Hot-stamping steel sheet, hot-stamped component, method for manufacturing hot-stamping steel sheet, and method for manufacturing hot-stamped component
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-06-04
- Publication Date
- 2026-08-13
Smart Images
Figure KR2025007656_13082026_PF_FP_ABST
Abstract
Description
Steel plate for hot stamping, hot stamping part, method for manufacturing a steel plate for hot stamping and method for manufacturing a hot stamping part
[0001] The present application relates to a steel plate for hot stamping, a hot stamping part, a method for manufacturing a steel plate for hot stamping, and a method for manufacturing a hot stamping part.
[0002] The steel industry is one of the industries with very high carbon emissions, and there is a growing demand for the development of eco-friendly steel materials utilizing electric furnaces instead of conventional blast furnaces to reduce these emissions. Unlike the conventional blast furnace method of manufacturing steel materials, which emits carbon through the reduction and oxidation of iron ore, electric furnaces utilize scrap to produce steel materials, thereby reducing carbon emissions. However, since scrap contains some tramp elements such as copper (Cu), antimony (Sb), and nitrogen (N), there are problems such as the degradation of steel material quality and difficulties in producing high-alloy cold-rolled ultra-high-strength steel.
[0003] Patent Document 1 (Korean Published Patent Application No. 10-1998-0009493) discloses a method for manufacturing steel for processing using an electric furnace-vacuum degassing process with iron scrap as the main raw material. However, a problem arises in that the material properties and bendability of the steel material are degraded due to the inclusion of a large amount of nitrogen.
[0004] Therefore, to solve these problems, a steel plate for hot stamping, a hot stamping part, a method for manufacturing a steel plate for hot stamping, and a method for manufacturing a hot stamping part are required.
[0005] The object of the present application is to provide a steel sheet for hot stamping having excellent mechanical properties of high strength and improved surface quality, and a method for manufacturing a steel sheet for hot stamping.
[0006] In addition, the objective of the present application is to provide a hot stamping part having high strength and excellent bendability, and a method for manufacturing the hot stamping part.
[0007] To solve the above problem, the hot stamping steel sheet of the present application comprises, in weight%, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: greater than 0.0010% and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder is composed of Fe and other unavoidable impurities, and can satisfy Formula 1 below.
[0008] [Equation 1]
[0009] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0010] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0011] In addition, the above-mentioned hot stamping steel plate can satisfy the following Equation 2.
[0012] [Equation 2]
[0013] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0014] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0015] In addition, the above-mentioned hot stamping steel plate may have a tensile strength of 500 MPa or more and 650 MPa or less, and a yield strength of 400 MPa or more and 500 MPa or less.
[0016] In addition, the hot stamping part of the present application comprises, in weight%, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: greater than 0.0010% and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder is Fe and other unavoidable impurities, and may satisfy Formula 1 below.
[0017] [Equation 1]
[0018] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0019] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0020] In addition, the above hot stamping part can satisfy the following Equation 2.
[0021] [Equation 2]
[0022] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0023] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0024] In addition, the hot stamping part comprises TiN precipitates, the average size of the TiN precipitates is 0.01㎛ or more and 2.5㎛ or less, and the number of TiN precipitates is 30ea / mm 2 It may be less than.
[0025] In addition, the hot stamping part may have an elongation of more than 5.5% and a bending angle of 38.0° or more.
[0026] In addition, the hot stamping part may have a tensile strength of 1400 MPa or more and a yield strength of 1000 MPa or more.
[0027] In addition, the method for manufacturing a steel sheet for hot stamping according to the present application comprises, in weight percent, the step of preparing a slab comprising C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; The method may include the step of reheating the above slab; the step of hot-rolling the reheated slab to produce a hot-rolled steel sheet; the step of cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; and the step of annealing the cold-rolled steel sheet, and may satisfy the following Equation 1.
[0028] [Equation 1]
[0029] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0030] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0031] In addition, the method for manufacturing the above-described steel sheet for hot stamping may further include the step of coiling the above-described hot-rolled steel sheet at less than 660°C prior to the step of manufacturing the above-described cold-rolled steel sheet.
[0032] In addition, the method for manufacturing the above-mentioned steel plate for hot stamping can satisfy the following Equation 2.
[0033] [Equation 2]
[0034] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0035] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0036] In addition, in the step of preparing the above slab, the slab may be manufactured by refining molten steel tapped from a converter or electric furnace in a vacuum degassing facility.
[0037] In addition, the above-mentioned hot stamping steel plate may have a tensile strength of 500 MPa or more and 650 MPa or less, and a yield strength of 400 MPa or more and 500 MPa or less.
[0038] In addition, the method for manufacturing a hot stamping part of the present application comprises the step of preparing a steel sheet for hot stamping comprising, in weight%, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; The method may include the step of heating the steel plate for hot stamping; the step of conveying the heated steel plate for hot stamping; the step of forming the conveyed steel plate for hot stamping; and the step of cooling the formed steel plate for hot stamping, and may satisfy the following Equation 1.
[0039] [Equation 1]
[0040] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0041] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0042] In addition, the method for manufacturing a hot stamping part of the present application can satisfy the following Equation 2.
[0043] [Equation 2]
[0044] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0045] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0046] In addition, the above-mentioned hot stamping steel plate may be manufactured using a slab produced by refining molten steel discharged from a converter or electric furnace in a vacuum degassing facility.
[0047] In addition, the method for manufacturing a hot stamping part of the present application comprises, said hot stamping part including a TiN precipitate, said TiN precipitate having an average size of 0.01 μm or more and 2.5 μm or less, and said number of TiN precipitates being 30 ea / mm 2 It may be less than.
[0048] In addition, the method for manufacturing a hot stamping part of the present application allows the hot stamping part to have an elongation of more than 5.5% and a bending angle of 38.0° or more.
[0049] In addition, the method for manufacturing a hot stamping part of the present application may have the hot stamping part having a tensile strength of 1400 MPa or more and a yield strength of 1000 MPa or more.
[0050] According to the hot stamping steel plate, hot stamping part, method for manufacturing a hot stamping steel plate, and method for manufacturing a hot stamping part of the present application, it is possible to provide a hot stamping steel plate having excellent mechanical properties of high strength and improved surface quality, and a hot stamping part having high strength and excellent bendability.
[0051] Figure 1 is a photograph showing whether surface cracks occurred on a hot stamping steel plate manufactured in Example 1 of the present invention using a scanning electron microscope (SEM).
[0052] FIG. 2 is a photograph showing whether surface cracks occurred on a hot stamping steel plate manufactured in Comparative Example 1 of the present invention using a scanning electron microscope (SEM).
[0053] Figure 3 is a photograph of TiN precipitates observed using a scanning electron microscope (SEM) on a hot stamping part manufactured in Example 5 of the present invention.
[0054] Figure 4 is a photograph of TiN precipitates observed using a scanning electron microscope (SEM) on a hot stamping part manufactured in Comparative Example 4 of the present invention.
[0055] Embodiments of the present invention will be described in detail below. Furthermore, the scope of the present invention is not limited to the embodiments described below, and may be implemented with arbitrary modifications within the scope that does not deviate from the essence of the present invention.
[0056] In the description of numerical ranges in this specification, the notation “X~Y” indicates X or greater and Y or less, unless otherwise specifically stated. Additionally, “greater than or equal to” may be replaced with “greater than,” and “less than or equal to” may be replaced with “less than.”
[0057] In the description of numerical ranges in this specification, the term “to” is used to mean that the values described before and after it are included as lower and upper limits, unless otherwise specifically stated.
[0058] In the numerical ranges described stepwise in this specification, an upper or lower limit value described in any numerical range may be substituted with an upper or lower limit value of another numerical range described stepwise, or may also be substituted with a value shown in the examples.
[0059] The present application relates to a steel sheet for hot stamping, comprising, in weight percent, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: greater than 0.0010% and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder may consist of Fe and other unavoidable impurities.
[0060] The composition of the above-mentioned hot stamping steel plate is described below.
[0061] C: 0.10 wt% or more, 0.50 wt% or less
[0062] Carbon (C) is an element that plays a role in increasing strength by causing an increase in the strength of martensite. If the carbon is included in the hot stamping steel sheet in an amount less than the lower limit of the aforementioned range, the strength may decrease. In addition, if the carbon is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, there is a risk of brittleness occurring or a decrease in bending performance. Accordingly, the carbon may be included in the hot stamping steel sheet in an amount of 0.10 wt% or more and 0.50 wt% or less, and specifically, in an amount of 0.10 wt% or more and 0.250 wt% or less.
[0063] Si: Greater than 0 wt% and less than or equal to 1.0 wt%
[0064] Silicon (Si) is an element that homogenizes the microstructure by controlling pearlite and Mn segregation zones and plays a role in the fine dispersion of ferrite. In addition, the silicon plays a role in controlling the non-uniformity of the strength of the martensite. If the silicon is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, there is a risk that the rolling load will increase during hot rolling and / or cold rolling, or that red scale will be excessively formed during hot rolling, and that the plating quality may deteriorate. Therefore, the silicon may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 1.0 weight%.
[0065] Mn: 0.10 wt% or more, 3.00 wt% or less
[0066] Manganese (Mn) is an element that plays a role in increasing hardenability and strength during heat treatment. In addition, if the manganese is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, heterogeneous microstructures such as manganese segregation or manganese bands may occur, which may degrade performance such as bendability. Therefore, the manganese may be included in the hot stamping steel sheet in an amount of 0.10 weight% or more and 3.00 weight% or less.
[0067] P: Greater than 0 wt% and less than or equal to 0.1 wt%
[0068] Phosphorus (P) is an element that contributes to strength improvement. If the phosphorus is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, it may cause a decrease in toughness and delayed fracture due to grain boundary weakening caused by grain boundary segregation. Therefore, the phosphorus may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.1 weight%.
[0069] S: Exceeding 0 wt% and up to 0.02 wt%
[0070] Sulfur (S) is an element that improves the performance of microstructures such as final martensite by suppressing the formation of MnS inclusions during the steelmaking process. If the sulfur is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, the toughness and weldability of the steel may be reduced due to the formation of coarse inclusions. Therefore, the sulfur may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.02 weight%.
[0071] Al: 0.01 wt% or more, 1.0 wt% or less
[0072] Aluminum (Al) is an element that contributes to inhibiting the formation of pearlite band structures by inhibiting the formation and coarsening of cementite. The aluminum may be included in the hot stamping steel sheet in an amount of 0.01 wt% or more and 1.0 wt% or less.
[0073] Ti: 0.010 wt% or more, 0.100 wt% or less
[0074] Titanium (Ti) is an element that plays a role in improving material properties by forming precipitates after hot stamping heat treatment. In addition, the titanium is an element that maximizes the quenching effect of solid solution B by combining with nitrogen in the steel to form TiN. If the titanium is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, the elongation and bendability may decrease due to the coarsening of precipitates. Therefore, the titanium may be included in the hot stamping steel sheet in an amount of 0.010 weight% or more and 0.100 weight% or less.
[0075] Cr: Greater than 0 wt% and less than or equal to 2.0 wt%
[0076] Chromium (Cr) is an element added to ensure hardenability and strength. If the chromium is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, toughness may be reduced and there is a problem of increased costs. Therefore, the chromium may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 2.0 weight%.
[0077] B: 0.0010 wt% or more, 0.0050 wt% or less
[0078] Boron (B) is an expensive element that is added to ensure hardenability and high strength, and is an element that suppresses ferrite, pearlite, and bainite phase transformations during cooling. If the boron is included in the hot stamping steel sheet in an amount less than the lower limit of the aforementioned range, the effect on hardenability may be negligible. In addition, if the boron is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, bendability may be reduced due to the occurrence of hard phase intergranular brittleness. Therefore, the boron may be included in the hot stamping steel sheet in an amount of 0.0010 weight% or more and 0.0050 weight% or less.
[0079] N: Greater than 0 wt% and less than or equal to 0.0200 wt%
[0080] Nitrogen (N) can combine with titanium during the steelmaking process to form TiN(C)-based precipitates, and their size grows during the high-temperature material manufacturing process. Additionally, the nitrogen can play a role in controlling the heating furnace application time and temperature during hot rolling. However, if the nitrogen is included in the cold-rolled steel sheet in excess of the upper limit, it can reduce bendability and reduce productivity due to the load on the hot rolling equipment. Therefore, the nitrogen may be included in the hot-stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.0200 weight%.
[0081] Cu: Exceeding 0 wt% and up to 0.30 wt%
[0082] Copper (Cu) is an element that can be excessively incorporated as a tramp element during the electric furnace steelmaking process and plays a role in increasing corrosion resistance and improving resistance to hydrogen embrittlement. If the copper is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, Cu enrichment occurs due to low scale solubility, and consequently, cracks may occur during hot rolling and cold rolling, which may degrade the surface quality of the final product. Therefore, the copper may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.20 weight%.
[0083] Sn: Greater than 0 wt% and less than or equal to 0.03 wt%
[0084] Tin (Sn) is an element that can be excessively incorporated as a tramp element during the electric furnace steelmaking process and plays a role in improving hydrogen release ability through the formation of voids within the Al-Si plating layer. If the tin is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, it can increase brittleness by reducing the solid solution rate and solidification point of Cu in the austenite phase, and consequently, ductility may decrease. Therefore, the tin may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.03 weight%.
[0085] Ni: Greater than 0 wt% and less than or equal to 0.15 wt%
[0086] Nickel (Ni) is an element effective in increasing strength and plays a role in preventing surface cracks caused by an increase in the solid solution content of Cu. If the nickel is included in the hot stamping steel sheet in an amount exceeding the upper limit of the aforementioned range, the alloy value increases, and internal oxidation and scale may occur, thereby deteriorating the properties of the base material interface. Therefore, the nickel may be included in the hot stamping steel sheet in an amount greater than 0 weight% and less than or equal to 0.15 weight%.
[0087] Remaining Fe and other unavoidable impurities
[0088] The aforementioned unavoidable impurities are impurities introduced during the manufacturing process of steelmaking and hot stamping steel sheets. Since this is widely known in the art, a detailed description is omitted. In one embodiment of this application, the addition of elements other than the components of the hot stamping steel sheet described above is not excluded, and various elements may be included within a scope that does not impair the technical concept of this application. If additional elements are included, they may be included to replace the remainder, which is iron (Fe).
[0089] In addition, the above-mentioned hot stamping steel plate can satisfy the following Equation 1.
[0090] [Equation 1]
[0091] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0092] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0093] The value calculated by the above Equation 1 may be 0.05 or more and less than 1.19, specifically, 0.05 or more and less than 1.00, 0.05 or more and less than 0.90, 0.05 or more and less than 0.80, 0.05 or more and less than 0.70, or 0.05 or more and less than 0.65. By satisfying the aforementioned range of the value calculated by the above Equation 1, fracture does not occur during cold rolling and penetration of Cu liquid phase into grain boundaries can be prevented, thereby enabling excellent mechanical properties of high strength and improved surface quality.
[0094] The hot stamping steel sheet of the present application can have excellent mechanical properties of high strength and improved surface quality by controlling the composition of the hot stamping steel sheet to satisfy the aforementioned range and the values of Cu, Sn, and Ni included in the hot stamping steel sheet to simultaneously satisfy the aforementioned range calculated by Equation 1.
[0095] In addition, the above-mentioned hot stamping steel plate can satisfy the following Equation 2.
[0096] [Equation 2]
[0097] 0.004 ≤(1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤0.021
[0098] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0099] The value calculated by the above Equation 2 may be 0.004 or greater and 0.021 or less, specifically, 0.005, 0.006, 0.007, or 0.008 or greater, and 0.020, 0.018, 0.016, 0.015, or 0.014 or less. By satisfying the aforementioned range of the value calculated by the above Equation 2, the formation of coarse TiN precipitates can be prevented, thereby preventing a decrease in ductility and bendability, and allowing for excellent mechanical properties of high strength and improved surface quality.
[0100] The hot stamping steel sheet of the present application can have excellent mechanical properties of high strength and improved surface quality by controlling the composition of the hot stamping steel sheet to satisfy the aforementioned range and the values of N and Ti included in the hot stamping steel sheet calculated by Equation 2 to simultaneously satisfy the aforementioned range.
[0101] In addition, the hot stamping steel sheet of the present application can have excellent mechanical properties of high strength and improved surface quality by controlling the composition of the hot stamping steel sheet to satisfy the aforementioned range, the values of Cu, Sn, and Ni included in the hot stamping steel sheet calculated by Equation 1 to satisfy the aforementioned range, and at the same time, the values of N and Ti included in the hot stamping steel sheet calculated by Equation 2 to simultaneously satisfy the aforementioned range.
[0102] In addition, the above-mentioned hot stamping steel sheet may have a microstructure comprising, in terms of area fraction, 70% or more and 100% or less of ferrite, 0% or more and 30% or less of pearlite, and the remainder being martensite and bainite.
[0103] In addition, the above-mentioned steel sheet for hot stamping may have a maximum surface crack depth of 45㎛ or less. The above-mentioned surface crack may occur during hot rolling and / or cold rolling. If the above-mentioned maximum surface crack depth exceeds the upper limit of the aforementioned range, the surface quality may deteriorate. Consequently, when manufacturing hot-stamped parts through hot stamping using the above-mentioned steel sheet, formability may be reduced, and in particular, elongation and bendability may be reduced. Therefore, the above-mentioned steel sheet for hot stamping may have a maximum surface crack depth of 45㎛ or less, specifically, 30㎛ or less, 20㎛ or less, or 10㎛ or less. Furthermore, since the occurrence of surface cracks may result in plate fracture during the cold rolling process, making the cold rolling process impossible or requiring additional processes to remove defects, which may entail increased costs, it is preferable that the above-mentioned steel sheet for hot stamping have a maximum surface crack depth of 0㎛.
[0104] In addition, the above-mentioned hot stamping steel plate may further include a plating layer on its surface.
[0105] Additionally, the plating layer may be an Al plating layer or an Al-Si plating layer. Specifically, the plating layer may comprise iron (Fe) and / or silicon (Si) and consist of the remainder being aluminum (Al) and other unavoidable impurities. For example, the plating layer may comprise 5 weight% or more and 11 weight% or less of silicon, more than 0 weight% and 4.5 weight% or less of iron, and the remainder being aluminum.
[0106] In addition, the above-mentioned hot stamping steel sheet can have excellent mechanical properties of strength and improved surface quality by further including the aforementioned plating layer on its surface.
[0107] In addition, the above-mentioned hot stamping steel plate may have a tensile strength (TS) of 500 MPa or more and 650 MPa or less, and specifically, 550 MPa or more and 650 MPa or less.
[0108] In addition, the above-mentioned steel plate for hot stamping may have a yield strength (YP) of 400 MPa or more and 500 MPa or less, and specifically, 410 MPa or more and 500 MPa or less.
[0109] In addition, the above-mentioned hot stamping steel sheet may have an elongation (EL) of 29.0% or more, specifically 29.5% or more or 29.8% or more.
[0110] The above tensile strength, yield strength, and elongation can be measured according to the measurement method of the embodiment described below. In addition, the above hot stamping steel sheet can have excellent mechanical properties of high strength by satisfying the aforementioned ranges for yield strength, tensile strength, and elongation.
[0111] The present application also relates to a hot stamping part. The hot stamping part may comprise, in weight percent, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: greater than 0.0010% and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder may consist of Fe and other unavoidable impurities.
[0112] A detailed description of the composition of the above-mentioned hot-stamping part is omitted because it is identical to the composition described in the above-mentioned hot-stamping steel sheet.
[0113] In addition, the above hot stamping part can satisfy the following Equation 1.
[0114] [Equation 1]
[0115] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0116] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0117] The value calculated by the above Equation 1 may be 0.05 or greater and less than 1.19, specifically, 0.05 or greater and less than 1.00, 0.05 or greater and less than 0.90, 0.05 or greater and less than 0.80, 0.05 or greater and less than 0.70, or 0.05 or greater and less than 0.65. The above hot stamping part can have high strength while also having excellent elongation and bendability by satisfying the aforementioned range of the value calculated by the above Equation 1.
[0118] The hot stamping part of the present application can have high strength while also having excellent elongation and bendability by controlling the composition of the hot stamping part to satisfy the aforementioned range and the values of Cu, Sn, and Ni included in the hot stamping part to simultaneously satisfy the aforementioned range calculated by Equation 1.
[0119] In addition, the above hot stamping part can satisfy the following Equation 2.
[0120] [Equation 2]
[0121] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0122] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0123] The value calculated by the above Equation 2 may be 0.004 or greater and 0.021 or less, specifically, 0.005, 0.006, 0.007, or 0.008 or greater, and 0.020, 0.018, 0.016, 0.015, or 0.014 or less. By satisfying the aforementioned range of the value calculated by the above Equation 2, the hot stamping part can prevent the formation of coarse TiN precipitates, thereby preventing a decrease in ductility and bendability, and can have high strength while having excellent elongation and bendability.
[0124] The hot stamping part of the present application can have high strength while also having excellent elongation and bendability by controlling the composition of the hot stamping part to satisfy the aforementioned range and the values of N and Ti included in the hot stamping part calculated by Equation 2 to simultaneously satisfy the aforementioned range.
[0125] In addition, the hot stamping part of the present application can have high strength while also having excellent elongation and bendability by controlling the composition of the hot stamping part to satisfy the aforementioned range, the values of Cu, Sn, and Ni included in the hot stamping part calculated by Equation 1 to satisfy the aforementioned range, and at the same time, the values of N and Ti included in the hot stamping part calculated by Equation 2 to simultaneously satisfy the aforementioned range.
[0126] Additionally, the hot stamping part may include precipitates. Additionally, the precipitates may be TiN precipitates. Additionally, the hot stamping part may have an average size (circular equivalent diameter) of the TiN precipitates ranging from 0.01 μm to 2.5 μm. By satisfying the aforementioned range for the average size of the TiN precipitates, elongation and bendability may be improved. Additionally, the hot stamping part may have a number of TiN precipitates of 30 ea / mm 2 It may be less than, specifically, 29ea / mm 2 Less than or equal to 28ea / mm 2It may be less than or equal to. If the number of TiN precipitates with an average size within the aforementioned range exceeds the upper limit of the aforementioned range, the flexibility may be reduced. Therefore, by satisfying the aforementioned ranges for the average size and number of TiN precipitates, it is possible to have high strength while also possessing excellent elongation and flexibility.
[0127] In addition, the hot stamping part may have a microstructure comprising, in terms of area fraction, 80% or more of martensite, 0% or more of bainite, and the remainder being ferrite.
[0128] In addition, the hot stamping part may have a yield strength (YP) of 1000 MPa or more and a tensile strength (TS) of 1400 MPa or more. In addition, the hot stamping part may have an elongation of 5.5% or more, specifically 6.0% or more, 6.5% or more, or 6.6% or more. The yield strength, tensile strength, and elongation may be measured according to the measurement method of the embodiment described below.
[0129] In addition, the hot stamping part may have a bending angle of 38.0° or more, specifically 45.0°, 52.0°, 53.0°, or 53.8° or more. The bending angle may refer to a V-bending angle in the rolling direction and may be measured according to the measurement method of the embodiment described below.
[0130] The above-mentioned hot stamping part can have high strength while also possessing excellent elongation and bendability by satisfying the aforementioned ranges for yield strength, tensile strength, elongation, and bending angle.
[0131] The present application also relates to a method for manufacturing a steel sheet for hot stamping. The method for manufacturing a steel sheet for hot stamping relates to a method for manufacturing the aforementioned steel sheet for hot stamping. Since specific details regarding the steel sheet for hot stamping described below can be applied in the same way as those described for the steel sheet for hot stamping, they will be omitted.
[0132] The method for manufacturing a steel sheet for hot stamping according to the present application comprises the step of preparing a slab comprising, in weight percent, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, and Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; and the slab The method includes a step of reheating, a step of hot-rolling the reheated slab to produce a hot-rolled steel sheet, a step of cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet, and a step of annealing the cold-rolled steel sheet.
[0133] A detailed description of the composition of the above slab is omitted because it is identical to the composition described in the above hot stamping steel plate.
[0134] In addition, in the step of preparing the above slab, the method of the solvent for manufacturing the above slab is not limited, and known methods such as a converter or an electric furnace may be adopted. For example, the above slab may be manufactured by refining molten steel tapped from a converter or an electric furnace in a vacuum degassing facility.
[0135] In addition, the step of reheating the slab is performed by reheating the slab. The reheating temperature of the slab may be 1150°C or higher and 1250°C or lower.
[0136] In addition, the step of manufacturing the hot-rolled steel sheet is a step for manufacturing a slab into a hot-rolled steel sheet, and is performed by reheating the slab and then hot-rolling it. At this time, the finishing rolling temperature during the hot rolling may be 800°C or higher and 1000°C or lower.
[0137] In addition, the step of manufacturing the hot-rolled steel sheet may have a reduction rate of 90% or more during hot rolling, and specifically, 95% or more, 97% or more, or 99% or more.
[0138] In addition, the thickness of the hot-rolled steel sheet may be 2.4 mm or more and 4.6 mm or less.
[0139] In addition, the above hot-rolled steel sheet may have a microstructure that includes ferrite and pearlite. Specifically, the above hot-rolled steel sheet may have a microstructure that includes 60% or more and 80% or less of ferrite and 20% or more and 40% or less of pearlite in terms of area fraction.
[0140] In addition, prior to the step of manufacturing the cold-rolled steel sheet, the step of winding the hot-rolled steel sheet may be further included. The step of winding the hot-rolled steel sheet may be performed by winding the hot-rolled steel sheet obtained by hot rolling at a temperature of less than 660°C.
[0141] In addition, the hot-rolled steel sheet may undergo further pickling. As a result, the oxide layer formed on the surface of the hot-rolled steel sheet can be removed through the pickling solution.
[0142] In addition, the step of manufacturing the above cold-rolled steel sheet is performed through cold rolling. At this time, the thickness of the above cold-rolled steel sheet may be 1.0 mm or more and 2.3 mm or less.
[0143] In addition, the reduction rate during the above cold rolling may be 40% or more and 70% or less.
[0144] In addition, the annealing step is performed by heat-treating the cold-rolled steel sheet. For example, the annealing step can be performed by heat-treating at a temperature of 730°C or higher and 830°C or lower.
[0145] In addition, the annealing step may include a cooling step after heat treatment at an average cooling rate of 1℃ / s or more and 40℃ / s or less.
[0146] In addition, the method for manufacturing a hot stamping steel sheet of the present application may further include the step of forming a plating layer on the surface by immersing the annealed heat-treated cold-rolled steel sheet in a plating bath.
[0147] In addition, the plating bath may contain Si of 8% or more and 10% or less by weight and Fe of more than 0% and less than 1% by weight, and the remainder may consist of Al and other unavoidable impurities.
[0148] In addition, the temperature of the plating bath may be 650°C or higher and 670°C or lower.
[0149] In addition, the step of forming the plating layer may include a step of controlling the plating adhesion amount. In addition, the plating adhesion amount is 40 g / m² 2 200g / m² or more 2 It may be less than or equal to the amount. In addition, the means or method for controlling the amount of plating deposited is not particularly limited and can be performed, for example, using an air knife.
[0150] According to the method for manufacturing a hot stamping steel sheet of the present application, the steps of preparing a slab, reheating the slab, manufacturing a hot-rolled steel sheet, coiling, manufacturing a cold-rolled steel sheet, annealing, and forming a plating layer satisfy the aforementioned conditions, thereby providing a hot stamping steel sheet having excellent mechanical properties of high strength and improved surface quality.
[0151] In addition, Cu, Sn, and Ni included in the above slab can satisfy the following Equation 1.
[0152] [Equation 1]
[0153] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19
[0154] In the above Equation 1, [Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.
[0155] The value calculated by the above Equation 1 may be 0.05 or greater and less than 1.19, specifically, 0.05 or greater and less than 1.00, 0.05 or greater and less than 0.90, 0.05 or greater and less than 0.80, 0.05 or greater and less than 0.70, or 0.05 or greater and less than 0.65. By satisfying the aforementioned range of the value calculated by the above Equation 1, fracture does not occur during cold rolling and penetration of Cu liquid phase into grain boundaries can be prevented, thereby providing a steel sheet for hot stamping that has excellent mechanical properties of high strength and improved surface quality.
[0156] In addition, by controlling the composition of the slab to satisfy the aforementioned range and the values of Cu, Sn, and Ni included in the slab calculated by Equation 1 to simultaneously satisfy the aforementioned range, it is possible to provide a steel plate for hot stamping that has excellent mechanical properties of high strength and improved surface quality.
[0157] In addition, N and Ti included in the above slab can satisfy the following Equation 2.
[0158] [Equation 2]
[0159] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021
[0160] In the above Equation 2, [N] and [Ti] represent the weight percent of N and Ti, respectively.
[0161] The value calculated by the above Equation 2 may be 0.004 or greater and 0.021 or less, specifically, 0.005, 0.006, 0.007, or 0.008 or greater, and 0.020, 0.018, 0.016, 0.015, or 0.014 or less. By satisfying the aforementioned range of the value calculated by the above Equation 2, the formation of coarse TiN precipitates can be prevented, thereby preventing a decrease in ductility and bendability, and providing a steel sheet for hot stamping that has excellent mechanical properties of high strength and improved surface quality.
[0162] In addition, by controlling the composition of the hot stamping steel plate to satisfy the aforementioned range and the values of N and Ti included in the hot stamping steel plate to simultaneously satisfy the aforementioned range calculated by Equation 2, it is possible to provide a hot stamping steel plate having excellent mechanical properties of high strength and improved surface quality.
[0163] According to the method for manufacturing a hot stamping steel plate of the present application, by controlling the composition of the slab to satisfy the aforementioned range, the values of Cu, Sn, and Ni included in the slab calculated by Equation 1 to satisfy the aforementioned range, and at the same time the values of N and Ti included in the slab calculated by Equation 2 to simultaneously satisfy the aforementioned range, a hot stamping steel plate having excellent mechanical properties of high strength and improved surface quality can be provided.
[0164] In addition, the above-described steel plate for hot stamping may have a tensile strength of 500 MPa or more and 650 MPa or less, and a yield strength of 400 MPa or more and 500 MPa or less. According to the method for manufacturing a steel plate for hot stamping of the present application, by satisfying the aforementioned ranges for tensile strength and yield strength, a steel plate for hot stamping having excellent mechanical properties of high strength can be provided.
[0165] This application also relates to a method for manufacturing a hot stamping part. The method for manufacturing the hot stamping part relates to a method for manufacturing the aforementioned hot stamping part. Since specific details regarding the hot stamping part described below can be applied in the same way as those described for the hot stamping part, they will be omitted.
[0166] The method for manufacturing a hot stamping part of the present application comprises the step of preparing a hot stamping steel sheet comprising, in weight percent, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, and Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; and the hot stamping steel sheet It may include a step of heating, a step of conveying the heated steel plate for hot stamping, a step of forming the conveyed steel plate for hot stamping, and a step of cooling the formed steel plate for hot stamping.
[0167] In addition, the above-mentioned hot stamping steel plate may be manufactured using a slab produced by refining molten steel discharged from a converter or electric furnace in a vacuum degassing facility.
[0168] A detailed description of the step for preparing the steel plate for hot stamping is omitted because it is identical to the description in the method for manufacturing the steel plate for hot stamping.
[0169] Additionally, the heating step may be performed by cutting the steel plate for hot stamping into a blank of a predetermined shape and then heating the cut blank. The heating step may be performed by heating the steel plate for hot stamping at an average heating rate of 3℃ / s or more, and heating it at a temperature of 900℃ or more and 970℃ or less for 240 seconds or more and 330 seconds or less.
[0170] Additionally, the transfer step may be performed by transferring the heated hot stamping steel plate (blank) from the heating to the mold. At this time, during the transfer step, the heated hot stamping steel plate may be air-cooled during transfer.
[0171] In addition, the forming step may be performed by applying pressure to the hot stamping steel plate transferred to the mold to form the hot stamping steel plate into the shape of a hot stamping part. In addition, the forming step may be performed at a forming start temperature of 600°C or higher and 770°C or lower.
[0172] In addition, the cooling step can be performed by cooling the formed hot stamping steel sheet, and can be carried out within the mold. In addition, the cooling step can be performed by cooling from Mf - 100°C to Mf + 100°C at an average cooling rate of 1°C / s or more and 40°C / s or less.
[0173] According to the method for manufacturing a hot stamping part of the present application, by satisfying the above conditions, the steps of preparing a steel plate for hot stamping, heating the steel plate for hot stamping, conveying the heated steel plate for hot stamping, forming the conveyed steel plate for hot stamping, and cooling the formed steel plate for hot stamping can provide a hot stamping part having high strength and excellent elongation and bendability.
[0174] Additionally, the hot stamping part may include TiN precipitates. Additionally, the hot stamping part may have an average size (circular equivalent diameter) of the TiN precipitates of 0.01 µm or more and 2.5 µm or less. Additionally, the hot stamping part may have 30 ea / mm of TiN precipitates. 2 It may be less than, specifically, 29ea / mm 2 Less than or equal to 28ea / mm 2 The following may apply. According to the method for manufacturing a hot stamping part of the present application, by satisfying the average size and number of TiN precipitates within the aforementioned range, a hot stamping part having high strength while also possessing excellent elongation and bendability can be provided.
[0175] In addition, the hot stamping part may have a yield strength (YP) of 1000 MPa or more and a tensile strength (TS) of 1400 MPa or more. In addition, the hot stamping part may have an elongation of 5.5% or more, specifically 6.0% or more, 6.5% or more, or 6.6% or more. The yield strength, tensile strength, and elongation may be measured according to the measurement method of the embodiment described below.
[0176] In addition, the hot stamping part may have a bending angle of 38.0° or more, specifically 45.0°, 52.0°, 53.0°, or 53.8° or more. The bending angle may refer to a V-bending angle in the rolling direction and may be measured according to the measurement method of the embodiment described below.
[0177] According to the method for manufacturing a hot stamping part of the present application, by satisfying the yield strength, tensile strength, elongation, and bending angle within the aforementioned ranges, it is possible to provide a hot stamping part having high strength while also possessing excellent elongation and bendability.
[0178]
[0179] The present application will be described in more detail below through embodiments according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the embodiments presented below.
[0180]
[0181] Manufacture of steel plates for hot stamping
[0182] Example 1
[0183] Steel having a composition consisting of the components shown in Table 1 below, the remainder being Fe and other unavoidable impurities, was melted in an electric furnace, subjected to secondary refining, and continuously cast to produce a slab. Subsequently, the slab was reheated at a temperature of 1220°C and then hot-rolled at a finishing rolling temperature of 875°C to produce a hot-rolled steel sheet with a thickness of 4.0 mm.
[0184] Afterwards, the above hot-rolled steel sheet was coiled at a coiling temperature of 544℃.
[0185] Afterwards, pickling was performed on the hot-rolled steel sheet, and the pickled hot-rolled steel sheet was cold-rolled to a thickness of 1.2 mm with a reduction rate of 70%.
[0186] Afterwards, a cold-rolled steel sheet was manufactured by raising the temperature to 780℃ and heat-treating it for 300 seconds, and then cooling it at an average cooling rate of 20℃ / s.
[0187] Subsequently, an Al-Si plating layer was formed on the surface by immersion in an Al-Si plating bath, wherein the Al-Si plating bath contained 8–10% Si and 1% Fe by weight, with the remainder being Al. Additionally, the temperature of the plating bath was 660℃, and the plating deposition amount was 80 g / m². 2 was.
[0188]
[0189] Examples 2 and 3, Comparative Examples 1 and 2
[0190] Each hot stamping steel plate was manufactured in the same manner as in Example 1, except that the composition of the slab was changed as shown in Table 1 below, and the finishing rolling end temperature and coiling temperature were changed as shown in Table 2 below.
[0191]
[0192] Evaluation Example 1. Evaluation of whether Equations 1 to 3 are satisfied
[0193] For the hot stamping steel sheets produced in each of the examples and comparative examples, it was calculated whether [Cu], [Sn], and [Ni] satisfied Equation 1, and whether [N] and [Ti] satisfied Equation 2. The results are shown in Table 1 below.
[0194]
[0195] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Slab Composition (wt%) C 0.238 0.213 0.20 10.29 6 0.237 Si 0.24 10.28 6 0.24 3 0.24 5 0.251 Mn 1.132 1.24 7 1.339 1.024 1.157 P 0.0100 0.012 0.00 98 0.0103 0.0102 S 0.0043 0.005 10.0038 0.0052 0.0044 Al 0.024 0.024 0.03 0.025 0.026 Ti 0.034 0.03 20.0300.0290.099Cr0.1920.1970.2040.2010.199B0.00340.00300.00280.00300.0027N0.00440.00980.00740.01970.0175Cu0.0240.0930.1510.2550.417Sn0.00100.00750.01100.03000.0153Ni0.0130.0390.0200.0600.087 Value calculated as 1 0.06 0.37 0.63 1.40 1.20 Formula Value calculated as 2 0.00 8 0.01 3 0.01 0 0.02 3 0.041
[0196]
[0197] Finishing Rolling End Temperature (°C) Coiling Temperature (°C) Example 1875544 Example 2823630 Example 3880621 Comparative Example 1853640 Comparative Example 2875771
[0198]
[0199] Evaluation Example 2. Observation of surface cracks
[0200] For the hot stamping steel sheets prepared in each of the examples and comparative examples, the surface was observed using a scanning electron microscope (SEM) to check for the occurrence of surface cracks, and if they occurred, the maximum surface crack depth was measured. The results are shown in Table 3 below.
[0201]
[0202] Evaluation Example 3. Measurement of Yield Strength (YP), Tensile Strength (TS), and Elongation (EL)
[0203] For the hot stamping steel sheets manufactured in each of the examples and comparative examples, tensile tests were performed using specimens taken according to JIS Standard No. 5 at a 90° angle to the rolling direction, and yield strength, tensile strength, and elongation were measured. The results are shown in Table 3 below.
[0204]
[0205] Presence of Surface Cracks Maximum Surface Crack Depth (㎛) Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) Example 1X-43356429.8 Example 2X-41655629.9 Example 3X-42156129.8 Comparative Example 104742655929.7 Comparative Example 205141255429.6
[0206]
[0207] As shown in Tables 1 to 3 above, the hot stamping steel sheets manufactured in each of Examples 1 to 3 satisfied a specific range for the composition of the hot stamping steel sheets, and the values calculated by Equation 1 and Equation 2 satisfied a specific range, and accordingly, it was confirmed that no surface cracks occurred after hot rolling and cold rolling. Specifically, as can be seen through Figure 1, it was confirmed that no surface cracks occurred in the hot stamping steel sheet manufactured in Example 1 after rolling. In addition, it was confirmed that the hot stamping steel sheets manufactured in each of Examples 1 to 3 also had excellent yield strength, tensile strength, and elongation.
[0208] In contrast, the hot stamping steel sheets manufactured in Comparative Examples 1 and 2, respectively, exhibited surface cracks after hot rolling and cold rolling as the composition of the hot stamping steel sheets deviated from a specific range and the values calculated by Equation 1 and Equation 2 deviated from a specific range. At this time, it was confirmed that the maximum surface crack depth also deviated from a specific range. Specifically, as can be seen in Fig. 2, it was confirmed that the hot stamping steel sheet manufactured in Comparative Example 1 exhibited surface cracks due to Cu segregation during rolling.
[0209]
[0210] Manufacturing of hot stamping parts
[0211] Example 4
[0212] The hot stamping steel plate of Example 1 was heated at an average heating rate of 5℃ / s and heated at a temperature of 950℃ for 300 seconds.
[0213] Afterwards, the heated steel plate for hot stamping was transferred to the mold.
[0214] Subsequently, the above-mentioned steel plate for hot stamping was pressed to form the shape of a hot stamping part. At this time, the forming start temperature was 660℃.
[0215] Subsequently, the hot stamping part was manufactured by cooling the formed steel plate for hot stamping to 200°C at an average cooling rate of 40°C / s.
[0216]
[0217] Examples 5 and 6, Comparative Examples 3 and 4
[0218] Each hot stamping part was manufactured in the same manner as in Example 4, except that the type of steel plate for hot stamping was changed as shown in Table 4 below.
[0219]
[0220] Steel plate for hot stamping Example 4 Example 1 Example 5 Example 2 Example 6 Example 3 Comparative Example 3 Comparative Example 1 Comparative Example 4 Comparative Example 2
[0221]
[0222] Evaluation Example 4. Observation of TiN precipitates
[0223] For the hot stamping parts prepared in each of the examples and comparative examples, TiN precipitates formed on the surface were observed using a scanning electron microscope, and the average size and number of TiN precipitates were calculated. The results are shown in Table 5 below.
[0224]
[0225] Evaluation Example 5. Measurement of Yield Strength (YP), Tensile Strength (TS), and Elongation (EL)
[0226] For each of the hot stamping parts manufactured in the examples and comparative examples, tensile tests were performed using specimens taken according to JIS Standard No. 5 at a 90° angle to the rolling direction, and yield strength, tensile strength, and elongation were measured. The results are shown in Table 5 below.
[0227]
[0228] Evaluation Example 6. Measurement of bending angle
[0229] For the hot stamped parts manufactured in each of the examples and comparative examples, the bending angle was measured in accordance with the VDA standard (VDA238-100). The results are shown in Table 5 below.
[0230]
[0231] Average size of TiN precipitates (㎛) Number of TiN precipitates (ea / mm) 2 Yield Strength (MPa) Tensile Strength (MPa) Elongation (%) Bending Angle (°) Example 4 0.9 17 100 6 142 6 6.8 5 4.4 Example 5 1.4 28 104 41 43 17.1 5 3.8 Example 6 1.3 22 102 114 21 6.6 5 6.3 Comparative Example 3 3.4 6 4 103 214 5 15.3 3 7.1 Comparative Example 4 42.8 5 7 103 41 44 6 5.5 3 5.7
[0232]
[0233] As shown in Tables 4 and 5 above, the hot stamping parts manufactured in each of Examples 4 to 6 had a composition of the steel sheet for hot stamping that satisfied a specific range, and the values calculated by Equation 1 and Equation 2 satisfied a specific range, and accordingly, it was confirmed that no surface cracks occurred after hot rolling and cold rolling. In addition, as can be seen through Figure 3, the average size and number of TiN precipitates after the hot stamping process satisfied a specific range, and accordingly, it was confirmed that the strength and bendability were excellent.
[0234] In contrast, for the hot stamping parts manufactured in Comparative Examples 3 and 4, surface cracks occurred after hot rolling and cold rolling as the composition of the steel plate for hot stamping deviated from a specific range and the values calculated by Equation 1 and Equation 2 deviated from a specific range. At this time, it was confirmed that the maximum surface crack depth also deviated from a specific range. In addition, as can be seen in Figure 4, it was confirmed that strength bendability decreased as the average size and number of TiN precipitates after the hot stamping process deviated from a specific range.
Claims
1. In wt%, comprising C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities, and A steel plate for hot stamping satisfying the following Equation 1. [Equation 1] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19 ([Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.) 2. In Paragraph 1, A steel plate for hot stamping satisfying the following Equation 2. [Equation 2] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021 ([N] and [Ti] represent the weight percent of N and Ti, respectively.) 3. In Paragraph 1, A steel plate for hot stamping having a tensile strength of 500 MPa or more and 650 MPa or less, and a yield strength of 400 MPa or more and 500 MPa or less.
4. In wt%, comprising C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.10% or more and 3.00% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities, A hot stamping part satisfying the following Equation 1. [Equation 1] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19 ([Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.) 5. In Paragraph 4, A hot stamping part satisfying the following Equation 2. [Equation 2] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021 ([N] and [Ti] represent the weight percent of N and Ti, respectively.) 6. In Paragraph 4, It includes TiN precipitates, The average size of the above TiN precipitates is 0.01㎛ or more and 2.5㎛ or less, and The number of the above TiN precipitates is 30ea / mm 2 Lee Ha-in, hot stamping parts.
7. In Paragraph 4, A hot stamping part having an elongation of more than 5.5% and a bending angle of 38.0° or more.
8. In Paragraph 4, A hot stamping part having a tensile strength of 1400 MPa or more and a yield strength of 1000 MPa or more.
9. A step of preparing a slab comprising, in wt%, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; Step of reheating the above slab; A step of manufacturing a hot-rolled steel sheet by hot-rolling the above-mentioned reheated slab; A step of manufacturing a cold-rolled steel sheet by cold-rolling the above hot-rolled steel sheet; and A method for manufacturing a steel sheet for hot stamping, comprising the step of annealing the above-mentioned cold-rolled steel sheet, A method for manufacturing a steel plate for hot stamping satisfying Formula 1 below. [Equation 1] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19 ([Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.) 10. In Paragraph 9, A method for manufacturing a steel sheet for hot stamping, further comprising, prior to the step of manufacturing the cold-rolled steel sheet, a step of coiling the hot-rolled steel sheet at a temperature of less than 660°C.
11. In Paragraph 9, A method for manufacturing a steel plate for hot stamping satisfying the following Equation 2. [Equation 2] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021 ([N] and [Ti] represent the weight percent of N and Ti, respectively.) 12. In Paragraph 9, A method for manufacturing a steel plate for hot stamping, wherein, in the step of preparing the above-mentioned slab, the slab is manufactured by refining molten steel tapped from a converter or electric furnace in a vacuum degassing facility.
13. In Paragraph 9, A method for manufacturing a hot stamping steel plate, wherein the above-mentioned hot stamping steel plate has a tensile strength of 500 MPa or more and 650 MPa or less, and a yield strength of 400 MPa or more and 500 MPa or less.
14. A step of preparing a steel sheet for hot stamping comprising, in weight%, C: 0.10% or more and 0.50% or less, Si: greater than 0% and 1.0% or less, Mn: 0.1% or more and 3.0% or less, P: greater than 0% and 0.1% or less, S: greater than 0% and 0.02% or less, Al: 0.01% or more and 1.0% or less, Ti: 0.010% or more and 0.100% or less, Cr: greater than 0% and 2.0% or less, B: 0.0010% or more and 0.0050% or less, N: greater than 0% and 0.0200% or less, Cu: greater than 0% and 0.30% or less, Sn: greater than 0% and 0.03% or less, Ni: greater than 0% and 0.15% or less, and the remainder being Fe and other unavoidable impurities; A step of heating the above-mentioned steel plate for hot stamping; A step of conveying the above-mentioned heated steel plate for hot stamping; A step of forming the above-mentioned steel plate for hot stamping; and A method for manufacturing a hot stamping part comprising the step of cooling the formed steel plate for hot stamping, wherein A method for manufacturing a hot stamping part satisfying the following Equation 1. [Equation 1] 0.05 ≤ 2.0 × [Cu] + 33 × [Sn] - 1.7 × [Ni] < 1.19 ([Cu], [Sn], and [Ni] represent the weight percent of Cu, Sn, and Ni, respectively.) 15. In Paragraph 14, A method for manufacturing a hot stamping part satisfying the following Equation 2. [Equation 2] 0.004 ≤ (1.08 × ([N] - 0.006)) + ([Ti] / 3.41) ≤ 0.021 ([N] and [Ti] represent the weight percent of N and Ti, respectively.) 16. In Paragraph 14, A method for manufacturing a hot stamping part, wherein the above-mentioned hot stamping steel plate is manufactured using a slab produced by refining molten steel discharged from a converter or electric furnace in a vacuum degassing facility.
17. In Paragraph 14, The above hot stamping part includes TiN precipitates, and The average size of the above TiN precipitates is 0.01㎛ or more and 2.5㎛ or less, and The number of the above TiN precipitates is 30ea / mm 2 Method for manufacturing hot stamping parts, including the above.
18. In Paragraph 14, A method for manufacturing a hot stamping part, wherein the hot stamping part has an elongation of more than 5.5% and a bending angle of 38.0° or more.
19. In Paragraph 14, A method for manufacturing a hot stamping part, wherein the hot stamping part has a tensile strength of 1400 MPa or more and a yield strength of 1000 MPa or more.