aluminum coated steel sheet and method for hot pressing aluminum coated steel sheet

专利摘要:
ALUMINUM-COATED STEEL SHEET, METHOD FOR HOT PRESSING ALUMINUM-COATED STEEL SHEET, AND AUTOMOTIVE PIECE. The present invention relates to an Al coated steel sheet which includes: a steel sheet; a layer of Al coating that is formed on one or both surfaces of the steel sheet and contains at least 85% or more of Al by weight%; and a surface coating layer that is laminated to the surface of the Al coating layer and contains ZnO and one or more lubricity-improving compounds.
公开号:BR112014024344B1
申请号:R112014024344-1
申请日:2013-04-15
公开日:2020-12-22
发明作者:Jun Maki；Masao Kurosaki；Kazuhisa Kusumi；Shintaro Yamanaka
申请人:Nippon Steel Corporation；
IPC主号:

专利说明:

Technical Field of the Invention
[001] The present invention relates to a steel plate coated with Al, a method for hot pressing the steel plate coated with Al, and an automotive part.
[002] Priority is claimed on Japanese Patent Application No. 2012-095014, registered on April 18, 2012 and on Japanese Patent Application No. 2012-100266, registered on April 25, 2012, whose contents are incorporated here for reference. Relative Technique
[003] In recent years there has been an increase in demand for cuts in the consumption of chemical fuels to protect the environment and prevent global warming, and these demands have had several effects on the production industry. For example, even the automobile, an indispensable means of transport in daily life and activities, is no exception, and improved fuel efficiency and the like is required by reducing the weight of the vehicle chassis and others means. In the case of automobiles, however, merely reducing the weight of the vehicle chassis is not acceptable from the point of view of product quality, and adequate safety must also be guaranteed.
[004] The components of an automobile are largely made of steel, particularly a steel plate, and reducing the weight of the steel plate is important for reducing the weight of the vehicle chassis. As already pointed out, however, the mere reduction in the weight of the steel sheet is not acceptable since the mechanical resistance of the steel sheet has to be guaranteed. Such demands for sheet steel are not limited to the automobile production industry, but are also applied similarly to several other production industries.
[005] Research and development were therefore conducted in relation to the steel plate which, by improving the mechanical strength of the steel plate, is capable of maintaining or increasing the mechanical resistance, even when made thinner than the steel plate. steel used so far.
[006] Generally, a material having high mechanical resistance tends to deteriorate in the capacity of fixing the shape, in the folding and other formations, so that the work itself becomes difficult in the case of forming into a complicated shape. One available means to overcome this problem of forming capacity is the so-called "hot pressing method" (also referred to as hot stamping method, hot pressing method, mold cooling method, or press hardening).
[007] In the hot pressing method, the material to be formed is heated once to a high temperature, softened, pressed, and then cooled. Since the hot pressing method softens the material by heating it once to a high temperature, the material can be easily pressed, while, in addition, the mechanical strength of the material can be increased by tempering through cooling after conformation. The pressing method therefore makes it possible to obtain a shaped product that at the same time achieves a satisfactory shape-fixing capacity and high mechanical resistance.
[008] However, when the hot pressing method is applied to a steel plate, heating to a high temperature of, for example, 800 ° C or more, oxidizes iron and the like on the surface, producing so scale (oxide). Consequently, a process of removing the scale (peeling process) is therefore necessary to conduct the hot pressing afterwards, which decreases productivity. In addition, in the case of a limb that requires corrosion resistance, it is necessary to be resistant to corrosion or to coat the surface of the limb with metal after work, which requires a surface cleaning process and a cleaning process. surface treatment and also decreases productivity.
[009] As a method to suppress such a decrease in productivity, a method of pre-providing a coating on the steel plate is used. Generally, various materials such as organic materials are used as material for coating steel sheet. Among these materials, a steel sheet having a zinc-based (Zn) coating that provides the steel sheet with a sacrificial protection effect is widely used for automotive steel sheets and the like, from the standpoint of anti-corrosion performance and steel plate production technology.
[0010] However, the heating temperature (700 ° C to 1000 ° C) in hot pressing is higher than the decomposition temperatures of organic materials or the melting points of metallic materials such as Zn-based material , and a coating layer on the surface is melted and evaporated during heating. Thus, the surface properties deteriorate significantly in some cases.
[0011] Consequently, like a steel plate that is hot pressed, for example, a steel plate having an aluminum-based metallic coating (Al), which has a higher melting point than that of a material of organic coating or a metallic coating based on Zn, that is, the so-called Al coated steel sheet is desirably used.
[0012] A metallic coating based on Al of the steel plate prevents scale from being generated on the surface of the steel plate and improves productivity by making flaking or another similar process unnecessary. In addition, the Al-based metallic coating has a corrosion resistance effect and thus, the post-paint corrosion resistance is improved.
[0013] Patent Document 1 describes a method that performs hot pressing using an Al coated steel plate, obtained by coating a steel plate having a predetermined component composition with an Al-based metal coating.
[0014] However, when the steel sheet is coated with an Al-based metal, depending on the heating conditions before hot pressing, the Al-based metal coating melts, and is changed to an Al- Fe by combining iron (Fe), which diffuses from the steel sheet, and aluminum, and the Al-Fe compound (hereinafter also referred to as an "Al-Fe alloy layer") is laminated to the surface of the steel sheet in some cases. Since the Al-Fe alloy layer is hard, the Al-Fe alloy layer is brought into contact with a mold, and thus process scratches can be generated on the surface of the steel sheet during pressing in some cases. .
[0015] The surface of the Al-Fe alloy layer is, by nature, relatively slip resistant and low in lubricity. In addition, the Al-Fe alloy layer is hard and thus relatively susceptible to fracture, so that the forming capacity may decrease due to fracture, spraying or the like of the coating layer. of the Al-Fe alloy exfoliated from the Al-Fe alloy layer adheres to the mold, the quality of the product conformed by pressing is degraded. In addition, when the surface of the Al-Fe alloy is heavily scratched and the Al-Fe alloy powder adheres to the mold, the quality of the product formed by pressing is degraded.
[0016] Therefore, it is necessary to remove the Al-Fe alloy dust that adheres to the mold during repair, which reduces productivity and increases costs.
[0017] In addition, since the Al-Fe compound is low in reactivity in phosphate treatment, a coating (a phosphate coating) is not formed in chemical conversion, which is an electrocoat pretreatment. The Al-Fe alloy layer has satisfactory coating adhesion even without the formation of the chemical conversion coating, and while the amount of Al-Fe alloy layer deposition is sufficient, the post-paint corrosion resistance also becomes satisfactory. However, when the amount of deposition of the Al-Fe alloy layer is increased, the previously mentioned mold adherence is caused.
[0018] As described above, adhesion to the mold is sometimes caused by exfoliation of the Al-Fe alloy layer, scratches on the surface of the Al-Fe alloy layer, etc. Although this last adherence to the mold (adhesion by scratches) is improved by improving the lubricity of the surface coating, the adhesion to the previous mold (adhesion by exfoliation) is relatively slightly improved. The most effective way to improve adhesion to the previous mold is to reduce the amount of deposition of the Al-Fe alloy layer. However, when the amount of deposition of the Al-Fe alloy layer is reduced, corrosion resistance deteriorates.
[0019] In contrast, in Patent Document 2, with powder intended to avoid scratching the process, it is described that the steel sheet having a predetermined component composition is coated with an Al-based metallic coating, and a coating of inorganic compound including at least one element between silicon (Si), zirconium (Zr), titanium (Ti), and phosphorus (P), an organic compound coating, or a complex compound coating is also formed in the metallic coating Al base.
[0020] With the steel sheet on which such a surface coating is formed, the surface coating remains during pressing after heating, so that the formation of process scratches during pressing can be avoided. In Patent Document 2, it is described that since the surface coating works as a lubricant during pressing, the foot forming ability is improved. However, in reality, sufficient lubricity cannot be obtained and another lubricant or alternative medium is needed.
[0021] In Patent Document 3 a method is described to solve a problem of deterioration of the surface by the evaporation of a galvanized layer in the hot pressing of the galvanized steel sheet. Specifically, a layer of zinc oxide (ZnO) having a high melting point is formed on the surface of the galvanized layer to function as a barrier layer to prevent the evaporation of the base galvanized layer.
[0022] However, the technique in Patent Document 3 assumes a galvanized layer. The amount of Al in the galvanized layer is allowed up to 0.4%. However, a lower concentration of Al is preferable and, in fact, the technique is a technique not essentially assumed in the Al-based metal coating. Since a problem in Patent Document 3 is evaporation of Zn from the galvanized layer, of course, the above problem cannot arise if the Al-based metal coating has a high melting point.
[0023] In Patent Document 4, a technique is described for coating the surface of an Al coated steel sheet with a wurtzite compound to improve the hot lubrication and chemical conversion properties. This technique is effective for improving lubricity and also improving resistance to post-paint corrosion. However, to improve lubricity, the required deposition amount of the coating is about 2 g / m2 in terms of Zn, and to obtain a more stable lubricity, its required deposition amount is about 3 g / m2 . However, when the coating deposition amount of 3 g / m2 is converted to the coating thickness, the thickness is about 1.5 μm. With such a thickness of the coating (when the amount of deposition of the coating is more than 3 g / m2), the resistance of the coating increases and the spot welding capacity deteriorates. As a result, there is concern about deterioration in cross-tensile strength. Therefore, there were demands for a technique to improve lubricity with less deposition of the coating. Prior Art Document Patent Document
[0024] Patent Document 1 - Japanese Unexamined Patent Application, First Publication No. 2000-38640
[0025] Patent Document 2 - Japanese Unexamined Patent Application, First Publication No. 2004-211151
[0026] Patent Document 3 - Japanese Unexamined Patent Application, First Publication No. 2003-129209
[0027] Patent Document 4 - PCT International Publication No. WO2009 / 131233 Description of the Invention Problems to be solved by the invention
[0028] As described above, it is expected that a coated steel sheet supplied with Al-based coating having a high melting point (an Al coated steel sheet) will be used as an automotive steel sheet that requires corrosion resistance , and several suggestions have been made for the hot press application. However, on a conventional Al-coated steel plate, satisfactory lubricity from an Al-Fe alloy layer formed on its surface was not able to be achieved. Thus, the capacity for forming by pressing was poor during hot pressing and the steel sheet was not easily applied to hot pressing in a complicated way.
[0029] The present invention was made in consideration of the circumstances mentioned above, and its objective is to provide an Al coated steel sheet having a more satisfactory lubricity than the conventional one, and capable of improving the conformability during hot pressing and productivity, a method for hot pressing Al coated steel sheet, and an auto part produced by the hot pressing method. Measures to Solve the Problem
[0030] The present invention adopts the following measures to solve the above problems and achieve the objective.
[0031] A steel plate coated with Al according to one aspect of the present invention includes: a steel plate, a layer of Al coating that is formed on a surface of the steel plate and contains at least 85% or more than Al in% by mass; and a surface coating layer that is laminated to the surface of the Al coating layer and contains ZnO and one or more compounds that improve lubricity.
[0032] (2) In the steel plate coated with Al according to item (1), the compound that improves lubricity can be a compound including one or more transition metallic elements.
[0033] (3) In the steel plate coated with Al according to item (2), the transition metallic element can be any one or more between Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, W, La, and Ce.
[0034] (4) In the Al coated steel plate according to item (2), an amount of compound that improves lubricity including the transition metal element in the surface coating layer can be 1% to 40% in in relation to the total amount of ZnO in terms of mass.
[0035] (5) In the Al coated steel plate according to item (1), the compound that improves lubricity can be a compound including one or more typical elements.
[0036] (6) In the steel plate coated with Al according to item (5), the typical element can be any one or more between Mg, Ca, Sr, Ba, P, Sn, and Ge.
[0037] (7) In the Al coated steel plate according to item (5), the amount of compound that improves lubricity including the element-typical in the surface coating layer can be 5% to 30% in relation to the quantity total ZnO in mass ratio.
[0038] (8) In Al-coated steel sheet according to any of items (1) to (7), the surface coating layer may contain 0.3 g / m2 to 7 g / m2of ZnO in terms of Zn.
[0039] (9) In the Al-coated steel plate according to any of the items (1) to (8), the surface coating layer can also contain 5% to 30% of an organic compound in relation to the quantity - total amount of ZnO in mass ratio.
[0040] (10) A method for hot pressing an Al coated steel sheet according to another aspect of the present invention includes cutting and then heating the Al coated steel sheet according to any of the items ( 1) to (9), and conform by pressing the steel sheet.
[0041] (11) In the method for hot pressing an aluminum-coated steel sheet, according to item (10), the average rate of temperature increase until the temperature of the Al-coated steel sheet can reach from 50 ° C up to a temperature 10 ° C lower than the maximum reach temperature can be 10 ° C / s to 300 ° C / a in heating before the hot pressing of the steel sheet.
[0042] (12) In the method for hot pressing an Al coated steel plate according to item (11), the heating before pressing the steel plate can be carried out by electric heating or induction heating ,
[0043] (13) An automotive part according to yet another aspect of the present invention is produced by the method of hot pressing an Al coated steel plate according to any of the items (10) to (12). Effects of the Invention
[0044] In accordance with the present invention, it is possible to supply an Al coated steel sheet that has a more satisfactory lubricity than that of the conventional sheet and is capable of improving forming capacity and productivity during pressing hot, using a method of hot pressing the Al coated steel sheet, and an automotive part produced by the hot pressing method. Brief Description of Drawings
[0045] Figure 1A is a view of the layer structure of an Al-coated steel sheet according to a first embodiment of the present invention.
[0046] Figure 1B is a view of the structure of an Al coated steel plate layer according to a second embodiment of the present invention.
[0047] Figure 2 is an external view showing a central pillar reinforcement material as an example of an automotive part of the present invention.
[0048] Figure 3 is a view showing the shape of an equipment to assess the lubricity of the Al coated steel sheet.
[0049] Figure 4 is a view showing the relationship between the zinc oxide content (amount of zinc oxide in terms of Zn) of a surface coating layer and the exfoliation rate of the coating.
[0050] Figure 5 is a view showing the relationship between the zinc oxide content (amount of zinc oxide in terms of Zn) of a surface coating layer and the hot lubricity (friction coefficient).
[0051] Figure 6 is a view showing the relationship between the zinc oxide content (amount of zinc oxide in terms of Zn) of a surface coating layer and the strength of a joint. Modalities of the Invention
[0052] Hereinafter, one embodiment of the present invention in relation to the drawings will be described in detail. First Mode
[0053] Initially, a first embodiment of the present invention will be described. Figure 1A is a view showing a layered structure of an Al 10 coated steel plate according to the first configuration. As shown in Figure 1A, the Al 10 coated steel plate according to the first embodiment includes a steel plate 11, an Al 12 coating layer that is formed on a surface (for example, on the top surface) of the plate of steel 11, and a surface coating layer 13 that is formed on the surface of the Al coating layer 12.
[0054] In Figure 1A, an example of a case is shown in which the Al 12 coating layer and the 13 surface coating layer are formed on a steel plate surface 11. However, the Al coating layer 12 ea and the surface coating layer 13 can be formed on both surfaces of the steel sheet 11.
[0055] Steel sheet 11 is a substrate of Al 10 coated steel sheet and has the necessary mechanical properties (tensile strength, elasticity limit, elongation, reduction, hardness, impact value, fatigue strength, strength sliding, and other properties such as mechanical deformation and fracture). For example, steel plate 11 contains, in mass%, 0.1% to 0.4% carbon (C), 0.01% to 0.6% silicon (Si), 0.5% to 3% manganese (Mn), 0.01% to 0.1% titanium (Ti), 0.0001% to 0.1% boron (B), and the balance, consisting of iron (Fe) and the inevitable impurities.
[0056] Hereinafter, the role of each of the elements mentioned above contained in steel sheet 11 will be described. In the following description, "%" refers to% by mass.
[0057] Carbon is an element to guarantee the mechanical strength of steel sheet 11. When the carbon content in steel sheet 11 is less than 0.1%, sufficient mechanical strength cannot be obtained. On the other hand, when the carbon content in steel sheet 11 is greater than 0.4%, the hardness (mechanical strength) of steel sheet 11 increases, but melting fractures are easily generated in steel sheet 11. Consequently, the carbon content in steel sheet 11 is desirably 0.1% to 0.4%.
[0058] Silicon is an element to guarantee the mechanical resistance of steel plate 11, similar to carbon. When the silicon content in steel plate 11 is less than 0.01%, the strength-enhancing effect cannot be seen and sufficient mechanical strength cannot be achieved. On the other hand, silicon is also an easily oxidizable element, and so when the silicon content in steel sheet 11 is greater than 0.6%, the wetting capacity deteriorates during the hot dip coating of the steel sheet. steel 11, and the coating detaches. Consequently, the silicon content in steel sheet 11 is desirably 0.01% to 0.6%.
[0059] Manganese is an element to increase the hardening capacity of steel sheet 11 to increase the strength of steel sheet 11. In addition, manganese combines with sulfur (S) which is an inevitable impurity in the steel sheet steel 11 to form manganese sulphide (MnS) and prevents hot embrittlement of steel plate 11 by sulfur. When the manganese content in steel plate 121 is less than 0.5%, the effect of the addition is not shown. On the other hand, when the manganese content in steel plate 11 is greater than 3%, the residual Y phase in steel plate 11 increases and the resistance decreases. As a consequence, the manganese content in the steel plate is approximately 0.5% to 3%.
[0060] Titanium is an element that improves strength and also an element that improves heat resistance of the Al 12 coating layer. When the titanium content in steel plate 11 is less than 0.01%, the effect of improving strength and heat resistance cannot be achieved. On the other hand, when the titanium content in steel plate 11 is greater than 0.1%, for example, carbides and nitrides are formed and steel plate 11 is capable of being softened. As a result, the desired mechanical strength cannot be achieved. Consequently, the titanium content in steel plate 11 is desirably 0.01% to 0.1%.
[0061] Boron is an element to increase the hardening capacity of steel sheet 11 to improve the strength of steel sheet 11. When the boron content in steel sheet 11 is less than 0.0001%, the effect of improving endurance cannot be shown. On the other hand, when the boron content in steel plate 11 is greater than 0.1%, the fatigue strength of steel plate 11 decreases due to the formation of inclusions. Consequently, the boron content in steel plate 11 is desirably 0.0001% to 0.1%.
[0062] Steel sheet 11 may contain unavoidable impurities mixed in other production processes within a range that does not impair the mechanical strength of steel sheet 11.
[0063] In steel plate 11 having the composition of components above, the mechanical strength is increased to about 1500 MPa or more by tempering in the hot pressing method. In the hot pressing method, since steel sheet 11 is formed by pressing in a state in which the steel sheet is softened, forming is easy. In addition, when steel sheet 11 is made thin to reduce weight, high mechanical strength is maintained.
[0064] The coating layer 12 is formed on a surface (for example, a top surface) of the steel sheet 11 and contains at least 85% or more of aluminum (Al) in weight%. For example, the Al 12 coating layer is desirably formed by a hot dip coating method. However, its forming method is not limited to the hot dip coating method.
[0065] As described above, the Al 12 coating layer preferably contains 85% or more aluminum and may contain components other than aluminum. Components other than aluminum are not particularly limited, but silicon is preferable for the following reasons.
[0066] Silicon is an element that has the function of suppressing the formation of an iron and aluminum alloy layer (hereinafter referred to as a Fe-Al alloy layer) during the hot dip coating of the steel sheet 11. When the silicon content of the Al 12 coating layer is less than 3%, the Fe-Al alloy layer grows thickly during the hot dip coating of the steel sheet 11, and thus the rupture of the layer coating is facilitated during the process and corrosion resistance can deteriorate. On the other hand, when the silicon content of the Al 12 coating layer is greater than 15%, the working capacity and corrosion resistance of the Al 12 coating layer deteriorates. Thus, the silicon content of the Al 12 coating layer is desirably 3% to 15%.
[0067] The Al 12 coating layer having the composition of components above has the function of preventing the corrosion of the steel plate 11 and preventing scales (iron oxides) from forming on the surface of the steel plate 11 due to the heating before hot pressing.
[0068] Consequently, a scale removal process, a surface cleaning process, a surface treatment process and the like can be omitted by the formation of the Al 12 coating layer on the steel plate 11, and thus the productivity of the Al 10 coated steel plate is improved. In addition, the Al 12 coating layer has a higher melting point than coatings made from organic materials and coatings made from other materials (eg Zn-based material) and can thus be processed at a high temperature during hot pressing.
[0069] Some aluminum contained in the Al 12 coating layer is bonded with iron to the steel plate 11 during hot dip coating or hot pressing. Consequently, the Al 12 coating layer is not necessarily formed into a single layer with a fixed component composition and may include a partially bonded layer (an alloy layer).
[0070] Furthermore, when the amount of deposition of the Al 12 coating layer in relation to the steel plate 11 is 80 g / m2 per surface, the thickness of the Al 12 layer per surface is about 15 μm.
[0071] The surface coating layer 13 is laminated to the surface of the Al 12 coating layer and contains at least zinc oxide (ZnO). For example, the surface coating layer 13 is formed by applying a solution in which fine zinc oxide particles are suspended to the surface of the Al 12 coating layer by a coating cylinder or the like. The surface coating layer 13 has an effect of improving lubricity during the hot pressing of Al 10 coated steel sheet and reactivity with a chemical conversion solution.
[0072] The surface coating layer 13 also contains one or more compounds that improve lubricity, in addition to the zinc oxide mentioned above. The lubricity-enhancing compound is preferably a compound including one or more metallic transition elements (elements that belong from the third group to the eleventh group in the periodic table).
[0073] Furthermore, the transition metal element mentioned above is preferably any one or more between titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), molybdenum (Mo), tungsten (W), lanthanum (La) and cerium (Ce).
[0074] In particular, a compound including any one or more elements including nickel, titanium, zirconium, manganese and copper has a notable effect on improving lubricity. Compounds of these elements are preferably oxides, nitrides, sulfides or phosphates. Although the compound of the transition metal element mentioned above contributes to the improvement of lubricity during hot pressing is not clear, it is considered that the effect of improving lubricity cannot be obtained only with the composition. of the transition metal element mentioned earlier, and thus lubricity is improved due to the compound effect or a synergistic effect with zinc oxide.
[0075] Although the zinc oxide essentially has the effect of improving the lubricity mentioned above, with the addition of the compound of the transition metal element, the zinc oxide and the compound of the transition metal element mentioned above reacted with each other during hot pressing to form a compound oxide. As a result, it is assumed that lubricity is improved.
[0076] For example, the coating layer of the surface 13 containing zinc oxide and the compound of the metallic transition element mentioned above (lubricity improving compound) is formed on the surface of the coating layer of Al 12 by the application of a coating containing zinc oxide and the lubricity-enhancing compound on the surface of the Al coating layer, and baking and drying the coating after applying the coating.
[0077] As a method for applying zinc oxide and the lubricity enhancing compound, for example, a method of forming a coating by mixing a suspension containing zinc oxide and the lubricity enhancing compound containing the metallic element transition with an organic binder, and apply the coating to the surface of the Al 12 coating layer, and a spray coating application method can be used.
[0078] As the lubricity-improving compound containing and transition metal element mentioned above, for example, nickel sulfate, manganese sulfate, titanium fluoride, zirconium nitrate, copper sulfate, or the like are preferably used. As an organic binder, for example, polyurethane resins, polyester resins, acrylic resins, silane binders, or the like are preferably used.
[0079] The lubricity-improving compound mentioned above and the organic binder are preferably aqueous to be mixed with the suspension containing zinc oxide respectively. In this way, the coating obtained by mixing the suspension containing zinc oxide and the lubricity-improving compound and the organic binder is applied to the surface of the steel plate coated with Al 12.
[0080] The particle size of zinc oxide is not particularly limited and its diameter is desirably 50 nm to 1000 nm. The zinc oxide particle size after heat treatment is the particle size after heat treatment is carried out. Specifically, the particle size of the zinc oxide is determined by observing the zinc oxide with a SEM or similar after the zinc oxide is retained in an oven at 900 ° C for 5 minutes and quickly cooled with a mold.
[0081] In the surface coating layer 13, the amount of the lubricity-improving compound containing the transition metal element is preferably 1% to 40% relative to a total amount of zinc oxide by weight. When the amount of the lubricity-improving compound is less than 1%, a sufficient lubricity-improving effect cannot be obtained during hot pressing. On the other hand, when the amount of the lubricity-improving compound is greater than 40%, the adhesion of the coating layer 13 deteriorates after heating.
[0082] The amount of the organic binder (organic compound) such as a resin component or a silane bonding agent in the surface coating layer 13 is desirably 5% to 30% in relation to the total amount of zinc oxide by weight .
[0083] When the amount of organic binder is less than 5%, a sufficient binder effect cannot be obtained and the coating before heating is easily exfoliated. To obtain the binder effect steadily, the amount of the organic binder is preferably 10% or more in relation to the total amount of zinc oxide by weight. When the amount of organic binder is greater than 30%, the odor emission becomes significant during heating, and thus an amount of more than 30% is not preferable.
[0084] The present inventors confirmed that the surface coating layer 13 according to the modality has greater lubricity compared to an inorganic compound coating containing at least one element between silicon, zirconium, titanium, and phosphorus described in the Patent 2, a coating of an organic compound, or a coating of its complex compound. Thus, according to the Al 10 coated steel sheet of the modality, a more satisfactory lubricity than that of the conventional sheet can be achieved and the improvement of forming capacity and productivity can be achieved during hot pressing.
[0085] The surface coating layer 13 preferably contains 0.3 g / m2 to 7 g / m2 of zinc oxide in terms of zinc.
[0086] Figure 4 is a view showing the relationship between the amount of zinc oxide (amount of zinc oxide in terms of zinc) in the coating layer of surface 13 and the exfoliation rate of the coating. The exfoliation rate of the coating is a value obtained by dividing the amount of exfoliated zinc from the surface coating layer 13 by a scratching residue by an amount of zinc contained in the surface coating layer 13 before the test. scratch, and is used as an index to assess lubricity.
[0087] As shown in Figure 4, when the amount of zinc oxide in the surface coating layer 13 is 0.3 g / m2 to 7 g / m2, the exfoliation rate of the coating is 15% or less, and the lubrication - the surface coating layer 13 is satisfactory. When the amount of zinc oxide in the surface coating layer 13 is greater than 7 g / m2, the thickness of the surface coating layer 13 increases and the exfoliation rate of the coating increases rapidly. Thus, the weldability and adhesion of the coating deteriorate.
[0088] Consequently, the amount of zinc oxide in the surface coating layer 13 on a steel sheet surface 11 is desirably 0.3 g / m2 to 7 g / m2 in terms of zinc. In addition, the amount of zinc oxide in the surface coating layer 13 is more desirably 0.6 g / m2 to 2 g / m2, and in addition to lubricity, the weldability and adhesion of the coating become more satisfactory during hot pressing.
[0089] As a method for baking and drying the coating containing zinc oxide, the lubricity-enhancing compound and the organic binder after applying the coating, for example, a method using a hot air oven, an oven induction heating, an oven near infrared, or the like, or a method in which these ovens are combined. Depending on the type of organic binder, instead of baking and drying after applying the coating, a curing method using ultraviolet rays or electron rays can be adopted. The method for forming the surface coating layer 13 is not limited to the above method and various methods of forming the coating can be adopted.
[0090] When the organic binder is not used, the surface coating layer 13 has a slightly low adhesion with the Al 12 coating layer before heating and is partially exfoliated when rubbed with great force in this way, since the coating layer on the surface 13 of the Al 10 coated steel plate has satisfactory lubricity during hot pressing, the forming capacity of the Al 10 coated steel plate is improved during hot pressing and the corrosion resistance of Al 10 coated steel plate after hot pressing is also improved.
[0091] In addition, the surface coating layer 13 of the Al 10 coated steel sheet has an effect of suppressing the adhesion of the Al coated steel sheet to a mold. If the Al 12 coating layer is sprayed, the surface coating layer 13 containing zinc oxide on the surface prevents the powder from adhering (Al-Fe powder or similar) to the next mold. Thus, a process of removing the Al-Fe alloy powder that adheres to the mold is not necessary and thus productivity is improved.
[0092] The surface coating layer 13 acts as a protective coating to prevent scratches of the steel sheet 11 and / or the coating layer of Al 12 or similar is generated during hot pressing, and thus the ability to conformation of Al 10 coated steel sheet is also improved. In addition, the surface coating layer 13 has the effect of suppressing the deterioration of spot welding of the Al 10 coated steel sheet and the adhesion of the coating or the like. By conforming the chemical conversion coating to the Al 10 coated steel sheet, the post-paint corrosion resistance of the Al 10 coated steel sheet is significantly improved, and thus the amount of deposition of the surface coating layer 13 can be reduced. As a result, when the Al 10 coated steel sheet is pressed quickly, the adhesion of the Al 10 coated steel sheet exfoliated powder to the mold is suppressed and productivity is also improved.
[0093] When the amount of deposition of the surface coating layer 13 in relation to the steel sheet 11 (Al 12 coating layer) is 1 g / m2 in terms of Zn, the thickness of the layer surface coating 13 is about 0.5 μm.
[0094] Al 10 coated steel sheet of the modality can be processed and shaped by several methods but is suitable for forming by a hot pressing method. Hereafter, a method for hot pressing the Al 10 coated steel sheet in the modality will be described.
[0095] In the method for hot pressing the Al 10 coated steel plate, initially the Al 10 coated steel plate is cut and then heated and softened. The softened Al 10 coated steel sheet is shaped by pressing it into a desired shape, and then cooled. Once the Al 10 coated steel sheet is softened once, the following press forming can be carried out easily. Then the Al coated steel sheet is tempered by heating and cooling to obtain a steel sheet having a high mechanical strength of 1500 MPa or more.
[0096] As a heating method in the hot pressing method, typical heating methods can be adopted using an electric oven, a radiant tube oven, infrared rays, or the like. When the Al 10 coated steel sheet is heated to an aluminum melting point or higher, the Al 12 coating layer is melted and aluminum and iron diffuse each other to form an aluminum and iron alloy layer (aluminum layer). Al-Fe alloy) or a layer of aluminum, iron and silicon alloy (Al-Fe-Si alloy layer). Both the Al-Fe alloy layer and the Al-Fe-Si alloy layer respectively have a high melting point and the melting point is about 1150 ° C.
[0097] In the Al 10 coated steel plate, several compounds that form the Al-Fe alloy layer and the Al-Fe-Si alloy layer are present. However, these compounds change to a compound having a high concentration of iron by heating these compounds to a high temperature or by heating these compounds for a long period of time. The final product of the Al10 coated steel sheet is deemed to have a surface state in which the bond extends to the surface and the iron concentration is not high in the alloy layer.
[0098] When the aluminum that is not bonded remains, only a portion in which the aluminum remains is quickly corroded and thus the coating blisters easily after painting. On the contrary, even when the iron concentration becomes excessively high in the Al-Fe alloy layer, the corrosion resistance of the Al-Fe alloy layer itself deteriorates, and the coating blisters easily after painting. The reason is that the corrosion resistance of the Al-Fe alloy layer is dependent on the concentration of aluminum in the alloy layer.
[0099] There is, therefore, a bonding state that is preferable to guarantee resistance to post-paint corrosion and the bonding state is determined by the amount of coating deposition and the heating condition.
[00100] In the method of hot pressing of the modality, the average rate of temperature increase until the temperature of the Al 10 coated steel sheet reaches from 50 ° C to a temperature 10 ° C below the maximum reach temperature can be set to 10 ° C / s to 300 ° C / s. The productivity of Al 10 coated steel sheet is affected by the average rate of temperature increase. However, the average rate of increase in general temperature is about 5 ° C / s in a case of atmospheric heating to a high temperature. An average temperature rise rate of 100 ° C / s or more can be achieved by electric heating or high frequency induction heating.
[00101] When the aforementioned high average rate of temperature increase is achieved, productivity is improved. In addition, the average rate of temperature increase affects the composition and thickness of the Al-Fe alloy layer and thus is an important factor in product quality control. In the case of Al 10 coated steel sheet of the modality, since the rate of temperature increase can increase up to 300 ° C / s, productivity is improved and the product quality can be controlled over a wide range.
[00102] In relation to heating before hot pressing, heating needs to be carried out in the austenite region based on the principle of hot pressing. The peak temperature (maximum temperature range) in heating is generally 900 ° C to 950 °. Although the maximum reach temperature na is particularly limited in the hot pressing method of the modality, a temperature below 850 ° C is not preferable since a sufficient hardness cannot be obtained. In addition, Al 12 coating layer needs to change to an Al-Fe alloy layer, so a temperature below 850 ° C is not preferable.
[00103] When the heating temperature is higher than 1000 ° C, the connection advances excessively, the concentration of iron in the Al-Fe alloy layer increases to cause deterioration in the resistance to post-paint corrosion. Although nothing at all can be said, the resistance to post-painting corrosion is dependent on the rate of temperature increase and the amount of deposition of the Al 12 coating layer, and thus heating to a temperature of more than 1000 ° C is not desirable in terms of economy efficiency.
[00104] As described above, on the Al 10 coated steel plate according to the first modality, the surface coating layer 13 containing zinc oxide and the lubrication-improving compound including the transition metallic element is formed on the surface of the Al 12 coating layer, a more satisfactory lubricity than that conventional can be obtained and the improvement of forming capacity and productivity can be achieved during hot pressing.
[00105] In addition, in the steel sheet coated with Al 10 according to the first configuration, the improvement in chemical conversion properties after hot pressing and the resistance to post-painting corrosion can be achieved.
[00106] The reason why the chemical conversion properties are improved by the formation of the surface coating layer 13 (the adhesion of the chemical conversion coating is improved) is not clear. However, the chemical conversion reaction progresses with an acid notch reaction towards the substrate acting as a trigger, the zinc oxide contained in the surface coating layer 13 is an amphoteric compound that dissolves in an acid. Consequently, it is considered that the reason why the chemical conversion properties are improved is that the zinc oxide contained in the surface coating layer 13 reacts easily with a chemical conversion solution.
[00107] In addition, the Al-coated steel sheet according to the model can be formed into machine parts having various shapes by applying the aforementioned hot pressing method and is particularly suitable for producing an automobile part that required weight reduction, high stiffness, and high corrosion resistance. Examples of auto parts include a door impact beam, a bumper beam, and press shaped parts such as a reinforcement material for the central pillar.
[00108] Figure 2 is an external view showing the reinforcement material of the central pillar as an example of an automotive part. As shown in Figure 2, a reinforcement material for the central pillar 100 is an automotive part shaped in a vertically long shape like this in plan view, an upper end 111 is fixed to the side rail of the roof of an automobile, and a lower end 12 is attached to the threshold of the lower portion of the car. Automobile collision safety can be improved by forming an Al 10 coated steel sheet of the modality to produce the reinforcement material of the central pillar 100. Second Mode
[00109] Next, a second embodiment of the present invention will be described. Figure 1B is a view showing a layer structure of an Al 20 coated steel plate according to the second configuration. As shown in Figure 1B, the Al 20 coated steel layer according to the second embodiment includes a steel plate 21, an Al 22 coating layer that is formed on a surface (for example, an upper surface) of the plate steel 21, and a surface coating layer 23 that is formed on the surface of the Al 22 coating layer.
[00110] In Figure 1B, a case is shown in which the Al 22 coating layer and the surface coating layer 23 are formed on a steel sheet surface 21, but the Al 22 coating layer and the layer 22 surface coating 23 can be formed on both surfaces of the steel sheet 21.
[00111] Steel sheet 21 is a substrate of Al 20 coated steel sheet and has the necessary mechanical properties (tensile strength, elasticity limit, elongation, reduction, hardness, impact value, fatigue resistance, slip resistance, and other properties related to mechanical deformation and fracture). For example, steel plate 21 contains, in mass%, 0.1 to 0.4% carbon (C), 0.01% to 0.6% silicon (Si), 0, 5% to 3% manganese (Mn), 0.01% to 0.1% titanium (Ti), 0.0001% 0.1% boron (B), and the balance consisting of iron (Fe) and the inevitable impurities.
[00112] Hereinafter the role of each of the elements mentioned above on steel plate 21 will be described. In the description below, "%" refers to% by mass.
[00113] Carbon is an element that guarantees the mechanical strength of steel sheet 21. When the carbon content in steel sheet 21 is less than 0.1%, sufficient mechanical strength cannot be obtained. On the other hand, when the carbon content in steel sheet 21 is greater than 0.4%, the hardness (mechanical strength) of steel sheet 21 increases, but melting fractures are easily generated in steel sheet 21. Consequently, the carbon content in the steel sheet 21 is desirably 0.1% to 0.4%.
[00114] Silicon is an element that guarantees the mechanical resistance of steel sheet 21, similar to carbon. When the silicon content in steel plate 21 is less than 0.01%, the strength-enhancing effect cannot be seen and sufficient mechanical strength cannot be achieved. On the other hand, silicon is also an easily oxidizable element, and so when the silicon content in steel sheet 21 is greater than 0.6%, wetting capacity during Al coating by hot dipping the steel sheet 21 an unbalance occurs ,. Consequently, the silicon content in steel sheet 21 is desirably 0.01% to 0.6%.
[00115] Manganese is an element that increases the hardness of steel sheet 21 to increase the strength of steel sheet 21. In addition, manganese combines with sulfur (S) which is an inevitable impurity in steel sheet 21 to form manganese sulfide (MnS) and avoid hot embrittlement on steel plate 21 by sulfur. When the manganese content in steel plate 21 is less than 0.5%, the effect of the addition is not shown. On the other hand, when the manganese content in steel plate 21 is greater than 3%, the residual y phase in steel plate 21 increases and the resistance decreases. Consequently, the manganese content in steel plate 21 is desirably 0.5% to 3%.
[00116] Titanium is a strength-enhancing element and also an element that improves the heat resistance of the steel sheet coated with Al 22. When the titanium content in steel sheet 21 is less than 0.01%, the effect of improving resistance and the effect of improving resistance to oxidation cannot be obtained. On the other hand, when the titanium content in steel plate 21 is greater than 0.1%, for example, carbides and nitrides are formed and steel plate 321 is capable of being softened. Thus, the desired mechanical strength cannot be achieved. Consequently, the titanium content in steel sheet 21 is desirably 0.01% to 0.1%.
[00117] Boron is an element that increases the hardening capacity of steel sheet 21 to improve the strength of steel sheet 21. When the boron content in steel sheet 21 is less than 0.0001%, the resistance-enhancing effect cannot be obtained. On the other hand, when the boron content in steel plate 21 is greater than 0.1%, the fatigue strength of steel plate 21 decreases due to the formation of inclusions. Consequently, the boron content in steel sheet 21 is desirably 0.0001% to 0.1%.
[00118] Steel sheet 21 may contain unavoidable impurities mixed in other production processes within a range that does not impair the mechanical strength of steel sheet 21.
[00119] In steel plate 21 having the composition of components above, the mechanical strength is increased to about 1500 MPa or more by quenching in the hot pressing method. In the hot pressing method, since the steel sheet 21 is shaped by pressing in a state in which the steel sheet is softened, forming is easy. In addition, when steel sheet 21 is made thin to reduce weight, high mechanical strength is maintained.
[00120] The Al 22 coating layer is formed on a surface (for example, a top surface) on steel sheet 21 and contains at least 85% or more of aluminum (Al) in weight%. For example, the Al 22 coating layer is desirably formed by a hot dip coating method. However, its forming method is not limited to the hot dip coating method.
[00121] As described above, the Al 22 coating layer preferably contains 85% or more aluminum and can contain components other than aluminum. Different aluminum components are not particularly limited, but silicon is preferable for the following reasons.
[00122] Silicon is an element that has the function of suppressing the formation of an iron and aluminum alloy layer (hereinafter referred to as Fe-Al alloy layer) during the hot dip coating of the plate steel 21. When the silicon content of the Al 22 coating layer is less than 3%, the Fe-Al alloy layer grows thickly during the hot dip coating of the steel sheet 21, and thus the rupture of the steel layer 21 coating is facilitated during the process and corrosion resistance can deteriorate. On the other hand, when the silicon content of the Al 22 coating layer is greater than 15%, the workability and corrosion resistance of the Al 22 coating layer deteriorate. Thus, the silicon content of the Al 22 coating layer is desirably 3% to 15%.
[00123] The Al 22 coating layer having the above component composition has the function of preventing corrosion of the steel sheet 21 and preventing scale (iron oxide) from forming on the surface of the steel sheet 21 due to heating before pressing.
[00124] Consequently, a scale removal process, a surface cleaning process, a surface treatment process, and the like can be omitted by forming the Al 22 coating layer on the steel plate 21, and thus productivity of Al 20 coated steel sheet is improved. In addition, the Al 22 coating layer has a higher melting point than coatings made from organic materials and coatings made from other metallic materials (for example, Zn-based materials) and thus can be processed at a high temperature during hot pressing.
[00125] Part of the aluminum contained in the Al 22 coating layer is bonded with the iron to the steel plate 21 during hot dip coating or during hot pressing. Consequently, the Al 22 coating layer is not necessarily formed with a single layer with a fixed component composition and may include a partially bonded layer (an alloy layer).
[00126] In addition, when the amount of deposition of the Al 22 coating layer in relation to the steel sheet 21 is 80 g / m2 per surface, the thickness of the Al 22 coating layer per surface is about 15 μm.
[00127] The surface coating layer 23 is laminated on the surface of the Al 22 coating layer and is a surface coating layer containing at least zinc oxide (ZO). For example, the surface coating layer 23 is formed on the surface of the Al 22 coating layer by applying a solution in which fine particles of zinc oxide are suspended to the surface of the Al 22 coating layer by a coated cylinder. - pain or similar. The surface coating layer 23 has an effect of improving lubricity during hot pressing of Al 20 coated steel sheet and reactivity with a chemical conversion solution.
[00128] The surface coating layer 23 also contains one or more lubricity-enhancing compounds, in addition to the zinc oxide mentioned above. In the first embodiment, a compound including the transition metallic element is used as a lubricity-improving compound. However, in the second modality, as a lubricity-enhancing compound, a compound including one or more typical elements (element belonging to the first group and the second group and from the twelfth group to the eighteenth group in the table is used) periodic) having an effect of improving the temperature-raising property (effect of improving the rate of temperature increase) of the Al 20 coated steel plate during heating, in addition to the effect of improving the lightness.
[00129] Particularly, the typical element mentioned above and preferably one or more between magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), phosphorus (P), tin (Sn), and germanium (Ge).
[00130] Compounds of these typical elements are desirably oxides and, for example, magnesium oxide, calcium oxide or the like are preferable. These compounds are considered to have a high emission capacity and effectively absorb heat in the heating furnace. Particularly, when an emitter body that emits infrared rays in the heating furnace is used, the temperature properties are significantly improved. It is assumed that the reason for this is that the oxide including zinc oxide has a high emission capacity in relation to the wavelength of a region beyond the infrared.
[00131] For example, the surface coating layer 23 including zinc oxide and the compound of the typical element mentioned above (lubricity improving compound) is formed on the surface of the Al 22 coating layer by applying a re - clothing containing zinc oxide and the lube-improving compound on the surface of the Al coating layer, and baking and drying the coating after applying the coating.
[00132] As a method to apply zinc oxide and lubricity-enhancing compound, for example, a method of forming a coating by mixing a suspension containing zinc oxide and a lubricity-enhancing compound containing the elemental metal typical with an organic binder, and applying the coating to the surface of the Al 22 coating layer, and a spray coating application method.
[00133] As a lubricity-enhancing compound including the typical element mentioned above, for example, magnesium oxide (MgO), calcium oxide (CaO), forsterite (Mg2SiO4), or the like are preferably used. In addition, as an organic binder, for example, polyurethane resins, polyester resins, acrylic resins, silane binder, or the like are preferably used. The lubricity-improving compounds and organic binders mentioned above are preferably aqueous to be mixed with the suspension containing zinc oxide respectively. In this way, the coating obtained by mixing the suspension containing zinc oxide and the lubricity-improving compound is applied to the surface of the Al 22 coated steel plate.
[00134] The particle size of zinc oxide is not particularly limited, and its diameter is desirably 50 nm to 1000 nm. The particle size of zinc oxide is the particle size after heat treatment is carried out. Specifically, the particle size of zinc oxide is determined by looking at zinc oxide with a SEM or similar after zinc oxide is retained in an oven at 900 ° C for 5 minutes to 6 minutes and quickly cooled with a mold .
[00135] The particle size of the lubrication enhancing compound including the typical element in the surface coating layer 23 is not particularly limited. However, its particle size is desirably the same as the particle size of zinc oxide.
[00136] The amount of lubricity-improving compound including the typical element in the surface coating layer 23 is preferably 5% to 30% with respect to the total amount of zinc oxide by weight. When the amount of the lubricity-improving compound is less than 5%, an effect of improving the temperature-raising property (effect of improving the rate of temperature increase) cannot be obtained in the heating furnace . On the other hand, when the amount of the lube-improving compound is greater than 30%, the reactivity with the chemical conversion solution is easily impaired after heating.
[00137] The amount of the organic binder (organic compound) such as a resin component or a silane bonding agent in the surface coating layer 23 is desirably 5% to 30% relative to the total amount of zinc oxide by weight . When the amount of organic binder is less than 5%, a sufficient binder effect cannot be obtained and the coating before heating is easily exfoliated. To obtain the binder effect stably, the amount of organic binder is preferably 10% or more in relation to the total amount of zinc oxide by weight. When the amount of organic binder is greater than 30%, the odor emission becomes significant during heating, and therefore the amount of more than 30% is not preferable.
[00138] The present inventors confirmed that the surface coating layer 23 according to the modality has greater lubricity when compared to an inorganic compound coating containing at least one element between silicon, zirconium, titanium, and phosphorus described in Patent Document 2, an organic compound coating, or a complex composite coating thereof. Thus, according to the Al 20 coated steel sheet of the modality, a more satisfactory lubricity than the conventional one can be achieved and the improvement of forming capacity and productivity can be achieved during hot pressing.
[00139] The surface coating layer 23 preferably contains 0.3 g / m2 to 7 g / m2 of zinc oxide in terms of zinc.
[00140] When the amount of zinc oxide is 0.3 g / m2 or more in the surface coating layer 23 in terms of zinc, the lubricity-improving effect is shown. On the other hand, when the amount of zinc oxide in the surface coating layer 23 is greater than 7 g / m2 in terms of zinc, the thickness of the coating layer of Al 22 and the coating layer of su - surfaces 23 are increased, thus the welding capacity and the adhesion of the coating deteriorate.
[00141] Consequently, the amount of zinc oxide in the surface coating layer is desirably 0.3 g / m2 to 7 g / m2 on a surface of the surface coating layer 23 in terms of zinc. From the point of view of guaranteeing lubricity during hot pressing and also of guaranteeing satisfactory welding capacity and adhesion of the coating, the amount of zinc oxide in the surface coating layer 13 is particularly desirably 0.5 g / m2 to 2g / m2.
[00142] As a method for baking and drying the coating containing zinc oxide, the lubricity-improving compound, and the binder after applying the coating, for example, a method using a hot air oven, a induction heating furnace, a furnace near infrared, etc., or a method in which these furnaces are combined. Depending on the type of organic binder, instead of baking and drying after applying the coating, a curing method can be adopted using ultraviolet rays or electron rays. The method for forming the surface coating layer 23 is not limited to the above method, and several coating forming methods can be adopted.
[00143] When the organic binder is not used, the surface coating layer 23 has a slightly low adhesion with the Al 22 coating layer before heating and partly exfoliated when it is rubbed with great force. Thus, since the surface coating layer 23 of the Al 20 coated steel sheet has satisfactory lubricity during hot pressing, the forming capacity of the Al 20 coated steel sheet is improved during hot pressing and the corrosion resistance of Al 20 coated steel sheet after hot pressing is also improved.
[00144] In addition, the surface coating layer 23 of the Al 20 coated steel sheet has the effect of suppressing the adhesion of the Al 20 coated steel sheet to the mold. If the Al 22 coating layer is sprayed, the surface coating layer 23 containing zinc oxide on the surface prevents the powder from adhering (Al-Fe powder or similar) to the next mold. Thus, a process of removing the Al-Fe alloy powder that adheres to the mold is not necessary, and thus productivity is improved.
[00145] The surface coating layer 23 acts as a protective layer to prevent scratches of the steel sheet 21 and / or the coating layer 22 or similar from being generated during hot pressing, and thus the forming capacity of Al 20 coated steel sheet is also improved. In addition, the surface coating layer 23 has the effect of suppressing the deterioration, in spot welding, of the Al 20 coated steel sheet and the adhesion of the coating, etc. By forming the chemical conversion coating on the aluminum coated steel sheet 20, the post-paint corrosion resistance of the Al 20 coated steel sheet is significantly improved, and thus the deposition amount of the surface coating layer 23 can be reduced. As a result, when the Al 20 coated steel sheet is pressed quickly, the adhesion of the exfoliated Al-Fe alloy powder from the Al 20 coated steel sheet to the mold is suppressed and productivity is also improved.
[00146] When the amount of deposition of the surface coating layer 23 in relation to the steel sheet 21 (Al 22 coating layer) is 1 g / m2 in terms of Zn, the thickness of the layer of surface coating 23 is about 0.5 μm.
[00147] The Al 20 coated steel sheet of the modality can be processed and shaped by several methods, but it is suitable for forming by a hot pressing method. Hereinafter, a method for hot pressing the Al 20 coated steel sheet in the modality will be described.
[00148] In the method for hot pressing the Al 20 coated steel sheet, the Al coated steel sheet is cut and then heated and softened. The softened Al coated steel sheet is formed by pressing it into a desired shape, and then cooled. Once the Al 20 coated steel sheet is softened once, the following pressing comfort can be easily performed. Then the Al 20 coated steel sheet is tempered by heating and cooling to obtain a steel sheet having high mechanical strength of 1500 MPa or more.
[00149] As a heating method in the hot pressing method, typical heating methods can be adopted using an electric oven, a radiant tube oven, infrared rays, etc. When the Al 20 coated steel sheet is heated to the aluminum melting point or higher, the Al 22 coating layer is melted and the aluminum and iron diffuse each other to form a layer of aluminum and iron alloy (Al-Fe alloy layer) or an aluminum, iron and silicon alloy layer (Al-Fe-Si alloy layer). Both the Al-Fe alloy layer and the Al-Fe-Si alloy layer respectively have a high melting point and the melting point is about 1150 ° C.
[00150] On Al 20 coated steel plate,
[00151] Then the Al 20 coated steel sheet is tempered by heating and cooling to obtain a steel sheet having high mechanical strength of 1500 MPa or more.
[00152] As a heating method in the hot pressing method, typical heating methods can be adopted using an electric oven, a radiant tube oven, infrared rays, etc. When the Al 20 coated steel sheet is heated to the aluminum melting point or higher, the Al 22 coating layer is melted and the aluminum and iron diffuse each other to form a layer of aluminum and iron alloy (Al-Fe alloy layer) or an aluminum, iron and silicon alloy layer (Al-Fe-Si alloy layer). Both the Al-Fe alloy layer and the Al-Fe-Si alloy layer respectively have a high melting point and the melting point is about 1150 ° C.
[00153] In the Al 20 coated steel plate, several compounds that form the Al-Fe alloy layer and the Al-Fe-Si alloy layer are present. However, these compounds change to compounds having a high concentration of iron by heating these compounds to a high temperature or by heating these compounds for a long period of time. A final product of the Al 20 coated steel sheet desirably has a surface state in which the strain bond to the surface and the iron concentration is not high in the alloy layer.
[00154] When the aluminum that is not bonded remains, only a portion in which the aluminum remains is corroded quickly, and thus the coating blisters easily after painting. Conversely, even when the iron concentration becomes excessively high in the alloy layer, the corrosion resistance of the alloy layer itself deteriorates, and the coating blisters easily after painting. The reason is that the corrosion resistance of the alloy layer is dependent on the concentration of aluminum in the alloy layer.
[00155] There is, therefore, a bonding state which is preferable to guarantee resistance to post-paint corrosion, and the bonding state is determined by the amount of coating deposition and the heating condition.
[00156] In the hot pressing method of the modality, an average rate of temperature increase until the temperature of the Al 20 coated steel sheet reaches from 50 ° C to a temperature 10 ° C below the maximum reach temperature can be adjusted to 10 ° C / s to 300 ° C / s. The productivity of the Al 20 coated steel sheet is affected by the average rate of temperature increase. However, the average rate of increase in general temperature is about 5 ° C / s in a case of atmospheric heating to a high temperature. The average rate of temperature rise of 100 ° C / s or greater can be achieved by electric heating or high frequency induction heating.
[00157] When the high average rate of temperature increase mentioned above is achieved, productivity is improved. In addition, the average rate of temperature increase affects the composition and thickness of the alloy layer and is thus an important factor in controlling product quality. In the case of Al 20 coated steel sheet of the modality, since the rate of temperature increase can increase to 300 ° C / s, productivity is improved and the quality of the product can be controlled over a wider range .
[00158] Regarding heating before hot pressing, heating needs to be carried out in the austenite region based on the principle of hot pressing. The peak temperature (maximum temperature range) in heating is generally 900 ° C to 950 ° C; Although the maximum reach temperature is not particularly limited in the method of hot pressing of the modality, a temperature of less than 850 ° C is not preferable since sufficient hardness cannot be achieved. In addition, the Al 22 coating layer needs to change to an alloy layer, so a temperature of less than 850 ° C is not preferable.
[00159] When the heating temperature is greater than 1000 ° C, the connection advances excessively, the concentration of iron in the alloy layer increases to cause deterioration in the resistance to corrosion after painting. Although nothing can be said at all, the resistance to post-painting corrosion is dependent on the rate of temperature increase and the amount of deposition of the Al 22 coating layer, and thus heating to a temperature of 1100 °. C or more is not desirable in terms of economic efficiency.
[00160] As described above, in the Al 20 coated steel plate according to the second modality, the surface coating layer 23 containing zinc oxide and the lubricating compound including the typical element is formed on the surface of the coating layer. Al 22, and thus more satisfactory than conventional lubricity can be obtained and the improvement of forming capacity and productivity can be achieved during hot pressing.
[00161] In addition, according to the Al 20 coated steel plate of the second modality, the improvement of the chemical conversion property after hot pressing and of the post-paint corrosion resistance can be performed.
[00162] In addition, according to the Al 20 coated steel plate of the second modality, in addition to the effect mentioned above, the effect of improving the temperature increase property (effect of improving the rate of increase temperature) during heating can be obtained.
[00163] The Al 20 coated steel sheet according to the second modality can be formed into machine parts having various shapes by applying the aforementioned hot pressing method, similarly to the first modality, and is particularly suitable for producing a automotive part requiring weight reduction, high rigidity, and high corrosion resistance (for example, a door impact beam, a bumper beam, and press formed parts such as the reinforcement material of the central column - tral). Examples
[00164] Although examples of the present invention are described below, the conditions employed in the examples are merely an example of a condition employed in order to confirm the operability and effect of the present invention, and the present invention is not limited to an example of a condition. The present invention can employ various conditions as long as the aim of the present invention is achieved without departing from the scope of the present invention. Example 1
[00165] A cold-rolled steel sheet having the composition of components shown in Table 1 (thickness of 1.4 mm) was coated with Al by the Sendzimir method. The annealing temperature was adjusted to about 800 ° C, and the Al coating bath contained 85% or more of Al and 9% or more of Si in% and mass, and additionally contained Fe eluted from the cap. of steel.

[00166] After the steel sheet has been coated by hot dip, the amount of deposition of the coating has been adjusted to 160 g / m2 on both surfaces of the steel sheet by the gas drying method. The steel sheet on which the Al coating layer was formed in this way was cooled, and then a coating treatment solution shown in Tables 2 and 3 (continued from Table 2) was applied to the surface of the coating layer. Al with a coating cylinder and cooked at about 80 ° C. Thus, the surface coating layer including zinc oxide and the lubricity-improving compound (particularly the transition metal element compound described in the first embodiment) was formed. Al coating treatment solutions shown in Tables 2 and 3 were suspensions or aqueous solutions in which the reagent and distilled water were mixed.
[00167] The properties of the steel plate on which the Al coating layer and the surface coating layer including the compound of the transition metal element were formed in this way (i.e., the corresponding Al coated steel plate to the first modality: hereinafter, referred to as the first Al-coated steel plate) were evaluated by the following methods. Hot Lubricity
[00168] The hot lubricity of the first Al coated steel sheet was assessed using the equipment shown in Figure 3. A specimen 1 having a size of 150 mm x 200 mm collected from the first Al coated steel sheet it was placed on a platform 4 of an oven 3 provided in the upper portion of a heater 2, and then the specimen 1 was heated to 900 ° C. Then, in a state in which a load P (pressing load) was applied to the specimen 1 using load application equipment 5 under a temperature condition of about 700 ° C, furnace 3 was operated by an oven operating equipment 6 along a ball way 7 to measure the load of the specimen 1.
[00169] The extraction load of the specimen 1 was measured by a load battery 8 connected to the load application equipment 5. The dynamic friction coefficient was calculated by dividing the extraction load by the pressing load. (2) Adhesion of the coating after heating
[00170] A specimen collected from the first steel plate coated with Al was placed in an atmospheric oven and was heated to 900 ° C for 6 minutes. Then, the specimen was removed from the atmospheric furnace, immediately fixed by a stainless steel mold, and cooled quickly. The rate of increase in the temperature of the specimen was about 5 ° C / s, and the cooling rate was about 150 ° C / s. Next, the specimen was cut to a size of 50 mm x 50 mm and was provided for a friction test. In the friction test, a gauze was rubbed the surface of the specimen 10 times with a load of 1.5 kgf over a width of 30 mm, and the amount of Zn deposition of the gauze before and after the test were measured to calculate the Zn reduction rate (%). (3) Resistance of the spot welded joint
[00171] A specimen collected from the first steel plate coated with Al was placed in an atmospheric oven and was heated to 900 ° C for 6 minutes. Then the specimen was removed from the atmospheric furnace, fixed immediately by a stainless steel mold, and quickly cooled. The rate of increase in the temperature of the specimen was about 5 ° C / s, and the cooling rate was about 150 ° C / s. Then, the tensile strength of the specimen was measured according to JIS Z3137 (1990). At that time, the welding conditions are as follows. In the test, the average value of the joint strength was calculated by adjusting the N number of samples in the specimen to 3 and measuring the resistance of each of the 3 samples.
[00172] Electrode: chrome-copper, DR (8 mmΦ tip of 40R)
[00173] Applied pressure: 880 kgf
[00174] Duration of energization: slope upwards 3 cycles - 22 cycles energized (60 Hz)
[00175] Welding current: 9.5 kA (4) Corrosion resistance after painting
[00176] A specimen collected from the first steel plate coated with Al was placed in an atmospheric oven and was heated to 900 ° C for 6 minutes. Then the specimen was removed from the atmosphere, immediately fixed by a stainless steel mold, and quickly cooled.
[00177] The rate of increase in temperature of the specimen was about 5 ° C / s, and the cooling rate was about 150 ° C / s. Then, the specimen was cut to a size of 70 mm x 150 mm and was subjected to chemical conversion using a chemical conversion solution (PB-SX35) produced by Nihon Parkerizing Co., Ltd. So, The specimen was painted with an electrodeposition coating (Powernics 110) produced by Nippon Paint Co., Ltd. to have a coating thickness of 20μm, and baked at 170 ° C.
[00178] The post-paint corrosion resistance of the specimen was evaluated by the method defined by JASO M609 (1991) defined by the Society of Automotive Engineers of Japan. A cutter was used to make a cut in the coating previously, and the width (maximum value on one side) of the coating bubble since cutting after the corrosion test was performed for 180 cycles (60 days) was measured. As a comparison example, a galvanized steel sheet with a deposition amount of 45 g / m2 on a surface was evaluated. At that time, the width of the bubble was 7 mm.
[00179] Each evaluation result is summarized in Tables 2 and 3 (continuation of Table 2). In addition, for comparison, a case in which the surface coating layer was not formed was also evaluated in the same way. The results of the evaluation are shown in Table 4.



[00180] Hot lubricity indicates the measured mechanical friction coefficient, coating adherence indicates Zn exfoliation rates before and after the test, the strength of the welded joint indicates the resistance to transverse traction, and the post-paint corrosion resistance indicates the maximum width of the bubble on a surface from the cross-section. Examples (nos. 1 to 23 in Tables 2 and 3) having the surface coating layer containing ZnO showed improved hot lubricity compared to the comparative examples (nos. 24 to 29 in Table 3) in which the surface coating is not formed.
[00181] However, if the amount of deposition of the surface coating layer is relatively small, sufficient hot lubricity cannot be obtained. When the amount of deposition of the surface coating layer is large, the strength of the welded joint, particularly the resistance to transverse traction, decreases. A decrease in the strength of the spot welded joint and a decrease in the transverse tensile strength are not desirable in terms of quality stability of auto parts. The reason why the resistance of the spot welded joint decreases when the amount of deposition of the surface covering layer is large is not clear. However, there is a possibility that oxides may remain in a welding nugget and the tension may be concentrated in the portion where the oxides remain during stamping;
[00182] In contrast, the surface coating layer (nos 7 to 13 in Table 2) including a compound of one or two or more transition metal elements (particularly i, V, Cr, Mn, Fe, Co, Ni, Cu , Zr, Mo, W, La and Ce) have excellent hot lubricity in a region with a small amount of deposition, and when the amount is 2 g / m2 or less in terms of Zn, the decrease in the strength of the welded joint by points can be deleted.
[00183] Although the reason why the aforementioned compound affects the resistance to post-paint corrosion is unclear, compared to steel sheets without the surface coating layer, all sheets showed excellent resistance to post corrosion. -painting. This is because the chemical conversion properties are improved.
[00184] The influence of the amount of deposition of the surface coating layer on the properties was investigated. For numbers 7 to 13 in Table 2 (Examples), numbers 24 to 29 in Table 3 (Comparative Examples), and in a case in which the surface coating layer was not formed in Table 4, the exfoliation rate of the coat - coating, hot lubricity (friction coefficient), and resistance of the welded joint by points are shown respectively in Figures 4, 5 and 6.
[00185] Compared to a system that does not include a compound of one or two or more transition metal elements (particularly Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, W, La and CE) , a system including these components has improved hot lubricity with less deposition.
[00186] When the amount of deposition of the surface coating layer increases, the resistance of the spot welded joint and the coating adhesion decrease. It has been found that, to increase the strength of the spot welded joint, the amount of deposition of the surface coating layer is preferably 2 g / m2 or less (refer to Figure 6), and to increase the coating adhesion, the deposition amount is preferably 7 g / m2 or less (refer to Figure 4). Example 2
[00187] The specimen 1 of Example 1 was heated quickly with near infrared rays. The rate of increase in temperature was adjusted to 21 ° C / s. The specimen temper was performed in the same way as in Example 1, and the following evaluation was also performed in the same way as in Example 1. The results of the evaluation are shown in Table 5. It was found that, although post-paint corrosion resistance is improved, there are no changes in properties other than post-paint corrosion resistance. From the results, it is also possible to expect an improvement in properties by rapid heating.
Example 3
[00188] An aqueous solution in which 20% urethane resin was added to ZnO was used as a base, and 10% sodium vanadate, sodium dichromate, ferrous sulfate, cobalt chloride, sodium molybdate, sodium, cerium nitrate, were added to the solution.
[00189] 1 g / m2 of the treatment solution thus prepared in terms of Zn was applied to the first Al coated steel sheet used in Example 1, and the hot lubricity was measured by the methods described in Example 1. As a result, a numerical value in the range of 0.60 to 0.65 was obtained in all methods. Thus, it has been found that all of the compounds mentioned above contribute to improving hot lubricity. Example 4
[00190] A cold-rolled steel sheet having the composition of components shown in Table 6 (thickness of 1.4 mm) was coated with Al by the Sendzimir method. The annealing temperature was adjusted to about 800 °, and the Al coating bath contained 85% or more of Al and 9% of Si in% by weight, and additionally contained Fe eluted from the steel plate.

[00191] After the steel sheet has been coated by hot dip, the amount of coating deposition has been adjusted to 160 g / m2 on both surfaces of the steel sheet by the gas drying method. The steel sheet on which the Al coating layer was formed in this way was cooled, and then a coating treatment solution shown in Table 7 was applied to the surface of the Al coating layer with a coating cylinder and cooked at about 80 ° C. Thus, the surface coating layer including zinc oxide and the lubrication-improving compound was formed (particularly, the typical element compound described in the second embodiment). All coating treatment solutions shown in Table 7 were suspensions or aqueous solutions in which a reagent and distilled water are mixed.
[00192] As described above, the properties of the steel plate including the Al coating layer and the surface coating layer containing the typical element compound (i.e., corresponding Al coated steel plate of the second embodiment: hereinafter referred to as second Al-coated steel plate) were evaluated by the following methods. Hot Lubricity
[00193] The hot lubricity of the second Al coated steel plate was assessed using the equipment shown in Figure 3. A specimen 1 having a size of 150 mm x 200 mm collected from the second Al coated steel plate it was placed on a specimen platform 4 of an oven 3 provided in the upper portion of a heater 2, and then the specimen 1 was heated to 900 ° C. Then, in a state in which the load P (pressing load) was applied to the specimen 1 using a load application equipment 5 under the temperature condition of about 700 ° C, oven 3 was operated by furnace operating equipment 6 along a steering ball 7 to measure the drawing load of the specimen 1. The drawing load of the specimen 1 was measured by a charging battery 8 connected to the measuring equipment load application 5. The dynamic friction coefficient was calculated by dividing the stretching load by the pressing load. (2) Temperature-raising properties during heating
[00194] After a thermocouple has been welded to a test piece having a size of 70 mm x 150 mm collected from the second Al coated steel plate, the test piece was placed in an atmospheric oven with the temperature adjusted to 900 ° C, and a time until the specimen temperature reached 50 ° to 890 ° C was measured to calculate the average rate of temperature increase. (3) Resistance of the spot welded joint
[00195] A specimen collected from the second steel plate coated with Al was placed in the atmospheric oven and was heated to 900 ° C for 6 minutes. Then, the specimen was removed from the atmospheric oven, immediately fixed by a stainless steel mold, and cooled quickly. The cooling rate of the specimen was about 150 ° C / s. Then the transverse tensile strength of the specimen was measured according to JIS Z3137. At this point, the welding conditions are as follows. In the test, an average value of the joint strength was calculated by adjusting the number of samples in the specimen to 3 and measuring the resistance of each of the 3 samples.
[00196] Electrode: chrome-copper, DR (8 mmΦ 40 R tip)
[00197] Applied pressure: 880 kgf
[00198] Duration of energization: slope upwards 3 cycles - 22 cycles energized (60 Hz)
[00199] Welding current: 9.5 kA (4) Corrosion resistance after painting
[00200] A specimen collected from the second steel plate coated with Al was placed in the atmospheric oven and was heated to 900 ° C for 6 minutes. Then, the specimen was removed from the atmospheric oven, fixed immediately by a stainless steel mold, and quickly cooled. The cooling rate of the specimen was about 150 ° C / s. The specimen was then cut to a size of 70 mm x 150 mm and was subjected to chemical conversion using a chemical conversion solution (PB-SX35) produced by Nihon Parkerizing Co., Ltd. So, The specimen was painted with an electroplating coating (Powernics 110) produced by Nippon Paint Co., Ltd. To have a thickness of 20 μm, and baked at 170 ° C.
[00201] The post-paint corrosion resistance of the specimen was evaluated by the method defined by JASO M609 defined by the Society of Automotive Engineers of Japan. A cutter was used to cross-cut the coating previously, and the width (maximum value on one side) of the coating bubble from the cross-cut after the corrosion test was performed for 180 cycles (60 days) was measured . As a comparison material, a galvanized steel sheet with a deposition amount of 45 g / m2 on a surface was evaluated. At that time, its bubble width was 7 mm.
[00202] Each evaluation result is summarized in Table 7. In addition, by comparison, a case in which the surface coating layer was not formed was also evaluated in the same way. The results of the assessment are shown in Table 8.


[00203] Hot lubricity indicates the measured dynamic friction coefficient, the rate of temperature increase indicates the value obtained by measuring the rate of temperature increase, the resistance of the welded joint by points indicates the resistance to transverse traction , and the post-paint corrosion resistance indicates the maximum bubble width on one side from the cross-section. Examples (refer to Table 7) having the surface coating layer containing ZnO showed improved hot lubricity and corrosion resistance after painting compared to Comparative Examples (refer to Table 8) on which the surface coating layer is not formed.
[00204] On the other hand, in relation to the rate of temperature increase, it was found that the Examples (nos. 1 to 7 in Table 7) containing a compound of one or more typical elements (particularly Mg, Ca, Sr, Ba , P, Sn and Ge) have excellent temperature-raising properties compared to sheets without a surface coating layer or the Comparative Example (No. 8 in Table 7) in which the surface coating layer was composed only of ZnO and a binder.
[00205] Nos. 9 to 14 in Table 7 are Examples in which the amount of deposition of the surface coating layer is changed, and Nos. 15 to 18 are Examples in which the amount of Ca compound in the surface coating layer is changed. It has been found that when the surface coating layer is thin, the hot lubricity is slightly low, and when the surface coating layer is thick, the strength of the spot welded joint decreases slightly. In addition, it has also been found that when the amount of Ca compound is large, the resistance to post-painting corrosion deteriorates slightly. Example 5
[00206] Specimens Nos 1 to 8 in Example 4 were heated with distant infrared rays. At that time, a furnace was used having a temperature rise oven and a holding oven and the movement between the ovens was performed manually. While the temperature of the temperature-increasing oven was set to 1150 ° C and the temperature of the holding oven was set to 900 ° C, a thermocouple was welded to each specimen having a size of 70 mm x 150 mm . When the specimen temperature reached 850 ° C in the temperature rise furnace, the specimen was moved to the holding furnace.
[00207] Similar to Example 4, the average rate of temperature increase was calculated at 50 ° C to 890 ° C. Quenching was carried out in the same manner as in Example 4 and the evaluation after quenching was also carried out in the same manner as in Example 4. The results of the evaluation are shown in Table 9. When the rate of temperature rise was high, it has been recognized that post-paint corrosion resistance has been improved. A higher rate of temperature increase was obtained at No. 1 compared to No. 8.
Example 6
[00208] For an aqueous solution in which 20% urethane resin was added to ZnO, and 1) 5% MgO and CaO were added respectively, 2) 5% CaO and SrO were added respectively, and 3) 5 % SnO2 and GeO2 were added respectively to prepare a treatment solution. 2 g / m2 of treatment solution in terms of Zn was applied to the second steel plate used in Example 4. As a result, the rate of temperature increase in a range of 8 ° C / s to 8.5 ° C / s was obtained in all methods. As seen from the result, it was found that all the compounds mentioned above contribute to improving lubricity. Industrial Applicability
[00209] According to the present invention, it is possible to improve the forming capacity and productivity in hot pressing by ensuring the lubricity of the Al coating layer in the hot pressing of the Al coated steel sheet. In addition Furthermore, according to the present invention, it is possible to improve the chemical conversion properties of the Al coated steel sheet after hot pressing, the post-paint corrosion resistance of the Al coated steel sheet, and the properties temperature increase of the Al coated steel plate in a heating oven. Thus, the present invention expands the application range for hot pressing of Al coated steel sheet and increases the applicability of Al coated steel sheet for automobiles and industrial equipment which are the final applications, and thus the industrial applicability is tall. Brief description of the Reference Symbols 1.20:: Al 11, 21 coated steel plate: Al 12, 22 steel plate: Al 13, 23 coating layer: Surface coating layer 1: Specimen 2: Heater 3: Oven 4: Specimen platform 5: Load application equipment 6: Oven operating equipment 7: steering ball 8: Charge battery

权利要求:
Claims (5)
[0001]
1. Al coated steel plate, characterized by the fact that it comprises: a steel plate; a layer of Al coating which is formed on one or both surfaces of the steel sheet and contains at least 85% or more of Al by weight%, 3 to 15% silicon and optionally iron; and a surface coating layer that is laminated to the surface of the Al coating layer and contains ZnO, one or more lubricity-enhancing compounds, and an organic binder, where the lubricity-enhancing compound is a compound including one or more transition metal elements selected from Ti, Mn, Ni, Cu, and Zr, the compound is nickel sulphate, manganese sulphate, titanium fluoride, zirconium nitrate or copper sulphate, an amount of lubricity-improving compound including the transition metal element in the surface coating layer is 1% to 40% relative to the total amount of ZnO by weight, and the surface coating layer contains 0.3 g / m2 at 7 g / m2 of ZnO in terms of Zn.
[0002]
2. Al coated steel plate, characterized by the fact that it comprises: a steel plate; a layer of Al coating which is formed on one or both surfaces of the steel sheet and contains at least 85% or more of Al by weight%, 3 to 15% silicon and optionally iron; and a surface coating layer that is laminated to the surface of the Al coating layer and contains ZnO, one or more lubricity-enhancing compounds, and an organic binder, where the lubricity-enhancing compound is a compound including one or more typical elements selected from Mg, Ca, Sr, Ba, P, Sn, and Ge, the compound is magnesium, forsterite, calcium oxide, strontium oxide, barium oxide, phosphorus oxide, tin dioxide, or germanium dioxide, an amount of lubricity-improving compound including the typical element in the surface coating layer is 5% to 30% relative to the total amount of ZnO by weight, and the surface coating layer contains 0.3 g / m2 to 7 g / m2 of ZnO in terms of Zn.
[0003]
3. Method for hot pressing an Al-coated steel sheet, characterized by comprising: cutting and then heating the Al-coated steel sheet as defined in claim 1 or 2 to a maximum reach temperature of 850 ° C at 950 ° C; and forming by pressing the steel sheet.
[0004]
4. Method for hot pressing an Al coated steel sheet according to claim 3, characterized by the fact that the average rate of temperature increase until the temperature of the Al coated steel sheet reaches 50 ° C until a temperature 10 ° C lower than the maximum reach temperature is 10 ° C / s to 300 ° C / s in heating before pressing by pressing the steel sheet.
[0005]
5. Method for hot pressing an Al-coated steel sheet according to claim 4, characterized by the fact that heating before pressing by pressing the steel sheet is carried out by electric heating or induction heating .

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法律状态:
2018-03-27| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2019-09-10| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2019-09-17| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

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2020-09-29| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2020-12-22| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 15/04/2013, OBSERVADAS AS CONDICOES LEGAIS. |

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