KR20230153887A - The steel sheet for the hot stamping, and method of manufacturing the same - Google Patents

Abstract

According to one aspect of the present invention, carbon (C): 0.26 to 0.40 wt%, silicon (Si): 0.02 to 2.0 wt%, manganese (Mn): 0.3 to 1.60 wt%, phosphorus (P): 0.03 wt% or less. , Sulfur (S): 0.008wt% or less, Chromium (Cr): 0.05~0.90wt%, Boron (B): 0.0005~0.01wt%, Molybdenum (Mo): 0.05~0.2wt%, Titanium (Ti): 0.001 In the hot stamping steel sheet containing ~0.095wt%, niobium (Nb): 0.001~0.095wt%, vanadium (V): 0.001~0.095wt%, and the remaining iron (Fe) and other inevitable impurities, the hot stamping The steel sheet contains ferrite: 60 to 99% and pearlite: 1 to 30% by area fraction, and includes at least a portion of a pearlite region in which pearlite is locally accumulated, and the pearlite region contains carbon (C): 0.27 to 0.70 wt. % and manganese (Mn): 1.0 to 5.0 wt%. A steel sheet for hot stamping is provided.

Description

Steel sheet for hot stamping and method of manufacturing the same {The steel sheet for the hot stamping, and method of manufacturing the same}

Embodiments of the present invention relate to a steel sheet for hot stamping and a method of manufacturing the same. More specifically, it relates to a steel sheet for hot stamping in which the molded part after hot stamping has excellent mechanical properties of high strength and high toughness and a method of manufacturing the same.

High-strength steel is used in automobile parts for weight reduction and stability. On the other hand, high-strength steel can secure high strength-to-weight characteristics, but as strength increases, press formability deteriorates, resulting in material breakage during processing or springback phenomenon, which makes it difficult to form products with complex and precise shapes. There are difficulties.

One way to improve these problems is the hot stamping method, and as interest in this method increases, research on materials for hot stamping is also being actively conducted. For example, as disclosed in Korean Patent Publication No. 10-2017-0076009, the hot stamping method is a forming technology that manufactures high-strength parts by heating a hot stamping steel sheet to a high temperature and then rapidly cooling it during molding in a press mold. .

In addition, as disclosed in Korean Patent Publication No. 10-2019-0095858, a representative example of a steel sheet for hot stamping is a steel sheet containing carbon (C) and manganese (Mn) and boron (B) as elements for improving heat treatment performance. The so-called boron steel (22MnB5) is used.

However, in these conventional hot stamping steel sheets and their manufacturing methods, the mechanical properties such as tensile strength and bending properties of the molded part after hot stamping are affected due to differences in strength in each region caused by the components and microstructure of the hot stamping steel sheet. This problem of deterioration existed.

Embodiments of the present invention are intended to solve various problems including the above problems, and are intended to provide a steel sheet for hot stamping in which the molded part after hot stamping has excellent mechanical properties such as high strength and high toughness, and a method of manufacturing the same. However, these tasks are illustrative and do not limit the scope of the present invention.

According to one aspect of the present invention, carbon (C): 0.26 to 0.40 wt%, silicon (Si): 0.02 to 2.0 wt%, manganese (Mn): 0.3 to 1.60 wt%, phosphorus (P): 0.03 wt% or less. , Sulfur (S): 0.008wt% or less, Chromium (Cr): 0.05~0.90wt%, Boron (B): 0.0005~0.01wt%, Molybdenum (Mo): 0.05~0.2wt%, Titanium (Ti): 0.001 In the hot stamping steel sheet containing ~0.095wt%, niobium (Nb): 0.001~0.095wt%, vanadium (V): 0.001~0.095wt%, and the remaining iron (Fe) and other inevitable impurities, the hot stamping The steel sheet contains ferrite: 60 to 99% and pearlite: 1 to 20% by area fraction, and includes at least a portion of a pearlite region in which pearlite is locally accumulated, and the pearlite region contains carbon (C): 0.27 to 0.70 wt. % and manganese (Mn): 1.0 to 5.0 wt%. A steel sheet for hot stamping is provided.

According to this embodiment, the average length of the pearlite region may be 0.01 ㎛ or more and 500 ㎛ or less.

According to this embodiment, the average thickness of the pearlite region may be 0.01 ㎛ or more and 30 ㎛ or less.

According to this embodiment, the average spacing between the pearlite regions may be 0.01 ㎛ or more and 10 ㎛ or less.

According to this embodiment, the area fraction of the pearlite region may be 0.1% or more and 15% or less.

According to this embodiment, the steel sheet for hot stamping includes a plurality of crystal grains including at least a portion of the pearlite region, and the long side (a) and short side of the pearlite region portion present in one crystal grain among the plurality of crystal grains. The ratio (a/b) of (b) may be 2 or less.

According to this embodiment, the pearlite region may include 50% or more of pearlite and 5% or less of ferrite in terms of area fraction.

According to this embodiment, some components of the steel sheet for hot stamping may satisfy Equation 1 below.

[Equation 1]

0.015≤0.25(Ti+Nb+V+0.25(Mo))≤0.060 (Unit: wt%)

According to this embodiment, the molded part after hot stamping the hot stamping steel sheet has a tensile strength of 1,700 MPa or more and can satisfy a bending angle of 50 degrees or more.

According to another aspect of the present invention, carbon (C): 0.26 to 0.40 wt%, silicon (Si): 0.02 to 2.0 wt%, manganese (Mn): 0.3 to 1.60 wt%, phosphorus (P): 0.03 wt% or less. , Sulfur (S): 0.008wt% or less, Chromium (Cr): 0.05~0.90wt%, Boron (B): 0.0005~0.01wt%, Molybdenum (Mo): 0.05~0.2wt%, Titanium (Ti): 0.001 Reheat the slab containing ~0.095wt%, Niobium (Nb): 0.001~0.095wt%, Vanadium (V): 0.001~0.095wt% and the remainder iron (Fe) and other unavoidable impurities at a temperature of 1,200~1,250°C. steps; Manufacturing a steel sheet by hot rolling the reheated slab at a temperature of 800 to 1000°C with a reduction ratio of 95% or more; and winding the steel sheet at a temperature of 580 to 680°C, wherein the steel sheet for hot stamping contains ferrite: 60 to 99% and pearlite: 1 to 30% as an area fraction, and at least a portion of the steel sheet contains pearlite. A method of manufacturing a steel sheet for hot stamping is provided, including a locally integrated pearlite region, wherein the pearlite region includes carbon (C): 0.27 to 0.70 wt% and manganese (Mn): 1.0 to 5.0 wt%. .

According to the present embodiment, cooling the steel sheet to a temperature ranging from the martensite transformation start temperature (Ms) to the pearlite transformation start temperature (Ps) + 40°C for less than 30 seconds, and winding the steel sheet. The step may be a step of winding the cooled steel sheet.

According to this embodiment, the average length of the pearlite region may be 0.01 ㎛ or more and 500 ㎛ or less.

According to this embodiment, the average thickness of the pearlite region may be 0.01 ㎛ or more and 30 ㎛ or less.

According to this embodiment, the average spacing between the pearlite regions may be 0.01 ㎛ or more and 10 ㎛ or less.

According to this embodiment, the area fraction of the pearlite region may be 0.1% or more and 15% or less.

According to this embodiment, the steel sheet for hot stamping includes a plurality of crystal grains including at least a portion of the pearlite region, and the long side (a) and short side of the pearlite region portion present in one crystal grain among the plurality of crystal grains. The ratio (a/b) of (b) may be 2 or less.

According to this embodiment, the pearlite region may include 50% or more of pearlite and 5% or less of ferrite in terms of area fraction.

According to this embodiment, some components of the steel sheet for hot stamping may satisfy Equation 1 below.

[Equation 1]

0.015≤0.25(Ti+Nb+V+0.25(Mo))≤0.060 (Unit: wt%)

According to this embodiment, the molded part after hot stamping the hot stamping steel sheet has a tensile strength of 1,700 MPa or more and can satisfy a bending angle of 50 degrees or more.

Other aspects, features and advantages other than those described above will become apparent from the detailed description, claims and drawings for carrying out the invention below.

According to an embodiment of the present invention made as described above, a steel sheet for hot stamping and a method of manufacturing the same can be implemented in which the molded part after hot stamping has excellent mechanical properties such as high strength and high toughness.

Specifically, by controlling the strength differences in each region of the hot stamping steel sheet by controlling the properties of the components and microstructure contained in the hot stamping steel sheet, the hot stamping molded part has excellent mechanical properties such as tensile strength and bending properties. A steel plate for stamping and its manufacturing method can be implemented. According to one embodiment of the present invention, of course, the scope of the present invention is not limited by this effect.

Figure 1 is an image showing part of the microstructure of a conventional steel sheet for hot stamping.
Figure 2 is an image showing part of the microstructure of a steel sheet for hot stamping according to an embodiment of the present invention.
Figure 3 is a flowchart schematically showing part of a method of manufacturing a steel sheet for hot stamping according to an embodiment of the present invention.
Figure 4 is an image schematically showing some of the grains of the microstructure of a molded part after hot stamping according to an embodiment of the present invention.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms.

In the following embodiments, terms such as first and second are used not in a limiting sense but for the purpose of distinguishing one component from another component.

In the following examples, singular terms include plural terms unless the context clearly dictates otherwise.

In the following embodiments, terms such as include or have mean the presence of features or components described in the specification, and do not exclude in advance the possibility of adding one or more other features or components.

In the drawings, the sizes of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are shown arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is shown.

In cases where an embodiment can be implemented differently, a specific process sequence may be performed differently from the described sequence. For example, two processes described in succession may be performed substantially at the same time, or may be performed in an order opposite to that in which they are described.

In this specification, “A and/or B” refers to A, B, or A and B. And, “at least one of A and B” indicates the case of A, B, or A and B.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. When describing with reference to the drawings, identical or corresponding components will be assigned the same reference numerals and redundant description thereof will be omitted. .

Figure 1 is an image showing part of the microstructure of a conventional steel sheet for hot stamping.

The microstructure of the steel sheet in Figure 1 may include ferrite and pearlite. Meanwhile, carbon (C) and/or manganese (Mn) may be segregated in pearlite. That is, the microstructure of the steel sheet for hot stamping may include pearlite with a relatively high carbon (C) content and/or manganese (Mn) content. Additionally, pearlite with a relatively high carbon (C) content and/or manganese (Mn) content may be locally accumulated within the steel sheet for hot stamping. In other words, the microstructure of a steel sheet for hot stamping may include a region where pearlite with a relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated (hereinafter referred to as “pearlite region”). there is.

In one embodiment, as shown in FIG. 1, the pearlite region may be formed in a strip shape (or band shape) within the steel sheet for hot stamping.

The strength in the pearlite region of a steel sheet for hot stamping and the strength in regions other than the pearlite region are different from each other. Specifically, the pearlite area may have a relatively high intensity, and areas outside the pearlite area may have a relatively low intensity. That is, the intensity of the pearlite region may be relatively higher than the intensity of regions other than the pearlite region. Accordingly, steel sheets for hot stamping have differences in strength by region. This difference in strength by region can act as a factor in lowering the mechanical properties such as tensile strength, yield strength, bending properties, and elongation of molded parts after hot stamping. Therefore, it is necessary to control the size, shape, area fraction, etc. of the pearlite region included in the steel sheet for hot stamping.

According to embodiments of the present invention, by controlling the content of the material constituting the hot stamping steel sheet, the microstructure of the hot stamping steel sheet, and the process conditions for manufacturing the hot stamping steel sheet, the hot stamping steel sheet includes The size, shape, and area fraction of the pearlite region can be controlled. Through this, it is possible to implement a steel plate for hot stamping that can satisfy the mechanical properties required for molded parts after hot stamping.

Figure 2 is an image showing part of the microstructure of a steel sheet for hot stamping according to an embodiment of the present invention.

Specifically, Figure 2 shows a hot stamping steel sheet manufactured by controlling the content of materials constituting the hot stamping steel sheet, the microstructure of the hot stamping steel sheet, and the process conditions for manufacturing the hot stamping steel sheet to meet preset conditions. This is an image representing a steel plate.

Referring to Figure 2, it can be seen that compared to the steel sheet of Figure 1, the area where pearlite with relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated has been significantly reduced. Specifically, it can be seen that the band-shaped (or band-shaped) area included in the steel sheet of FIG. 1 is significantly reduced in the steel sheet of FIG. 2. This can be understood as controlling the content of materials constituting the steel sheet for hot stamping, the composition of the microstructure of the steel sheet for hot stamping, and the process conditions for manufacturing the steel sheet for hot stamping to satisfy preset conditions, and detailed information about this can be achieved. The explanation is provided later.

The steel sheet for hot stamping of this embodiment may be a steel sheet manufactured by performing a hot rolling process and/or a cold rolling process on a slab cast to contain a predetermined content of a predetermined alloy element.

Steel sheets for hot stamping are made of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), boron (B), calcium (Ca), molybdenum (Mo), It may contain titanium (Ti), niobium (Nb), vanadium (V) and the remaining iron (Fe) and other inevitable impurities. In one embodiment, the steel sheet for hot stamping contains carbon (C): 0.26 to 0.40 wt%, silicon (Si): 0.02 to 2.0 wt%, manganese (Mn): 0.3 to 1.60 wt%, and phosphorus (P): 0.03 wt. % or less, sulfur (S): 0.008wt% or less, chromium (Cr): 0.05~0.90wt%, boron (B): 0.0005~0.01wt%, molybdenum (Mo): 0.05~0.2wt%, titanium (Ti) : 0.001~0.095wt%, Niobium (Nb): 0.001~0.095wt%, Vanadium (V): 0.001~0.095wt%, and the remainder may contain iron (Fe) and other inevitable impurities. Additionally, optionally, calcium (Ca): 0.00001 to 0.0060 wt% may be further included.

Carbon (C) acts as an austenite stabilizing element in steel sheets. Carbon is a major element that determines the strength and hardness of steel sheets, and is added to increase hardenability and strength during heat treatment. This carbon may be included in an amount of 0.26 wt% to 0.40 wt% based on the total weight of the steel sheet. If the carbon content is less than 0.26wt%, it is difficult to secure a hard phase (eg, martensite, etc.), making it difficult to satisfy the mechanical strength of the molded part after hot stamping. Conversely, if the carbon content exceeds 0.40 wt%, it may cause a decrease in the processability of the steel sheet or a decrease in the bending performance of the molded part after hot stamping.

Silicon (Si) acts as a ferrite stabilizing element in steel sheets. Silicon improves the strength of steel sheets as a solid solution strengthening element and improves carbon concentration in austenite by suppressing the formation of low-temperature carbides. In addition, silicon is a key element in hot rolling, cold rolling, hot press tissue homogenization, and ferrite fine dispersion. Silicon acts as a martensite strength heterogeneity control element and plays a role in improving collision performance. Such silicon may be included in an amount of 0.02 wt% to 2.0 wt% based on the total weight of the steel sheet. If the silicon content is less than 0.02 wt%, it is difficult to obtain the above-mentioned effect, and cementite formation and coarsening may occur in the martensite structure of the molded part after hot stamping. Conversely, if the silicon content exceeds 2.0 wt%, hot rolling and cold rolling loads increase, and the plating characteristics of the steel sheet may deteriorate.

On the other hand, when silicon (Si) is preferably added in an amount of 0.3 wt% or more, the excessive formation of pearlite regions in which pearlite is integrated in the hot stamping steel sheet is suppressed, so that the pearlite region is formed at a minimum content in the hot stamping steel sheet. You can.

Manganese (Mn) acts as an austenite stabilizing element in steel sheets. Manganese is added to increase hardenability and strength during heat treatment. Manganese may be included in an amount of 0.3 wt% to 1.60 wt% based on the total weight of the steel sheet. If the manganese content is less than 0.3 wt%, the hardenability effect may not be sufficient, and the hardenability may be insufficient, resulting in a hard phase fraction in the molded part after hot stamping. On the other hand, if the manganese content exceeds 1.60wt%, areas where manganese-segregated pearlite is concentrated may occur, which may reduce ductility and toughness, cause deterioration in bending performance of molded parts after hot stamping, and cause heterogeneity. Microstructure may occur.

Phosphorus (P) is an element that contributes to strength improvement. In order to prevent deterioration of the toughness of the steel sheet, phosphorus may be included in an amount greater than 0 and less than or equal to 0.03 wt% based on the total weight of the steel sheet. If the phosphorus content exceeds 0.03 wt%, iron phosphide compounds are formed, which reduces toughness and weldability and may cause cracks in the steel sheet during the manufacturing process.

Sulfur (S) is an element that contributes to improving processability. Such sulfur may be contained in an amount greater than 0 and less than or equal to 0.008 wt% based on the total weight of the steel sheet. If the sulfur content exceeds 0.008wt%, hot workability, weldability, and impact properties deteriorate, and surface defects such as cracks may occur due to the creation of large inclusions.

Chromium (Cr) is added to improve hardenability and strength during heat treatment. Chromium makes it possible to refine grains and secure strength through precipitation hardening. Chromium may be included in an amount of 0.05 wt% to 0.9 wt% based on the total weight of the steel sheet. If the chromium content is less than 0.05 wt%, the precipitation hardening effect is poor. Conversely, if the chromium content exceeds 0.9 wt%, the amount of Cr-based precipitates and matrix solids increases, which reduces toughness and increases production costs. may increase.

Boron (B) is added to secure hardenability and strength during heat treatment by suppressing ferrite, pearlite, and bainite transformation and securing a martensite structure. In addition, boron is segregated at grain boundaries to lower the grain boundary energy, thereby increasing hardenability, and has the effect of grain refinement by increasing the austenite grain growth temperature. This boron may be included in an amount of 0.0005 wt% to 0.01 wt% based on the total weight of the steel sheet. When boron is included in the above range, hard phase grain boundary embrittlement can be prevented and high toughness and bendability can be secured. If the boron content is less than 0.0005wt%, the hardenability effect is insufficient. Conversely, if the boron content exceeds 0.01wt%, the solid solubility is low and it easily precipitates at the grain boundaries depending on the heat treatment conditions, resulting in deterioration of hardenability. It may cause embrittlement at high temperatures, and toughness and bendability may decrease due to hard grain boundary embrittlement.

Calcium (Ca) may be added to control precipitates. Calcium has a high bonding power with sulfur, forming CaS precipitates, which can suppress the production of MnS, which impairs weldability. Calcium may be included in an amount of 0.00001 wt% to 0.006 wt% based on the total weight of the steel sheet. When the calcium content is less than 0.00001% by weight, the MnS control effect is reduced. If the calcium content exceeds 0.006% by weight, playability may be reduced.

Titanium (Ti) can effectively contribute to grain refinement by forming precipitates at high temperatures. Such titanium may be included in an amount of 0.001 wt% to 0.095 wt%, preferably 0.005 wt% to 0.06 wt%, based on the total weight of the steel sheet. When titanium is included in the above content range, poor playing and coarsening of precipitates can be prevented, the physical properties of the steel can be easily secured, and defects such as cracks on the surface of the steel can be prevented. If the titanium content is below the above lower limit, the above effect cannot be properly achieved. On the other hand, if the titanium content exceeds the upper limit, the precipitates may become coarse, causing a decrease in elongation and bendability.

Niobium (Nb) and vanadium (V) can increase strength and toughness as the martensite packet size decreases. Niobium and vanadium may each be included in an amount of 0.005 wt% to 0.06 wt% based on the total weight of the steel sheet. When niobium is included in the above range, the grain refining effect of steel sheets is excellent in the hot rolling and cold rolling processes, the occurrence of cracks in the slab and brittle fracture of the product during steelmaking/rolling are prevented, and the generation of steelmaking coarse precipitates is minimized. You can. If the niobium content is less than 0.005wt%, the above effect cannot be properly achieved. On the other hand, when the niobium content exceeds 0.06wt%, the strength and toughness due to the increase in niobium content are no longer improved and exist in a dissolved state in the ferrite, which poses a risk of lowering the impact toughness. Vanadium may also exhibit similar tendencies to the niobium described above.

Molybdenum (Mo) is a substitutional element that improves the strength of steel through a solid solution strengthening effect. Molybdenum is added for the purpose of suppressing precipitate coarsening and improving hardenability. Additionally, molybdenum (Mo) can play a role in improving the hardenability of steel. Molybdenum may be included in an amount of 0.05 wt% to 0.2 wt% based on the total weight of the steel sheet. If the molybdenum content is less than 0.05 wt%, the above effects cannot be properly achieved. On the other hand, if the molybdenum content exceeds 0.2wt%, there is a risk of lowering rolling productivity and elongation, and there is a problem of increasing manufacturing costs without additional effects.

In one embodiment, the steel sheet for hot stamping may preferably contain 0.005 to 0.06 wt% of titanium (Ti), niobium (Nb), and vanadium (V). Titanium (Ti), niobium (Nb), vanadium (V), and molybdenum (Mo) can act as elements that control the formation of pearlite regions in hot stamping steel sheets. Additionally, it is possible to control the formation of precipitates within the molded part after hot stamping. Therefore, when titanium (Ti), niobium (Nb), and vanadium (V) are included at 0.005 to 0.06 wt% each, and molybdenum (Mo) is included at 0.05 to 0.2 wt%, the pearlite region within the hot stamping steel sheet is easily formed. It is possible to control and further satisfy conditions that make it easy to control precipitates in molded parts after hot stamping.

In one embodiment, the contents of titanium (Ti), niobium (Nb), vanadium (V), and molybdenum (Mo) contained in the steel sheet for hot stamping are expressed in weight percent as [Ti], [Nb], [V], and When expressed as [Mo], the following equation 1 can be satisfied.

[Equation 1]

0.015≤0.25([Ti]+[Nb]+[V]+0.25[Mo])≤0.060 (Unit: wt%)

Through this, it is possible to control the shape of the pearlite region formed within the hot stamping steel sheet. The pearlite region affects the size and coarsening of grains after hot stamping, which can be a factor that reduces hydrogen embrittlement and bending angle (e.g., V-bending angle) performance of molded parts after hot stamping. Therefore, if the contents of titanium (Ti), niobium (Nb), vanadium (V), and molybdenum (Mo) in the steel sheet for hot stamping satisfy the above [Equation 1], the hydrogen embrittlement and bending angle of the molded part after hot stamping (e.g. V-bending angle) performance can be secured.

The steel sheet for hot stamping according to this embodiment is controlled so that the content of the materials constituting the steel sheet for hot stamping, the composition of the microstructure of the steel sheet for hot stamping, and the process conditions for manufacturing the steel sheet for hot stamping satisfy preset conditions. Accordingly, the area where relatively high pearlite is locally accumulated can be reduced and minimized and controlled so that an appropriate ratio of pearlite areas is formed and remains in the steel sheet for hot stamping. The pearlite region formed in the steel sheet for hot stamping can be completely removed during the process of hot stamping the steel sheet, and therefore, the molded part after hot stamping does not contain the pearlite region, thereby ensuring excellent hydrogen embrittlement and bending angle performance.

The microstructure of a steel sheet for hot stamping may include ferrite and pearlite. In one embodiment, the steel sheet for hot stamping may include ferrite: 50 to 99% and pearlite: 0.1 to 50% by area fraction. Additionally, the steel sheet for hot stamping may contain other unavoidable structures. For example, a steel sheet for hot stamping may contain 0% or more and less than 5% of other unavoidable structures. Meanwhile, in one embodiment, the average grain size of ferrite contained in a steel sheet for hot stamping may be controlled to satisfy 2 ㎛ or more and 10 ㎛ or less.

Since carbon (C) and/or manganese (Mn) may be segregated in pearlite, the microstructure of a steel sheet for hot stamping may include pearlite with a relatively high carbon content and/or manganese content. Additionally, pearlite with a relatively high carbon content and/or manganese content may locally accumulate within the steel sheet to form a pearlite region. Here, the “perlite region” refers to an area where pearlite with a relatively high carbon content and/or manganese content is locally accumulated.

There is a way to minimize the pearlite area of the steel sheet for hot stamping by lowering the carbon (C) content and the manganese (Mn) content, but this depends on the hardenability of the steel sheet for hot stamping and the mechanical properties of the molded part after hot stamping. It may cause problems that degrade. Therefore, the steel sheet for hot stamping according to an embodiment of the present invention contains the above-described optimized amounts of carbon and manganese, but the size, density, and area fraction of the pearlite region of the steel sheet for hot stamping satisfy preset conditions. It can be controlled. Through this, it is possible to control the mechanical properties such as tensile strength, yield strength, bending properties, and elongation of molded parts after hot stamping. For example, the tensile strength of the molded part after hot stamping may satisfy 1,700 MPa or more, and preferably 1,760 MPa or more and 1,950 MPa or less. In addition, the yield strength of the molded part after hot stamping may satisfy 1,150 MPa or more, and preferably 1,200 MPa or more and 1,350 MPa or less. Additionally, molded parts after hot stamping may satisfy a bending angle of 50 degrees or more and have an elongation of 5% or more. Here, “bending angle” may mean the V-bending angle in the rolling direction (RD).

Meanwhile, the microstructure of the steel sheet for hot stamping, that is, the size, density, and area fraction conditions of the pearlite region can be controlled by adjusting the process conditions of the steel sheet for hot stamping. A detailed description of this will be provided later with reference to FIG. 3 .

The pearlite region may have different degrees of influence on the mechanical properties of the molded part after hot stamping depending on the content of carbon (C) and manganese (Mn) contained in the pearlite integrated in the pearlite region. Specifically, it is the locally concentrated area of pearlite containing more than 0.27 wt% carbon and more than 1.0 wt% manganese that affects the mechanical properties of the molded part after hot stamping. On the other hand, areas where pearlite with a carbon content of less than 0.27 wt% or a manganese content of less than 1.0 wt% is locally concentrated has a minimal effect on the mechanical properties of the molded part after hot stamping. Therefore, in the steel sheet for hot stamping according to an embodiment of the present invention, the size, density, and area fraction of the area where pearlite containing more than 0.27 wt% carbon and more than 1.0 wt% manganese are locally concentrated are controlled to satisfy preset conditions. do.

The steel sheet for hot stamping according to an embodiment of the present invention is pearlite in which pearlite containing 0.27 to 0.70 wt% of carbon (C) and/or pearlite containing 1.0 to 5.0 wt% of manganese (Mn) are locally integrated. Can include areas. The size, shape, and area fraction of these pearlite regions can be controlled to satisfy preset conditions.

In one embodiment, the average length of the pearlite region may be controlled to satisfy 0.01 ㎛ or more and 500 ㎛ or less, preferably 0.1 ㎛ or more and 100 ㎛ or less. In addition, the average thickness of the pearlite band structure can be controlled to satisfy 0.01 ㎛ or more and 30 ㎛ or less. Additionally, the average spacing between pearlite band structures can be controlled to be 0.01 ㎛ or more and 10 ㎛ or less.

In one embodiment, the area fraction of the pearlite band structure in the steel sheet for hot stamping may be controlled to satisfy 0.1% or more and 15% or less.

Meanwhile, the steel sheet for hot stamping may include a plurality of grains as shown in FIG. 2. The pearlite region may be distributed throughout the steel sheet for hot stamping, and at least some of the plurality of crystal grains may include the pearlite region.

In one embodiment, the shape and size of the pearlite region within one of the plurality of crystal grains in the steel sheet for hot stamping may exhibit a predetermined tendency. As an example, the ratio (a/b) of the long side (a) and short side (b) of the pearlite band structure portion present in one crystal grain among the plurality of crystal grains may be 2 or less. That is, the pearlite band structure portion present in one crystal grain among the plurality of crystal grains may not have a spherical or circular shape but a shape close to an ellipse formed long in one direction or a shape close to a bar type.

This pearlite region may contain 50% or more of pearlite and 5% or less of ferrite in area fraction. Additionally, optionally, it may contain 5% or less of precipitates, low-temperature phase structures such as martensite and/or bainite, etc.

Figure 3 is a flowchart schematically showing part of a method of manufacturing a steel sheet for hot stamping according to an embodiment of the present invention.

As shown in Figure 3, the method of manufacturing a material for hot stamping according to an embodiment of the present invention includes a reheating step (S100), a hot rolling step (S200), a cooling/winding step (S300), and a cold rolling step (S400). ), an annealing heat treatment step (S500), and a plating step (S600).

For reference, steps S100 to S600 are shown as independent steps in FIG. 3, but some of steps S100 to S600 may be performed in one process, and some of steps S100 to S600 may be omitted if necessary.

First, prepare a slab in a semi-finished state that is the subject of the process of forming a steel sheet for hot stamping. The slab contains carbon (C): 0.26 to 0.40 wt%, silicon (Si): 0.02 to 2.0 wt%, manganese (Mn): 0.3 to 1.60 wt%, phosphorus (P): 0.03 wt% or less, and sulfur (S). : 0.008wt% or less, chromium (Cr): 0.05~0.90wt%, boron (B): 0.0005~0.01wt%, molybdenum (Mo): 0.05~0.2wt%, titanium (Ti): 0.001~0.095wt%, It may contain niobium (Nb): 0.001~0.095wt%, vanadium (V): 0.001~0.095wt%, and the remaining iron (Fe) and other inevitable impurities. Additionally, optionally, calcium (Ca): 0.00001 to 0.0060 wt% may be further included.

Meanwhile, in an optional embodiment, the slab may contain 0.005 to 0.06 wt% of titanium (Ti), niobium (Nb), and vanadium (V), respectively.

Meanwhile, in an optional embodiment, the contents of titanium (Ti), niobium (Nb), vanadium (V), and molybdenum (Mo) contained in the slab are expressed in weight percent as [Ti], [Nb], [V], and When expressed as [Mo], the following equation 1 can be satisfied.

[Equation 1]

0.015≤0.25([Ti]+[Nb]+[V]+0.25[Mo])≤0.060 (Unit: wt%)

Through this, it is possible to control the pearlite area where pearlite is accumulated formed within the hot stamping steel sheet formed through the slab. The band structure in which pearlite is integrated affects the size and coarsening of grains after hot stamping, which can be a factor in reducing hydrogen embrittlement and bending angle (e.g., V-bending angle) performance of molded parts after hot stamping. Therefore, if the contents of titanium (Ti), niobium (Nb), vanadium (V), and molybdenum (Mo) in the steel sheet for hot stamping satisfy the above [Equation 1], the hydrogen embrittlement and bending angle of the molded part after hot stamping (e.g. V-bending angle) performance can be secured.

The reheating step (S100) is a step of reheating the slab having the above composition within a predetermined slab reheating temperature (SRT) range for hot rolling. In the reheating step (S100), the slab obtained through the continuous casting process is reheated in a predetermined temperature range to re-employ the components segregated during casting. The slab reheating temperature (SRT) can be controlled within a preset temperature range to maximize austenite refinement and precipitation hardening effects.

In one embodiment, the slab reheat temperature (SRT) may be controlled between 1,200°C and 1,250°C. If the slab reheating temperature (SRT) is less than 1,200°C, there is a problem in that the components segregated during casting (e.g., Ti, Nb, Mo, etc.) are not sufficiently re-dissolved, making it difficult to significantly homogenize the alloy elements. On the other hand, the higher the slab reheating temperature (SRT), the more advantageous it is for homogenization, but if it exceeds 1,250°C, the austenite crystal grain size increases, which not only makes it difficult to secure strength, but also increases the manufacturing cost of the steel plate due to the excessive heating process. .

The hot rolling step (S200) is a step of manufacturing a steel sheet by hot rolling the slab reheated in the reheating step (S100) in a predetermined finishing delivery temperature (FDT) range.

In one embodiment, the finish rolling temperature (FDT) range may be controlled from 860°C to 950°C. If the finish rolling temperature (FDT) is less than 860℃, it is difficult to secure the workability of the steel sheet due to the occurrence of a mixed structure due to abnormal region rolling, and there is a problem of deterioration of workability due to microstructure unevenness and rapid phase change during hot rolling. In the meantime, problems with commutability may arise. Conversely, if the finish rolling temperature (FDT) exceeds 950°C, austenite grains and precipitates may become coarse, making it difficult to secure strength.

In one embodiment, the reduction rate during hot rolling may be controlled to satisfy 95% or more. Through this, the size, density, and area fraction of the region (perlite region) where pearlite with a relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated can be controlled to satisfy the above-mentioned conditions. .

Meanwhile, in the reheating step (S100) and the hot rolling step (S200), some of the fine precipitates may precipitate at grain boundaries where the energy is unstable. At this time, the fine precipitates precipitated at the grain boundaries act as a factor that hinders the grain growth of austenite, thereby providing the effect of improving strength through austenite refinement.

The cooling/winding step (S300) may include cooling the hot-rolled steel sheet in the hot rolling step (S200) and winding the cooled steel sheet.

The step of cooling the hot-rolled steel sheet may be a step of ROT (run out table) cooling the hot-rolled steel sheet for a preset cooling time up to a predetermined cooling end temperature range.

In one embodiment, the cooling end temperature range is from the martensite transformation start temperature (Ms) to the pearlite transformation start temperature (Ps) + 40°C, and the preset time may be 30 seconds or less. The cooling end temperature range and cooling time in the step of cooling this hot-rolled steel sheet are determined by the region (pearlite region) where pearlite with relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated. Affects size, density and area fraction. Specifically, when the cooling end temperature range and the cooling time are satisfied, the size, density, and area fraction of the pearlite region can be controlled to satisfy the above-mentioned conditions, and a uniform hot rolled structure of the ferrite matrix can be formed. there is. On the other hand, when cooling is terminated in a temperature range exceeding the cooling end temperature range or exceeding the cooling time, the size, density, and/or area fraction of the pearlite region do not satisfy the above-mentioned conditions, resulting in strength and bending characteristics. etc. may deteriorate.

The step of winding the cooled steel sheet may be a step of winding the cooled steel sheet within a predetermined coiling temperature (CT) range.

In one embodiment, the coiling temperature (CT) may be controlled between 580°C and 680°C. The coiling temperature (CT) affects the size, density, and area fraction of a region (perlite region) where pearlite with a relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated. Specifically, when the coiling temperature (CT) satisfies 580°C to 680°C, the size, density, and area fraction of the pearlite region can be controlled to satisfy the above-mentioned conditions. On the other hand, when the coiling temperature (CT) is less than 580°C, the low-temperature phase fraction increases due to overcooling, which raises the risk of increased strength and increased rolling load during cold rolling, and a sharp decrease in ductility. Conversely, if the coiling temperature exceeds 680°C, the size, density, and/or area fraction of the pearlite region may not satisfy the above-mentioned conditions, and strength and bending characteristics may be reduced, and abnormal crystal grain growth or excessive crystals may occur. There is a problem that formability and strength deteriorate due to grain growth.

The cold rolling step (S400) is a step in which the steel sheet wound in the cooling/coiling step (S300) is uncoiled, pickled, and then cold rolled. At this time, pickling is performed for the purpose of removing scale from the wound steel sheet, that is, the hot rolled coil manufactured through the above hot rolling process.

In one embodiment, the reduction rate during cold rolling may be controlled to 30% to 70%. Through this, the size, density, and area fraction of the region (perlite region) where pearlite with a relatively high carbon (C) content and/or manganese (Mn) content is locally accumulated can be controlled to satisfy the above-mentioned conditions. . For example, if the reduction ratio is less than 30%, the gap between pearlites may narrow and the area where pearlite is locally concentrated may increase, which may result in a decrease in strength and bending characteristics.

The annealing heat treatment step (S500) is a step of annealing the steel sheet cold-rolled in the cold rolling step (S400) at a temperature of 700°C or higher. In one embodiment, the annealing heat treatment step (S500) may be a step of annealing the cold rolled steel sheet at a temperature range of 760°C to 850°C. Meanwhile, annealing heat treatment may include heating a cold-rolled sheet and cooling the heated cold-rolled sheet at a predetermined cooling rate.

The plating step (S600) is a step of forming a plating layer on the annealed heat-treated steel sheet. In one embodiment, the plating step (S600) may include forming an Al-Si plating layer on the steel sheet annealed in the annealing heat treatment step (S500).

Specifically, the plating step (S600) involves immersing the steel sheet in a plating bath having a temperature of 610°C to 710°C to form a hot-dip galvanizing layer on the surface of the steel sheet, and cooling the steel sheet on which the hot-dip galvanizing layer is formed to form a plating layer. May include steps. At this time, the plating bath may include Si, Fe, Al, Mn, Cr, Mg, Ti, Zn, Sb, Sn, Cu, Ni, Co, In and/or Bi as additional elements, but is not limited thereto. For example, the plating bath may contain 5-12% Si, 1-4% Fe, and other Al. Additionally, the plating amount for the front and back sides can be controlled to satisfy 30 to 200 g/m ² .

In this way, by performing a hot stamping process on the steel sheet for hot stamping manufactured through steps S100 to S600, the molded part after hot stamping satisfies the required mechanical properties (e.g., tensile strength, yield strength, bending characteristics, elongation, etc.) can be manufactured.

The hot stamping process may include the steps of heating a blank manufactured using a hot stamping steel plate, hot stamping the blank to form a molded body, and cooling the molded body to form a hot stamping part. In one embodiment, the step of heating the blank may include heating the blank to a temperature of Ac3 or higher. In addition, the step of cooling the molded body to form a hot stamping part may include cooling the molded body to 300°C or less at an average cooling rate of 25°C/s or more. However, process conditions such as temperature range and cooling rate applied to the hot stamping process are not limited to the above-mentioned examples and may be modified in various ways.

In one embodiment, a steel sheet for hot stamping manufactured to satisfy the content conditions and process conditions described above may satisfy the conditions for the composition of the microstructure described above (e.g., size, density, area fraction, etc. of the pearlite region). . Accordingly, the tensile strength of the molded part after hot stamping can satisfy 1,700 MPa or more, and preferably 1,760 MPa or more and 1,950 MPa or less. In addition, the yield strength of the molded part after hot stamping may satisfy 1,150 MPa or more, and preferably 1,200 MPa or more and 1,350 MPa or less. In addition, molded parts after hot stamping may satisfy a bending angle of 50 degrees or more and have an elongation of 5% or more.

Figure 4 is an image schematically showing some of the grains of the microstructure of a molded part after hot stamping according to an embodiment of the present invention. Specifically, Figure 4 is an image showing a portion of a molded part after performing a hot stamping process on a steel sheet for hot stamping manufactured to satisfy the content conditions and process conditions described above.

Molded parts after hot stamping may contain martensite, bainite, ferrite and/or austenite. The ratio of microstructure and the average grain size of the microstructure of the molded part after hot stamping can be controlled to satisfy preset conditions. Through this, it is possible to control the mechanical properties such as tensile strength, yield strength, bending properties, and elongation of molded parts after hot stamping. For example, the tensile strength of the molded part after hot stamping may satisfy 1,700 MPa or more, and preferably 1,760 MPa or more and 1,950 MPa or less. In addition, the yield strength of the molded part after hot stamping may satisfy 1,150 MPa or more, and preferably 1,200 MPa or more and 1,350 MPa or less. In addition, molded parts after hot stamping may satisfy a bending angle of 50 degrees or more and have an elongation of 5% or more.

In one embodiment, the microstructure of the molded part after hot stamping may include more than 70% martensite, less than 30% bainite and ferrite, and less than 5% residual carbide and retained austenite.

In one embodiment, the microstructure included in the molded part after hot stamping may be refined. Specifically, the average grain size of the microstructure included in the molded part after hot stamping can be controlled to satisfy 2㎛ or more and 15㎛ or less.

Below, the present invention will be described in more detail through examples and comparative examples. However, the following examples and comparative examples are intended to illustrate the present invention in more detail, and the scope of the present invention is not limited by the following examples and comparative examples. The following examples and comparative examples can be appropriately modified and changed by those skilled in the art within the scope of the present invention.

C Si Mn P S Cr B Ca 0.25(Ti+Nb+V+0.25Mo) 0.26~
0.40 0.02~
2.00
0.30~
1.60
0.03
below 0.008
below 0.05~
0.90
0.0005~0.01 0.00001~
0.0060 0.015 ~0.060

Psalter pearlite area
average length
(μm) pearlite area
average thickness
(μm) pearlite area
average interval
(μm) pearlite area
Area fraction
(%) Ratio (a/b) of the long side (a) and short side (b) of the pearlite region within one crystal grain. After H/S
molded parts
tensile strength
(MPa) After H/S
molded parts
bending angle
(˚) A 0.03 0.01 0.03 0.03 1.2 1789 54 B 8.03 3.09 1.13 2.16 1.3 1776 54 C 28.35 4.65 3.21 3.51 1.4 1785 53 D 78.83 6.89 3.86 4.76 1.5 1799 53 E 123.47 7.05 4.11 8.56 1.6 1786 53 F 166.65 8.34 5.22 10.55 1.6 1801 52 G 211.1 14.59 6.23 12.11 1.7 1795 52 H 252.2 18.77 7.43 13.89 1.8 1792 51 I 297.0 25.99 8.87 14.96 1.9 1798 50 J 318.19 30.22 14.32 15.13 2.3 1795 48 K 372.02 32.45 15.33 16.99 2.8 1794 46 L 435.44 34.77 16.21 18.86 3.98 1786 44 M 558.03 37.33 17.22 20.11 4.86 1802 44 N 605.01 38.43 17.33 23.45 5.26 1800 43 O 605.01 38.43 17.65 23.45 6.26 1800 43

Table 1 shows the composition of the slab used for manufacturing the steel sheet for hot stamping, and Table 2 shows the specimens corresponding to the steel sheet for hot stamping manufactured by performing the steps S100 to S600 described above for the slab having the same composition as Table 1. Indicates measured values. For reference, the measured values are based on a unit area of 160mm ² or more according to ASTM standards.

In addition, the bending angle is a V-bending angle measured according to the standards of the German Automobile Industry Association (VDA: Verband Der Automobilindustrie), and means the value of the rolling direction (RD).

Meanwhile, the “perlite region” refers to an area where pearlite containing 0.27 to 0.70 wt% of carbon (C) and 1.0 to 5.0 wt% of manganese (Mn) is locally accumulated.

Among the specimens in Table 2, specimens A to I correspond to examples, and specimens J to O correspond to comparative examples, respectively.

Specimens J to O of the comparative examples were manufactured by applying the same content conditions (see Table 1) and the above-described process conditions as those of the examples, but specimens J to L were manufactured by differentially applying only the coiling temperature (CT) as a variable, Specimens M to O are specimens manufactured by differentially applying only the annealing temperature as a variable. Specifically, specimens A to I, which are examples, are specimens to which a coiling temperature (CT) and annealing temperature of 580 to 680°C (Ps ±100°C) are applied, and specimens J to N, which are comparative examples, are specimens to which a coiling temperature (CT) and annealing temperature of 700°C or higher are applied. These are specimens to which annealing temperature was applied.

Referring to Table 2, specimens A to I have an average length of the pearlite region of 0.001 ㎛ or more and 500 ㎛ or less, an average thickness of the pearlite region of 0.01 ㎛ or more and 30 ㎛ or less, and an average spacing of the ends of the pearlite region. It satisfies 0.01㎛ or more and 10㎛ or less, the area fraction of the pearlite region satisfies 0.1% or more and 15% or less, and the ratio of the long side (a) and short side (b) of the pearlite region portion present in one crystal grain ( It can be confirmed that a/b) satisfies 2 or less. As a result, it can be confirmed that the specimens A to I satisfy the tensile strength of the molded part after hot stamping of 1,700 MPa or more and the bending angle of 50 degrees or more. This can be understood as the size, shape, and area fraction of the pearlite region being controlled within a preset range by applying a coiling temperature (CT) and annealing temperature of 580 to 680°C.

On the other hand, specimens J to N are specimens that do not satisfy at least some of the microstructure conditions of hot stamping steel sheets, and it can be seen that the bending angle of the molded part after hot stamping is smaller compared to specimens A to I. there is. It can be understood that by applying a coiling temperature (CT) above 680°C, the size, density, and area fraction of the pearlite region were not controlled within the preset range.

In the case of specimen J, the average thickness of the pearlite region is 30.22 ㎛, which exceeds 30 ㎛, the average spacing of the pearlite region is 14.32 ㎛, which exceeds 10 ㎛, and the area fraction of the pearlite region is 15.13%, which exceeds 15%, The ratio (a/b) of the long side (a) and short side (b) of the pearlite region existing within one crystal grain is 2.3, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen J is only 48°.

For specimen K, the average thickness of the pearlite region is 32.45 ㎛, which exceeds 30 ㎛, the average spacing of the pearlite region is 15.33 ㎛, which exceeds 10 ㎛, and the area fraction of the pearlite region is 16.99%, which exceeds 15%, The ratio (a/b) of the long side (a) and short side (b) of the pearlite region existing within one crystal grain is 2.8, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen K is only 47°.

In the case of specimen L, the average thickness of the pearlite region is 34.77 ㎛, which exceeds 30 ㎛, the average spacing of the pearlite region is 16.21 ㎛, which exceeds 10 ㎛, and the area fraction of the pearlite region is 18.86%, which exceeds 15%, The ratio (a/b) of the long side (a) and short side (b) of the pearlite region existing in one crystal grain is 3.99, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen L is only 44°.

For specimen M, the average length of the pearlite region is 558.03 ㎛, which exceeds 500 ㎛, the average thickness of the pearlite region is 37.33 ㎛, which exceeds 30 ㎛, and the average spacing of the pearlite region is 17.22 ㎛, which exceeds 10 ㎛, The area fraction of the pearlite region is 20.11%, which exceeds 15%, and the ratio (a/b) between the long side (a) and short side (b) of the pearlite region portion present in one crystal grain is 4.86, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen L is only 44°.

For specimen N, the average length of the pearlite region is 605.01 ㎛, which exceeds 500 ㎛, the average thickness of the pearlite region is 38.43 ㎛, which exceeds 30 ㎛, and the average spacing of the pearlite region is 17.33 ㎛, which exceeds 10 ㎛, The area fraction of the pearlite region is 23.45%, which is more than 15%, and the ratio (a/b) between the long side (a) and short side (b) of the pearlite region portion present in one crystal grain is 5.26, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen L is only 43°.

For specimen O, the average length of the pearlite region is 605.01 ㎛, which exceeds 500 ㎛, the average thickness of the pearlite region is 38.43 ㎛, which exceeds 30 ㎛, and the average spacing of the pearlite region is 17.65 ㎛, which exceeds 10 ㎛, The area fraction of the pearlite region is 23.45%, which is more than 15%, and the ratio (a/b) of the long side (a) and short side (b) of the pearlite region portion present in one crystal grain is 6.26, which is 2 or more. Accordingly, it can be confirmed that the bending angle of specimen L is only 43°.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the attached patent claims.

Claims (19)

Carbon (C): 0.26~0.40wt%, Silicon (Si): 0.02~2.0wt%, Manganese (Mn): 0.3~1.60wt%, Phosphorus (P): 0.03wt% or less, Sulfur (S): 0.008wt % or less, chromium (Cr): 0.05~0.90wt%, boron (B): 0.0005~0.01wt%, molybdenum (Mo): 0.05~0.2wt%, titanium (Ti): 0.001~0.095wt%, niobium (Nb) ): 0.001 to 0.095 wt%, vanadium (V): 0.001 to 0.095 wt%, and the remaining iron (Fe) and other inevitable impurities in the steel sheet for hot stamping,
The steel sheet for hot stamping contains ferrite: 60 to 99% and pearlite: 1 to 20% in area fraction, and includes a pearlite region in which pearlite is locally integrated at least in part, and the pearlite region contains carbon (C): Steel sheet for hot stamping, containing 0.27~0.70wt% and manganese (Mn): 1.0~5.0wt%. According to paragraph 1,
A steel sheet for hot stamping, wherein the average length of the pearlite region is 0.01 ㎛ or more and 500 ㎛ or less. According to paragraph 1,
A steel sheet for hot stamping wherein the average thickness of the pearlite region is 0.01 ㎛ or more and 30 ㎛ or less. According to paragraph 1,
A steel sheet for hot stamping, wherein the average spacing between the pearlite regions is 0.01 ㎛ or more and 10 ㎛ or less. According to paragraph 1,
A steel sheet for hot stamping, wherein the area fraction of the pearlite region is 0.1% or more and 15% or less. According to paragraph 1,
The steel sheet for hot stamping includes a plurality of crystal grains including at least a portion of the pearlite region, and the ratio of the long side (a) and the short side (b) of the pearlite region portion present in one crystal grain among the plurality of crystal grains ( a/b) is 2 or less, steel sheet for hot stamping. According to paragraph 1,
A steel sheet for hot stamping wherein the pearlite region contains 50% or more of pearlite and 5% or less of ferrite by area fraction. According to paragraph 1,
Some components of the steel sheet for hot stamping satisfy the following equation 1.
[Equation 1]
0.015≤0.25(Ti+Nb+V+0.25(Mo))≤0.060 (Unit: wt%) According to paragraph 1,
A steel sheet for hot stamping, wherein the molded part after hot stamping the hot stamping steel sheet has a tensile strength of 1,700 MPa or more and satisfies a bending angle of 50 degrees or more. Carbon (C): 0.26~0.40wt%, Silicon (Si): 0.02~2.0wt%, Manganese (Mn): 0.3~1.60wt%, Phosphorus (P): 0.03wt% or less, Sulfur (S): 0.008wt % or less, chromium (Cr): 0.05~0.90wt%, boron (B): 0.0005~0.01wt%, molybdenum (Mo): 0.05~0.2wt%, titanium (Ti): 0.001~0.095wt%, niobium (Nb) ): 0.001 to 0.095 wt%, vanadium (V): 0.001 to 0.095 wt%, and the remaining iron (Fe) and other unavoidable impurities, reheating the slab at a temperature of 1,200 to 1,250°C;
Manufacturing a steel sheet by hot rolling the reheated slab at a temperature of 800 to 1000°C with a reduction ratio of 95% or more; and
Winding the steel sheet at a temperature of 580 to 680°C;
Including,
The steel sheet for hot stamping contains ferrite: 60 to 99% and pearlite: 1 to 30% in area fraction, and includes a pearlite region in which pearlite is locally integrated at least in part, and the pearlite region contains carbon (C): Method for manufacturing a steel sheet for hot stamping, comprising 0.27 to 0.70 wt% and manganese (Mn): 1.0 to 5.0 wt%. According to clause 10,
Cooling the steel sheet to a temperature ranging from the martensite transformation start temperature (Ms) to the pearlite transformation start temperature (Ps) + 40°C for less than 30 seconds,
The winding step is a method of manufacturing a steel sheet for hot stamping, which is a step of winding a cooled steel sheet. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the average length of the pearlite region is 0.01 ㎛ or more and 500 ㎛ or less. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the average thickness of the pearlite region is 0.01 ㎛ or more and 30 ㎛ or less. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the average spacing between the pearlite regions is 0.01 ㎛ or more and 10 ㎛ or less. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the area fraction of the pearlite region is 0.1% or more and 15% or less. According to clause 10,
The steel sheet for hot stamping includes a plurality of crystal grains including at least a portion of the pearlite region, and the ratio of the long side (a) and the short side (b) of the pearlite region portion present in one crystal grain among the plurality of crystal grains ( a/b) is 2 or less, a method of manufacturing a steel sheet for hot stamping. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the pearlite region contains 50% or more of pearlite and 5% or less of ferrite in area fraction. According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein some components of the steel sheet for hot stamping satisfy the following equation 1.
[Equation 1]
0.015≤0.25(Ti+Nb+V+0.25(Mo))≤0.060 (Unit: wt%) According to clause 10,
A method of manufacturing a steel sheet for hot stamping, wherein the molded part after hot stamping the hot stamping steel sheet has a tensile strength of 1,700 MPa or more and satisfies a bending angle of 50 degrees or more.