizing layer provided on at least one surface of the base steel sheet. In this modality, the base steel plate contains Si and Mn. In addition, the hot dip galvanizing layer is formed on the surface of the base steel sheet by a hot dip galvanizing treatment described later.
[0056] Subsequently, the components that make up the base steel sheet described above and its contents will be explained. Incidentally, in the present description, the percentage [%] used for the content is% by mass unless explained differently. C: 0.05 to 0.50%
[0057] Carbon (C) is a useful element to increase the strength of the base steel plate by stabilizing an austenite phase of the base steel plate, and therefore is an essential component of the base steel plate. Here, when the percentage of the C content is adjusted to less than 0.05%, the strength of the base steel sheet becomes insufficient, and when it is adjusted to more than 0.50%, on the other hand, the capacity of base steel sheet work gets worse. Thus, the percentage of the C content is in the range of not less than 0.05% or more than 0.50%, and is preferably in the range of not less than 0.10% or more than 0.40%. Incidentally, even if the base steel sheet is exposed to a decarburizing atmosphere condition defined in the present invention, the percentage of the C content is unlikely to change.
[0058] Si: 0.1 to 3.0%
[0059] Silicon (Si) is a useful element to improve the strength of the base steel plate by the concentration of the solute-solid C component dissolved in a ferrite phase of the base steel plate in an austenite phase to increase the resistance to softening in the tempering of steel, and therefore is one of the essential components of the base steel plate. Here when the percentage of Si content is adjusted to less than 0.1%, the strength of the base steel sheet becomes insufficient, and when it is adjusted to more than 3.0%, on the other hand, the working capacity the base steel sheet becomes worse and it is not possible to sufficiently improve the coating wetting capacity and the coating adhesion capacity of the hot dip galvanized steel sheet. Thus, the percentage of Si content is in the range of not less than 0.1% or more than 2.0%, and is preferably in the range of not less than 0.5% or more than 2.0%. Mn: 0.5 to 5.0%
[0060] Manganese (Mn) is a useful element to increase the strength of the base steel plate by increasing the hardening capacity of the base steel plate, and therefore is one of the essential components for the base steel plate. Here, when the percentage of the Mn content is adjusted to less than 0.5%, the strength of the base steel sheet becomes insufficient, and when it is adjusted to more than 5.0%, on the other hand, the capacity of The work of the base steel sheet becomes worse and it is not possible to sufficiently improve the wetting capacity of the coating and the adhesion capacity of the coating of the hot-dip galvanized steel sheet. Thus, the percentage of the Mn content is in the range of not less than 0.5% or more than 5.0%, and is preferably in the range of 1.0% or more to less than 3.0%. P: 0.001 to 0.5%
[0061] Phosphorus (P) is an element that contributes to the improvement in the strength of the base steel plate, and therefore is a component to be added to a raw material of the base steel plate according to the magnitude of the resistance required for the base steel plate. Here, when the percentage of the P content exceeds 0.5%, the material of the base steel plate deteriorates due to segregation at the grain edges. Thus, the upper limit of the percentage of P content is 0.5%. On the other hand, a considerable cost is necessary to adjust the percentage of the P content to less than 0.001% in the steel production stage, so that the lower limit of the percentage of the P content is 0.001%. S: 0.001 to 0.03%
[0062] Sulfur (S) is an impurity inevitably contained in the raw material of the base steel plate. The S component forms inclusions in the form of MnS plates in the cold rolled base steel plate to impair the working capacity of the base steel plate, so that the percentage of the S content is desirably low. However, excessively decreasing the percentage of the S content (desulfurization) causes an increase in cost in a steel production stage. Thus, the percentage of the S content is in the range of not less than 0.001% or more than 0.03%. Al: 0.005 to 1.0%
[0063] Aluminum (Al) is an element capable of fixing dissolved-solid N on the base steel plate as precipitated because it has a high affinity for nitrogen (N) on the base steel plate, and therefore is useful as a component to improve the working capacity of the base steel plate. On the other hand, when an excessive amount of Al is added to the raw material of the base steel plate, on the contrary, it deteriorates the working capacity of the base steel plate. Thus, the percentage of Al content is in the range of not less than 0.005% or more than 1.0%.
[0064] The component other than the components mentioned above (balance) of the base steel plate is composed of Fe and the inevitable impurities. As an example of unavoidable impurities, Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B, Ca and a rare earth metal (REM) can be mentioned. The percentage of the content of each of the unavoidable impurities is in the range of no less than 0% and no more than 1%. Incidentally, in the steel production stage, adjustments can also be made so that the percentage of the content of each of the unavoidable impurities contained in the base steel plate can fall within the range of no less than 0.0001% or more than 1 %. Thus, the effect that the wetting capacity of the coating and the adherence capacity of the hot-dip galvanized steel sheet can be improved is presented. Incidentally, it is thought that the reason why the adherence capacity of the coating is improved is that during a hot dip galvanizing treatment, these elements improve the reactivity of the molten zinc and the base steel plate. However, the mechanism for improving reactivity is not revealed. The effect described above cannot be presented sufficiently when the percentage of the content of each of the elements is less than 0.0001%, but the effect described above is saturated when the percentage of the content of each of the elements is greater than 1% .
[0065] Incidentally, in a modified example of this modality, one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, WB Ca and a rare earth element (REM) mentioned as unavoidable impurities in the mode described above, they can also be intentionally added to the raw material of the base steel plate so that each percentage of content can fall within the range of no less than 0.0001% or more than 1%. Thus, the same effect as described above can be seen. Incidentally, it is uneconomical to add each of the elements to the raw material of the base steel plate so that each percentage of content can become greater than 1%.
[0066] The production method of the base steel plate is not particularly limited, and may be a known production method. As an example of the known production method, starting the preparation of the raw material of the base steel plate, the casting, hot rolling, pickling and cold rolling are carried out in that order, and thus a steel plate can be produced. cold rolled (a thin steel sheet). The cold-rolled steel sheet obtained in this way has a predetermined thickness in the range of 0.1 mm or more to 3.5 mm, and preferably is in the range of not less than 0.4 mm or more than 3 mm. However, in the first embodiment of the present invention and in the modified example, the hardness of the base steel plate produced needs to be defined by the predetermined parameters as will be described in detail below. Therefore, when producing such a base steel plate having a hardness defined by the predetermined parameters, at least part of the production method to be described later as the second embodiment of the present invention is preferably employed.
[0067] Subsequently, the hardness of the base steel plate that must be produced in the first embodiment of the present invention and in the modified example will be explained in detail.
[0068] In this modality, roughly, the hardness of the surface layer of the base steel plate described above is less than that of an arbitrary location of a different portion from the surface layer (a deeper portion). That is, on the base steel plate, a treatment is performed so that the hardness of the surface layer can become less than that of the deep portion. Incidentally, an example of the treatment will be explained in the second embodiment of the present invention described below.
[0069] Concretely, in this modality, when the first hardness representing the average hardness of the surface layer varying from the interface between the base steel sheet and the hot dip galvanizing layer to a depth of 50 pm and the second hardness representing the medium hardness of the deep portion varying from the interface to more than 50 pm in depth are represented by the average Vickers hardnesses HA and HB respectively, all the relational expressions (1) to (3) below are satisfied.

[0070] Here, the average Vickers hardness (HA) is calculated by averaging the Vickers hardness measured at various measuring points on one side of the cross-section of the exposed base steel sheet obtained by removing the dip galvanizing layer at hot dip galvanized steel sheet. Here Vickers hardness is measured based on the "Vickers hardness test-Test method" from Japan Industrial Standard JIS Z 2244: 2009 (corresponding to the International Standard ISSO 6507-4: 2005). For measuring Vickers hardness, several measuring points are set on the side surface (cross section) of the base steel plate. Thus, the base steel plate is placed on a support table so that the lateral surface (cross section) of the base steel plate can be positioned vertically in the direction of movement of a Vickers hardness tester. However, in this modality, the load used for measuring Vickers hardness is adjusted to 10 gf (0.00102 N), as the depths of the measurement point (depth from the surface of the base steel plate) are used to 10 pm, 20 pm, 30 pm, 40 pm and 50 pm, and at each of the depths, 3 point measurements (N3 measurement) are performed, and thus the Vickers HA hardness is calculated. In addition, the measuring points are adjusted on the lateral surface (cross section) of the base steel plate, and each interval between the various measuring points is adjusted in the range of not less than 40 pm or more than 100 pm so that the measurement signal formed at one measurement point will not affect measurements at other measurement points. Incidentally, Vickers hardness measurement can also be performed before the hot dip galvanizing layer is supplied to the surface of the base steel plate. The average Vickers hardness (HB) is also calculated in the same way as the average Vickers hardness (HA), and in this modality, as depths of the measuring points, the range of 60 pm to a position a quarter of the thickness of the steel plate The base is used at a 10-pm step and at each depth, the 3-point measurement (N3 measurement) is performed, and thus the average Vickers HB hardness is calculated. Incidentally, in the different portion of the surface layer of the base steel plate (deep portion), the hardnesses can be said to be substantially fixed, so that the average value of the hardnesses measured at the various measuring points does not have to be calculated, and in that case if the hardness measured at an arbitrary measurement point in the deep portion is referred to as the average Vickers hardness described above (HB).
[0071] As described above, the values of HA and HB are each no less than 50 or more than 500 (see the relational expressions (1) and (2) described above). This is also reflected in the graph shown in FIG. 1. Here, from the results of the examples and the Comparative Examples whose results are described in the graph of FIG.1 (see also Table 1, Tables 2-1 to 2-4, Tables 3-1 to 3-2 and Tables 4- 1 to Table 4-2 provided in the Examples section to be described later), the following is clarified. When the values of HA and HB are each less than 50, the base steel plate is easily deformed locally due to contact with the metal mold during the pressing work and the hot dip galvanizing layer does not it can follow the deformation and peeling of the base steel sheet, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in both coating wetting capacity and coating adhesion capacity. In addition, when the values of HA and HB are each greater than 500, a fracture is caused in the base steel plate when pressing, and because of this a fracture is also caused in the plating layer by immersion at hot, and the base steel sheet is exposed, resulting in the fact that the hot-dip galvanized steel sheet is rated as being poor in both coating wetting capacity and coating adhesion capacity. Incidentally, more preferable values of the HA and HB values are each in the range of no less than 100 or more than 500 (see FIG. 1).
[0072] The HA / HB value is not less than 0.5 nor greater than 0.9 in this modality (see the relational expression (3) described above). This is also reflected in the graph shown in FIG. 2. In addition, the results of the corresponding examples (Examples and Comparative Examples) are clarified as follows. When the HA / HB value is less than 0.5, the surface layer (with a depth of 50 pm or less) of the base steel plate is easily deformed locally at the time of pressing work and the dip galvanizing layer Hot melting cannot follow the deformation and peeling of the base steel sheet, resulting in the fact that the hot-dip galvanized steel sheet is rated as being poor in both coating wetting capacity and coating adhesion capacity. In addition, when the HA / HB value is greater than 0.9, the deformation force and shear stress when pressing work are concentrated in the hot dip galvanizing layer, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in both coating wetting capacity and coating adhesion capacity. Incidentally, a more preferable HA / HB value is in the range of not less than 0.6 or more than 0.8 (see FIG. 2).
[0073] From the above, the relational expressions (1) to (3) of the base steel sheet are all satisfied, and thus the hot-dip galvanized steel sheet can be made excellent also in working capacity in that particular modality , although the base steel sheet contains Si and Mn in order to have increased resistance (hardness), the hot-dip galvanized steel sheet can have the effects described above.
[0074] Furthermore, the difference in hardness between the deep portion and the surface layer of the base steel sheet described above can also be expressed by the difference in the percentage of the content of the components contained in the base steel sheet. In the case where the formation of the surface layer of the base steel plate is carried out using a heating oven and a rinsing oven, for example, when attention is focused on Si and Mn and the atmosphere of the treatment in the furnaces is a decarburizing atmosphere, this modality is also expressed as follows. Incidentally, it goes without saying that the base steel sheet is defined by both the difference in hardness and the difference in the percentage of component content, thus making it possible to supply a hot-dip galvanized steel sheet that has uniform quality.
[0075] Wc (A), WSÍ (A) and WMΠ (A) representing the percentages of the contents of C, Si and Mn in mass% in the surface layer of the base steel plate respectively and WC (B), WSÍ ( B> and WMΠ (B) representing the percentages of the contents of C, Si and Mn in% by mass in the deep portion of the base steel plate, respectively, satisfy all the relational expressions (4) to (6) below.

[0076] Here, the measurements of WC <A), WSÍ (A) and WMΠ (A) are performed by performing the analysis in the direction of depth with the surface of the base steel plate being approximately the starting point. Concretely, the surface of the hot-dip galvanized steel sheet is analyzed by XPS (X-ray photoelectronic spectroscopy) while it is micropulverized at 10 pm intervals in this modality, Wc (A), WSÍ (A) and WMΠ (A) mean mean values of the analysis values of the respective components (the percentage of the content of C, the percentage of the content of the simple element Si, and the percentage of the content of the simple element Mn) in the range of the position where Zn is not detected substantially at 50 pm depth. Similarly, WC (B), WSÍ (B) and WMΠ (B) mean, mean values of the analysis values, the analysis values being in the deepest position that where Zn is not substantially detected, of the respective components (the percentage of the content of C, the percentage of the content of the simple element Si, and the percentage of the content of the simple element Mn) in the range of 100 pm to 200 pm in depth.
[0077] Relational expressions (4) to (6) are also reflected in the graphs shown in FIG. 3 and in FIG. 4. In addition, from the results of the corresponding examples (Examples and Comparative Examples), the following is clarified. When the values of WC (A) / WC (B), WSÍ (A) / WSÍ (B) and WMn (A) / WMn (B) are. each, no less than 0.1 nor more than 0.5, such hot-dip galvanized steel sheet is rated as being excellent in both the wetting capacity of the coating and the adhesion capacity of the coating. On the other hand, when the values of these ratios are each less than 0.1, C, Si and Mn dissolved-solids in the base steel plate are segregated in the direction of depth within the base steel plate and the concentration distribution is generated, the hardness and working capacity (ductility) of the base steel plate vary greatly and, due to the variations, the base steel plate is deformed locally at the time of pressing work and the coating is easily peeled from the plate base steel, resulting in the fact that such hot-dip galvanized steel sheet is assessed to be poor in coating wetting capacity and coating adhesion capacity. When the values of these ratios are each greater than 0.5, C, Si and Mn dissolved - solids in the base steel sheet, inhibit the reaction at the interface between the base steel sheet and the hot dip galvanizing layer, and furthermore due to the hardness of the base steel plate being uniform, the deformation force and shear stress when the pressing work is concentrated on the hot dip galvanizing layer, resulting in the fact that such steel plate is galvanized by hot dipping is rated as poor in coating wetting capacity and in coating adhesion capacity. More preferably, the WC (A) / WC (B), WSÍ (A) / WSÍ (B) and WMn (A) / WMn (B) values are each in the range of no less than 0.15 nor more than 0.4 (see FIG. 3 and FIG. 4).
[0078] Furthermore, in a more preferable aspect of this modality, the hot-dip galvanizing layer of the hot-dip galvanized steel sheet has a thickness in the range of no less than 1 pm and no more than 30 pm. In addition, the hot dip galvanizing layer contains no less than 4% by weight nor more than 14% by weight of Fe and not less than 0.1% by weight nor more than 1% by weight of Al, and contains a balance being composed of Zn and the inevitable impurities. Satisfying these conditions, such hot-dip galvanized steel sheet is rated as being more excellent in wetting capacity of the coating and in adherence capacity of the coating. This is reflected in the graphs shown in FIG. 5 and in FIG. 6. In addition, from the results of the corresponding examples (Examples and Comparative Examples), the following is clarified.
[0079] When the thickness of the hot dip galvanizing layer is less than 1 pm, the rust prevention property of the hot dip galvanized steel sheet becomes insufficient, and also the uniform adhesion of the coating to the surface of the sheet base steel becomes difficult and defects in the non-coating of hot-dip galvanized steel sheet are caused. That is, a problem of worsening the wetting capacity of the coating is caused. When the thickness of the hot dip galvanized steel sheet is greater than 30 pm, the effect of improving the corrosion resistance is saturated and is uneconomical, and also, inside the hot dip galvanizing layer, the stress increase, resulting in the fact that, on the contrary, the adhesion capacity of the coating becomes worse. Incidentally, in this embodiment, the thickness of the hot dip galvanizing layer is calculated in a way that a region having a size of 100 pm x 100 pm in a cross section of the hot dip galvanizing layer is observed by a SEM ( scanning electron microscope), the thickness of the hot dip galvanized layer is measured by N = 5, and the values of the measurement results obtained are averaged.
[0080] Furthermore, when the percentage of Fe content in the hot dip galvanizing layer is less than 4%, the reactivity of the hot dip galvanizing layer and the base steel plate is poor, resulting in the fact that that such hot-dip galvanized steel sheet is assessed to be poor in coating wetting capacity and in coating adhesion capacity. On the other hand, when the percentage of Fe content is greater than 14%, at the interface between the galvanizing layer and the base steel plate, a r phase or a Ti phase of the Fe-Zn hard alloy is formed in large quantities, resulting in in the fact that such hot-dip galvanized steel sheet is assessed to be poor in coating wetting capacity and in coating adhesion capacity.
[0081] Furthermore, when the percentage of the Al content of the hot dip galvanizing layer is less than 0.1, it becomes impossible to sufficiently exhibit an effect that the sliding ability of the coating can be improved by containing Al in the coating, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in the coating's wetting capacity and in the coating's adhesion capacity. On the other hand, when the percentage of Al content is greater than 1%, the hot-dip galvanizing layer becomes hard, resulting in the fact that such hot-dip galvanized steel sheet is rated as being low in capacity of wetting of the coating and in adherence capacity of the coating.
[0082] Incidentally, the percentage of the Fe content and the percentage of the Al content in the hot dip galvanizing layer are calculated, for example, as follows. A sample having a size of 30 mm x 30 mm cut from the hot-dip galvanized steel sheet is immersed in a 5% aqueous hydrochloric acid solution to which 0.02% by volume of an inhibitor (IBIT700A produced by ASASHI Chemical Corp. Ltd.) is added, so that only the coating layer is dissolved. Subsequently, the solution obtained is analyzed by an ICP (an emission spectrochemical analyzer), and from this analysis it results that the mass of Fe, the mass of Zn, and the mass of Al are discovered. Then, the mass of Fe is divided by (mass of Fe + the mass of Zn + the mass of Al) and is multiplied by 100, and thus the percentage of Fe content is calculated. In addition, the mass of Al is divided by (mass of Fe + mass of Zn + mass of Al) and is multiplied by 100, and thus the percentage of Al content is calculated.
[0083] Next, the method of producing a hot-dip galvanized steel sheet according to the second embodiment of the present invention will be explained.
[0084] In this second modality, the hot-dip galvanized steel sheet is produced by performing a hot-dip galvanizing treatment on a base steel sheet containing basically Si and Mn. More specifically, the production method according to this modality includes at least the following steps.
[0085] Annealing step: an annealing step of carrying out an annealing treatment by heating the base steel plate mentioned above in the presence of a first mixture of gases containing carbon monoxide and carbon dioxide in a heating furnace.
[0086] Rinsing and retention stage: a rinsing and retention stage to retain the base steel plate having performed the aforementioned annealing treatment at a fixed temperature in the presence of a second mixture of gases containing carbon monoxide and dioxide carbon in a rinsing oven connected to the heating oven mentioned above; and
[0087] Coating step: a coating step of performing the hot dip galvanizing treatment on the base steel plate obtained after undergoing the aforementioned rinsing and retention step.
[0088] Additionally, in the production method according to this modality, a production method of the base steel plate, components of the base steel plate and their percentages of contents, a production equipment, heating furnace conditions in the annealing stage, rinse oven conditions in the rinse and retention stage, treatment conditions in the coating stage, and the like, are adjusted as follows.
[0089] • Production method of the base steel plate and components of the base steel plate and their percentages of contents.
[0090] The base steel plate contains the components explained in the first modality and in the example basically modified. Concretely, the base steel sheet is obtained after undergoing a casting step, a hot rolling step, a pickling step, a cold rolling step, the annealing step described above, and the rinsing and retention step described above, and contains, in mass%, C: not less than 0.05% nor more than 0.50%, Si: not less than 0.1% nor more than 3.0%, Mn: not less than 0 , 5% not more than 5.0% P: not less than 0.001% nor more than 0.5% S: not less than 0.001% nor more than 0.03% Al: not less than 0.005% nor more than 1, 0%, and one or two or more elements selected from Ti, Nb, Cr., Mo, Ni, Cu, Zr, V, W, B, Ca and a metal element rare earth REM: not less than 0% nor more than 1% each, and the balance being made up of Fe and the inevitable impurities. • Production equipment
[0091] As a production equipment, a continuous hot dip galvanizing equipment explained in the background column is used. That is, the annealing step and the rinse and retention step are performed in a continuous hot dip galvanizing equipment equipped with a radiant tube type heating oven such as a heating oven and a rinsing oven. Thus, the base steel sheet (a cold rolled steel sheet) can be passed through the heating furnace and the rinsing furnace without being exposed to an oxidizing atmosphere such as air. • Heating oven conditions in the annealing stage
[0092] The annealing step is performed in order to satisfy the following conditions of the heating oven.
[0093] Heating temperature: a temperature of the To [° C] sheet representing the maximum temperature that, when the cold-rolled steel sheet obtained after undergoing the cold rolling step is heated in the heating furnace, the steel sheet reaches in the range of no less than the temperature Ti [° C] nor greater than the temperature T2 [° C].
[0094] Heating time period: the heating time period So [seconds] in the heating oven is in the range of no less than the time period Si [seconds] nor more than the time period S2 [seconds], and
[0095] Atmospheric gas: an atmosphere of nitrogen containing carbon dioxide and carbon monoxide in which log (PCO2 / PCO) being the logarithmic value of a value, in the heating furnace, of the partial pressure value of divided carbon dioxide the value of the partial pressure of the carbon monoxide presents a value in the range of no less than -2 nor more than 1.
[0096] Here, the Ti and T2 temperatures and the Si and S2 time periods described above are defined as follows. Ti: a temperature [° C] that satisfies the relational expression (7) below using WSÍ (B) and WMΠ (B) to represent the percentages of Si and Mn contents in% by mass in a deep portion ranging from the surface of the cold rolled steel sheet to more than 50 pm in depth respectively.
T2: a temperature [° C] that satisfies the relational expression (8) below using the temperature TAC3 [° C] corresponding to the transformation point AC3 of the cold rolled steel sheet.
Si: a period of time [seconds] that satisfies the relational expression (9) below using WSÍ (B) [mass%] representing the percentage of Si and WMΠ content (B) [mass%] representing 0 percentage of Mn content in the deep portion of the cold-rolled steel plate; and
S2: a period of time [seconds] that satisfies the relational expression (10) below using WC (B) [mass%] representing the percentage of the C content in the deep portion of the cold rolled steel sheet
• Heating oven conditions in the rinsing and retention stage
[0097] The rinsing and retention step is performed in order to satisfy the conditions of the rinsing oven below.
[0098] Rinse and hold time period: a period of time during which the cold-rolled steel sheet is kept in the rinse oven is in the range of not less than 100 seconds or more than 600 seconds, and
[0099] Atmospheric gas: a nitrogen atmosphere containing carbon dioxide and carbon monoxide in which the log value (PCO2 / PCO) in the rinsing oven is in the range of -5 or more to less than -2. • Treatment conditions for the coating step
[00100] In the coating step, the hot dip galvanizing layer containing not less than 4% by mass nor more than 14% by mass of Fe, not less than 0.1% by mass nor more than 1% by mass of Al, and the balance being composed of Zn and the inevitable impurities is formed on the surface of the base steel plate so as to have a thickness of not less than 1 pm and not more than 30 pm.
[00101] Subsequently, the respective conditions described above are explained in more detail. • Regarding the relational expression (7)
[00102] As expressed in the relational expression (7), the temperature Ti is a function that uses the percentages of the Si and Mn contents as variables, and here the percentages of the contents are the percentages of the Si and Mn contents in the portion depth of the base steel plate (incidentally values of these percentages of contents are substantially equal to those of the percentages of Si and Mn contents obtained before the surface layer was formed on the base steel plate respectively). From the graph shown in FIG. 7, the types of elements (Si and Mn), the number of elements, the percentages of the contents of the respective elements, etc., a coefficient (weighing) that must be added to the percentage of the content of each of the elements (a variable of the right side of the relational expression (7)) can be determined. Incidentally, when the base steel plate also contains Cr and / or B as an easily oxidizable element in addition to Si and Mn, variable terms or a variable term in relation to the percentages of the contents or the percentage of the content of the elements or element can be provided in a relational expression equivalent to the relational expression (7), and on the other hand, considering several types of easily oxidizable elements as a type of easily oxidizable element, a single necessary variable term can also be provided in the relational expression. Incidentally, for the production of the hot-dip galvanized steel sheet explained in the first embodiment, the temperature of the To sheet is determined so that it falls within the range shown as a full part in the graph of FIG. 7. As above, while the temperature To [° C] is in the range of no less than Ti [° C] nor more than T2 [° C] and the heating time period So [seconds] is in the range of no less than Si [seconds] or more than S2 [seconds], improvements in the coating's wetting capacity and in the coating's adhesion capacity can be expected. • Regarding the relational expression (8)
[00103] As expressed in the relational expression (8), the temperature T2 is a function of the temperature TAC3 which corresponds to the transformation point AC3. So, as is found in relation to FIG. 7, the temperature T2 must be a temperature equal to or greater than the temperature of the To plate. A constant term on the right side of the relational expression (8) is determined experimentally or empirically, for example. One of the reasons that the T2 temperature is expressed as a function of the TAC3 temperature is conceivably because the transformation to an austenite phase from a ferrous phase in the base steel plate and around the AC3 transformation point and increases in diffusion speeds of C, Si and Mn dissolved-solids in the base steel plate are affected. Incidentally, a constant term shown on the right side of the relational expression (8) is not limited to "+ 40", but when the temperature T2 is expressed by the relational expression (8), a good result can be obtained. • Regarding the temperature of To steel
[00104] So that both the value of (To -Ti) and the value of (T2 - To) shown in FIG. 7 can become 0 or more, the temperature value of the To [° C] sheet which represents the maximum temperature that the cold rolled steel sheet reaches must be in the range of no less than Ti nor more than T2. Here, when the temperature of the To [° C] plate is less than Ti ° C, the internal oxidation reaction of Si and Mn does not progress sufficiently, and furthermore, dissolved C, Si and Mn-solids in the steel plate inhibit the reaction at the interface between the base steel sheet and the hot-dip galvanizing layer, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in wetting capacity of the coating and in adherence capacity the coating. On the other hand, when the temperature of the To [° C] plate is higher than T2 ° C, the internal oxidation reaction of Si and Mn progresses excessively to cause an intercrystalline fracture caused by the internal oxides to occur at the edges of the layer grains surface of the base steel plate, and also the carbon in the surface layer of the base steel plate oxidizes excessively to be released from the base steel plate and the hardness of the base steel plate decreases significantly, resulting in the fact that such a plate hot dip galvanized steel is rated as poor in coating wetting capacity and in coating adhesion capacity. A more preferable value for the To plate temperature is in the range of not less than (Ti + 50) ° C nor more than (T2 - 20) ° C.
[00105] The rate of temperature increase when heating in the heating oven is not particularly limited, but when it is very low, the productivity of the base steel plate or the hot-dip galvanized steel plate becomes worse, when it is very high, on the other hand the cost of maintaining heating equipment is required. Thus, the rate of temperature increase is preferably selected from the range of not less than 0.5 ° C / s or more than 20 ° C / s.
[00106] The temperature of the plate when the base steel plate is introduced into the heating furnace is not particularly limited, but when it is too high, the base steel plate is oxidized and the coating's wetting capacity and The coating's adhesion capacity becomes worse, and when it is very low, on the other hand, a cooling cost is required. Thus, the temperature of the plate is preferably in the range of not less than 0 ° C or more than 100 ° C. • Regarding relational expressions (9) and (10)
[00107] As expressed in the relational expression (9), the time period S1 is a function that uses the percentages of the contents of Si and Mn as variables, and also the time period S2 is, as expressed in the relational expression (10) , a function that uses 0 percent C content as a variable. In this modality, coefficients (weighing) of the variables in these functions are determined experimentally or empirically, for example. When the relational expression (9) and the relational expression (10) are satisfied, a good result can be obtained. • Regarding the heating time So [seconds] in the heating oven.
[00108] So that both the value of (So - Si) and the value of (S2 - So) shown in FIG. 8 become 0 or more, the value of the heating time period So [seconds] in the heating oven must be in the range of no less than Si nor more than S2. Here, when the heating period So [seconds] is less than Si seconds, the internal oxidation reaction of Si and Mn does not progress sufficiently, and furthermore C, Si and Mn dissolved-solids in the base steel plate inhibit the reaction at the interface between the base steel sheet and the hot-dip galvanizing layer, resulting in the fact that such hot-dip galvanized steel sheet is assessed as being poor in wetting capacity of the coating and in adherence capacity of the coating. On the other hand, when the heating time period [seconds] is greater than S2 seconds, the internal oxidation reaction of Si and Mn progresses excessively to cause an intercrystalline fracture caused by internal oxides to occur at the grain edges of the surface of the base steel sheet, and also the carbon in the surface layer of the base steel sheet oxidizes excessively to be released from the base steel sheet and the hardness of the base steel sheet decreases significantly, resulting in the fact that such steel sheet hot dip galvanized is rated as poor in coating wetting capacity and in coating adhesion capacity. A more preferable value for the heating time period So is in the range of no less than (Si + 50) seconds or more than (S2 - 50) seconds. • Regarding the atmosphere gas in the annealing stage
[00109] In this modality, under a nitrogen gas from an atmosphere of reduction of Fe, log (PCO2 / PCO) where the logarithmic value of a value in the heating furnace, the value of the partial pressure of carbon dioxide divided by the value of the pressure partial carbon monoxide is adjusted to have a value in the range of no less than - 2 nor more than 1. This is also reflected in FIG. 9. In addition, from the results of the corresponding examples (Examples and Comparative Examples), the following is clarified. When the log value (PCO2 / PCO) in the heating furnace is less than -2, the internal oxidation reaction of Si and Mn does not progress sufficiently, and also dissolved-solid C, Si and Mn in the base steel plate do not react and remain on the base steel sheet and these remaining elements inhibit the reaction at the interface between the base steel sheet and the hot dip galvanizing layer after the subsequent hot dip galvanizing treatment, resulting in the fact that such hot-dip galvanized steel sheet is assessed to be poor in coating wetting capacity and in coating adhesion capacity. When the log value (PCO2 / PCO) in the heating furnace is greater than 1, the internal oxidation reaction of Si and Mn progresses excessively to cause an intercrystalline fracture caused by internal oxides to occur at the grain edges of the surface layer of the base steel sheet, and also the carbon in the surface layer of the base steel sheet oxidizes excessively to be released from the base steel sheet and the hardness of the base steel sheet decreases significantly, resulting in the fact that such a galvanized steel sheet by hot immersion it is evaluated as being poor in coating wetting capacity and in coating adhesion capacity. Incidentally,. a preferable log value (PCO2 / PCO) in the heating furnace is in the range of no less than -1.5 nor more than 0.5.
[00110] In this modality, using the nitrogen atmosphere containing carbon dioxide and carbon monoxide, the partial pressure of carbon monoxide in the atmosphere is adjusted, so that it is possible to suppress excessive occurrences of release (decarburization) caused by the oxidation reaction of dissolved-solid C in the base steel plate. Incidentally, as long as the condition that the log value (PCO2 / PCO) in the heating furnace is in the range of no less than -2 nor more than 1 is satisfied, the gas in the atmosphere may also contain at least one between hydrogen, water vapor, oxygen, and the inevitable impurities, and also, instead of nitrogen, another inert gas can be used. However, when the atmosphere gas contains hydrogen, the hydrogen concentration is adjusted to be in the range of no less than 1% by volume or more than 20% by volume. Therefore, the coating wetting capacity and the coating adhesion capacity of a hot-dip galvanized steel sheet that can be obtained can be made excellent. On the other hand, when the hydrogen concentration is less than 1% by volume, it becomes difficult to adjust the hydrogen concentration industrially, and also when the hydrogen concentration is greater than 20% by volume, the base steel plate becomes fragile by hydrogen, resulting in the fact that a hot dip galvanized steel sheet that can be obtained is evaluated as being poor in adhesion and wetting of the coating.
[00111] A method for adjusting the partial pressure ratio of carbon dioxide and carbon monoxide in the heating furnace is not particularly limited, but because of the ease of adjustment, a mixture of carbon dioxide and monoxide gas of carbon that are previously set to a fixed partial pressure ratio is preferably supplied in the furnace containing the nitrogen atmosphere. The flow rate of the gas mixture is most preferably determined taking into account at least one parameter of volume and gas flow in the furnace, and the surface area of the base steel plate to be treated in the furnace. Incidentally, as a method of adjusting the partial pressure ratio, a second method in which the furnace is filled with a nitrogen atmosphere containing carbon monoxide and then carbon dioxide is supplied to the furnace at a predetermined flow rate, or a third method in which the furnace is filled with a nitrogen atmosphere containing carbon dioxide and then carbon monoxide is supplied to the furnace at a predetermined flow rate, it can also be employed. In terms of preventing the explosion of carbon monoxide in the oven and intoxication by carbon monoxide in an out-of-oven working environment, it is industrially preferred to employ the second method described above. Incidentally, one of the methods described above is also employed for a method of adjusting the partial pressure ratio of carbon dioxide and carbon monoxide in the rinsing furnace.
[00112] In addition, the carbon dioxide to be supplied to the oven can be a commercially available carbon dioxide gas, it can be carbon dioxide generated by the complete burning of a substance selected from a mixed CO and H2 gas, a hydro gas - carbide such as CH4 or C2H6, a hydrocarbon gas such as gasoline or light oil, alcohols such as CH2OH or C2H2OH, a commercially available organic solvent, and a mixture thereof. In addition, the carbon monoxide to be supplied in the furnace can be a commercially generated carbon monoxide gas generated by mixing the carbon dioxide generated by the method described above with hydrogen. Incidentally, the water or water vapor generated when carbon dioxide or carbon monoxide is generated can be absorbed by a moisture absorber such as silica gel or calcium chloride, can be discharged using a flushing equipment. , or they can also be brought into contact with the coke obtained by heating carbon dioxide. • Regarding the retention time period in the rinse and retention step
[00113] In this mode, the rinse and hold time period in the rinse and hold step to be performed in the rinse oven is in the range of no less than 100 seconds or more than 600 seconds. When the rinse and retention time is less than 100 seconds, the recrystallization of the base steel plate does not progress sufficiently, and thus the strength and ductility of the base steel plate to be obtained after treatment decreases, and when the plate hot-dip galvanized steel sheet is pressed, a fracture is caused in the base steel sheet, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in coating wetting capacity and in adhesion capacity the coating. On the other hand, when the rinse and retention time is longer than 600 seconds, C, Si and Mn dissolved-solids in the base steel plate are diffused to the surface layer of the base steel plate that is formed by heating to inhibit the reaction at the interface between the base steel sheet and the hot-dip galvanizing layer, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in coating wetting capacity and in coating adhesion.
[00114] The treatment temperature in the rinsing oven is preferably set to the same temperature as the temperature of the To plate, which represents the maximum final temperature of the plate in the heating furnace. Incidentally, the treatment temperature is allowed to vary between ± 20 ° C industrially. • Regarding atmosphere gas in the rinsing and retention stage
[00115] In this mode, log (PCO2 / PCO) in the rinsing oven is adjusted to present a value that falls within the range of -5 or more to less than -2. This is also reflected in FIG. 9. In addition, from the results of the corresponding examples (Examples and Comparative Examples), the following is clarified. When the log value (PCO2 / PCO) in the heating furnace is less than -5, part of the Si and Mn that are oxidized internally is reduced, and thus C ,. Si and Mn dissolved-solids in the surface layer of the base steel sheet are increased in quantity, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in coating wetting capacity and in adhesion capacity the coating. On the other hand, when the log value (PCO2 / PCO) in the rinse furnace becomes -2 or more, the internal oxidation reaction of Si and Mn progresses excessively to cause an intercrystalline fracture caused by internal oxides to occur at the edges of the grains from the base layer of the base steel plate, and also the carbon in the surface layer of the base steel plate oxidizes excessively to be released from the base steel plate and the hardness of the base steel plate decreases significantly, resulting in the fact that such hot-dip galvanized steel sheet is assessed to be poor in coating wetting capacity and in coating adhesion capacity.
[00116] Incidentally, after performing the annealing step in the heating oven and the rinsing and retention step in the rinsing oven, and before executing the coating step, other treatment steps can also be performed. As such a treatment step, at least one step selected from a slow cooling step, a quick cooling step, an aging step, a second cooling step, a quick water cooling step, and a reheat step is performed. Similarly, after performing the coating step, other treatments can also be performed. • Coating step
[00117] Furthermore, the bath temperature of a hot dip galvanizing bath is preferably 440 ° C or more and less than 550 ° C. When the bath temperature is below 440 ° C, there is a possibility that the molten zinc will solidify in the bath, so this temperature is inadequate, and when it exceeds 550 ° C, the evaporation of the molten zinc is difficult on the bath surface, and thus in terms of operating cost and also in terms of the connection of the vaporized zinc to the interior of the oven, operational problems are caused. • Treatment conditions at the coating stage
[00118] The treatment conditions in the coating step will be explained.
[00119] Schematically, the components of the hot dip galvanizing layer and the percentages of their contents are defined, and the thickness of the hot dip galvanizing layer is defined. In this modality, as previously explained, the hot dip galvanizing layer is defined to contain not less than 4% by mass nor more than 14% by mass of Fe and not less than 0.1% by mass or more than 1% by mass of Al and contains a balance made up of Zn and the inevitable impurities, and the thickness of the hot dip galvanizing layer formed on the surface of the base steel plate is set to fall within the range of no less than 1 pm nor more than 30 pm.
[00120] In a preferable aspect of this modality, the concentration of Al in a melt in the hot dip galvanizing bath to be used in the coating step is adjusted to be in the range of not less than 0.05% or more than 0.20%. Thus, it is possible to produce a hot-dip galvanized steel sheet with excellent coating wetting capacity and coating adhesion. This is also reflected in FIG. 11. In addition, from the results of the corresponding examples (Examples and Comparative Examples), the following is clarified. When the concentration of Al becomes less than 0.05%, a Ç phase is formed in large quantities, resulting in the fact that such hot-dip galvanized steel sheet is evaluated as being poor in adhesion capacity of the coating. On the other hand, when the concentration of Al becomes greater than 0.2%, the amount of Al oxidized inside the hot dip galvanizing bath or on the hot dip galvanizing bath increases and the reactivity of the dip galvanizing hot and base steel sheet becomes worse, resulting in the fact that such hot-dip galvanized steel sheet is rated as being poor in coating wetting capacity and in coating adhesion capacity.
[00121] In addition, in another preferable aspect of this modality, after performing the annealing step in the heating oven and the rinsing and retention step in the rinsing oven, and before performing the hot dip galvanizing treatment, cooling the base steel plate is performed, and the temperature maintenance is performed according to the need. Furthermore, in this respect, after carrying out the hot dip galvanizing treatment, a bonding treatment is carried out.
[00122] During the bonding treatment described above, the heating temperature when heating is in the range of not less than 450 ° C nor more than 560 ° C. Thus, the hot dip galvanized steel sheet that can be obtained can be made excellent in coating wetting capacity and in coating adhesion capacity. The range of this heating temperature is also shown in FIG. 11. In addition, in addition to the results of the corresponding examples (Examples and Comparative Examples), the following is clarified. When the heating temperature of the bonding treatment is less than 440 ° C, the bonding reaction does not progress sufficiently, so that a hot-dip galvanized steel sheet that can be obtained is evaluated as being poor in wetting capacity. coating and the coating's adhesion capacity. On the other hand, when the heating temperature of the bonding treatment is greater than 560 ° C, due to the super-bonding, the Tou phase or the Ti phase of hard and brittle Zn-Fe alloy is formed in large quantities in an iron base interface , the coating's adhesion capacity becomes worse or deteriorates, and also Fe carbide is formed, and thus the balance between strength and ductility of the base steel plate also becomes worse. This is incidentally caused even if the base steel plate is a DP steel or a TRIP steel. Thus, even if the heating temperature is very high, the hot-dip galvanized steel sheet that can be obtained is evaluated as being poor in the wetting capacity of the coating and in the adhesion capacity of the coating. Example
[00123] Hereinafter, examples according to the present invention (the examples and comparative examples) will be explained concretely.
[00124] Cold rolled steel sheets obtained after undergoing normal casting, hot rolling, pickling, and cold rolling and having a thickness of 1 mm were prepared as sample materials 1 to 72 (see Table 1). In these sample materials, an annealing treatment and a hot dip galvanizing treatment were carried out in a continuous hot dip galvanizing equipment equipped with a radiant tube type heating furnace. The radiant tube type heating furnace was used, so that the handle on the cylinder is not easily provoked, and productivity is also good. The TAC3 temperature corresponding to an AC3 point being the transformation point in Table 1 was calculated using an expression for calculating the transformation temperature provided on the Welding Technology Information Center network page of Japan Welding Engineering Society (http: // www -it.jwes.or.jp/weld_simulator/cal1 .jsp). Table 1 Composition of cold rolled steel sheet



[00125] Tables 2-1 to 4-2 below show the treatment conditions in the heating oven and the rinsing oven and the logarithmic value log (PCO2 / PCO) of a partial pressure value of the divided carbon dioxide partial pressure of carbon monoxide. Comparative examples are shown in Table 4-1 and Table 4-2. Incidentally, the treatment atmosphere in the furnaces was adjusted to a nitrogen gas containing carbon dioxide and carbon monoxide. Carbon dioxide and carbon monoxide were supplied to the oven as a mixed gas. Table 2-1 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)


Table 2-2 Production conditions, analysis results, and results of the evaluation of the coating's wetting capacity and the coating's adhesion capacity (examples)


Table 2-3 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)






Table 2-4 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)









Table 3-1 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)



Table 3-2 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)



Table 4-1 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (examples)





Table 4-2 Production conditions, analysis results, and results of the evaluation of the wetting capacity of the coating and the adhesion capacity of the coating (comparative examples)






[00126] After treatment in the rinsing oven, the sample materials underwent a common slow cooling step, rapid cooling step, an aging step, a second cooling step and were immersed in a hot dip galvanizing bath. The conditions of the hot dip galvanizing bath and the connecting oven are also shown in Tables 2- 1 to 4-2. Each thickness of the hot dip galvanizing layers was adjusted by washing with nitrogen gas. The wetting capacity of the coating and the adherence capacity of the coating of the hot-dip galvanized steel sheets obtained were evaluated. The results of the assessment are also shown in Tables 2-1 to 4-2.
[00127] Of the hot-dip galvanized steel sheets obtained, the hardnesses Vickers HA and HB and WC <A), WSÍ (A), WMΠ (A), WC (B), WSÍ (B) and VVMΠ (B) were discovered by the methods previously described. In addition, of the hot dip galvanizing layers, the thicknesses, the percentages of Fe contents, and the percentages of Al contents were also discovered by the methods previously described. The respective results are shown in Tables 2 to 4.
[00128] The adhesion capacity of the coating was measured by a spray test, and the case of a peeled width of the hot dip galvanizing layer greater than 2 mm was assessed as rejection (x) due to the poor adhesion, the case of the peeled width being 2 mm or less and greater than 0.5 mm was assessed as passable (o) because the adhesion was good, and the case of the peeled width being 0.5 mm or less was assessed as passable (©) because the grip was extremely good. The spray test is a method of inspecting the adhesion capacity, in which, for a hot-dip galvanized steel sheet, a Sellotape (trademark) is applied, the tape surface is folded at 90 ° and is folded comes back, and then the tape is removed, and the stripped width made at that time is measured.
[00129] Regarding the coating's wetting capacity, after the coating's adhesion capacity was measured by the spray test, a coating surface having a size of 200 pm x 200 pm in the measured adhesion portion was subjected to EPMA mapping Zn and Fe, and the case of the area ratio of a location where there is no exposed Zn and Fe to be no less than 20% or more than 100% was assessed as rejection (x) because the wetting capacity was poor, the case of the area ratio being 5% or more and less than 20% was assessed as passable (o) because the wetting capacity was good, and the case in which the area ratio was less than 5% was assessed as passable (®) because the wetting capacity was extremely good.
[00130] The results of examining the coating wetting capacity and the coating adherence capacity of the examples of the present invention and the comparative examples were classified with points, in which ® was considered as 2 points, o was considered as 1 point ex it was considered as 0 point. Then the sum of points of the coating's wetting capacity and points of the coating's adhesion capacity was adjusted to a total of points. In relation to the total evaluation, the evaluation of the wetting capacity of the coating was o or ®, the evaluation of the adhesion capacity of the coating was o or ®, and the total of points was 2 points or more (2 points to 4 points) , which was considered passable. Levels A1 to A72, B1 to B72 and C1 to C72 in Tables 2-1 to 3-2 which are examples of the present invention have been found to be excellent in coating wetting capacity and in coating adhesion capacity compared to Levels D1 to D56 in Tables 3-1 to 4-2 which are comparative examples. Industrial Applicability
[00131] Hot dip galvanized steel sheet according to the present invention is excellent in coating wetting capacity and in coating adhesion capacity, so as to be usable as a product member in an automotive field, an appliance field household appliances, or a field of building material, for example.

权利要求:
Claims (6)
[0001]
1. Hot-dip galvanized steel sheet, characterized by the fact that it includes a base steel sheet and a hot-dip galvanizing layer formed on at least one surface of the base steel sheet, on which the sheet base steel contains, in% by weight, C: not less than 0.05% or more than 0.50%, Si: not less than 0.1% nor more than 3.0%, Mn: not less than 0, 5% not more than 5.0%, P: not less than 0.001% nor more than 0.5%, S: not less than 0.001% nor more than 0.03%, Al: not less than 0.005% nor more than 1.0%, and one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B, Ca and a REM rare earth element: 0% to no more than 1 % each, and the balance being made up of Fe and the inevitable impurities, and on the base steel plate, the HA value that represents the average Vickers hardness in a surface layer varying from the interface between the base steel plate and the layer hot dip galvanizing to a depth of 50 pm and an HB value that represents the medium Vickers hardness in a deep portion ranging from the interface to more than 50 pm in depth satisfies all the relational expressions (1) to (3) below.
[0002]
2. Hot-dip galvanized steel sheet according to claim 1, characterized by the fact that Wc (A), WSÍ (A), and WMΠ (A) representing the percentages of the contents of C, Si and Mn in% by mass in the surface layer of the base steel sheet respectively and WC (B), WSÍ (B), θ WMΠ (B) representing the percentages of the contents of C, Si and Mn in% by mass in the deep portion of the sheet base steel respectively satisfy all relational expressions (4) to (6) below.
[0003]
3. Hot-dip galvanized steel sheet according to claim 1 or 2, characterized by the fact that the base steel sheet contains one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B, Ca and a REM rare earth element of not less than 0.0001% or more than 1% each.
[0004]
4. Hot-dip galvanized steel sheet according to any of claims 1 to 3, characterized in that the hot-dip galvanizing layer has a thickness in the range of no less than 1 pm nor more than 30 pm , and contains no less than 4 wt% nor more than 14 wt% Fe, no less than 0.1 wt% nor more than 1 wt% Al, and the balance being composed of Zn and the inevitable impurities .
[0005]
5. Method for producing hot-dip galvanized steel sheet, as defined in claim 1, by performing a hot-dip galvanizing treatment on the base steel sheet, characterized by the fact that the base steel sheet is obtained after undergoing a stripping step, a hot rolling step, a stripping step, a cold rolling step, an annealing step, and a rinsing and retention step, and contains, in mass%, C : not less than 0.05% or more than 0.50%, Si: not less than 0.1% nor more than 3.0%, Mn: not less than 0.5% or more than 5.0%, P: not less than 0.001% or more than 0.5%, S: not less than 0.001% nor more than 0.03%, Al: not less than 0.005% or more than 1.0%, and one or two or more elements selected from Ti, Nb, Cr, Mo, Ni, Cu, Zr, V, W, B, Ca and a rare earth element REM: 0% to no more than 1% each, and the balance being composed of Fe and the inevitable impurities, the annealing step and the rinsing and retention step executed in a continuous hot dip galvanizing equipment equipped with a radiant tube type heating oven as a heating oven and as a rinsing oven, the annealing step is performed in order to satisfy the following conditions of the heating oven : heating temperature: a temperature of the To plate [° C] representing the maximum temperature that, when the cold rolled steel sheet obtained after undergoing the cold rolling step is heated in a heating oven, the rolled steel sheet cold is in the range of no less than a Ti temperature [° C] nor more than a T2 temperature [° C]; heating time period: a heating time period So [seconds] in the heating oven is in the range of no less than a time period Si [seconds] nor more than a time period S2 [seconds]; and atmosphere gas: a nitrogen atmosphere containing carbon dioxide and carbon monoxide in which log (PCO2 / PCO) being the logarithmic value of a value, in the heating furnace, of the value of the partial pressure of carbon dioxide divided by the value of the partial pressure of the carbon monoxide has a value in the range of no less than -2 nor more than 1, here the temperatures Ti and T2 and the time periods Si and S2 are defined as follows: Ti: a temperature [° C ] that satisfies the relational expression (7) using WSÍ (B) and WMn (B) to represent the percentages of Si and Mn contents in% by mass in a deep portion varying from the surface of the cold rolled steel sheet up to more than 50 pm in depth respectively.
[0006]
6. Method according to claim 5, characterized by the fact that during the execution of the hot dip galvanizing treatment, the base steel sheet obtained after undergoing the rinsing and retention step is immersed in a galvanizing bath by hot dip containing no less than 0.05% by mass and no more than 0.20% by mass of Al, and then undergoes a bonding treatment in which heating is carried out to a heating temperature in the range of no less than 450 ° C or more than 560 ° C.

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US20150225829A1|2015-08-13|

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JPWO2014021452A1|2016-07-21|

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法律状态:
2018-03-06| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|

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2018-03-13| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|

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2018-03-20| B06I| Technical and formal requirements: publication cancelled|Free format text: ANULADA A PUBLICACAO CODIGO 6.6.1 NA RPI NO 2462 DE 13/03/2018 POR TER SIDO INDEVIDA. |

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2019-09-10| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

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2019-10-08| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|

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2020-06-09| B09A| Decision: intention to grant|

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2020-11-10| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 02/08/2013, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2012-172739|2012-08-03|

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JP2012172739|2012-08-03|

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PCT/JP2013/071004|WO2014021452A1|2012-08-03|2013-08-02|Galvanized steel sheet and manufacturing method therefor|

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