Plated steel material

Abstract

Provided is a plated steel material having a plating layer disposed on the surface of the steel material, wherein: the plating layer is a Zn-based plating layer that has an average chemical composition containing 4.0-70.0 mass% of Al and 0.3-12.5 mass% of Mg, with the balance consisting of Zn and impurities; the metal structure of the plating layer includes at least a Zn phase, an Al phase, and a MgZn2 phase; and when an average KAM value is measured with respect to a rectangular measurement region of 125 μm × 300 μm set on the surface of the plating layer, by means of EBSD with a measurement interval of 0.25 μm / step, the average KAM value (KZn) of the Zn phase is in the range of 0.30-1.70°, the average KAM value (KAl) of the Al phase is in the range of 0.20-1.00°, and the average KAM value (KMgZn2) of the MgZn2 phase is in the range of 0.20-1.00°.

Description

Plated steel

[0001] This application claims priority to Japanese Patent Application No. 2024-069483, filed on April 23, 2024, the contents of which are incorporated herein by reference.

[0002] As an example of a steel sheet provided with a coating layer made of a Zn alloy, a hot-dip zinc alloy-plated steel sheet is known. Because the coating layer made of a Zn alloy has excellent durability, the hot-dip zinc alloy-plated steel sheet is used in a wide range of applications, such as automobiles, building materials, and home appliances.

[0003] The Zn alloy coating layer of hot-dip zinc alloy-coated steel sheets has a sacrificial corrosion protection effect on steel, protecting the underlying steel in atmospheric corrosive environments. The metal structure of Zn alloys containing Al and Mg is mainly composed of a phase with a high Al concentration and a phase with a high Zn concentration, and it is believed that Al improves the dissolution resistance of the coating layer, while Zn exerts a sacrificial corrosion protection effect.

[0004] That is, it is believed that the corrosion prevention performance of hot-dip zinc alloy plated steel sheets is developed in stages as described in the following (1) and (2).

[0005] That is, (1) when the entire surface of the base steel is covered with a plating layer (Zn alloy), the dissolution rate of the plating layer is low, and corrosion protection due to the barrier effect of the plating layer is maintained. Also, (2) when the base steel is exposed due to partial loss of the plating layer, the plating layer dissolves preferentially, and the effect of sacrificial corrosion protection of the base steel is maintained for a long period of time. The sacrificial corrosion protection effect improves the corrosion resistance of the steel, for example, at the cut end surface of a hot-dip zinc alloy-plated steel sheet.

[0006] From the above, in order to improve the corrosion resistance of hot-dip zinc alloy-plated steel sheets, it is necessary to control the chemical composition and metal structure of the Zn alloy constituting the plating layer so as to achieve both high levels of dissolution resistance and sacrificial corrosion protection of the plating layer.

[0007] An example of a method focusing on controlling the coating structure is Patent Document 1. Patent Document 1 focuses on thermal spraying as a method other than hot-dip galvanizing, and discloses a coated steel sheet coated with a coating layer of Zn alloy particles containing Mg. Thermal spraying is a coating method that does not require immersion in molten metal, and has advantages such as a wide melting point tolerance range for metals or alloys that can be coated. However, there are concerns about reduced adhesion and productivity for coating layers containing particles with a particle size of less than 5 μm.

[0008] International Publication No. 2017 / 057638

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated steel material that can improve both the corrosion resistance of flat surfaces and the corrosion resistance of end surfaces.

[0010] In order to solve the above problems, the present invention employs the following configuration: [1] A steel material, and a plating layer disposed on at least a part of the surface of the steel material, wherein the plating layer is a Zn-based plating layer having an average chemical composition of 4.0 mass % to 70.0 mass % Al, 0.3 mass % to 12.5 mass % Mg, and the balance being Zn and impurities, and the metal structure of the plating layer contains a Zn phase, an Al phase, and an MgZn phase. ２ and a Zn phase, and when the average KAM value is measured by an EBSD method with a measurement interval of 0.25 μm / step in a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer, the average KAM value (K Ｚｎ ) is in the range of 0.30 to 1.70°, and the average KAM value (K Ａｌ ) is in the range of 0.20 to 1.00°, and the MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２) is in the range of 0.20 to 1.00°. [2] The plated steel material according to [1], wherein the plating layer further contains, in average composition, an element selected from either or both of Group A and Group B below. [Group A] Si: 0.0001 to 2 mass%. [Group B] One or more of Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM, in a total amount of 0.0001 to 2 mass%. [3] The plated steel material according to [1] or [2], which satisfies the relationships of the following formulas (1) and (2): 0.15≦K Ａｌ / K Ｚｎ ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 ... (2) However, K in formulas (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is the MgZn ２ [4] When a rectangular measurement area of ​​30 μm × 60 μm set on the surface of the coating layer is measured by EBSD at a measurement interval of 0.05 μm / step, and the average grain size is measured by the Number method, defining a region surrounded by a grain boundary having an average crystal orientation misorientation of 15° or more as a crystal grain, the average grain size of the Zn phase is in the range of 0.10 to 2.00 μm, the average grain size of the Al phase is in the range of 0.10 to 5.00 μm, and the average grain size of the MgZn phase is in the range of 0.10 to 2.00 μm. ２ [5] The plated steel material according to any one of [1] to [3], wherein the average crystal grain size of the MgZn phase is in the range of 0.10 to 2.00 μm. [6] When X-ray diffraction measurement is performed on the surface of the plated layer, the half width of the X-ray diffraction peak of the (102) plane of Zn, the half width of the X-ray diffraction peak of the (111) plane of Al, and the half width of the X-ray diffraction peak of the MgZn ２ The plated steel material according to any one of [1] to [4], wherein the half width of the X-ray diffraction peak of the (201) plane satisfies the relationships of the following formulas (3) and (4): 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ≦1.4 ... (4) However, B in equations (3) and (4) Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn ２ [6] A steel material, and a plating layer disposed on at least a part of a surface of the steel material, wherein the plating layer is a Zn-based plating layer having an average chemical composition of 4.0 mass% to 70.0 mass% Al, 0.3 mass% to 12.5 mass% Mg, and the balance being Zn and impurities, and the metal structure of the plating layer contains a Zn phase, an Al phase, and an MgZn phase. ２ and a Zn phase, and when the average KAM value is measured by an EBSD method with a measurement interval of 0.25 μm / step in a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer, the average KAM value (K Ｚｎ ) is in the range of 0.30 to 1.70°, and the average KAM value (K Ａｌ ) is in the range of 0.20 to 1.00°, and the MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) is in the range of 0.20 to 1.00°, and when the average crystal grain size is measured by the Number method using an EBSD method with a measurement interval of 0.05 μm / step in a rectangular measurement area of ​​30 μm × 60 μm set on the surface of the plating layer, with a region surrounded by a grain boundary having an average crystal orientation misorientation of 15° or more defined as a crystal grain, the average crystal grain size of the Zn phase is in the range of 0.10 to 2.00 μm, the average crystal grain size of the Al phase is in the range of 0.10 to 5.00 μm, and the MgZn ２ The average crystal grain size of the MgZn phase is in the range of 0.10 to 2.00 μm, and when X-ray diffraction measurement is performed on the surface of the plating layer, the half width of the X-ray diffraction peak of the (102) plane of Zn, the half width of the X-ray diffraction peak of the (111) plane of Al, and ２ The full width at half maximum of the X-ray diffraction peak of the (201) plane of the plated steel satisfies the relationships of the following formulas (1) to (4): 0.15≦K Ａｌ / K Ｚｎ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 ... (2) 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4 ... (4) However, K in equations (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is the MgZn ２ The average KAM value of the phase. Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn ２ The full width at half maximum of the X-ray diffraction peak of the (201) plane of [7]. The plated steel material according to [6], wherein the plating layer further contains, in average composition, an element selected from either or both of Group A and Group B below: [Group A] Si: 0.0001 to 2 mass%. [Group B] One or more of Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM, in a total amount of 0.0001 to 2 mass%.

[0011] According to the present invention, it is possible to provide a plated steel material that can improve both the corrosion resistance of flat surfaces and the corrosion resistance of edge surfaces.

[0012] Schematic diagram illustrating the average KAM value.

[0013] The present inventors have conducted extensive research to improve the corrosion resistance of plated steel materials having a plating layer containing Al, Mg, and Zn.

[0014] The hot-dip coating layer contains 4.0 to 70.0 mass% Al, 0.3 to 12.5 mass% Mg, and the balance being Zn and impurities. The hot-dip coating layer contains a Zn phase mainly composed of Zn, an Al phase mainly composed of Al, and an MgZn phase. ２ phase and MgZn phase. ２The Al phase exerts so-called sacrificial corrosion protection, protecting the base steel by forming corrosion products when the coating layer corrodes. Loss of sacrificial corrosion protection results in the corrosion of the base steel, resulting in the formation of red rust. On the other hand, the Al phase is passivated by forming aluminum oxidation products, thereby exerting barrier properties and improving the flat corrosion resistance of the coating layer. However, passivation can also lead to the formation of white rust. The inventors focused on the average KAM value in the course of their investigations into suppressing the formation of both white rust and red rust and achieving both sacrificial corrosion protection and flat corrosion resistance. The average KAM value is believed to enable evaluation of the amount of strain in each phase. A smaller average KAM value suggests a smaller amount of local strain.

[0015] The inventors have found that when the average KAM value of a phase constituting a coating layer is small, that phase is relatively difficult to dissolve during corrosion, whereas when the average KAM value is large, that phase is relatively easy to dissolve during corrosion. Based on this finding, it was expected that, in a coating layer containing Al, Mg, and Zn, by making the amount of local strain in the Al phase relatively small, dissolution of the Al phase during corrosion would be suppressed, thereby suppressing the occurrence of white rust and improving flat surface corrosion resistance. Furthermore, it was expected that by making the amount of local strain in the Zn phase relatively large, dissolution of the Zn phase would be promoted, thereby exerting sacrificial corrosion protection, suppressing corrosion of the base steel, and further improving edge corrosion resistance.

[0016] Therefore, we have investigated means for controlling the local strain of each phase contained in the hot-dip coating layer, and have found that by subjecting the coated steel material on which the hot-dip coating layer has been formed to temper rolling a predetermined time after the end of coating, followed by heat treatment, it becomes possible to introduce strain according to the hardness of each phase constituting the coating layer, and the amount of strain can be controlled for each phase. ２ By controlling the amount of strain in each phase so that the KAM value is maintained higher than that of the other phases, the occurrence of red rust and white rust in the early stages of corrosion is suppressed, and we have succeeded in achieving both corrosion resistance in both flat surfaces and edge surfaces.

[0017] Furthermore, it has been found that when the average grain size of each phase of the plating layer is within a preferred range, the corrosion resistance of the flat surface portion is further improved due to the synergistic effect of strain control and grain refinement.

[0018] Hereinafter, a plated steel material according to an embodiment of the present invention will be described. The plated steel material according to this embodiment has a steel material and a plating layer disposed on at least a part of the surface of the steel material. The plating layer is a Zn-based plating layer having an average chemical composition of 4.0 mass % to 70.0 mass % Al, 0.3 mass % to 12.5 mass % Mg, and the balance being Zn and impurities. The metal structure of the plating layer includes a Zn phase, an Al phase, and an MgZn phase. ２ phase, and when the average KAM value is measured by the EBSD method with a measurement interval of 0.25 μm / step in a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer, the average KAM value (K Ｚｎ ) is in the range of 0.30 to 1.70°, and the average KAM value (K Ａｌ ) is in the range of 0.20 to 1.00°, and MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) is in the range of 0.20 to 1.00°.

[0019] Furthermore, the plated steel material of this embodiment preferably satisfies the relationships of the following formulas (1) and (2): 0.15≦K Ａｌ / K Ｚｎ ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 ... (2) However, K in formulas (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is MgZn ２ The mean KAM value for the phase.

[0020] Furthermore, in the plated steel material of this embodiment, when a rectangular measurement area of ​​30 μm × 60 μm set on the surface of the plated layer is measured by EBSD with a measurement interval of 0.05 μm / step, and the average crystal grain size is measured by the Number method, defining a region surrounded by grain boundaries with an average crystal orientation misorientation of 15° or more as a crystal grain, the average crystal grain size of the Zn phase is in the range of 0.10 to 2.00 μm, the average crystal grain size of the Al phase is in the range of 0.10 to 5.00 μm, and the average crystal grain size of the MgZn phase is in the range of 0.10 to 2.00 μm. ２ The average crystal grain size of the phase is preferably in the range of 0.10 to 2.00 μm.

[0021] In addition, when X-ray diffraction measurement is performed on the surface of the plated layer, the plated steel material of this embodiment has a half-width of the X-ray diffraction peak of the (102) plane of Zn, a half-width of the X-ray diffraction peak of the (111) plane of Al, and a half-width of the X-ray diffraction peak of the (111) plane of MgZn. ２ It is preferable that the half width of the X-ray diffraction peak of the (201) plane of B satisfies the relationships of the following formulas (3) and (4): 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4 ... (4) However, B in equations (3) and (4) Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn ２ is the half-width of the X-ray diffraction peak of the (201) plane of the sample.

[0022] In the following description, the "%" used to indicate the content of each element in the average chemical composition means "mass %." Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. When the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit.

[0023] Furthermore, flat surface corrosion resistance refers to the property of the plating layer itself being resistant to corrosion. Edge corrosion resistance refers to the property of inhibiting corrosion of steel at exposed steel portions (e.g., cut end surfaces of plated steel). Sacrificial corrosion protection refers to the property of inhibiting corrosion of the base steel at exposed steel portions (e.g., cut end surfaces of plated steel, cracked portions of the plating layer during processing, and portions where the steel is exposed due to peeling of the plating layer). Furthermore, "plating layer" refers to a plating film produced by so-called hot-dip plating.

[0024] The steel material to be plated will now be described. There are no particular limitations on the shape of the steel material. Examples of steel materials include steel plates, steel pipes, civil engineering and construction materials (fences, corrugated pipes, drainage ditch covers, sand-flying plates, bolts, wire mesh, guardrails, water-stop walls, etc.), home appliance components (air conditioner outdoor unit casings, etc.), and automobile parts (undercarriage components, etc.). Various plastic processing techniques, such as press working, roll forming, and bending, can be used for the forming process. There are no particular limitations on the quality of the steel material. Various types of steel can be used, such as general steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (e.g., steels containing strengthening elements such as Ni and Cr). The steel material may be, for example, a steel plate. There are no particular limitations on the conditions for the steel material manufacturing method and the steel plate manufacturing method (hot rolling, pickling, cold rolling, etc.). The steel may be pre-plated steel.

[0025] The plating layer disposed on the surface of the steel material may be disposed on at least a part of the steel material. When the steel material is a steel plate, the plating layer may be formed on one surface in the plate thickness direction, or on both surfaces in the plate thickness direction. In addition, the plating layer may be formed on the end surface of the steel plate.

[0026] The plating layer is primarily composed of a Zn—Al—Mg alloy layer due to its chemical composition, which will be described later. The plating layer may also include an Fe—Al-based interfacial alloy layer, primarily composed of Fe and Al, located between the steel material and the Zn—Al—Mg alloy layer. That is, the plating layer may have a single-layer structure of the Zn—Al—Mg alloy layer, or a laminated structure including the Zn—Al—Mg alloy layer and the Fe—Al-based interfacial alloy layer. In the case of a laminated structure, the Zn—Al—Mg alloy layer is preferably the layer that constitutes the surface of the plating layer. Note that an oxide film of the plating layer constituent elements is formed on the surface of the plating layer, with a thickness of approximately 50 nm. However, because its thickness is small compared to the overall thickness of the plating layer, this oxide film is not considered to constitute the main part of the plating layer.

[0027] There are no particular limitations on the upper and lower limits of the coating weight of the plating layer. For example, the coating weight of the plating layer is 10 to 400 g / m per side. ２ The coating weight of the plating layer is correlated with corrosion resistance, with a thicker coating being more corrosion-resistant. On the other hand, applying a thicker coating layer requires a large amount of metal, which increases costs. Therefore, the coating weight of the plating layer is preferably 400 g / m. ２ It is preferable that the coating weight of the plating layer is 10 g / m or less. ２ If the coating weight is less than 10 g / m, the corrosion resistance will decrease. ２ That's good enough.

[0028] Next, the average chemical composition of the plating layer will be described.

[0029] Al: 4.0 to 70.0% by mass. Al forms an Al phase in the Zn-Al-Mg alloy layer of the coating layer. The Al phase has a small amount of strain, is energetically stable, and is less likely to dissolve. This suppresses the formation of white rust during corrosion, maintains barrier properties against the steel material, and improves flat surface corrosion resistance. To achieve this effect, an Al content of 4.0% by mass or more is required. On the other hand, if the Al content exceeds 70.0% by mass, the Zn content becomes relatively low, resulting in a decrease in sacrificial corrosion protection and further a decrease in end surface corrosion resistance. Therefore, the Al content is set to 4.0 to 70.0% by mass. The Al content may be 5.0% by mass or more, 6.0% by mass or more, 10.0% by mass or more, 15.0% by mass or more, or 20.0% by mass or more. The Al content may also be 60.0% by mass or less or 55.0% by mass or less.

[0030] Mg: 0.3 to 12.5 mass% Mg is an element that has the effect of increasing the corrosion resistance of the plating layer. In particular, Mg contributes to the formation of MgZn in the Zn-Al-Mg alloy layer of the plating layer. ２ This phase improves the sacrificial corrosion protection of the coating layer and further improves the corrosion resistance of the edge surface. To achieve this effect, the Mg content must be 0.3% by mass or more. On the other hand, if the Mg content exceeds 12.5% ​​by mass, the effect of improving corrosion resistance saturates and the workability of the coating layer may decrease. Furthermore, manufacturing problems such as an increase in the amount of dross generated in the coating bath may occur. Therefore, the Mg content is set to 12.5% ​​by mass or less. The Mg content may be 1.0% by mass or more or 3.0% by mass or more. The Mg content may also be 10.0% by mass or less, 8.0% by mass or less, or 6.0% by mass or less.

[0031] The balance: Zn and impurities. Zn is present in the Zn-Al-Mg alloy layer of the plating layer as a Zn phase and MgZn. ２Since Zn is an element that forms a phase and improves the sacrificial corrosion protection of the plating layer, it is contained as the balance. If the Zn content decreases relatively due to an increase in the Al and Mg contents, the sacrificial corrosion protection of the plating layer will decrease, so the Al content and Mg content need to be limited to 70.0 mass% or less and 12.5 mass% or less, respectively. The Zn content is more preferably 40.0 mass% or more, and may be 60.0 mass% or more, 80.0 mass% or more, 90.0 mass% or more, or 92.0 mass% or more.

[0032] Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally added. Examples of impurities include oxygen and Fe. The maximum amount of impurities is 1% or less, preferably 0.1% or less.

[0033] The plating layer of this embodiment may further contain, in average composition, one or two elements selected from the group consisting of Group A and Group B below: [Group A] Si: 0.0001 to 2 mass %. [Group B] One or more elements selected from Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM, in a total amount of 0.0001 to 2 mass %.

[0034] The plating layer may contain 0.0001 to 2 mass% of Si as an element of Group A in its average composition. Si is an element effective for improving the adhesion of the plating layer. By including 0.0001 mass% or more of Si in the plating layer, the effect of improving the adhesion of the plating layer is realized, so it is preferable to include 0.0001 mass% or more of Si. On the other hand, even if the Si content exceeds 2 mass%, the effect of improving the plating adhesion saturates, so even when Si is included in the plating layer, the Si content is set to 2 mass% or less. From the viewpoint of plating adhesion, the Si content in the plating layer may be 0.0010 to 1 mass%, or 0.0100 to 0.8 mass%.

[0035] The plating layer may contain, as elements of group B, one or more of Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM in an average composition of 0.0001 to 2 mass% in total. The inclusion of these elements can further improve the corrosion resistance of the plating layer. Here, REM refers to one or more rare earth elements with atomic numbers 59 to 71 in the periodic table.

[0036] To identify the average chemical composition of the plating layer, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of steel material to obtain an acid solution. The obtained acid solution is then measured using ICP atomic emission spectroscopy or ICP-MS to obtain the chemical composition. The chemical composition is measured as the average chemical composition. There are no particular restrictions on the type of acid, as long as it is an acid that can dissolve the plating layer. By measuring the area and weight before and after stripping, the adhesion amount (g / m ２ As the acid containing an inhibitor, for example, a 10% hydrochloric acid solution containing 0.06% by mass of an inhibitor (Ivit 710K, manufactured by Asahi Chemical Industry Co., Ltd.) can be used.

[0037] Next, the structure of the plating layer will be described. The plating layer of this embodiment contains a Zn phase, an Al phase, and an MgZn phase. ２ phase and at least

[0038] The average KAM values ​​described below are the results of measurements performed by the EBSD method on a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer at a measurement interval of 0.25 μm / step. The measurement area may be set at any position on the surface of the plating layer.

[0039] The Al phase is a phase containing mainly Al. The Al phase of this embodiment has smaller local strain and a smaller average KAM value than the other phases constituting the coating layer, making it energetically stable and less likely to dissolve during corrosion. This enhances the barrier properties of the coating layer against the steel material and improves the corrosion resistance of flat surfaces. Furthermore, because it is less likely to dissolve during corrosion, no corrosion products are produced, and the occurrence of white rust is suppressed.

[0040] The average KAM value of the Al phase (K Ａｌ ) must be in the range of 0.20 to 1.00°. The average KAM value (K Ａｌ If the average KAM value (K) exceeds 1.00°, the Al phase is likely to dissolve during corrosion, and corrosion products are likely to be produced, which leads to the formation of white rust, and the corrosion resistance of the flat surface is reduced. Ａｌ On the other hand, the average KAM value (K Ａｌ The lower limit of the angle θ is not particularly limited, but since it is difficult to manufacture the plating layer if it is less than 0.20°, the lower limit is set to 0.20° or more.

[0041] The Al phase preferably contains 65 mass % or more of Al. The Al phase may contain Zn in addition to Al. The Al phase may also have an Al content of 100%.

[0042] The Al phase in this embodiment may exist as a single phase in the plating layer. Alternatively, the Al phase may form a eutectic structure together with other phases. For example, a Zn / Al / MgZn ２ It may be contained as an Al phase constituting the ternary eutectic structure.

[0043] The Zn phase is a phase that mainly contains Zn. In this embodiment, the Zn phase has a larger local strain and a higher average KAM value than the other phases that make up the coating layer, and therefore dissolves preferentially during corrosion to form corrosion products. This improves the sacrificial corrosion protection of the coating layer against the steel material. Furthermore, when the steel substrate of the steel material is exposed through processing, the generated corrosion products cover the steel substrate, thereby improving the corrosion resistance of the end surface. This also suppresses the generation of red rust.

[0044] Average KAM value of the Zn phase (K Ｚｎ ) must be in the range of 0.30 to 1.70°. The average KAM value of the Zn phase (K Ａｌ If the average KAM value (K) of the Zn phase exceeds 1.70°, the Zn phase will be easily dissolved excessively during corrosion, resulting in a decrease in the corrosion resistance of the flat surface. ＺｎIf the average KAM value (K) of the Zn phase is less than 0.30°, the preferential dissolution of the Zn phase is difficult to occur during corrosion, and the sacrificial corrosion resistance and the corrosion resistance of the end face portion are reduced. Ｚｎ ) is in the range of 0.30 to 1.70°.

[0045] The Zn phase preferably contains 70 mass % or more of Zn. The Zn phase may contain Al in addition to Zn. The Zn phase may also have a Zn content of 100%.

[0046] The Zn phase in this embodiment may exist as a single phase in the plating layer. Alternatively, the Zn phase may form a eutectic structure together with other phases. For example, a Zn / Al / MgZn ２ It may be contained as a Zn phase constituting the above ternary eutectic structure.

[0047] MgZn ２ The MgZn phase is a region in the coating layer where Mg is 16 mass% (±5%) and Zn is 84 (±5%). ２ The MgZn phase dramatically improves the corrosion resistance of the plating layer. ２ The phase dissolves Mg during corrosion and deposits Mg on the steel substrate. ２＋ This quickly moves and forms corrosion products on the steel substrate. This improves, for example, the corrosion resistance around the cross-cut area where there are scratches that reach the steel substrate, the corrosion resistance in the processed area where cracks in the plating layer are likely to occur, and the corrosion resistance of the end surface at the cut end surface. ２ The Al phase has smaller local strain and a lower average KAM value than the Zn phase, and therefore dissolves after the Zn phase dissolves preferentially during corrosion, improving the corrosion resistance of flat surfaces and the sacrificial corrosion protection.

[0048] MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) must be in the range of 0.20° to 1.00°. MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ If the angle θ exceeds 1.00°, dissolution occurs together with the Zn phase during corrosion, resulting in a decrease in the corrosion resistance of the flat surface. ２ The average KAM value of the phase (K ＭｇＺｎ２If the angle is less than 0.20°, the preferential dissolution of the Zn phase during corrosion is difficult to occur, and the sacrificial corrosion resistance and the corrosion resistance of the end face portion are reduced. ２ The average KAM value of the phase (K ＭｇＺｎ２ ) is in the range of 0.20° to 1.00°.

[0049] MgZn in this embodiment ２ The MgZn phase may exist as a single phase in the plating layer. ２ The phase may form a eutectic structure with other phases, for example, Zn / Al / MgZn ２ MgZn that constitutes the ternary eutectic structure ２ It may be contained as a phase.

[0050] Furthermore, the plating layer of this embodiment preferably satisfies the relationships of the following formulas (1) and (2).

[0051] 0.15≦K Ａｌ / K Ｚｎ ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 … (2)

[0052] K in equations (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is MgZn ２ The mean KAM value for the phase.

[0053] K Ａｌ / K Ｚｎ Since the ratio is in the range of 0.15 to 1.40, the dissolution of the Al phase into the Zn phase during corrosion is less likely to proceed, the generation of white rust is suppressed, and the barrier properties are maintained, further improving the corrosion resistance of the flat surface. In addition, the dissolution of the Zn phase is prioritized, further improving the sacrificial corrosion protection and the corrosion resistance of the end surface. Furthermore, K ＭｇＺｎ２ / K Ｚｎ is in the range of 0.20 to 1.40, MgZn ２ The dissolution of the Zn phase takes precedence over the Al phase, resulting in further improvements in sacrificial corrosion resistance and end face corrosion resistance.

[0054] The KAM value (Kernel Average Misorientation) in this embodiment is the average value of the misorientation between a pixel of interest and an adjacent pixel when the crystal orientation of each crystal grain constituting a polycrystalline metal structure is analyzed by electron backscattering diffraction (ESBD). It is often used as a parameter indicating local strain and is generally expressed, for example, by the following formula (A) (Source: Journal of the Japan Institute of Metals, Vol. 74, No. 7 (2010) pp. 467-474). The degree of local strain can be determined by this KAM value. A larger value indicates a larger local strain.

[0055]

[0056] In equation (1), α ｉｊ is the crystal orientation misorientation between measurement point i and measurement point j, and n is the number of adjacent pixels.

[0057] 1, the average of the misorientation values ​​α1 to α6 between the central hexagonal pixel and its six neighboring pixels is calculated using the following formula (B), and this value is defined as the KAM value of the central pixel. The average KAM value is the average of the KAM values ​​of each pixel in the measurement area. The possible values ​​of the average KAM value are in the range of 0 to 5°, with the closer to 0° the smaller the local strain and the closer to 5° the larger the local strain.

[0058]

[0059] Next, the average crystal grain size of each phase will be described. When a rectangular measurement area of ​​30 μm × 60 μm set on the surface of the coating layer was measured by EBSD with a measurement interval of 0.05 μm / step, and the average crystal grain size was measured by the Number method, defining the area surrounded by grain boundaries with an average crystal orientation misorientation of 15° or more as a crystal grain, the average crystal grain size of the Zn phase was in the range of 0.10 to 2.00 μm, the average crystal grain size of the Al phase was in the range of 0.10 to 5.00 μm, and the average crystal grain size of the MgZn phase was in the range of 0.10 to 2.00 μm. ２ It is preferable that the average grain size of the Zn phase and the MgZn phase is in the range of 0.10 to 2.00 μm. ２By setting the average crystal grain size of the Al phase to 2.0 μm or less and the average crystal grain size of the Al phase to 5.0 μm or less, the distance between the anode and cathode during corrosion is reduced, and the pH change of the solution near the plating layer is reduced, thereby improving the corrosion resistance of the flat surface. Note that the measurement interval in the EBSD method is 0.05 μm steps, and the lower limit for the measurement of the average crystal grain size of each phase is 0.05 μm. There is no particular restriction on the lower limit of the crystal grain size of each phase, but as mentioned above, it is sufficient for each phase to be 0.1 μm or more.

[0060] Here, we will explain how to measure the average KAM value and average crystal grain size. First, the surface of the plating layer is polished to a thickness of several μm using #1500 silicon carbide paper, then polished to a mirror finish using a liquid containing alcohol and diamond powder with a particle size of 1 to 6 μm dispersed in it, and then final polishing is performed using colloidal silica. In this way, the measurement sample is prepared.

[0061] The measurement sample is observed using a scanning electron microscope. The scanning electron microscope is equipped with an EBSD analyzer and an EDS measurement device. For example, the scanning electron microscope may be a field emission scanning electron microscope (FE-SEM: SU-70) manufactured by Hitachi High-Tech Corporation, the EBSD analyzer may be DigiView (manufactured by TSL Solutions), and the EDS measurement device may be Octan elect super (manufactured by Ametec).

[0062] The measurement area for the KAM value is a 125 × 300 μm region on the surface of the plating layer. The measurement interval is 0.25 μm steps. On the other hand, the measurement area for the average crystal grain size is a rectangular region of 30 μm × 60 μm on the surface of the plating layer, with a measurement interval of 0.05 μm / step. For both the KAM value and the average crystal grain size measurements, the acceleration voltage is 15 kV, the working distance is 15 mm, and secondary electron images are taken with a scanning electron microscope.

[0063] Next, in each measurement region, an EBSD analysis is performed at an analysis speed of 200 to 300 points / second using an EBSD analyzer. The Al phase, Zn phase, and MgZn phase are analyzed using the software "OIM Analysis (registered trademark)" attached to the EBSD analyzer. ２The average crystal grain size of the phase is calculated. For the crystal orientation information obtained by EBSD analysis, regions surrounded by grain boundaries with an average crystal orientation difference of 15° or more are defined as crystal grains by the Number method, and the average crystal grain size is calculated. When calculating the average crystal grain size, the measurement targets are crystal grains with a grain size of 0.25 μm or more.

[0064] Next, the average KAM value of each phase is measured under the following conditions using the software "OIM Analysis (registered trademark)".

[0065] ・Nearest neighbor: 1st (If it is 1st, the azimuth difference is calculated using the nearest neighbor pixel.) ・Perimeter only ・If the azimuth difference is 5° or more, all azimuth differences are set to 5°. ・Maximum azimuth difference: Within 5°.

[0066] Next, the half-width of the X-ray diffraction peak will be explained. The larger the half-width of the X-ray diffraction peak, the smaller the crystallite size contained in the phase tends to be. On the other hand, generally, when a metal is subjected to severe processing and strain is introduced, many dislocations are generated in the structure, and the crystallite size becomes smaller. Therefore, the half-width of the X-ray diffraction peak can be regarded as a parameter representing the degree of strain. In other words, the larger the half-width of the X-ray diffraction peak, the greater the strain applied. In this embodiment, when X-ray diffraction measurement is performed on the surface of the plating layer, the half-width of the X-ray diffraction peak of the (102) plane of Zn, the half-width of the X-ray diffraction peak of the (111) plane of Al, and the half-width of the X-ray diffraction peak of MgZn are measured. ２ It is preferable that the half width of the X-ray diffraction peak of the (201) plane satisfies the relationships of the following formulas (3) and (4):

[0067] 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4 … (4)

[0068] However, B in equations (3) and (4) Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn２ is the half-width of the X-ray diffraction peak of the (201) plane of the sample.

[0069] B Ａｌ / B Ｚｎ Since the value of B is in the range of 0.5 to 1.8, the dissolution of the Al phase into the Zn phase during corrosion is less likely to proceed, the generation of white rust is suppressed, and the barrier properties are maintained, further improving the corrosion resistance of the flat surface. In addition, the dissolution of the Zn phase is prioritized, further improving the sacrificial corrosion protection and the corrosion resistance of the end surface. ＭｇＺｎ２ / B Ｚｎ is in the range of 0.4 to 1.4, so MgZn ２ The dissolution of the Zn phase takes precedence over the Al phase, and the sacrificial corrosion resistance and the corrosion resistance of the end face portion are further improved.

[0070] The half-width of the X-ray diffraction peak is measured as follows. A test piece having a size of 20 mm x 20 mm square on the surface of the plating layer is cut out from the plated steel material, and an X-ray diffraction image is obtained from the surface of the plating layer of the test piece. The X-ray diffraction measurement is carried out under the measurement conditions shown in Table 1 below, and the X-ray diffraction peak of the (102) plane of Zn, the X-ray diffraction peak of the (111) plane of Al, and the X-ray diffraction peak of the (111) plane of MgZn are obtained. ２ The X-ray diffraction peak position 2θ and half-width B are determined by fitting with a Lorentz function after removing the background and Kα2 radiation. The half-width derived from the instrument is determined by fitting with a standard sample (LaB ６ The true half-width is calculated by subtracting the "instrument-derived half-width" from the "sample half-width." An example of an X-ray diffraction device is the Rigaku X-ray diffractometer Ultima III, and an example of analysis software is Spectris Expert High Score Plus.

[0071]

[0072] Next, a method for manufacturing the plated steel material according to this embodiment will be described. The plated steel material according to this embodiment can obtain the effects as long as it has the above-mentioned characteristics regardless of the manufacturing method, but can be manufactured by a manufacturing method including the following steps.

[0073] (I) a plating step of forming a plating layer on the surface of a steel material by hot dip plating, (II) a temper rolling step of temper rolling the steel material on which the plating layer has been formed (plated steel material), and (III) a heat treatment step of heat treating the plated steel material after temper rolling.

[0074] Preferred conditions for each step will be explained below.

[0075] [Plating Process] In the plating process, a steel material such as a steel sheet is immersed in a plating bath containing Zn to form a plating layer on the surface. Conventional methods can be used to ensure sufficient plating adhesion. The composition of the plating bath can be adjusted depending on the chemical composition of the desired plating layer. After the steel material is removed from the plating bath, the coating weight of the plating layer can be adjusted as needed by wiping. The cooling conditions after removal from the plating bath are not particularly limited up to 300°C, and any cooling conditions can be used. Strain can be introduced into the plating layer by quenching the plating layer between 300°C and 150°C or less. Specifically, strain can be introduced into the plating layer by setting the average cooling rate of the plating layer between 300°C and 150°C or less to 15.0°C / s. Around 300°C is a temperature range in which the atomic diffusion rate in the plating begins to slow. Quenching the plating from this temperature range forcibly stops atomic diffusion and allows strain to remain in each plating phase. When the average cooling rate exceeds 35.0°C / s, the Zn phase, the Al phase, and the MgZn phase are ２ The phase distortion becomes large and it becomes impossible to adjust the KAM value to the desired value.

[0076] [Temper Rolling Step] Next, the coating layer formed on the surface of a steel material such as a steel sheet is subjected to temper rolling. The start time of temper rolling is between 30.0 and 120.0 seconds after the end of cooling in the coating step. In this embodiment, in order to impart sufficient strain to each phase constituting the coating layer, temper rolling is performed using rolls with a relatively small arithmetic mean roughness Ra under conditions that result in a relatively large elongation.

[0077] Specifically, in the temper rolling, the temper rolling is started within 30.0 to 120.0 seconds after the end of cooling in the plating step, and the temper rolling is performed using a rolling roll having an arithmetic mean roughness Ra of the roll surface in the range of 1.5 to 2.5 μm under conditions such that the elongation is 1.8 to 2.5%.

[0078] By setting the start time of temper rolling to be between 30.0 and 120.0 seconds after the end of cooling in the plating process, MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) can be controlled in the range of 0.20 to 1.00°.

[0079] The end of cooling in the coating process, which is the basis for the start time of temper rolling, is the time when spraying of a cooling medium such as cooling gas onto the coating layer ends. The start time of temper rolling is the time when the temper rolling rolls come into contact with the coating layer. Note that if the post-coating cooling equipment and the temper rolling equipment are arranged in series and the plated steel material passes through the cooling equipment and the temper rolling equipment in series, the start time of temper rolling will be constant regardless of the location of the plated steel material.

[0080] In addition, by setting the elongation rate of the plated steel material during temper rolling to 1.8 to 2.5%, the Al phase, Zn phase, and MgZn phase can be ２ By rapidly cooling the plating layer at 300°C or less, and then allowing a time interval of 30.0 to 120.0 seconds after quenching, skin-passing is performed so as to achieve a relatively large elongation, thereby making it possible to introduce sufficient strain into each phase.

[0081] Furthermore, by setting the roughness Ra of the roll surface in the range of 1.5 to 2.5 μm, it is possible to impart strain relatively uniformly to the surface of the plating layer, making it possible to adjust the KAM value to a predetermined value.

[0082] [Heat Treatment Step] Next, the coating layer formed on the surface of a steel material such as a steel sheet and subjected to temper rolling is subjected to heat treatment. In this embodiment, in order to recover strain in each phase constituting the coating layer to some extent, the heat treatment is performed by setting the maximum temperature to a relatively low value, holding the temperature for a relatively short time, and controlling the cooling rate after the holding time to within an appropriate range.

[0083] Specifically, in the heat treatment process, the heat treatment is performed under the conditions of a maximum temperature of 100 to 150°C, a holding time of 0.5 to 10.0 seconds, and an average cooling rate of 10.0 to 25.0°C / second during cooling after the holding time has elapsed. The cooling end temperature is 50°C or less. By setting the maximum temperature to 100 to 150°C, it becomes possible to recover the strain of the Zn phase, which contains a large amount of Zn, a metal with a low melting point. In addition, by performing the heat treatment, the Al phase and MgZn ２ Furthermore, by setting the holding time to 0.5 to 10.0 seconds and the average cooling rate during cooling after the holding time to 10.0 to 25.0°C / second, excessive recovery of the strain in the Zn phase can be prevented, and the strain state can be controlled.

[0084] As described above, by controlling the cooling conditions after plating and the conditions for temper rolling, larger strain is applied to each phase of the plating layer compared to when cooling after plating and temper rolling are performed under conventional conditions, and strain according to the hardness of each phase is introduced, resulting in the formation of Al phase, Zn phase, and MgZn phase. ２ Furthermore, by performing heat treatment after temper rolling, the average KAM value of each phase can be adjusted. In this way, the plated steel material of this embodiment can be manufactured.

[0085] After production of the plated steel material, various chemical conversion treatments and painting treatments may be performed. However, various chemical conversion treatments and painting treatments require a drying or baking process. In other words, after the heat treatment for strain adjustment described above, the steel may be subjected to further heat treatment for another purpose (e.g., chemical conversion treatment, painting). In this case, it is advisable to adjust the heat treatment conditions so that the KAM values ​​of each phase of the plating layer do not deviate from the range of the present application. For example, the heat treatment performed after the heat treatment for strain adjustment may have a maximum temperature of less than 100°C and a holding time of 0.5 to 10 seconds.

[0086] The plated steel material of this embodiment may have a coating formed on the plating layer. One or more coatings may be formed. Examples of the coatings that may be formed directly on the plating layer include chromate coatings, phosphate coatings, and chromate-free coatings. The chromate treatment, phosphate treatment, and chromate-free treatment that form these coatings can be performed by known methods.

[0087] Chromate treatments include electrolytic chromate treatments that form a chromate film by electrolysis, reactive chromate treatments that form a film by utilizing a reaction with the material and then wash away excess treatment solution, and paint-on chromate treatments that apply a treatment solution to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0088] Examples of electrolytic chromate treatments include electrolytic chromate treatments using chromic acid, silica sol, resins (phosphoric acid, acrylic resins, vinyl ester resins, vinyl acetate acrylic emulsions, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resins, etc.), and hard silica.

[0089] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0090] Chromate-free treatments are particularly suitable because they do not place a burden on the environment. Chromate-free treatments include electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and paint-on chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0091] Furthermore, one or more organic resin coatings may be provided on the coating directly on the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. Here, the term "modified version" refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group.

[0092] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-rust pigment. Water-based organic resins obtained by dissolving or dispersing them in water may also be used.

[0093] It is also possible to impart a design by utilizing the uneven pattern on the surface of the plating layer, or by applying a plating layer of Cr, Ni, Au, etc. and then painting it. To further improve corrosion resistance, touch-up paint or thermal spraying treatment for repair may be performed on welded parts, processed parts, etc.

[0094] Examples are described below. A 4.5 mm thick hot-rolled steel sheet meeting JIS G 3193:2019 was prepared as the steel material. This steel sheet was subjected to hot-dip galvanization to form a coating layer having the chemical composition shown in Tables 3A and 3B. The impurity concentration (content) in the coating layer was 0.1% or less. In the hot-dip galvanization method, the average cooling rate from 300°C to 150°C was as shown in Tables 4A and 4B. Cooling was performed by spraying cooling gas. Next, the steel sheet on which the coating layer was formed was subjected to skin pass rolling (skin pass) under the conditions shown in Tables 4A and 4B after the time shown in Tables 4A and 4B had elapsed since the end of cooling. Furthermore, heat treatment was performed after the skin pass was completed. As shown in Tables 4A and 4B, the heat treatment was carried out under the conditions of a maximum temperature of 90 to 160°C, a holding time of 0.1 to 15.0 seconds, and an average cooling rate of 8.0 to 30.0°C / second when cooling to 50°C after the holding time had elapsed.

[0095] The end of cooling in the coating process, which is the basis for the start time of temper rolling, was defined as the time when spraying of cooling gas onto the coating layer finished. The start time of temper rolling was defined as the time when the temper rolling rolls came into contact with the coating layer. In this example, the post-coating cooling equipment and the temper rolling equipment were arranged in series, and the plated steel material passed through the cooling equipment and the temper rolling equipment in series. This made the start time of temper rolling consistent regardless of the location of the plated steel material.

[0096] The coating weight of the plating layer is 135 g / m per side on both the front and back sides of the plated surface. ２ It was decided.

[0097] In this manner, plated steel materials Nos. 1-1 to 1-37 and 2-1 to 2-23 were produced.

[0098] The Zn phase, Al phase and MgZn contained in the plating layer of the obtained plated steel material were ２ Average KAM value of the phase, average crystal grain size, half width of the X-ray diffraction peak of the (102) plane of Zn, half width of the X-ray diffraction peak of the (111) plane of Al, MgZn ２ The half-width of the X-ray diffraction peak of the (201) plane of each sample was measured. The respective measurement methods and conditions were as follows:

[0099] (Average KAM value, average crystal grain size) The surface of the plating layer was polished using #1500 silicon carbide paper, then mirror-finished using a liquid containing alcohol and diamond powder with a particle size of 1 to 6 μm dispersed therein, and then final polishing was performed using colloidal silica. In this way, the measurement samples were prepared.

[0100] The measurement samples were observed using a scanning electron microscope. The scanning electron microscope used was equipped with an EBSD analyzer and an EDS measurement device. The scanning electron microscope used was a field emission scanning electron microscope (FE-SEM: SU-70) manufactured by Hitachi High-Tech Corporation. The EBSD analyzer used was DigiView (manufactured by TSL Solutions). The EDS measurement device used was Octan elect super (manufactured by Ametec Co., Ltd.).

[0101] The measurement area for the KAM value was a 125 × 300 μm region on the surface of the plating layer. The measurement interval was 0.25 μm / step. On the other hand, the measurement area for the average crystal grain size was a rectangular region of 30 μm × 60 μm on the surface of the plating layer, with a measurement interval of 0.05 μm / step. For both the KAM value and the average crystal grain size, the acceleration voltage was 15 kV, the working distance was 15 mm, and secondary electron images were taken with a scanning electron microscope.

[0102] Next, the same field of view was subjected to EBSD analysis at an analysis speed of 200 to 300 points / second using an EBSD analyzer. The Al phase, Zn phase, and MgZn phase were analyzed using the software "OIM Analysis (registered trademark)" attached to the EBSD analyzer. ２ The average crystal grain size of the phase was calculated. Using the crystal orientation information obtained by EBSD analysis, regions surrounded by grain boundaries with an average crystal orientation difference of 15° or more were defined as crystal grains by the Number method, and the average crystal grain size was calculated. When calculating the average crystal grain size, the measurement targets were crystal grains with a grain size of 0.25 μm or more. The results are shown in Tables 6A and 6B.

[0103] Next, the average KAM value of each phase was measured under the following conditions using the software "OIM Analysis (registered trademark)." The results are shown in Tables 5A and 5B.

[0104] ・Nearest neighbor: 1st (If it is 1st, the azimuth difference is calculated using the nearest neighbor pixel.) ・Perimeter only ・If the azimuth difference is 5° or more, all azimuth differences are set to 5°. ・Maximum azimuth difference: Within 5°.

[0105] (Fulfillment width at half maximum of X-ray diffraction peak) A test piece having a surface size of 20 mm × 20 mm square of the plating layer was cut out from the plated steel material, and an X-ray diffraction image of the plating layer surface of the test piece was obtained. X-ray diffraction measurement was performed under the measurement conditions shown in Table 2 below, and the X-ray diffraction peak of the (102) plane of Zn, the X-ray diffraction peak of the (111) plane of Al, and the X-ray diffraction peak of the (111) plane of MgZn were obtained. ２ The X-ray diffraction peak of the (201) plane was identified. The diffraction peak position 2θ and half-width B were determined by fitting with a Lorentz function after removing the background and Kα2 radiation. The half-width derived from the instrument was determined by fitting with a standard sample (LaB ６ The true half-width was calculated by interpolation using the half-width of the sample. The true half-width was calculated by subtracting the "instrument-derived half-width" from the "sample half-width." The X-ray diffractometer used was an Ultima III manufactured by Rigaku Corporation, and the analysis software used was Expert High Score Plus manufactured by Spectris. The results are shown in Tables 6A and 6B.

[0106]

[0107] The average chemical composition of the plating layer was determined by preparing an acid solution by peeling and dissolving the plating layer with an acid containing an inhibitor that suppresses corrosion of the steel material, and then measuring the acid solution using ICP atomic emission spectroscopy and ICP-MS. The inhibitor-containing acid was a 10% hydrochloric acid solution to which 0.06 mass% of an inhibitor (Ivit 710K, manufactured by Asahi Chemical Industry Co., Ltd.) had been added.

[0108] (Flat Corrosion Resistance) Flat corrosion resistance was evaluated as follows. The obtained plated steel material was cut into test pieces with a surface size of 100 mm x 50 mm for the plating layer, and a salt spray test in accordance with JIS Z 2371 (2015) was performed on the plating layer of the test pieces for up to 96 hours. The flat corrosion resistance was evaluated based on the corrosion weight loss of the test pieces after the test. The evaluation criteria for flat corrosion resistance are shown below. "SS", "S", "AA", and "A" were considered to be acceptable. The results are shown in Tables 6A and 6B.

[0109] SS: 0.020 (g / m ２ / hr) or less S: More than 0.020 to 30 (g / m ２ / hr) or less AA: More than 0.030 to 0.040 (g / m ２ / hr) or less A: More than 0.040 to 0.10 (g / m ２ / hr) or less B: More than 0.10 to 0.50 (g / m ２ / hr) or less C: 0.50 (g / m ２ / hr) super

[0110] (End Surface Corrosion Resistance) The obtained plated steel material was cut using an electric shear so that the surface of the plating layer had a size of 100 mm x 50 mm, leaving a burr on the surface. This formed a cut end surface with a portion having a plating layer and a portion where the end surface of the steel material was exposed, and these were used as test specimens. Note that no non-plated portion was formed on the surface side of the plating layer. An exposure test was conducted on the cut plated steel material, and the area ratio of red rust on the end surface after 50 days was determined. The exposure conditions were as follows. The plated steel material sample was tilted 30° from the horizontal and placed facing south, so that the treated cut end surface was on top and the plated portion of the side end surface (100 mm x 4.5 mm) was on top. After exposure, the sample was evaluated as follows based on the ratio of the area where red rust occurred to the area where the plating layer was not formed. A grade of SS, S, AA, or A was determined to have excellent end surface corrosion resistance. The results are shown in Tables 6A and 6B.

[0111] SS: 70% or less S: More than 70%, 80% or less AA: More than 80%, 90% or less A: More than 90%, 100% or less B: More than 100%, 115% or less C: More than 115%

[0112] As shown in Tables 3A to 6B, Nos. 1-1 to 1-37 had average chemical compositions of the coating layer and average KAM values ​​of each phase that satisfied the ranges of the present invention, and both flat surface corrosion resistance and edge surface corrosion resistance were excellent. ２ The average grain size of each phase is within a preferred range (average grain size of Zn phase: 0.10 to 2.00 μm, average grain size of Al phase: 0.1 to 5.0 μm, MgZn ２ The half-width ratios of Nos. 1-1 to 1-24 were all outside the preferred range (0.5≦B Ａｌ / B Ｚｎ ≦1.8, 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4), and therefore the values ​​were not listed in Table 6A.

[0113] In Nos. 2-1 to 2-4, the average chemical composition of the plating layer was outside the range of the present invention, and therefore, the Zn phase, Al phase, or MgZn phase was not included. ２ The average KAM value of any of the phases was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0114] In No. 2-5, the average chemical composition of the coating layer satisfied the range of the present invention, but the average cooling rate between 300°C and 150°C was outside the preferred condition, so the average KAM value of the Al phase was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0115] In No. 2-6, the average chemical composition of the coating layer satisfied the range of the present invention, but the average cooling rate between 300°C and 150°C was outside the preferred conditions, so the Zn phase, Al phase, and MgZn phase were ２ The average KAM value of the phases was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0116] No. 2-7 was temper rolled within 30 seconds of the end of cooling in the plating process, so MgZn２ The average KAM value of the phases was outside the range of the present invention, and both the corrosion resistance of the flat surface and the corrosion resistance of the edge surface were inferior.

[0117] No. 2-8 was subjected to temper rolling 120 seconds after the end of cooling in the plating process, so MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the corrosion resistance of the flat surface and the corrosion resistance of the edge surface were inferior.

[0118] In Nos. 2-9 and 2-10, the average chemical composition of the coating layer satisfied the range of the present invention, but the elongation rate of temper rolling was outside the preferred condition, so MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the corrosion resistance of the flat surface and the corrosion resistance of the edge surface were inferior.

[0119] In Nos. 2-11 and 2-12, the average chemical composition of the coating layer satisfied the range of the present invention, but the roll roughness of the temper rolling was outside the preferred conditions, so the Zn phase or MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the corrosion resistance of the flat surface and the corrosion resistance of the edge surface were inferior.

[0120] In Nos. 2-13 to 2-18, the average chemical composition of the plating layer satisfied the range of the present invention, but the heat treatment conditions were outside the preferred range, so the average KAM value of the Zn phase or Al phase was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0121] In No. 2-19, the average chemical composition of the coating layer satisfied the range of the present invention, but because temper rolling and heat treatment were not performed, the Zn phase and MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the corrosion resistance of the flat surface and the corrosion resistance of the edge surface were inferior.

[0122] In No. 2-20, the average chemical composition of the coating layer satisfied the range of the present invention, but because heat treatment was not performed, the average KAM value of the Zn phase was outside the range of the present invention, and both the flat surface corrosion resistance and the end surface corrosion resistance were inferior.

[0123] No. 2-21 had an average chemical composition of the coating layer that satisfied the range of the present invention, but because temper rolling was not performed, MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0124] In No. 2-22, the average chemical composition of the coating layer satisfied the range of the present invention, but the average cooling rate between 300°C and 150°C was outside the preferred conditions, and no heat treatment was performed, so the Al phase and MgZn ２ The average KAM value of the phases was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0125] In No. 2-23, the average chemical composition of the coating layer satisfied the range of the present invention, but the average cooling rate between 300°C and 150°C was outside the preferred conditions, and temper rolling was not performed, so the Zn phase, Al phase, and MgZn phase were ２ The phase average KAM value was outside the range of the present invention, and both the flat surface corrosion resistance and the edge surface corrosion resistance were inferior.

[0126] In addition, the Zn phase, Al phase, and MgZn phase of Nos. 2-1 to 2-23 ２ The average grain size and half width ratio of the phases were not measured because the average KAM value was outside the preferred range.

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135] The present invention has industrial applicability in that it can provide a plated steel material that can improve both the corrosion resistance of flat surfaces and the corrosion resistance of edge surfaces.

Claims

1. A steel material having a plating layer disposed on at least a part of the surface of the steel material, wherein the plating layer is a Zn-based plating layer having an average chemical composition of 4.0 mass% to 70.0 mass% Al, 0.3 mass% to 12.5 mass% Mg, and the balance being Zn and impurities, and the metal structure of the plating layer contains a Zn phase, an Al phase, and an MgZn phase. ２ and a Zn phase, and when the average KAM value is measured by an EBSD method with a measurement interval of 0.25 μm / step in a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer, the average KAM value (K Ｚｎ ) is in the range of 0.30 to 1.70°, and the average KAM value (K Ａｌ ) is in the range of 0.20 to 1.00°, and the MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) is in the range of 0.20 to 1.00°.

2. The plated steel product according to claim 1, wherein the plating layer further contains, in average composition, elements listed in either or both of the following Group A and Group B: [Group A] Si: 0.0001 to 2 mass%. [Group B] One or more of the following elements: Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM, in a total amount of 0.0001 to 2 mass%.

3. The plated steel material according to claim 1, which satisfies the following formulas (1) and (2): 0.15≦K Ａｌ / K Ｚｎ ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 ... (2) However, K in formulas (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is the MgZn ２ The mean KAM value for the phase.

4. When a rectangular measurement area of ​​30 μm x 60 μm set on the surface of the plating layer is measured by EBSD with a measurement interval of 0.05 μm / step, and the area surrounded by grain boundaries with an average crystal orientation difference of 15° or more is defined as a crystal grain, and the average crystal grain size is measured by the Number method, the average crystal grain size of the Zn phase is in the range of 0.10 to 2.00 μm, the average crystal grain size of the Al phase is in the range of 0.10 to 5.00 μm, and the MgZn ２ 2. The plated steel material according to claim 1, wherein the phase has an average crystal grain size in the range of 0.10 to 2.00 μm.

5. When X-ray diffraction measurement is performed on the surface of the plating layer, the half-width of the X-ray diffraction peak of the (102) plane of Zn, the half-width of the X-ray diffraction peak of the (111) plane of Al, and the MgZn ２ 2. The plated steel material according to claim 1, wherein the half width of the X-ray diffraction peak of the (201) plane satisfies the relationships of the following formulas (3) and (4): 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4 ... (4) However, B in equations (3) and (4) Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn ２ is the half-width of the X-ray diffraction peak of the (201) plane of the sample.

6. A steel material having a plating layer disposed on at least a part of the surface of the steel material, wherein the plating layer is a Zn-based plating layer having an average chemical composition of 4.0 mass% to 70.0 mass% Al, 0.3 mass% to 12.5 mass% Mg, and the balance being Zn and impurities, and the metal structure of the plating layer contains a Zn phase, an Al phase, and an MgZn phase. ２ and a Zn phase, and when the average KAM value is measured by an EBSD method with a measurement interval of 0.25 μm / step in a rectangular measurement area of ​​125 μm × 300 μm set on the surface of the plating layer, the average KAM value (K Ｚｎ ) is in the range of 0.30 to 1.70°, and the average KAM value (K Ａｌ ) is in the range of 0.20 to 1.00°, and the MgZn ２ The average KAM value of the phase (K ＭｇＺｎ２ ) is in the range of 0.20 to 1.00°, and when the average crystal grain size is measured by the Number method using an EBSD method with a measurement interval of 0.05 μm / step in a rectangular measurement area of ​​30 μm × 60 μm set on the surface of the plating layer, with a region surrounded by a grain boundary having an average crystal orientation misorientation of 15° or more defined as a crystal grain, the average crystal grain size of the Zn phase is in the range of 0.10 to 2.00 μm, the average crystal grain size of the Al phase is in the range of 0.10 to 5.00 μm, and the MgZn ２ The average crystal grain size of the MgZn phase is in the range of 0.10 to 2.00 μm, and when X-ray diffraction measurement is performed on the surface of the plating layer, the half width of the X-ray diffraction peak of the (102) plane of Zn, the half width of the X-ray diffraction peak of the (111) plane of Al, and ２ The full width at half maximum of the X-ray diffraction peak of the (201) plane of the plated steel satisfies the relationships of the following formulas (1) to (4): 0.15≦K Ａｌ / K Ｚｎ ≦1.40 ... (1) 0.20≦K ＭｇＺｎ２ / K Ｚｎ ≦1.40 ... (2) 0.5≦B Ａｌ / B Ｚｎ ≦1.8 … (3) 0.4≦B ＭｇＺｎ２ / B Ｚｎ ≦1.4 ... (4) However, K in equations (1) and (2) Ｚｎ is the average KAM value of the Zn phase, and K Ａｌ is the average KAM value of the Al phase, and K ＭｇＺｎ２ is the MgZn ２ The average KAM value of the phase. Ｚｎ is the half-width of the X-ray diffraction peak of the (102) plane of Zn, and B Ａｌ is the half-width of the X-ray diffraction peak of the (111) plane of Al, and B ＭｇＺｎ２ is MgZn ２ is the half-width of the X-ray diffraction peak of the (201) plane of the sample.

7. The plated steel product according to claim 6, wherein the plating layer further contains, in average composition, elements listed in either or both of the following Group A and Group B: [Group A] Si: 0.0001 to 2 mass%. [Group B] One or more of the following elements: Ni, Ti, Sr, Fe, Sb, Pb, Sn, Ca, Co, V, Nb, Cu, Mn, B, Bi, In, Cr, Y, La, Ce, and REM, in a total amount of 0.0001 to 2 mass%.

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