Hot stamped compact

Abstract

This hot-stamp-molded object comprises a steel material and a plating layer. The chemical composition of the plating layer contains, in mass%, 0-70% of Al, 10-60% of Fe, 0-20% of Si, and a total of 0.00001-0.3% of a C-group element which is one or two of Li and Y, and optionally further contains one or more of Sb, Pb, B, Cu, Ti, Cr, Nb, Ni, Mn, Mo, Ag, Co, Sn, and Bi, the remaining portion being Zn impurities. In the plating layer, a η-Zn phase or a Zn-containing phase is included.

Description

[Technical Field]

[0001] The present invention relates to a hot-stamped body. This application claims priority based on Japanese Patent Application No. 2021-167251, filed on October 12, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Hot stamping is known as a technique for press-forming difficult-to-form materials such as high-strength steel sheets. Hot stamping is a hot forming technique in which the material to be formed is heated before being formed. With this technique, the steel is soft and has good formability when formed, because the material is heated before being formed. Therefore, even high-strength steel can be formed with high precision into complex shapes. In addition, because the steel is quenched simultaneously with forming using a press die, the steel after forming is known to have sufficient strength.

[0003] For example, Patent Document 1 describes a plated steel sheet for a hot-stamped body, which is coated with a metal coating containing 2.0 to 24.0 wt. % zinc, 7.1 to 12.0 wt. % silicon, an optional element 1.1 to 8.0 wt. % magnesium, an optional element less than 0.3 wt. % selected from Pb, Ni, Zr, and Hf, the balance being aluminum and impurities, and having an Al / Zn ratio of more than 2.9.

[0004] Patent Document 2 also describes a method for producing a hot-stamped body, in which a steel sheet coated with a metal coating containing 2.0 to 24.0 wt. % zinc, 7.1 to 12.0 wt. % silicon, an optional element 1.1 to 8.0 wt. % magnesium, an optional element less than 0.3 wt. % selected from Pb, Ni, Zr, and Hf, the balance being aluminum and impurities, and having an Al / Zn ratio of more than 2.9, is heated to 840 to 950°C, hot-formed, and further cooled to obtain a part having steel composed of martensite. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 017513 [Patent Document 2] International Publication No. 2017 / 017514 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Documents 1 and 2, when the steel sheet is heated for hot stamping, the Zn contained in the metal coating (plating layer) of the steel sheet evaporates, which causes a problem that the sacrificial corrosion protection performance of the hot stamped product is reduced, and the red rust resistance is reduced, which in turn reduces the corrosion resistance and paint adhesion after painting.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot-stamped product that is excellent in corrosion resistance and paint adhesion after painting. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A steel plate having a steel material and a plating layer, The chemical composition of the plating layer is, in mass%, Al: 0-70%, Fe: 10-60%, Si: 5 ~20%, C group elements: one or two of Li and Y, the total content of which is 0.00001 to 0.3%; Furthermore, Sb: 0 to 0.5% Pb: 0~0.5% B: 0~0.5%, Cu: 0-1.0% Ti: 0 to 1.0% Cr: 0 to 1.0%, Nb: 0 to 1.0% Ni: 0 to 1.0% Mn: 0 to 1.0% Mo: 0-1.0% Ag: 0~1.0%, Co: 0-1.0% Sn: 0 to 1.0% Bi: 0 to 1.0%, containing one or more of 0 to 5% in total, The balance consists of Zn and impurities. A hot-stamped product, characterized in that the plating layer contains an η-Zn phase or a Zn-containing phase. [2] The hot-stamped product according to [1], wherein the chemical composition of the plating layer contains one or two of an A group element and a B group element. A group elements: 0.0010 to 15% of Mg and one or both of Ca and Sr, with the total content being 0.0001% or more and less than 5.5%. B group elements: one or more of Zr, La, and Ce, with a total content of 0.0001 to 0.5%. [3] The hot-stamped product according to [1] or [2], wherein the total amount of the C group elements is 0.001 to 0.3%. [4] The Mg content in the A group elements is 1 to 15%. [2] The hot stamped body according to claim 1. [Effects of the Invention]

[0009] According to the present invention, a hot stamped product having excellent corrosion resistance after painting can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors have conducted extensive research into means for preventing the evaporation of Zn from the coating layer of a heated coated steel sheet during hot stamp forming. A coated steel sheet was used as a blank, which contained specific elements in a predetermined range in the coating layer and had its surface oxidized by steam during coating layer formation. The present inventors have found that this method can suppress the evaporation of Zn from the coated steel sheet during hot stamp forming, allowing Zn to remain in the coating layer.

[0011] Furthermore, when a plated steel sheet is heated during hot stamping, the base steel of the steel sheet reacts with the constituent elements of the plating layer to form an alloy layer, and the alloy layer is modified by including specific elements in the plating layer within a predetermined range. The inventors have found that this makes it less likely for paint blistering to occur when evaluating the corrosion resistance after painting, and further improves the corrosion resistance after painting and paint adhesion of the hot-stamped product.

[0012] Hereinafter, a hot-stamped steel sheet having excellent corrosion resistance after painting and excellent paint adhesion, a method for manufacturing the hot-stamped steel sheet, and a method for manufacturing a plated steel sheet for hot stamping, which are embodiments of the present invention, will be described.

[0013] First, a description will be given of a plated steel sheet for hot stamping, which is the raw material of the hot stamped steel of this embodiment, and a method for producing the same.

[0014] The plated steel sheet for hot stamping includes a steel sheet and a plating layer formed on the surface of the steel sheet. The plating layer may be formed on one side or both sides of the steel sheet.

[0015] The type of steel sheet is not particularly limited and may be determined depending on the product to be applied, the required strength, thickness, etc. For example, a hot-rolled steel sheet as specified in JIS G3193:2008 or a cold-rolled steel sheet as specified in JIS G3141:2017 can be used.

[0016] The steel sheet is not particularly limited, but may have a chemical composition containing 0.1-0.5% C, 0.001-3% Si, 0.3-3% Mn, 0.0002-2% Al, and the balance being Fe and impurities. In the description of the chemical composition of the steel sheet, "%" means "% by mass."

[0017] The plating layer has a chemical composition containing 0-70% Al, 0-15% Fe, 0-20% Si, C group elements, and the remainder being Zn and impurities. The reasons for limiting each element in the chemical composition of the plating layer will be explained below. In the explanation of the chemical composition of the plating layer, "%" means "% by mass."

[0018] Al: 0 to 70% Al is an element that enhances the barrier properties of the coating layer of a coated steel sheet for hot stamping and is contained as needed. Furthermore, Al reacts with the base steel of the steel sheet during hot stamping to form an alloy layer. The lower limit of the Al content is 0% or more. The upper limit of the Al content is 70% or less. If the Al content exceeds 70%, the Zn content decreases relatively, which prevents Zn from remaining in the coating layer after hot stamping, reducing the sacrificial corrosion protection of the coating layer and the corrosion resistance after painting of the hot-stamped body, which is undesirable. The lower limit of the Al content may be 20% or more or 30% or more. The upper limit of the Al content may be 65% or less or 60% or less.

[0019] Fe: 0-15% Fe may be contained in the coating layer of the coated steel sheet for hot stamping. When the coating layer is formed by hot-dip galvanizing, Fe may be contained in the coating layer by diffusing from the steel sheet to the coating layer. A portion of Fe bonds with Al, etc. in the coating layer to form an alloy. Furthermore, Fe diffuses from the steel sheet to the coating layer during hot stamping and bonds with Al, etc. in the coating layer to form an alloy layer. The Fe content is 0% or more. Also, the Fe content is 15% or less. An Fe content exceeding 15% is undesirable because the Fe content in the coating layer after hot stamping becomes excessive, making red rust more likely to occur. The lower limit of the Fe content in the coating layer of the coated steel sheet for hot stamping may be 1% or more or 2% or more. The upper limit of the Fe content may be 5% or less or 4% or less.

[0020] Si: 0 to 20% Si may be added because it is an element that has the effect of preventing an excessively thick alloy layer from being formed between the steel sheet and the coating layer when a coating layer is formed on the steel sheet by hot-dip galvanizing, thereby improving the adhesion between the steel sheet and the coating layer. Furthermore, when Si is added together with Mg, it forms a compound with Mg, contributing to improving corrosion resistance after painting. The lower limit of the Si content is 0% or more. The lower limit of the Si content may be 1% or more, or 2% or more. On the other hand, if the Si content exceeds 20%, the workability of the coating layer may be reduced, and cracks or the like may occur in the coating layer after hot stamping. Therefore, the Si content is set to 20% or less. The upper limit of the Si content may be 10% or less, or more preferably 5% or less.

[0021] The coating layer also contains the following C group elements. These elements are more easily oxidized than Al, Fe, Si, and Zn, and are likely to form oxides in the coating layer during hot stamping. It is presumed that by including these elements in the coating layer, the oxides of these elements suppress the evaporation of Zn from the heated coating layer during hot stamping.

[0022] C group elements (either one or both of Li and Y, 0.00001 to 0.3% in total) The inclusion of C group elements can also suppress Zn evaporation during hot stamping. The total content of C group elements is 0.00001 to 0.3%. The total amount of C group elements is more preferably 0.001 to 0.3%. The total amount of C group elements may be 0.001% or more, or 0.01% or more, or 0.2% or less, or 0.1% or less. If the total content of C group elements is below the lower limit, the effect of suppressing Zn evaporation becomes insufficient. On the other hand, if the total content of C group elements exceeds the upper limit, the plating layer after hot stamping is excessively oxidized, resulting in reduced corrosion resistance and paint adhesion after painting.

[0023] The coating layer may also contain one or two of the following group A and group B elements. Like the group C elements, these elements are more easily oxidized than Al, Fe, Si, and Zn, and are likely to form oxides in the coating layer during hot stamping.

[0024] A group elements (0.0010-15% Mg and one or two of either Ca or Sr, with a total content of 0.0001% or more but less than 5.5%) When an A group element is contained, Mg and one or both of Ca and Sr are contained. That is, when an A group element is contained, the combinations of the elements are Mg and Ca, Mg and Sr, or Mg, Ca and Sr. This can suppress Zn evaporation during hot stamping. Furthermore, excellent coating adhesion can be obtained. The Mg content is preferably 0.0010 to 15%, and more preferably 1 to 15%. The Mg content may be 1% or more or 3% or more, and may be 14% or less or 10% or less. Furthermore, the total amount of one or both of Ca and Sr is preferably 0.0001% or more and less than 5.5%. The total amount of Ca and Sr may be 0.0002% or more or 0.01% or more, and may be 5% or less or 4% or less. If the content of each element is less than the respective lower limits, the effect of suppressing Zn evaporation becomes insufficient. Furthermore, if the content of each element exceeds the respective upper limits, the plating layer after hot stamping is excessively oxidized, resulting in a decrease in corrosion resistance after painting.

[0025] B group elements (Zr, La, Ce, one or more of these, 0.0001 to 0.5% in total) The inclusion of B group elements can also suppress Zn evaporation during hot stamping. Furthermore, excellent coating adhesion can be obtained. The total content of B group elements is preferably 0.0001 to 0.5%. The total amount of B group elements may be 0.0002% or more, or 0.01% or more, or may be 0.4% or less, or 0.3% or less. If the total content of B group elements is below the lower limit, the effect of suppressing Zn evaporation becomes insufficient. On the other hand, if the total content of B group elements exceeds the upper limit, the plating layer after hot stamping is excessively oxidized, reducing corrosion resistance after painting.

[0026] Furthermore, the coating layer of this embodiment may contain, in place of a portion of Zn, one or more of the following in a total range of 0 to 5%: Sb: 0 to 0.5%, Pb: 0 to 0.5%, B: 0 to 0.5%, Cu: 0 to 1.0%, Ti: 0 to 1.0%, Cr: 0 to 1.0%, Nb: 0 to 1.0%, Ni: 0 to 1.0%, Mn: 0 to 1.0%, Mo: 0 to 1.0%, Ag: 0 to 1.0%, Co: 0 to 1.0%, Sn: 0 to 1.0%, and Bi: 0 to 1.0%. If the total of these elements exceeds 5%, the viscosity of the coating bath increases, making it difficult to prepare the coating bath itself, and it becomes impossible to produce a coated steel sheet with good coating properties.

[0027] Sb, Pb, and B are elements that can be added to the coating layer. The inclusion of these elements in the coating layer improves the corrosion resistance of the flat portions of the coating layer before and after hot stamping. The corrosion resistance of the flat portions refers to the corrosion resistance of the coating surface of the coating layer. A content of 0.001% or more, preferably 0.01% or more or 0.1% or more, clearly improves corrosion resistance, so it is preferable to include 0.001% or more of each of these elements. As long as these elements are included in a range of 0.5% or less, the viscosity of the coating bath does not increase, making it possible to prepare the coating bath and producing a coated steel sheet with good coating properties.

[0028] Cu, Ti, Cr, Nb, Ni, Mn, Mo, Ag, and Co are metal elements that can be optionally contained in the coating layer. The inclusion of these elements has the effect of improving the corrosion resistance of the flat portion of the coating layer before and after hot stamping. A clear improvement in corrosion resistance has been confirmed when the content of each of these elements is 0.0001% or more, 0.001% or more, or 0.10% or more. Therefore, it is preferable to contain 0.0001% or more of each of these elements. As long as these elements are contained in a range of 1.0% or less, the viscosity of the coating bath does not increase, making it possible to prepare the coating bath and producing a coated steel sheet with good coating properties.

[0029] Sn and Bi are elements that can be added optionally. The inclusion of Sn and Bi improves the sacrificial corrosion protection of the coating layer before and after hot stamping. The improved sacrificial corrosion protection effect can be confirmed when the content is 0.001% or more, or 0.01% or more, respectively. However, excessive Sn and Bi content improves the sacrificial corrosion protection of the coating layer, making the coating layer more susceptible to leaching, which adversely affects the corrosion resistance of flat areas, etc. Furthermore, the appearance of the coating layer is more likely to change. Therefore, the Sn and Bi contents are each set to 1.0% or less.

[0030] The remainder of the chemical composition of the coating layer is Zn and impurities. Zn improves the sacrificial corrosion protection of the hot stamping coated steel sheet. Zn also remains in the coating layer after hot stamping and forms an η-Zn phase or a Zn-containing phase in the coating layer of the hot stamped body. This improves the post-painting corrosion resistance of the hot stamped body. Therefore, Zn is contained as the remainder. As long as Zn is contained as the remainder, its content is not particularly limited, but it is sufficient that the Zn content be 5% or more, and more preferably 8% or more.

[0031] Impurities are components contained in raw materials or components that are mixed in during the manufacturing process but are not intentionally added. For example, trace amounts of impurities can be mixed into the coating layer due to atomic diffusion between the steel sheet (base steel) and the coating bath.

[0032] Moreover, the surface of the plating layer of the plated steel sheet for hot stamping according to this embodiment is subjected to a steam oxidation treatment.

[0033] The coating weight of the coating layer of hot stamping coated steel sheets is 20 to 160 g / m 2 It is preferable to set it in the range of

[0034] Next, a method for producing a plated steel sheet for hot stamping will be described. The method for producing a plated steel sheet for hot stamping comprises a hot dip coating step and an exposure step.

[0035] In the hot-dip galvanizing process, a steel sheet is immersed in a hot-dip galvanizing bath prepared to a predetermined chemical composition and then pulled out, thereby depositing the molten metal that constitutes the galvanizing bath onto the surface of the steel sheet. The composition of the hot-dip galvanizing bath is approximately the same as the composition of the coating layer to be formed, so it can be adjusted according to the chemical composition of the coating layer to be obtained. For example, the plating bath may contain, by mass%, 0-70% Al, 0-15% Fe, 0-20% Si, and a C group element, and may further contain 0-5% total of one or more of Sb: 0-0.5%, Pb: 0-0.5%, B: 0-0.5%, Cu: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Ni: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Co: 0-1.0%, Sn: 0-1.0%, and Bi: 0-1.0%, with the balance consisting of Zn and impurities. Furthermore, the plating bath composition may further contain one or two of the above A group and B group elements.

[0036] Prior to the hot-dip galvanizing step, the steel sheet may be subjected to reduction annealing under known conditions, for example, by heating to 750 to 900°C in a 5% H2-N2 gas atmosphere with a dew point of -10°C or higher and holding for 30 to 240 seconds. Immediately after the steel sheet is removed from the plating bath, it is advisable to adjust the coating weight of the plating layer by gas wiping with N2 gas.

[0037] Next, in the exposure step, the coating layer undergoing cooling after the hot-dip coating step is exposed to an N2 atmosphere containing HO and having a dew point of 0°C or higher for 3 to 300 seconds. The exposure is carried out while the temperature of the coating layer is in the temperature range of 700 to 460°C. The exposure step causes steam oxidation of the surface of the coating layer. In particular, it is presumed that the exposure step preferentially oxidizes the group A elements, group B elements, and group C elements contained in the coating layer. The average cooling rate while the coating layer is in the temperature range of 700 to 460°C is preferably in the range of 5 to 60°C / second.

[0038] The exposure process is carried out while the coating layer is at a temperature in the range of 700 to 460°C. If the exposure process is carried out when the surface temperature of the coating layer is relatively high, above 700°C, the coating layer will be excessively oxidized. On the other hand, if the exposure process is carried out when the surface temperature of the coating layer is relatively low, below 460°C, steam oxidation of the coating layer surface will not progress, making it impossible to suppress Zn evaporation during hot stamping.

[0039] The exposure process is performed in an N2 atmosphere containing H2O and with a dew point of 0°C or higher. If oxygen is present in the atmosphere, oxygen oxidation will take precedence over steam oxidation, and as a result, it will be impossible to suppress the evaporation of Zn during hot stamping. Therefore, the amount of oxygen contained in the atmosphere is set to be below the impurity level.

[0040] The dew point of the N2 atmosphere containing HO is preferably 0°C or higher. If the dew point is lower than 0°C, steam oxidation of the coating layer surface will not proceed sufficiently, making it impossible to suppress Zn evaporation during hot stamping. A higher dew point is more advantageous for steam oxidation, so there is no need to set an upper limit for the dew point.

[0041] The exposure time is 3 to 300 seconds. If the exposure time is less than 3 seconds, the steam oxidation of the coating layer surface will not progress sufficiently, and the evaporation of Zn will not be suppressed during hot stamping. On the other hand, if the exposure time exceeds 300 seconds, the effect will saturate, so the exposure time should be 300 seconds or less.

[0042] In this manner, the plated steel sheet for hot stamping according to this embodiment is manufactured.

[0043] Next, the hot-stamped steel and the method for manufacturing the hot-stamped steel according to this embodiment will be described.

[0044] The hot-stamped steel includes a steel material and a plating layer formed on a surface of the steel material. The plating layer may be formed on one side or both sides of the steel material.

[0045] The type of steel is not particularly limited and may be determined based on the product to be applied and the required strength, plate thickness, etc. For example, hot-rolled steel sheets as specified in JIS G3193:2008 and cold-rolled steel sheets as specified in JIS G3141:2017 can be used. The metal structure of the steel contains a large amount of martensite structure due to rapid cooling from high temperature in the hot stamping process.

[0046] The steel may have a chemical composition of 0.1-0.5% C, 0.001-3% Si, 0.3-3% Mn, 0.0002-2% Al, and the balance being Fe and impurities. In the description of the chemical composition of the steel sheet, "%" means "% by mass."

[0047] The coating layer has a chemical composition containing 0-70% Al, 10-60% Fe, 0-20% Si, C group elements, and the remainder being Zn and impurities. The coating layer may further contain one or two of the A group elements and the B group elements. The reasons for limiting the chemical composition of the coating layer are explained below. However, the reasons for limiting Al, Si, and C group elements, and the reasons for limiting elements such as Sb and Pb contained in place of a portion of Zn, are the same as those explained for the coated steel sheet for hot stamping. Therefore, the reason for limiting Fe will be explained below.

[0048] Fe: 10-60% Fe is contained in the coating layer of a coated steel sheet for hot stamping in a range of 0 to 15%. When the coated steel sheet for hot stamping is subjected to hot stamping, Fe further diffuses from the steel sheet toward the coating layer, resulting in a coating layer containing 10% or more Fe after hot stamping. The diffused Fe by hot stamping, together with the original Fe, combines with Al or Zn contained in the coating layer to form an alloy layer. Forming an alloy layer can improve the corrosion resistance of the hot-stamped product after painting, as described below. On the other hand, an Fe content exceeding 60% is undesirable because it reduces the red rust resistance of the hot-stamped product and ultimately reduces the corrosion resistance after painting. The lower limit of the Fe content may be 15% or more or 20% or more. The upper limit of the Fe content may be 50% or less or 40% or less.

[0049] Remainder: Zn and impurities The balance consists of Zn and impurities. Here, impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally contained in the plated steel sheet. There are no particular restrictions on the Zn content, but it is sufficient that the Zn content be 5% or more, and more preferably 8% or more.

[0050] The coating layer of the hot stamped steel contains an η-Zn phase or a Zn-containing phase. An example of the Zn-containing phase is the ZnO phase. In particular, when an A group element is contained, Zn forms intermetallic compounds with the A group element, such as the MgZn2 phase, Mg2Zn3 phase, MgZn phase, and CaZn 11 phase, CaZn 13 Phase, SrZn 11 Phase, SrZn 13The η-Zn phase or Zn-containing phase may be contained in the coating layer as a phase. When a ZnO phase or an intermetallic compound phase of Zn and an A-group element is present, the chemical conversion treatability of the coating layer is improved. The η-Zn phase or Zn-containing phase is located closer to the surface of the coating layer than the half-thickness position of the coating layer. The η-Zn phase or Zn-containing phase is also distributed at the grain boundaries of the alloy layer, which will be described later. The inclusion of the η-Zn phase or Zn-containing phase imparts sacrificial corrosion protection to the coating layer of the hot-stamped body, improving corrosion resistance after painting. Red rust resistance is also improved.

[0051] The presence of the η-Zn phase or Zn-containing phase can be confirmed by performing X-ray diffraction measurement on the coating layer surface of the hot-stamped body and identifying the η-Zn phase or Zn-containing phase from the X-ray diffraction pattern. Specifically, XRD measurement is performed on the coating layer surface using a Cu tube as the X-ray source. If a peak is present at 2θ between 42.9 and 43.6°, it is determined that the η-Zn phase is present. Furthermore, for other Zn-containing phases, if a peak is present within a range of ±0.3° from the peak of the reflection with the highest intensity on the ICDD card, it is determined that the Zn-containing phase is present in the coating layer.

[0052] When the coating layer of the hot-stamped steel contains Al, the remaining structure of the coating layer is an Fe-Al alloy layer in which Fe and Al in the coating layer are alloyed. The above-mentioned η-Zn phase or Zn-containing phase is contained in the grain boundaries of the crystal grains that make up the alloy layer. As mentioned above, intermetallic compounds of Zn and A-group elements may also be distributed in the surface layer of the coating layer (above the 1 / 2t portion). t refers to the coating thickness. The Al content of the coating layer may be 0%, and if there is no Fe-Al alloy layer, Fe is alloyed with Zn, and the η-Zn phase is present on the Fe-Zn alloy layer.

[0053] The coating weight of the plating layer on the hot stamped body is 20 to 160 g / m 2 It is preferable to set it in the range of

[0054] The chemical composition of the plating layer of the plated steel sheet for hot stamping and the hot stamped product may be measured by the following method. First, an acid solution is obtained by stripping and dissolving the plating layer using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material). The resulting acid solution is then measured using ICP analysis to determine the chemical composition of the plating layer. There are no particular restrictions on the type of acid, as long as it can dissolve the plating layer. The chemical composition is measured as an average chemical composition. Since ICP analysis cannot analyze O, the above chemical composition is the content of elements without taking into account the presence of O in the plating layer.

[0055] Next, a method for producing a hot-stamped product according to this embodiment will be described. The above-mentioned plated steel sheet for hot stamping is cut into a predetermined shape to form a blank. Next, the blank is heated to a holding temperature of 850°C or higher and held at the holding temperature for 200 seconds or less. The heated blank is then formed into a desired shape using a die and rapidly cooled in the die.

[0056] Heating to a holding temperature of 850°C or higher may cause Zn to evaporate from the coating layer of the coated steel sheet for hot stamping, but the inclusion of C group elements in the coating layer of the coated steel sheet for hot stamping suppresses Zn evaporation. Furthermore, the inclusion of C group elements in the coating layer causes the coating layer to contain an η-Zn phase or a Zn-containing phase. In this manner, the hot-stamped steel of this embodiment is produced.

[0057] As described above, the method for producing a plated steel sheet for hot stamping according to the present embodiment makes it possible to produce a blank for a hot-stamped steel sheet having excellent corrosion resistance and paint adhesion after painting. Furthermore, the hot-stamped steel sheet according to the present embodiment makes it possible to improve the corrosion resistance and paint adhesion after painting compared to conventional methods. [Example]

[0058] Examples of the present invention will be described below.

[0059] A cold-rolled steel sheet (0.2% C-1.3% Mn) having a thickness of 1.6 mm was prepared as the steel sheet to be plated. The steel sheet was cut into 100 mm × 200 mm pieces, and then subjected to reduction annealing and hot-dip galvanization in succession using a batch-type hot-dip galvanization test device. The sheet temperature was measured using a thermocouple spot-welded to the center of the original sheet. The reduction annealing was carried out in a furnace with an oxygen concentration of 20 ppm or less, in an atmosphere of gas containing 5% H2 gas and the remainder N2, at 800°C for 120 seconds. After reduction annealing, the steel sheet was air-cooled with N2 gas, and when the steel sheet temperature reached the bath temperature + 20°C, it was immersed in the plating bath for about 3 seconds and then pulled up at a pulling speed of 20 to 200 mm / sec.

[0060] The plating bath contained, in mass%, 0-70% Al, 0-15% Fe, 0-20% Si, the above-mentioned C group elements, and also contained 0-5% total of one or more of Sb: 0-0.5%, Pb: 0-0.5%, B: 0-0.5%, Cu: 0-1.0%, Ti: 0-1.0%, Cr: 0-1.0%, Nb: 0-1.0%, Ni: 0-1.0%, Mn: 0-1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Co: 0-1.0%, Sn: 0-1.0%, and Bi: 0-1.0%, with the balance consisting of Zn and impurities. Additionally, one or two of the above-mentioned A group elements and B group elements were also contained.

[0061] However, Nos. 1 to 33, 52 to 56, and 67 to 76 did not contain any C group elements. In addition, Nos. 77 to 79 had C group element contents outside the preferred range. In addition, Nos. 80 to 87 were not subjected to the exposure step.

[0062] The coating weight of the coated base sheet on which the coating layer was formed was adjusted using N2 wiping gas, and then the sheet was cooled. During this exposure process, during cooling after hot-dip coating, the coating layer was exposed to the atmospheres listed in Tables 1B, 1D, and 1F while the temperature was in the range of 700 to 460°C. The exposure time was in the range of 3 to 300 seconds. In Tables 1B, 1D, and 1F, "N2 (dew point x°C)" refers to an N2 atmosphere containing HO with a dew point of x°C. The average cooling rate while the coating layer was in the temperature range of 700 to 460°C was in the range of 5 to 60°C / second.

[0063] Next, the obtained plated steel sheet was inserted into a muffle furnace in an air atmosphere set to 900°C, heated to 900°C, held for 100 seconds, removed, and hot stamped by pressing with a flat mold and quenching to obtain a hot stamped body.

[0064] The presence or absence of an η-Zn phase or a Zn-containing phase in the coating layer of the obtained hot-stamped product was measured using the method described above. The results are shown in Tables 1A to 1F. Tables 1A to 1F also show the composition of the coating layer of the hot-stamped product.

[0065] The composition of the plating layer was measured by immersing a sample cut to 30 mm x 30 mm in a 10% HCl aqueous solution containing an inhibitor to remove the plating layer by pickling, and then performing ICP analysis of the elements eluted into the aqueous solution.

[0066] Furthermore, the hot stamped bodies were evaluated for corrosion resistance after painting. Specifically, a 50 x 100 mm sample was taken from the hot-stamped compact and subjected to Zn phosphate treatment (SD5350 system: Nippon Paint Industrial Coating standard), after which electrocoating (PN110 Powernix (registered trademark) Gray: Nippon Paint Industrial Coating standard) was applied to a thickness of 20 μm, and the sample was baked at a baking temperature of 150°C for 20 minutes, after which a cut was made in the center of the sample that reached down to the base steel.

[0067] The specimens were then subjected to a cyclic corrosion test in accordance with JASO (M609-91) to measure the number of cycles required for red rust to form in the cut area. A grade was given for over 120 cycles until red rust formed, an "AA" grade for 60-120 cycles, and a "B" grade for less than 60 cycles. AA and A were considered pass, while B was considered fail.

[0068] Furthermore, the paint adhesion of the hot stamped body was evaluated. After painting, the specimens were treated in the same way as for corrosion resistance, and then immersed in a 5% sodium chloride solution at 55°C for 10 days. Afterward, the specimens were removed, and Nichiban tape (product number: "CT405A-24") was applied to the cuts and immediately peeled off. The paint adhesion was evaluated based on the paint peel width, which was the length of the area where the paint peeled off from the cut. A paint peel width of less than 1.5 mm was rated "AA," a paint peel width of 1.5 mm to 2 mm was rated "A," and a paint peel width of 2 mm or more was rated "B." AA and A were considered pass, and B was considered fail.

[0069] As can be seen from Tables 1A to 1F, the hot-stamped products (Nos. 1 to 33, 52 to 56) with coating layers that did not contain group C elements had excellent corrosion resistance after painting, but poor paint adhesion. On the other hand, the hot-stamped products (Nos. 34 to 51, 57 to 66) with coating layers that contained group C elements had excellent corrosion resistance after painting and excellent paint adhesion. In particular, the hot-stamped products with a Mg content of 1% or more or a total content of group C elements of 0.001 to 0.3% had better corrosion resistance after painting. Furthermore, the hot-stamped products (Nos. 57 to 66) that contained one or two of group A and B elements had better corrosion resistance after painting. In Tables 1E and 1F, the hot-stamped products with coating layers that did not contain C-group elements (Nos. 67 to 76), the hot-stamped products with coating layers containing C-group elements outside the preferred range (Nos. 77 to 79), and the hot-stamped products that had not undergone an exposure process and were manufactured outside the range of manufacturing conditions (Nos. 80 to 87) all had poor corrosion resistance after painting and poor paint adhesion. Furthermore, the hot-stamped product with Y element vapor-deposited on the coating layer (No. 87) also had poor corrosion resistance after painting because it had not undergone an exposure process and was manufactured outside the range of manufacturing conditions.

[0070] [Table 1A]

[0071] [Table 1B]

[0072] [Table 1C]

[0073] [Table 1D]

[0074] [Table 1E]

[0075] Table 1F

Claims

1. A steel plate having a steel material and a plating layer, The chemical composition of the plating layer is, in mass%, Al: 0 to 70%, Fe: 10-60%, Si: 5 to 20%, C group elements: one or two of Li and Y, the total content of which is 0.00001 to 0.3%; Furthermore, Sb: 0 to 0.5%, Pb: 0 to 0.5%, B: 0 to 0.5%, Cu: 0 to 1.0%, Ti: 0 to 1.0%, Cr: 0-1.0%, Nb: 0 to 1.0%, Ni: 0-1.0%, Mn: 0 to 1.0%, Mo: 0-1.0%, Ag: 0-1.0%, Co: 0 to 1.0%, Sn: 0 to 1.0%, Bi: 0 to 1.0%, and a total of 0 to 5% of one or more of these. The balance is composed of Zn and impurities. The hot-stamped article is characterized in that the plating layer contains an η-Zn phase or a Zn-containing phase.

2. The hot-stamped product according to claim 1 , wherein a chemical composition of the plating layer contains one or two of an A group element and a B group element. A group elements: 0.0010 to 15% of Mg and one or both of Ca and Sr, with the total content being 0.0001% or more and less than 5.5%. B group elements: one or more of Zr, La, and Ce, the total content of which is 0.0001 to 0.5%.

3. The hot-stamped steel according to claim 1 or 2, wherein the total amount of the C group elements is 0.001 to 0.3%.

4. The hot-stamped steel according to claim 2, wherein the Mg content in the A group elements is 1 to 15%.

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