GALVANIZED LAYER, YOUR METHOD FOR PRODUCTION AND STEEL SHEET

专利摘要:
galvanized and annealed layer and steel sheet comprising the same and method for its production. the present invention relates to a sheet of galvanized and annealed steel, reliably and sufficiently improved in the adhesiveness of a sheet plated with a base steel sheet, such as a sheet of galvanized and annealed steel, prepared by the use of a sheet of high strength steel as a base material; and a method for producing the galvanized and annealed steel sheet. the galvanized and annealed steel sheet, wherein a galvanized and annealed layer is formed on a base steel sheet, including a high-strength steel that has a predetermined component composition; the average amount of fe in the galvanized and annealed layer is in the range of 8.0 to 12.0%; and the absolute value (delta) fe of a difference between the amount of fe in the vicinity of an interface with the base steel sheet (the amount of fe in the vicinity of an inner side) and the amount of fe in the vicinity of the outer surface of the plated layer (the amount of fe in the vicinity of an external side) in the plated layer is in the range of 0.0 to 3.0%. moreover, in a method for the production of the galvanized and annealed steel sheet, the treatment of plated intraclay diffusion to level the gradient of fe concentration in the plated layer is carried out after finishing the hot dip galvanization and treatment of alloy formation.
公开号:BR112014002203B1
申请号:R112014002203-8
申请日:2012-07-27
公开日:2020-10-06
发明作者:Hiroyuki Kawata；Naoki Maruyama；Akinobu Murasato；Akinobu Minami；Takeshi Yasui
申请人:Nippon Steel Corporation；
IPC主号:

专利说明:

Technique Field
[0001] The present invention relates to a galvanized and annealed layer and a plated steel sheet, the galvanized and annealed layer being formed on a surface of a high strength steel sheet as a base material. In particular, the present invention relates to a galvanized and annealed layer and a plated steel sheet, improved in the adhesiveness of a galvanized layer with a base steel sheet, and to a method for producing the galvanized and annealed layer. Background of the Technique
[0002] In recent years, the highest strength of steel plates used in various components and structures, such as automotive exterior plates (bodywork sheets), construction machinery, and in addition, civil engineering and construction structures building construction, have been increasingly needed, and a high-strength steel plate with a maximum tensile strength limit of 900 MPa or more has also been used. In addition, steel sheets containing such uses usually need excellent resistance to corrosion because it is generally used on the outside.
[0003] Conventionally, steel sheets containing such uses, hot-dip galvanized steel sheets subjected to hot-dip galvanizing have been widely used. Recently, there is a galvanized and annealed steel plate subjected to alloy formation treatment including hot dip galvanizing, thereby heating a plated layer to a temperature that is not less than the melting point of Zn to diffuse Fe from a base steel plate to the plated layer, and forming the plated layer as a layer based on a Zn-Fe alloy has also been widely used. Such an annealed and galvanized steel sheet is known to have excellent surface appearance and corrosion resistance when compared to a hot dip galvanized steel sheet that is not subjected to alloy formation treatment.
[0004] However, in uses for automotive exterior plates and the like, the periphery of a plate is usually subjected to severe bending work (edge formation) through press work; and, not only in automotive outer plates, but also in other uses, such a plate, subjected to severe bending work, expansion work by drilling, or the like through press work, is normally used. In addition, when a conventional galvanized and annealed steel sheet is subjected to severe bending work, bore expansion work or the like, a plated layer can peel off from a base steel sheet in a portion worked in such a way. When the plated layer flakes in such a way, there is a problem that the corrosion resistance of an area where the plated layer flakes is lost to corrode and prematurely rust the base steel plate. Even when the plated layer does not peel off the loss of adhesion between the plated layer and the base steel plate to produce even some gaps in an area where the adhesive is lost, it causes outside air and moisture to enter the gaps, the function anti-corrosion of the plated layer is lost, and the base steel plate is prematurely corroded and rusted in the same way as described above. Thus, there is a strong desire to develop a galvanized and annealed layer and a plated steel plate, which has excellent adhesion of the plated layer with a base steel plate, for uses in which such severe or similar work is carried out.
[0005] Several ways have been proposed to improve the adhesiveness of a plated layer with a base steel plate on a galvanized and annealed steel plate, and some examples of these are described in Patent Literature 1 to 8. List of Literature Citation Patent Literature Patent 1: Publication Open Patent to Public Inspection in JP 2009-68061 Patent Literature 2: Patent Publication Open to Public Inspection in JP 2008-26678 Patent Literature 3: Publication of Patent Open to Public Inspection in JP 2005-256041 Patent Literature 4: Patent Publication Open to Public Inspection in JP 2002-173756 Patent Literature 5: Patent Publication Open to Public Inspection in JP 9-13147 Patent Literature 6: Patent Publication Open to Public Inspection in JP 6-235077 Patent Literature 7: Patent Publication Open to Public Inspection in JP 2002-146503 Patent Literature 8: Patent Publication Open to Public Inspection in JP 5-311371 SUMMARY OF THE INVENTION Technique Problem
[0006] As mentioned above, an annealed galvanized layer and a plated steel plate, subjected to bending or similar work and used, desirably have the excellent adhesiveness of a plated layer with a base steel plate; however, conventional methods for improving adhesiveness, as described in Patent Literature 1 to 8, have still been insufficient, and it has been difficult to safely and steadily prevent the plated layer from peeling particularly when the galvanized and annealed layer and the plated steel sheet are subjected to very severe work such as edge forming work or drilling expansion work are used.
[0007] For example, Patent Literature 7 describes that the recesses and projections of a plating coating can be eliminated by bending or the like before hot dip galvanizing. This is assumed to be because a large number of preferred nucleation sites are generated at a base material interface through folding or similar work prior to plating, to accelerate the formation of alloy. However, there is neither a description nor a suggestion that the concentration of Fe in a plated layer is controlled by the folding work after a plating treatment step.
[0008] Additionally, Patent Literature 8 describes that an alloying rate can be improved by the work of bending in alloying by heating after plating. This is because Fe-AI-Zn which decreases a Fe-Zn alloy formation rate is broken down by the folding work, to accelerate AA Fe-Zn alloy formation. However, temperature in the formation of alloys through heating is not described in any way, and there is no description or suggestion that the concentration of Fe in a plated layer is controlled by adjusting the temperature.
[0009] The present invention was carried out in relation to the above circumstances as an antecedent and is aimed at providing a galvanized and annealed layer and a plated steel plate, safely and sufficiently perfected in the adhesiveness of a plated layer with a steel plate. base, such as a galvanized and annealed layer and a plated steel sheet, prepared using a high strength steel sheet as a base material and providing a method for producing the galvanized and annealed layer. Solution to the Problem
[00010] As a result of the repetition of several experiments and examinations of the adhesiveness of a plated layer on a galvanized and annealed steel sheet, the present inventors have found that in a hot dip galvanized layer that is bonded, the amount concentration gradient of Fe in the thickness direction of the plated layer has a great influence on the adhesiveness of the plated layer with a base steel plate. In other words, when the hot dip galvanized layer is subjected to alloying treatment, Fe diffuses from the inside of the base steel sheet to the plated layer and the plated layer has a structure based on Zn-Fe alloy ; however, in this case, since the diffusion of Fe proceeds from a side closer to the base steel plate, the concentration of Fe in the plated layer after the alloy formation treatment is usually higher on the side closest to the steel plate base and smaller on a side closer to the outer surface of the plated layer. On the other hand, the Zn-Fe alloy that forms the bonded galvanized layer is softer with a decrease in the concentration of Fe, but is more fragile with an increase in the concentration of Fe. Therefore, decreasing the concentration of Fe in the vicinity of the outer surface due to the Fe concentration gradient as mentioned above, the outer surface is softened during press work and therefore adheres to an ink causing stripping. In contrast, when the Fe concentration is increased in the vicinity of an interface with the base steel plate due to the aforementioned Fe concentration gradient to make the surroundings brittle, the plated layer is fractured in the region through severe work, easily causing spray.
[00011] As a result of additionally continuous experiments and examinations based on such findings, it was found that by carrying out the treatment in which Fe in a plated layer is diffused into the layer while preventing Fe from diffusing from a base steel sheet in the plated layer as much as possible after the alloying treatment of a hot dip galvanized layer, the gradient of Fe concentration in the plated layer can be reduced (the gradient of the Fe concentration is leveled) equalize the concentration of Fe in the plated layer to a favorable concentration (about 10%), which peel resistance is excellent, in any portion in the direction of its thickness, to thereby improve the adhesiveness of the galvanized layer and annealed with the base steel sheet more than ever before, and the present invention has thus been accomplished.
[00012] The present invention was carried out on the basis of such innovative findings as described above and is basically to provide a galvanized and annealed layer and a plated steel plate, improved in the adhesiveness of the plated layer with a base steel plate, leveling the gradient of Fe concentration in the plated layer of the plated steel sheet in which the galvanized and annealed layer is formed on a surface of a high-strength steel sheet as a base material. In addition, the present invention is to provide a method for producing a galvanized and annealed layer, including a treatment step to reduce the gradient of Fe concentration in a hot dip galvanized layer.
[00013] Thus, the present invention is summarized as follows: (1) A galvanized and annealed layer formed on a surface of a base steel plate, where the average amount of Fe in the galvanized and annealed layer is in a range of 8 , 0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe at a position 1/8 the thickness of the plated layer (the amount of Fe in the vicinity of an inner side) and the amount of Fe at a position 7/8 of the thickness of the plated layer (the amount of Fe in the vicinity of an external side) in the galvanized and annealed layer, the thickness being from an interface between the galvanized and annealed layer and the base steel plate for the outer surface of the plated layer, is in a range of 0.0 to 3.0%. (2) A galvanized and annealed steel sheet, in which the galvanized and annealed layer according to (1) is formed on a surface of a base steel sheet including, in mass%, C: 0.050 to 0.300%, Si : 0.10 to 2.50%, Mn: 0.50 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.005 to 1.500%, O: 0, 0001 at 0.0100%, N: 0.0001 at 0.0100%, and the balance in Fe and unavoidable impurities. (3) The galvanized and annealed steel sheet, according to the above (2), in which the base steel sheet additionally includes, in mass%, one or two or more selected from Cr: 0.01 to 2 , 00%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Ti: 0.005 to 0.150%, Nb: 0.005 to 0.150%, V: 0.005 to 0.150%, Mo: 0 , 01 to 1.00%, and B: 0.0001 to 0.0100%. (4) The galvanized and annealed steel sheet according to the above (2) or (3), where the base steel sheet additionally includes 0.0001 to 0.5000% in the total of one or two or more selected from of Ca, Ce, Mg, Zr, Hf and REM. (5) The galvanized and annealed steel sheet according to any of the above (2) to (4), in which a coating that includes a P oxide and / or a complex oxide containing P is formed on a surface of the layer galvanized and annealed. (6) A method for producing a galvanized and annealed layer, including: in mass%, a hot dip galvanizing step to subject a base steel sheet surface to hot dip galvanizing to obtain a steel sheet hot dip galvanized; an alloy formation treatment step to heat a hot dip galvanized layer, formed in the hot dip galvanizing step, to a temperature in the range of 470 to 650 ° C to form a galvanized and annealed layer and to produce a galvanized and annealed steel plate; and an intragalvanized and annealed diffusion treatment step to, after the alloy formation treatment step, allow the galvanized and annealed steel sheet to remain at a temperature in the range of 250 to 450 ° C and submit the galvanized and annealed steel sheet at one or more times of folding and unfolding work in the temperature range to diffuse Fe in the galvanized and annealed layer. (7) The method for producing a galvanized and re-baked layer according to the above (6), in which the galvanized and annealed steel sheet is obtained, in which, after the diffusion treatment step of the intragalvanized and annealed layer, the average amount of Fe in the galvanized and annealed layer is in the range of 8.0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe at a position 1/8 the thickness of the plated layer (the amount of Fe in the vicinity of an inner side) and the amount of Fe at a position 7/8 of the thickness of the plated layer (the amount of Fe in the vicinity of an external side) in the galvanized and annealed layer, the thickness being from an interface between the galvanized and annealed layer and the base steel plate for the outer surface of the plated layer, is in a range of 0.0 to 3.0%. (8) The method for producing a galvanized and re-baked layer according to the above (6) or (7), in which in the diffusion treatment step of the intragalvanized and annealed layer, the folding work is carried out so that a deformation of the maximum amount of traction on a steel sheet surface is in the range of 0.0007 to 0.0910. (9) The method for producing a galvanized and annealed steel sheet according to any of the above (6) to (8), wherein a surface of the galvanized and annealed layer is subjected to phosphate coating treatment to form a coating including an oxide P and / or a complex oxide containing P after the stage of diffusion treatment of intragalvanized and annealed layer. (10) The method for producing a galvanized and annealed layer according to any one of (6) to (9), in which a base steel plate including, in mass%, C: 0.050 to 0.300%, Si: 0 , 10 to 2.50%, Mn: 0.50 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.005 to 1.500%, O: 0.0001 to 0.0100%, N: 0.0001 to 0.0100%, and the balance of Fe and unavoidable impurities is used as the base steel plate. (11) The method for producing a galvanized and annealed layer according to the above (10), in which the steel sheet which additionally includes, in mass%, one or two or more selected from Cr: 0, 01 to 2.00%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Ti: 0.005 to 0.150%, Nb: 0.005 to 0.150%, V: 0.005 to 0.150%, Mo: 0.01 to 1.00%, and B: 0.0001 to 0.0100% is used as the base steel plate. (12) The method for producing a galvanized and annealed layer according to any of the above (10) to (11), wherein the steel sheet additionally including, in mass%, 0.0001 to 0.5000% in total one or two or more selected from Ca, Ce, Mg, Zr, Hf, and REM is used as the base steel plate. Advantageous Effects of the Invention
[00014] According to the present invention, a galvanized layer and a plated steel plate, sufficiently and safely perfected in the adhesiveness of a plated layer with a base steel plate, can be obtained as a galvanized and annealed layer and a plated steel plate, on which a steel plate, particularly a high-strength steel plate, is used as a base material and therefore the plated layer can be effectively prevented from being fractured and peeled even in uses subjected to severe work such as bending work or bore expansion work. BRIEF DESCRIPTION OF THE DRAWINGS
[00015] Figure 1 is a graph that indicates a relationship between the average amount of Fe and the absolute value of the amount of ΔFe in a plated layer and the appearance of the plated layer.
[00016] Figure 2 is a graph that indicates a relationship between the limit of tensile strength and an elongation in the galvanized and annealed steel sheet, according to the present invention. DESCRIPTION OF THE MODALITIES
[00017] The present invention will be explained in detail below.
[00018] In the galvanized and annealed layer and plated steel sheet of the present invention, basically a high strength steel sheet having a predetermined component composition is used as a base material and a galvanized and annealed layer is formed on the surface of the base steel plate. In addition, particularly for the galvanized and annealed layer, not only the average amount of Fe in the plated layer is specified, but also a distribution of the Fe concentration (Fe concentration gradient) in the thickness direction of the plated layer is specified.
[00019] In other words, the galvanized and annealed layer is an alloy layer formed through alloy formation treatment including the formation of a plated layer of Zn on the surface of the base steel plate through hot-dip galvanizing and reheating , thereafter, the plated layer at a temperature that is not less than the melting point of Zn to diffuse Fe in the base steel plate in the plated layer and has a structure based on a Zn-Fe alloy. In the present invention, the average amount of Fe in the galvanized and annealed layer is, in mass%, in the range of 8.0 to 12.0%, and the absolute value of the difference ΔFe between the amount of Fe in the vicinity of the external side and the amount of Fe in the vicinity of the inner side is specified in the range of 0.0 to 3.0% as a gradient condition of Fe concentration in the thickness direction in the galvanized and annealed layer. In this way, the reasons for limiting conditions will be explained. Average Amount of Fe in the Plated Layer: 8.0 to 12.0%
[00020] When the average amount of Fe in the galvanized and annealed layer is less than 8.0%, the plated layer becomes soft and easily adheres to a paint for press work and therefore exfoliation (flaky flaking) it occurs easily during press work. Thus, the average amount of Fe in the plated layer is preferably 8.0% or more from the point of view of resistance to exfoliation. Preferably, the average amount of Fe is 9.0% or more. On the other hand, the average amount of Fe in the galvanized and annealed layer is more than 12.0%, the plated layer becomes brittle and is easily fractured, and spraying (powdery flaking) easily occurs during press work. Thus, the average amount of Fe in the plated layer is preferably 12.0% or less from the point of view of spray resistance. Preferably, the average amount of Fe is 11.0% or less. Thus, an average concentration of Fe in a range of 8.0 to 12.0%, preferably in a range of 9.0 to 11.0%, causes both exfoliation and spraying to hardly occur and the adhesiveness of the plated layer to become good. [Gradient Condition of Fe in the Plated Layer: Absolute ΔFe value from 0.0 to 3.0%]
[00021] As mentioned above, in a hot dip galvanized layer subjected to alloy formation treatment, a gradient of Fe concentration usually exists in the direction of its thickness. In the Fe concentration gradient, there is a general tendency for the Fe concentration to be high near an interface with a base steel plate and for the Fe concentration to be low near the outer surface of the plated layer. In a region close to the surface, where the Fe concentration is low, the plated layer becomes soft to adhere to a paint during press and exfoliation work and peeling occurs easily. On the other hand, in the vicinity of the interface with the base steel plate, in which the Fe concentration is low, the plated layer becomes brittle and spraying and flaking occur easily. Thus, in any case, the flaking of the plated layer occurs easily when severe work is carried out. Thus, in the present invention, the Fe concentration gradient in the plated layer is reduced to specify a Fe concentration gradient condition so that the favorable Fe concentration (8.0 to 12.0%, preferably 9.0 at 11.0%) which exfoliation or spraying hardly occurs in any portion in the direction of its thickness is achieved. In other words, it is specified that the absolute value of the difference ΔFe between the amount of Fe in the vicinity of the interface with the base steel plate (the amount of Fe in the vicinity of the inner side) and the amount of Fe in the vicinity of the outer surface of the plated layer (the amount of Fe in the vicinity of the external side) is in the range of 0.0 to 3.0%. The amount of Fe in the vicinity of the inner side means the amount of Fe at 1/8 of the total thickness of the plated layer from the interface with the base steel plate to the outer surface of the plated layer, while the amount of Fe in the proximity to the outer side means the amount of Fe in the 7/8 position of the total thickness of the plated layer from the interface with the base steel plate to the outer surface of the plated layer (that is, the 1/8 position the total thickness of the plated layer from the outer surface of the plated layer to the interface with the base steel plate).
[00022] The absolute value of ΔFe of more than 3.0% results in the insufficient effect of improving the adhesiveness of the plated layer. Thus, it is specified that the absolute value of ΔFe is in the range of 0.0 to 3.0%. The absolute value of ΔFe of 3.0% or less results in less chance that flaking due to exfoliation or spraying will occur on the plated layer even when severe work is carried out, so that the adhesiveness of the plated layer is improved. Furthermore, in order to obtain the adhesion enhancing effect more safely, the absolute value of ΔFe is preferably 2.0% or less, additionally more preferably 1.5% or less.
[00023] Furthermore, the amount of galvanized and annealed layer coating is not particularly limited, but it is desirably 20 g / m2 or more from the point of view of corrosion resistance and 150 g / m2 or less from the point of view view of economic efficiency.
[00024] In addition, the galvanized and annealed layer is prepared by forming Fe alloy based on Zn; however, even when the galvanized and annealed layer contains Zn and Fe as well as a small amount of one or two or more of Al, Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, Sr, I, Cs, and REM, the effects of the present invention are not impaired and a preferential effect such as improving corrosion resistance or workability can be provided depending on the quantity.
[00025] The reasons for limiting the composition of the steel sheet component used as the base material for the galvanized and annealed steel sheet of the present invention will be explained below. In the description below, all "%" represents% by mass. [C: 0.050 to 0.300%]
[00026] C is contained to increase the strength of a high-strength steel sheet. However, a C content of more than 0.300% results in insufficient weldability. The C content is preferably 0.250% or less, more preferably 0.220% or less, from the point of view of weldability. On the other hand, a C content of less than 0.050% results in decreased strength and prevents the setting of a maximum tensile strength limit of 900 MPa or more. The C content is preferably 0.075% or more, more preferably 0.100% or more, to further improve the strength. [Si: 0.10 to 2.50%]
[00027] Si is an element that suppresses the generation of an iron-based carbide in a steel plate and improves strength and moldability. However, a Si content of more than 2.50% results in the weakening of the steel plate and the deterioration of ductility. The Si content is preferably 2.20% or less, more preferably 2.00% or less, from the point of view of ductility. On the other hand, a Si content of less than 0.10% results in the generation of a large amount of coarse iron-based carbide during the treatment of alloy formation of a plated layer and in the deterioration of strength and moldability. From the point of view of the above, the lower limit of Si is preferably 0.30% or more, more preferably 0.45% or more. [Mn: 0.50 to 3.50%]
[00028] Mn is added to improve the strength of a steel plate. However, an Mn content of more than 3.50% results in the generation of a concentrated unit Mn coarse in the center in the sheet thickness of the steel plate to cause embrittlement to occur easily and cause problems such as the rupture of a cast plate occurs easily. An Mn content of more than 3.50% also results in deterioration of weldability. Thus, the Mn content is preferably 3.50% or less. The Mn content is preferably 3.20% or less, more preferably 3.00% or less, from the point of view of weldability. On the other hand, since an Mn content of less than 0.50% results in the formation of a large amount of soft structure during cooling after annealing, thereby preventing the setting of a maximum tensile strength limit 900 MPa or more, the Mn content is preferably 0.50% or more. The Mn content is preferably 1.50% or more, more preferably 1.70% or more, to further improve the strength. [P: 0.001 to 0.030%]
[00029] P tends to segregate in the center in the plate thickness of a steel plate and weakens a weld. Since a P content of more than 0.030% results in great weld embrittlement, the upper limit of the P content is 0.030%. On the other hand, since a P content of less than 0.001% results in a much increased production cost, the lower limit of this is 0.001%. [S: 0.0001 to 0.0100%]
[00030] S adversely affects weldability as well as productivity in casting and hot rolling. Thus, the upper limit of the S content is 0.0100% or less. In addition, S is linked to Mn to form MnS which is coarse and to deteriorate ductility and stretch flange properties and is therefore preferably 0.0050% or less, more preferably 0.0025% or less. On the other hand, since an S content of less than 0.0001% results in a much increased production cost, the lower limit is 0.0001%. [Al: 0.005 to 1.500%]
[00031] Al suppresses the generation of an iron-based carbide and improves the strength and moldability of a steel plate. However, an Al content of more than 1,500% results in deteriorated weldability and the upper limit of the Al content is therefore 1,500%. From the point of view of the above, the Al content is preferably 1,200% or less, more preferably 0.900% or less. Al is also an element that is effective as a deoxidation material; however, since an Al content of less than 0.005% results in an insufficient effect as the deoxidation material, the lower limit of the Al content is 0.005%. The amount of Al is preferably 0.010% or more to obtain a more sufficient deoxidation effect. [N: 0.0001 to 0.0100%]
[00032] Since N forms a coarse nitride and deteriorates the ductility and stretch flange properties, the amount of N added is preferably reduced. Since an N content of more than 0.0100% results in the significant trend from above, the upper limit of the N content is 0.0100%. Since N also causes the generation of bubbles in welding, its lower content is better. The effects of the present invention are applied even when the lower limit of the N content is not particularly specified; however, since an N content of less than 0.0001% results in a greatly increased production cost, the N content is 0.0001% or more. [O: 0.0001 to 0.0100%]
[00033] Since O forms an oxide and deteriorates the ductility and stretching flange properties, the content of the oxide is preferably reduced. Since an O content of more than 0.0100% results in significant deterioration of the stretch flange properties, the upper limit of the O content is 0.0100%. In addition, the O content is preferably 0.0080% or less, more preferably 0.0060% or less. The effects of the present invention are applied even when the lower limit of the O content is not particularly specified; however, since an O content of less than 0.0001% results in a greatly increased production cost, the lower limit is 0.0001%.
[00034] In addition, the elements described below can optionally be added to the base steel sheet for the annealed and galvanized steel sheet of the present invention. [Cr: 0.01 to 2.00%]
[00035] Cr is an element that suppresses the phase transformation at high temperature and is effective for the highest resistance and can be added instead of part of C and / or Mn. Since a Cr content of more than 2.00% results in deteriorated hot workability to reduce productivity, the Cr content is 2.00% or less. Although the effects of the present invention are applied even when the lower limit of the Cr content is not particularly specified, the Cr content is preferably 0.01% or more to sufficiently achieve the effect of achieving higher strength by adding Cr. [Ni: 0.01 to 2.00%]
[00036] Ni is an element that suppresses the phase transformation at high temperature and is effective for the highest resistance and can be added instead of part of C and / or Mn. Since a Ni content of more than 2.00% results in deteriorated weldability, the Ni content is 2.00% or less. Although the effects of the present invention are applied even when the lower limit of the Ni content is not particularly specified, the Ni content is preferably 0.01% or more to sufficiently obtain the effect of achieving higher strength by adding Ni. [Cu: 0.01 to 2.00%]
[00037] Cu is an element that exists as fine particles in a steel, thereby improving strength and can be added instead of part of C and / or Mn. Since a Cu content of more than 2.00% results in deteriorated weldability, the Cu content is 2.00% or less. Although the effects of the present invention are applied even when the lower limit of the Cu content is not particularly specified, the Cu content is preferably 0.01% or more to sufficiently achieve the effect of achieving higher resistance by adding Cu. [Ti: 0.005 to 0.150%]
[00038] Ti is an element that contributes to the increase in the strength of a steel plate through the strengthening of precipitate, the strengthening of fine grain due to the suppression of ferrite crystal grain growth, and the strengthening of displacement through suppression recrystallization. However, since a Ti content of more than 0.150% results in an increase in precipitated carbonitrides to deteriorate moldability, the Ti content is 0.150% or less. The Ti content is more preferably 0.100% or less, additionally preferably 0.070% or less, from the point of view of moldability. Although the effects of the present invention are applied even when the lower limit of the Ti content is not particularly specified, the Ti content is preferably 0.005% or more to sufficiently obtain the effect of increasing the strength by adding Ti. Ti content is more preferably 0.010% or more, additionally preferably 0.015% or more, to additionally achieve the highest strength of the steel sheet. [Nb: 0.005 to 0.150%]
[00039] Nb is an element that contributes to the increase in the strength of a steel plate through the strengthening of precipitate, the strengthening of fine grain due to the suppression of the growth of ferrite crystal grain, and the strengthening of displacement through su-pressure recrystallization. However, since an Nb content of more than 0.150% results in an increase in precipitated carbonitrides to deteriorate moldability, the Nb content is 0.150% or less. The Nb content is more preferably 0.100% or less, additionally preferably 0.060% or less, from the point of view of moldability. Although the effects of the present invention are applied even when the lower limit of the Nb content is not particularly specified, the Nb content is preferably 0.005% or more to sufficiently obtain the effect of increased strength by adding Nb . The Nb content is more preferably 0.010% or more, additionally preferably 0.015% or more, to further achieve the higher strength of the steel sheet. [V: 0.005 to 0.150%]
[00040] V is an element that contributes to the increase in the strength of a steel plate through the strengthening of precipitate, the strengthening of fine grain due to the suppression of the growth of ferrite crystal grain, and the strengthening of displacement through the suppression recrystallization. However, since a V content of more than 0.150% results in an increase in precipitated carbonitrides to deteriorate moldability, the V content is 0.150% or less. Although the effects of the present invention are applied even when the lower limit of the V content is not particularly specified, the V content is preferably 0.005% or more to sufficiently achieve the effect of increasing strength by adding V. [Mo: 0.01 to 1.00%]
[00041] Mo is an element that suppresses the phase transformation at high temperature and is effective for higher resistance and can be added instead of part of C and / or Mn. Since a Mo content of more than 1.00% results in deteriorated hot workability to reduce productivity, the Mo content is 1.00% or less. Although the effects of the present invention are applied even when the lower limit of the Mo content is not particularly specified, the Mo content is preferably 0.01% or more to sufficiently achieve the effect of achieving the highest strength by adding Mo . [W: 0.01 to 1.00%]
[00042] W is an element that suppresses the phase transformation at high temperature and is effective for the highest resistance and can be added instead of part of C and / or Mn. Since a W content of more than 1.00% results in deteriorated hot workability to reduce productivity, the W content is preferably 1.00% or less. Although the effects of the present invention are applied without particularly specifying the lower limit of the W content, the W content is preferably 0.01% or more to obtain, sufficiently higher resistance due to W. [B: 0.0001 to 0.0100%]
[00043] B is an element that suppresses the phase transformation at high temperature and is effective for higher resistance and can be added instead of part of C and / or Mn. Since a B content of more than 0.0100% results in deteriorated hot workability to reduce productivity, the B content is 0.0100% or less. The B content is more preferably 0.0050% or less, in addition to preference 0.0030% or less, from the point of view of productivity. Although the effects of the present invention are applied even when the lower limit of the B content is not particularly specified, the B content is preferably 0.0001% or more to obtain sufficiently the effect of achieving higher strength by adding B. The B content is more preferably 0.0003% or more, more preferably 0.0005% or more, for additionally higher strength.
[00044] In addition, 0.0001 to 0.5000% in total of one or two or more among Ca, Ce, Mg, Zr, Hf and REM as additional elements can be added to the base steel plate on the galvanized steel plate and annealed of the present invention. The reason for adding the elements is described below.
[00045] Ca, Ce, Mg, Zr, Hf and REM are effective elements to improve the moldability and one or two or more of them can be added. However, since a total of the contents of one or two or more among Ca, Ce, Mg, Zr, Hf and REM greater than 0.5000% may, instead, result in deteriorated ductility, the total contents of the respective elements is preferably 0.5000% or less. Although the effects of the present invention are exercised even when the lower limit of the lower limit of the content of one or two or more among Ca, Ce, Mg, Zr, Hf and REM is not particularly specified, the total content of the respective elements is preferably 0.0001% or more to sufficiently obtain the effect of improving the moldability of a steel sheet. The total content of one or two or more among Ca, Ce, Mg, Zr, Hf and REM is preferably 0.0005% or more, more preferably 0.0010% or more, from a point of view. moldability. REM is an abbreviation for Rare Earth Metal and refers to an element that belongs to the lanthanide series. In the present invention, REM and Ce are often added in a mischmetal, which may contain an element from the series of element lanthanides as well as La and Ce in a complex. The effects of the present invention are exercised even when the element of the element lanthanide series as well as La and Ce described above are contained as unavoidable impurities. In addition, the effects of the present invention are exercised even when the metals La and Ce are added.
[00046] The balance in addition to the respective elements above can be Fe and unavoidable impurities. In addition, each of Cr, Ni, Cu, Ti, Nb, V, Mo, W and B mentioned above can be contained as an impurity in a small amount less than the lower limit thereof. Ca, Ce, Mg, Zr, Hf and REM can also be contained as impurities in a residual amount less than the lower limit of their total amount.
[00047] The structure of the high-strength steel sheet used as the base material for the galvanized and annealed steel sheet of the present invention will be explained below.
[00048] The high-strength steel sheet used as the base material for the galvanized and annealed steel sheet of the present invention preferably includes, in fraction of volume, ferrite: 10 to 75%, bainitic ferrite and / or bainite: 10 to 50%, tempered martensite: 10 to 50%, initial martensite: 15% or less and retained austenite: 20% or less as their microstructures in the range of 1/8 to 3/8 of a thickness of plate assuming that 1/4 of the thickness is a center. When the high strength steel sheet as the base material has these structures, the galvanized and annealed steel sheet that has superior moldability is made. Therefore, the preferred conditions for each of the structures will be explained below. [Ferrite: 10 to 75%]
[00049] Ferrite is an effective structure for improving ductility and is preferably contained in a volume fraction of 10 to 75% in a steel plate structure. A fraction of ferrite volume less than 10% can result in insufficient ductility. Ferrite is more preferably contained in the steel sheet structure in a volume fraction of 15% or more, more preferably 20% or more, from the point of view of ductility. On the other hand, since ferrite is a soft structure, a fraction of a ferrite volume greater than 75% can result in insufficient strength. The volume fraction of ferrite contained in the steel sheet structure is preferably 65% or less, more preferably 50% or less, to enhance the tensile strength of the steel sheet. [Bainitic and / or Bainite ferrite: 10 to 50%]
[00050] Bainitic ferrite and / or bainite are excellent structures in the balance between strength and ductility and are preferably contained in a volume fraction of 10 to 50% in a steel plate structure. Additionally, bainitic ferrite and / or bainite are microstructures that have resistance between those of soft and rigid martensite and between those of tempered and retained austenite and are more preferably contained by 15% or more, more preferably contained by 20% or more, from the point of view of folding capacity and stretching flange properties. On the other hand, a volume fraction of bainitic and / or bainite ferrite greater than 50% is not preferred because it results in excessively increased yield stress and deteriorated shape fixation capacity. [Temperate Martensite: 10 to 50%]
[00051] Tempered martensite is a structure that greatly improves tensile strength and can be contained in a volume fraction of 50% or less in a steel plate structure. The volume fraction of tempered martensite is preferably 10% or more from the point of view of tensile strength. On the other hand, the volume fraction of tempered martensite contained in the steel plate structure, greater than 50%, is not preferred because it results in excessively increased yield stress and deteriorated shape fixation capacity. [Initial Martensite: 15% or less]
[00052] The initial martensite greatly improves the tensile strength, but it becomes a source of fracture to greatly deteriorate the folding capacity and the volume fraction thereof is therefore preferably limited to 15% or less in a structure of steel sheet. The volume fraction of initial martensite is more preferably 10% or less, more preferably 5% or less, to enhance bending capacity and stretching flange properties. [Austenite retained: 20% or less]
[00053] Retained austenite greatly improves strength and ductility and can therefore be contained in an amount that has an upper limit of 20% on a steel plate. On the other hand, retained austenite becomes a source of fracture to greatly deteriorate stretching flange properties and the volume fraction thereof is therefore preferably 17% or less, more preferably 15% or less. [Other Structures]
[00054] The steel plate structure of the high strength steel plate as the base material in the present invention may contain structures in addition to the above, such as perlite and / or coarse cementite. However, the folding capacity is impaired when there is a large amount of coarse perlite and / or cementite in the steel plate structure of the high strength steel plate. Therefore, the fraction of total volume of perlite and / or coarse cementite contained in the steel sheet structure is preferably 10% or less, more preferably 5% or less.
[00055] The volume fraction of each structure contained in the steel plate structure of the high strength steel plate used as the base material in the present invention can be measured, for example, by a method described below.
[00056] For the fraction of the volume of austenite retained, X-ray analysis is performed with a surface that is parallel to the surface of the steel sheet and is 1/4 of the thickness of the sheet as an observation surface, to calculate a fraction of area, which can be considered as the fraction of volume.
[00057] For the volume fraction of each of the structures, that is, ferrite, bainitic ferrite, bainite, tempered martensite and initial martensite, a sample is collected with a transversal cut in the plate thickness parallel to the lamination direction of the plate. steel as an observation surface, the observation surface is polished and etched by nital and the range of 1/8 to 3/8 thickness, assuming that 1/4 thickness is a center, is observed with a scanning electron microscope by field emission (FE-SEM) to measure a fraction of area, which can be considered as the fraction of volume.
[00058] The method for producing a galvanized and annealed layer and a plated steel sheet of the present invention will be explained below.
[00059] In the production method of the present invention, the steps before obtaining the base steel sheet are not particularly limited and therefore, each step for forming the galvanized and annealed layer on the base steel sheet having a predetermined sheet thickness is first explained. However, each step to form the galvanized and annealed layer can also be incorporated into an annealing step after cold rolling in a process to produce the base steel sheet, particularly a cooling process and the above points are explained again later with the explanation of the production method of the base steel plate.
[00060] In the method for producing a galvanized and annealed layer and a plated steel sheet of the present invention, the process for forming the galvanized and annealed layer on the surface of the base steel sheet basically includes a hot dip galvanizing step, a alloy formation treatment step and an intrachap layer diffusion treatment step. In some cases, a phosphate coating formation treatment can also be carried out after the treatment step by diffusion of the intrachaped layer. The conditions of the stages will be explained below. [Hot dip galvanizing step]
[00061] Hot dip galvanizing can be carried out by continuous or discontinuous immersion of the base steel sheet in a hot dip galvanizing bath in the same way as the known technique. The temperature of the hot dip galvanizing bath in performance is basically preferentially not less than the melting point (about 420 ° C) of Zn; however, since Zn can be solidified locally due to the fluctuation of bath temperature to make an operation unstable when it is almost at the melting point, the temperature generally preferentially 440 ° C or more. On the other hand, since a bath temperature greater than 480 ° C can result in the generation of a Fe-Al-Zn phase that inhibits the formation of alloy, the temperature is generally preferably 480 ° C or less. Furthermore, there is no particular problem even when Zn is a small amount of one or two or more among Al, Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be , Bi, Sr, I, Cs and REM are contained or mixed in the hot dip galvanizing bath and a preferential effect such as improving corrosion resistance or workability can be provided depending on the quantity, as mentioned above.
[00062] Furthermore, the coating weight of the plating metal on galvanizing and annealing is preferably 20 g / m2 or more from the point of view of corrosion resistance and preferably 150 g / m2 or less from the point of from the point of view of economic efficiency and immersion time (plate jump rate), bath temperature and the like can be adjusted appropriately so that this coating weight is achieved. [Alloy formation treatment step]
[00063] The alloy formation treatment step is a step to diffuse Fe from the base steel sheet in the hot dip galvanized layer formed on the surface of the base steel sheet in the preceding step and may include heating to a temperature in a range of 470 to 650 ° C to maintain the temperature in the range or heating to a temperature in a range of 470 to 650 ° C to perform annealing to the solidification temperature (about 420 ° C) of Zn. When the heating temperature for the alloy treatment is less than 470 ° C, it becomes difficult to sufficiently diffuse Fe in the base steel plate in the plated layer or a long time is required to diffuse a sufficient amount of Fe to deteriorate productivity. On the other hand, when the heating temperature for the alloy treatment is greater than 650 ° C, a problem that a coarse iron-based carbide is generated in the steel plate occurs. Therefore, the heating temperature for the alloy treatment is specified in the range of 470 to 650 ° C. When the alloy treatment is carried out keeping the temperature in the range of 470 to 650 ° C through heating, the time for maintenance is desirably in the range of 10 to 120 seconds. In addition, the annealing time in the case of heating to the temperature in the range of 470 to 650 ° C to perform the annealing to the solidification temperature (about 420 ° C) of Zn is preferably 15 to 200 seconds. [Stage of diffusion treatment of Plated Intracaayer]
[00064] The hot dip galvanized layer subjected to the alloy treatment in the preceding step is subjected to diffusion treatment to diffuse Fe in the plated layer to reduce the concentration gradient of the amount of Fe in the plated layer, that is, treatment to achieve the absolute value of a difference ΔFe between the amount of Fe in the vicinity of the interface with the base steel plate (the amount of Fe in the vicinity of an inner side) and the amount of Fe in the vicinity of the outer surface of the plated layer (the amount Fe in the vicinity of the external side) in the range of 0.0 to 3.0%. The diffusion treatment of the embedded layer includes allowing the hot-dip galvanized steel sheet subjected to the alloy treatment to remain at a temperature in the range of 250 to 450 ° C and to subject the hot-dip galvanized steel sheet one or more times of folding and unfolding work in the temperature range. Through folding and unfolding work one or more times at a temperature in the range of 250 to 450 ° C in this way, Fe can be easily diffused into the plated layer while suppressing the diffusion of Fe from the base steel sheet into the plated layer, thereby reduce the gradient of Fe concentration in the plated layer. The reason why Fe in the plated layer can be easily diffused while suppressing the diffusion of Fe from the base steel sheet in the folding and unfolding work in the above range can be considered as follows: a defect such as an atomic vacancy and / or a displacement is introduced mainly in the plated layer by the folding and unfolding work, to activate the diffusion of Fe atoms in the plated layer, while the diffusion of Fe atoms in the base steel plate does not occur due to the sufficiently low temperature and therefore, the diffusion of Fe from the base steel plate in the plated layer can only occur strictly.
[00065] When the temperature in the treatment by diffusion of the intrachaped layer is less than 250 ° C, the diffusion of Fe in the plated layer does not proceed sufficiently; while, at a temperature greater than 450 ° C, the melting of the plated layer can be initiated to rapidly diffuse Fe from the base steel sheet into the plated layer and, conversely, to increase the gradient of Fe concentration and the immersion metal the hot one adheres simultaneously to a cylinder for folding and unfolding work due to the melting of the plated layer, to make it practically impossible to perform the folding and unfolding work. Therefore, the temperature in the treatment by diffusion of intrachaped layer is in the range of 250 to 450 ° C.
[00066] A bending job is preferably carried out so that the amount of maximum tensile strain on the steel sheet surface varies from 0.0007 to 0.0910. An amount of maximum tensile strain less than 0.0007 results in an insufficient alloy acceleration effect. The amount of maximum tensile strain is preferably 0.0010 or more to sufficiently accelerate the alloy. On the other hand, an amount of maximum tensile strain greater than 0.0910 results in the impossibility of maintaining the shape of the steel plate to deteriorate the flatness. The amount of maximum tensile strain is preferably 0.0500 or less, more preferably 0.0250 or less, in order to maintain the shape of the steel sheet.
[00067] The sheet thickness of the steel sheet of the present invention is 0.6 mm to 10.0 mm. This is because the thickness less than 0.6 mm results in the impossibility of maintaining sufficiently the flat shape of the plate while the thickness greater than 10.0 mm results in difficult temperature control to make it impossible to obtain predetermined characteristics.
[00068] A cylinder diameter can be selected depending on the steel plate so that the amount of deformation in the folding work has an appropriate value and preferably ranges from 50 mm to 800 mm taking into account a maintenance cost. The amount of maximum tensile strain introduced on the surface of the steel sheet is a value obtained by dividing the thickness t of the sheet by the sum (D + t) of the cylinder diameter D and the thickness t of the sheet.
[00069] This galvanized and annealed steel sheet from which the alloy treatment has been completed can be submitted as a product sheet without processing the sheet for coating or pressure work for an automotive outer sheet or the like and can be submitted in addition to phosphate coating treatment as described below. [Phosphate Coating Formation Stage]
[00070] The phosphate coating formation step is a step to form a coating that includes a complex of oxide and / or an oxide of P containing P on the surface of the galvanized and annealed layer subjected to the diffusion layer treatment ada. In other words, in some cases, an oxide layer containing P (phosphate coating) has been formed conventionally by treating the plated surface of the steel sheet with a treatment liquid that includes phosphoric acid or an oxide containing P in order to accentuate the moldability by pressure and deep stamping of the galvanized and annealed steel sheet, thereby giving the steel sheet wedge with adhesion and lubricity prevention properties; and the galvanized and annealed steel sheet of the present invention can also be subjected to treatment to form that coating and the effects of the present invention are not impaired even in the case. The specific conditions for the phosphate coating treatment step are not particularly limited, but the step can be carried out under the same conditions as conventional conditions.
[00071] A desirable embodiment of the method for producing a high strength steel sheet that becomes the base material for the annealed, galvanized steel sheet of the present invention will be explained below. As mentioned above, hot-dip galvanizing on the surface of the steel sheet, alloy treatment, and in addition, diffusion treatment of the intrachaped layer can be incorporated in one step to produce a base steel sheet, particularly in a process of cooling in an annealing step after cold rolling and the steps related to plating in the case will also be explained together. In addition, several conditions described in the explanation of the method for producing the base steel sheet below are strictly described as desirable conditions and the method for producing the base steel sheet is not limited to the conditions.
[00072] To produce the high-strength steel plate as the base steel plate, first, a plate that has the chemical components mentioned above (composition) is melted and the flame is hot rolled.
[00073] As the sheet subjected to hot rolling, a sheet continuously cast or a sheet produced by a thin sheet melter or similar can be used. The method for producing the high strength steel sheet of the present invention is adapted for a process such as direct rolling and continuous casting (CC-DR) in which hot rolling is carried out immediately after casting.
[00074] In the hot rolling stage, the plate heating temperature is 1,050 ° C or more. When the plate heating temperature is excessively low, the finishing laminating temperature is lower than the Ara transformation temperature to result in ferrite and austenite double-phase lamination, the hot-rolled plate structure becomes a structure of heterogeneous duplex grain, the heterogeneous structure does not disappear even through the steps of cold rolling and annealing and the ductility and folding capacity are poor. Since there is a concern that the reduction in the finishing laminating temperature will result in an excessive increase in a laminating load to prevent lamination or result in the defect of the laminated steel plate formation, the plate heating temperature is preferably 1,050 ° C or more. The effects of the present invention are exercised without specifying particularly the upper limit of the plate heating temperature; however, since the excessively high heating temperature is economically unfavorable, the upper limit of the plate heating temperature is desirably 1,350 ° C or less.
[00075] The transformation temperature of Ars above is calculated using the following expression: Ar3 = 901-325xC + 33xSi- 92x (Mn + Ni / 2 + Cr / 2 + Cu / 2 + Mo / 2) + 52xAI
[00076] In the above expression, each of C, Si, Mn, Ni, Cr, Cu, Mo and Al represents the content [mass%] of each element.
[00077] The upper and lower limits of the finishing lamination temperature of the hot lamination are the highest within 800 ° C and the temperature of Ars and 1,000 ° C, respectively. There is a concern that a finish laminating temperature less than 800 ° C results in an increase in a laminating load on the finish laminate to prevent hot rolling or result in a defect in the shape of hot-rolled steel sheet obtained after hot rolling. When the finishing laminating temperature is lower than the Ars temperature, the hot rolling can become a double-phase laminate of ferrite and the austenite and the structure of the hot-rolled steel plate can become a grain structure heterogeneous duplex.
[00078] On the other hand, the effects of the present invention are exercised without specifying particularly the upper limit of the finishing laminating temperature; however, when the finishing laminating temperature is too high, the excessively high plate heating temperature is preferred to ensure the temperature. Therefore, the upper temperature limit of the finishing laminating temperature is desirably 1,000 ° C or less.
[00079] The laminated steel sheet (hot rolled steel sheet) is normally immediately wound in the form of a coil. Since winding at a temperature greater than 800 ° C results in the excessively increased thickness of an oxide formed on the surface of the sheet to deteriorate the pickling properties, the winding temperature is 750 ° C or less. The winding temperature is preferably 720 ° C or less, more preferably 700 ° C or less, to enhance the stripping properties. On the other hand, since the winding temperature less than 500 ° C results in the excessively increased resistance of the hot-rolled steel sheet to prevent cold rolling, the winding temperature is 500 ° C or more. The en-bearing temperature is preferably 550 ° C or more, more preferably 600 ° C or more, to reduce a cold rolling load.
[00080] The hot-rolled steel plate produced in this way is pickled. Stripping makes it possible to remove an oxide on the surface of the steel sheet and is therefore important for the hot-dip properties of the steel sheet as the base material for the galvanized and annealed steel sheet. In addition, pickling can be carried out once or several times.
[00081] Although the pickled steel sheet can undergo an annealing step without being processed, the steel sheet which has a high sheet thickness accuracy and an excellent shape is obtained by being subjected to cold rolling in a reduction by rolling from 35 to 75%. Since the lamination reduction of less than 35% makes it difficult to maintain the flat shape to deteriorate the ductility of a product, the lamination reduction is 35% or more. On the other hand, cold rolling in a rolling reduction greater than 75% results in an excessively large cold rolling load to prevent cold rolling. Therefore, the upper limit of the lamination reduction is 75% or less.
[00082] In addition, the effects of the present invention are exercised without the particular limitation on the number of lamination times and the reduction by lamination on each pass.
[00083] Then, the cold rolled steel sheet obtained is subjected to annealing treatment. The hot dip galvanizing treatment, the alloy treatment and, in addition, the diffusion treatment of the intrachaped layer of the steel sheet surface are desirably incorporated into a cooling process in the annealing step. In this way, the annealing treatment of the base steel sheet to which the steps related to the plating are incorporated will be explained.
[00084] It is desirable to heat the steel sheet so that the maximum heating temperature is within the range of 740 to 870 ° C and then to cool the steel sheet so that an average cooling rate is 1.0 to 10 , 0 ° C / s to 680 ° C and an average cooling rate is 5.0 to 200.0 ° C / s over a range of 500 ° C to 680 ° C, in the annealing treatment. The maximum heating temperature greater than 870 ° C results in significantly deteriorated plating properties. Preferably, the maximum heating temperature is 850 ° C or less. In addition, the maximum heating temperature below 740 ° C causes a large amount of carbide based on cast iron to remain, deteriorating the folding capacity. Preferably, the maximum heating temperature is 760 ° C or more. When a cooling rate condition after heating to the maximum heating temperature deviates from the above range, it is impossible to obtain a steel plate that satisfies the preferred microstructure conditions of such base steel plate as mentioned above.
[00085] After cooling so that the average cooling rate in the range of 500 ° C to 680 ° C is 5.0 to 200.0 ° C / s as mentioned above, the cooling is temporarily carried out at 350 to 450 ° C and reheating is then carried out or the steel sheet is immersed without being processed in a hot dip galvanizing tank to perform the hot dip galvanizing treatment. The hot dip treatment can be carried out under the conditions described in the section mentioned above [Hot dip galvanizing step],
[00086] After the hot-dip galvanizing treatment, cooling is carried out at a temperature that is lower than the solidification temperature of Zn in order to solidify Zn that adheres to the surface of the steel plate, followed by the performance of the alloy treatment of the hot-dip galvanized layer. In other words, reheating is carried out at 470 to 650 ° C and annealing is carried out at 420 ° C for 15 to 200 seconds in order to promote the formation of alloy in the plated layer. Alternatively, the formation of alloy in the plated layer can also be promoted by reheating to a temperature in the range of 470 to 650 ° C and maintaining a temperature in the range for 10 to 120 seconds. The conditions in the alloy treatment are the same as those described in the section mentioned above [Alloy formation treatment step].
[00087] Subsequently, a diffusion treatment is carried out to level the gradient of Fe concentration in the plated layer. In other words, the permanence is carried out for 60 to 1,000 seconds at a temperature in a range of 250 to 420 ° C in the cooling process after the alloy treatment or cooling to room temperature or about room temperature is temporarily carried out after alloy treatment, reheating is then carried out at a temperature in the range of 250 to 420 ° C and the stay is carried out at a temperature in the range for 60 to 1,000 seconds. In addition, the fold-unfold transformation is performed one or more times in the temperature range. For the repeated fold-fold transformation in the diffusion treatment, it is desirable to use a cylinder that has a radius in a range of 50 to 800 mm, for example, a cylinder that has a radius of 800 mm as mentioned above.
[00088] In the annealing step mentioned above, modification and surface improvement of the plating properties can be attempted by controlling an atmosphere in a furnace, discarding an oxidation zone and a reduction zone and causing a reduction reaction by oxidation of Fe and alloy elements in the surface layer of the steel plate. Specifically, the plating treatment can be carried out while making the Si inhibiting plating properties remain on the steel forming an oxidation zone that mainly includes Fe in the oxidation zone at a combustion air ratio of 0.9 or more and 1.2 or less, additionally causing Si to participate in it to fix Si to the steel and then performing the reduction in the reduction zone in an atmosphere in which the logarithm log (PH2O / PH2) of a partial pressure of water and a partial hydrogen pressure is -3.0 or more and 0.0 or less, to reduce only one iron oxide in the surface layer.
[00089] After the annealing treatment that serves as each step for the plating treatment, cooling can be carried out at room temperature, followed by cold lamination again at 0.05 to 3.00% to correct a shape.
[00090] Furthermore, a coating that includes an oxide complex and / or a P oxide containing P can be formed by this phosphate coating formation treatment as mentioned above.
[00091] The present invention is explained specifically below with reference to the examples. It will be appreciated that the examples described below are intended to describe the specific effects of the present invention and the conditions described in the examples do not limit the technical scope of the present invention. Examples
[00092] Plates containing the chemical components (compositions) from A to BD listed in Table 1 and Table 2 (note: the left end of Table 2 follows the right end of Table 1 in Table 1 and Table 2 indicates each chemical component ) were cast and subjected to hot rolling, cooling, rolling and preservation under conditions listed in Table 3 to Table 5 immediately after casting. Then, Experiment Examples 3, 9, 27, 32, 35 and 44 were not processed, but the other Experiment Examples were cold rolled in lamination reductions listed in Table 3 to Table 5, followed by annealing the examples under conditions listed in Table 6 to Table 8 to produce steel sheets in Experiment Examples 1 to 83 and 101 to 116.
[00093] Plate thicknesses after cold rolling are 1.0 mm in Experiment Examples 1 to 29 and 81 to 83, 2.4 mm in Experiment Examples 30 to 48, 0.8 mm in Experiment Examples 49 at 66 and 1.6 mm in Experiment Examples 67 to 80. The plate thicknesses in Experiment Examples 101 to 116 are listed in Table 8.
[00094] The heating was carried out up to the maximum heating temperatures listed in Table 6 to Table 8 in the annealing stage after cold rolling and, in the subsequent cooling process, with the cooling being carried out at "cooling rates 1 "in Table 6 to Table 8 from the maximum heating temperatures at 680 ° C, with the cooling being carried out at" cooling rates 2 "from 680 ° C to 500 ° C and the cooling was additionally carried out to" temperatures cooling stop ". When the cooling stop temperature was below 430 ° C, reheating was carried out to 430 ° C or more. In addition, the immersion was carried out in a galvanizing bath to perform hot-dip galvanizing treatment, heating was then carried out up to alloying temperatures listed in Table 6 to Table 8 as an alloy formation treatment step and annealing was performed at 420 ° C for the treatment times listed in Table 6 to Table 8.
[00095] Then, the rest was performed at average temperatures listed in Table 6 to Table 8 in a range of 250 to 420 ° C for the times listed in Table 6 to Table 8 as a stage of treatment by diffusion of intrachaped layer, during which the folding and unfolding work with cylinders that have radii listed in Table 6 to Table 8 was carried out in stretch quantities and the number of work times listed in Table 6 to Table 8, followed by cooling to room temperature .
[00096] After cooling to room temperature, cold rolling at 0.15% was carried out in conditions 7 to 24, with cold rolling at 0.60% being carried out in conditions 25 to 44 and lamination 0.25% cold was performed under conditions 45 to 83.
[00097] In addition, condition 26 or 31 is an example in which a coating that includes a P-based oxide complex has been applied to the surface of a plated layer and provides good characteristics.
[00098] The results of the analysis of the microstructures of the steel plate in Experiment Examples 1 to 83 and 101 to 116 are listed in Table 9 to Table 11. In microstructure fractions, the amount of austenite retained (y retained) was measured by X-ray diffraction in a plane at a parallel thickness of 1/4 to a plate surface. The others, which were the results of measuring fractions of microstructures in the range from a thickness of 1/8 to a thickness of 3/8, were measured by cutting a plate thickness cross-section parallel to a rolling direction, engraving by nital the polished cross section to be a mirrored surface and observing the cross section using a field emission scanning electron microscope (FE-SEM).
[00099] The results of the evaluation of the plated layers and characteristics of the steel sheets in Experiment Examples 1 to 83 and 101 to 116 are listed in Table 12 to Table 14. For% in Fe of the plated layer,% in Fe was measured in the range of (1/8 x plated layer thickness) to (7/8 x plated layer thickness) starting from a ferrite / plated layer interface using EDX, to determine the average amount of Fe , and the absolute value of a difference ΔFe between the amount of Fe in a position of (1/8 x plated layer thickness) and the amount of Fe in a position of (7/8 x plated layer thickness), that is, the value of | Δ% in Fe | It was determined. In addition, a relationship between the value of the average amount of Fe, the value of | Δ% in Fe |, and the appearance of the plated layer in each experiment example is shown in Figure 1.
[000100] The tensile test pieces according to JIS Z 2201 were collected from the steel plates in Experiment examples 1 to 83 and 101 to 116 and were subjected to a tensile test according to JIS Z 2241 to measure the conventional limits of elasticity, limits of tensile strength, and total elongations thereof.
[000101] In addition, a 90 degree V-fold test was conducted. Test pieces of 35 mm x 100 mm were cut from the steel plates in Experiment examples 1 to 83 and 101 to 116, the shear cutting planes of these were mechanically ground to make a bending radius twice a plate thickness , and a test piece in which compensation and / or training did not occur at all was assessed as accepted (O) while a test piece in which any of the same was observed was assessed as rejected (x ).
[000102] Additionally, for the TS tensile strength limit, the case of TS> 900 MPa can be assessed as accepted, and for ductility, the case of TS x EL> 15000 MPa-% can be assessed as accepted.
[000103] In addition, as a test to evaluate the appearance of a plated layer, the unfolding of a test piece was performed, an adhesion tape (cellophane tape) was attached to the test piece and was removed, and the degree of peeling of plating adhesion to the adhesion tape was visually observed. A test piece in which a plated layer was not peeled was rated as accepted (O), while a test piece in which the plating was considerably peeled was rated as rejected (x).
[000104] In Experiment Examples 1 to 83 and 101 to 116, Experiment Examples 1 to 3, 5 to 9, 11 to 14, 19, 20, 23, 25 to 64, 67, 68, 73 to 80, 101 at 102, 104 to 105, 107 to 108, 110 to 111, and 113 to 116 are examples of the invention. All examples of the invention have been confirmed not only to be excellent in mechanical performance, but also to have good practicality, particularly good bending capacity and to have good resistance to flaking of a plated layer.
[000105] On the other hand, in each experiment example corresponding to a comparative example, poor performance was displayed as described below.
[000106] In other words, Experiment Example 16 is a comparative example in which the hot rolling finish temperature was low and the folding capacity was weak due to the fact that a microstructure stretched in one direction and became heterogeneous.
[000107] Experiment Example 15 is a comparative example in which the winding temperature was high after hot rolling, a stripping property was deteriorated, and the resistance to flaking of a plated layer thus becomes weak.
[000108] Experiment examples 4 and 69 are comparative examples in which the annealing after the cold rolling was carried out under the condition of high maximum heating temperature and the resistance to flaking of each plated layer was weak.
[000109] Experiment example 5 is a comparative example in which the annealing after the cold rolling was carried out under the condition of low maximum heating temperature, a coarse iron-based carbide was present, and the ability to bend the plate steel was weak since a large amount of the iron-based coarse carbide that became a source of fracture was contained. However, a plated layer has not been peeled off to provide a good appearance.
[000110] Experiment example 11 is a comparative example in which a cooling rate 1 was low in an annealing cooling process, an iron-based coarse carbide was generated, and the steel sheet bending capacity it was weak. However, a plated layer has not been peeled off to provide a good appearance.
[000111] Experiment example 12 is a comparative example in which a cooling rate 1 was high in an annealing cooling process, a light structure was not sufficiently generated, and the ductility and flange stretching property of the steel sheet were weak. However, a plated layer has not been peeled off to provide a good appearance.
[000112] Experiment example 6 is a comparative example in which a cooling rate 2 was low in an annealing cooling process, a coarse iron-based carbide was generated, the flange stretching property of the steel sheet was weak, and the folding capacity of it was therefore weak. However, a plated layer has not been peeled off to provide a good appearance.
[000113] Experiment example 10 is a comparative example in which the alloy treatment temperature of a hot dip galvanized layer was high, the plated layer was excessively bonded, the amount of Fe in the plated layer was excessive, a carbide coarse iron-based was generated in the steel plate, the folding capacity was weak, and the resistance to flaking of the plated layer was also weak.
[000114] Experiment example 70 is a comparative example in which the temperature alloy treatment was low, the alloy formation of a plated layer did not proceed, and the resistance to flaking of the plated layer was weak.
[000115] The example of experiment 17 is a comparative example in which the treatment of alloy time was short, the formation of alloy of a plated layer did not proceed, and the resistance to flaking of the plated layer was weak.
[000116] Experiment example 18 is a comparative example in which the temperature alloy treatment was long, a plated layer became an excessive alloy, a coarse iron-based carbide was generated in the steel plate, the bending capacity was weak, and the peeling resistance of the plated layer was weak.
[000117] The examples of experiments 21 and 65 are comparative examples in which the permanence temperature was low in the diffusion layer treatment stage, the flattening of% in Fe did not proceed in a plated layer, and the resistance the flaking of the plated layer was weak.
[000118] The examples of experiments 22 and 72 are comparative examples in which residence time was short in the diffusion layer treatment step, the flattening of% in Fe did not proceed in a plated layer, and the resistance to peeling - the plated layer was weak.
[000119] Experiment example 23 is a comparative example in which the residence time was very long in the diffusion treatment step of the intrachaped layer, an iron-based coarse carbide was generated in the steel plate, and the folding capacity of the steel sheet was weak. However, a plated layer has not been peeled off to provide a good appearance.
[000120] Experiment examples 24, 66, and 71 are comparative examples in which the number of working times was insufficient in the diffusion layer treatment step, the flattening of% in Fe in a plated layer did not proceed, and the peeling resistance of the plated layer was weak.
[000121] Experiment examples 81 to 83 are examples in which chemical components deviated from predetermined ranges and any sufficient characteristics were not obtained in all examples.
[000122] Experiment examples 103 and 112 are comparative examples in which the amount of working stress in the intracamped layer diffusion treatment step was large, the shape of the steel sheet was not flat, it was impossible to conduct a tensile test , a folding test and an unfolding test, and the examples were inappropriate as products.
[000123] Experiment examples 106 and 109 are comparative examples in which the amount of working stress in the intrachaped layer diffusion treatment step was small, the flattening of% Fe in a plated layer did not proceed, and the resistance to flaking of the plated layer was weak.
[000124] Consequently, it is clear from the above experimental results that the present invention is effective in improving the adhesion of the galvanized and annealed layer with the base steel plate. Table 1

Table 2

Table 3
Table 4

Table 5

Table 6

Table 7

Table 8

Table 9
Table 10

Table 11

Table 12
Table 13
Table 14

INDUSTRIAL APPLICABILITY
[000125] The present invention can preferably be applied to components in uses for hot dip galvanizing and work such as bending work, between components that need strength, such as structural members and reinforcement members for automobiles, construction machines, and the like and can be applied particularly to components that need the excellent adhesiveness of a plated layer.

权利要求:
Claims (5)
[0001]
1. Galvanized layer formed on a base steel plate surface, characterized by the fact that the average amount of Fe in the galvanized layer is in the range of 8.0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe in a position 1/8 the thickness of the galvanized layer and the amount of Fe in a position 7/8 the thickness of the galvanized layer in the galvanized layer, where the thickness is from an interface between the galvanized layer and the base steel sheet to the outer surface of the galvanized layer, it is in a range of 0.3 to 3.0%, where the base steel sheet consists of, in mass% , C: 0.050 to 0.300%, Si: 0.10 to 2.50%, Mn: 0.50 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.005 to 1.500%, O: 0.0001 to 0.0100%, N: 0.0001 to 0.0100%, and the balance in Fe and unavoidable impurities, where the base steel plate still consists of% by mass, in one or more selected from Cr: 0.01 to 2.00%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Ti: 0.005 to 0.150%, Nb: 0.005 to 0.150%, V: 0.005 to 0.150%, Mo: 0.01 to 1.00%, and B: 0.0001 to 0.0100%, and where the base steel plate still consists of 0.0001 to 0, 5000% in total of one or two or more selected den tre Ca, Ce, Mg, Zr, Hf and Rare earths.
[0002]
2. Galvanized steel sheet, characterized by the fact that a coating comprising a P oxide and / or a complex oxide containing P is formed on a surface of the galvanized layer, as defined in claim 1.
[0003]
3. Method for the production of a galvanized layer, as defined in claim 1, characterized by the fact that it comprises: a step of hot-dip galvanizing to sub-meter a surface of a base steel sheet to dip galvanizing hot to obtain a hot dip galvanized steel sheet; an alloy formation treatment step to heat a hot dip galvanized layer, formed in the hot dip galvanizing step, to a temperature in the range of 470 to 650 ° C to form a galvanized layer and to produce a sheet galvanized steel; and an intragalvanized layer diffusion treatment step to, after the alloy formation treatment step, allow the galvanized steel sheet to remain at a temperature in the range of 250 to 450 ° C and subject the steel sheet galvanized at one or more times of folding and unfolding work in the temperature range to diffuse Fe in the galvanized layer, in which the galvanized steel sheet is obtained, in which, after the intragalvanized layer diffusion treatment step, the average amount Fe in the galvanized layer is in the range of 8.0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe in a position 1/8 the thickness of the galvanized layer and the amount of Fe in a position 7/8 the thickness of the galvanized layer in the galvanized layer, where the thickness is from an interface between the galvanized layer and the base steel sheet to the outer surface of the galvanized layer, it is in a range of 0.3 to 3.0%, where the base steel sheet consists of, in mass% , C: 0.050 to 0.300%, Si: 0.10 to 2.50%, Mn: 0.50 to 3.50%, P: 0.001 to 0.030%, S: 0.0001 to 0.0100%, Al: 0.005 to 1.500%, O: 0.0001 to 0.0100%, N: 0.0001 to 0.0100%, and the balance in Fe and unavoidable impurities is used as the base steel plate, where the steel plate base also consists of mass%, in one or more selected from Cr: 0.01 to 2.00%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Ti: 0.005 at 0.150%, Nb: 0.005 to 0.150%, V: 0.005 to 0.150%, Mo: 0.01 to 1.00%, and B: 0.0001 to 0.0100%, and what the base steel plate consists of still, in mass%, in 0.0001 to 0.5000 % in total of one or two or more selected from Ca, Ce, Mg, Zr, Hf and Rare earths.
[0004]
4. Method for the production of a galvanized layer, according to claim 3, characterized by the fact that in the diffusion treatment stage of the intragalvanized layer, the bending work is carried out so that a maximum tensile deformation amount in a steel sheet surface ranges from 0.0007 to 0.0910.
[0005]
5. Method for the production of a galvanized layer, according to claim 3 or 4, characterized in that a surface of the galvanized layer is subjected to phosphate coating treatment to form a coating comprising a P and / or oxide or a complex oxide containing P after the intragalvanized layer diffusion treatment step.

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同族专利:

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公开号 | 公开日

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CA2842896C|2016-11-08|

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US20140193665A1|2014-07-10|

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CN103732781A|2014-04-16|

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JP5510607B2|2014-06-04|

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KR20140031337A|2014-03-12|

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CN103732781B|2016-07-06|

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JPWO2013018726A1|2015-03-05|

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ZA201401303B|2014-11-26|

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TW201311930A|2013-03-16|

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EP2738283B1|2020-06-24|

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EP2738283A1|2014-06-04|

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CA2842896A1|2013-02-07|

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MX2014001118A|2014-02-27|

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US9551057B2|2017-01-24|

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RU2572901C9|2016-06-20|

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RU2014107481A|2015-09-10|

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EP2738283A4|2015-11-11|

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WO2013018726A1|2013-02-07|

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KR101587968B1|2016-01-22|

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BR112014002203A2|2017-02-21|

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RU2572901C2|2016-01-20|

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TWI489000B|2015-06-21|

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法律状态:
2018-03-27| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|

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2019-08-06| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|

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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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2020-05-12| B09A| Decision: intention to grant|

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2020-10-06| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 27/07/2012, 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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JP2011-167779|2011-07-29|

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JP2011167779|2011-07-29|

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PCT/JP2012/069229|WO2013018726A1|2011-07-29|2012-07-27|Alloyed hot-dip zinc coat layer, steel sheet having same, and method for producing same|

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