KR102608377B1 - Hot stamping component and method of manufacturing the same - Google Patents

Abstract

The present invention includes the steps of introducing a blank on which a plating layer is formed on at least one surface of a base material into a heating furnace having a plurality of sections having different temperature increase rate ranges; and a step of heating the blank, wherein the heating time of the blank in the step of heating the blank satisfies the following equation.
<Equation>

(At this time, in the equation, λ _n is the heating time (s), a _n is the heat loss correction coefficient by heating, T _n is the heating temperature (℃), b _n is the Ac3 temperature correction coefficient, t is the material thickness (mm), c _n is the high temperature material thickness sensitivity correction coefficient)

Description

Hot stamping component and method of manufacturing the same}

The present invention relates to hot stamping parts and methods for manufacturing the same.

As environmental and fuel efficiency regulations are strengthened worldwide, the need for lighter vehicle materials is increasing. Accordingly, research and development on ultra-high strength steel and hot stamping steel is being actively conducted.

The hot stamping process generally consists of heating/forming/cooling/trimming, and can take advantage of the phase transformation and microstructure of the material during the process. The heating process in the hot stamping process is a process in which the blank is heated in a heating furnace, and the cooling process in the hot stamping process is a process in which the hot stamped molded body is cooled in the mold. Additionally, the blank heated through the heating process may be exposed to room temperature and air-cooled while being introduced from the heating furnace into the mold.

As a related technology, there is Korean Patent Registration No. 10-2070579 (title of invention: hot stamping method).

No. 10-2070579

Embodiments of the present invention can improve the quality of manufactured hot stamping parts by controlling the heating time of the blank in consideration of various parameters such as blank material, blank thickness, and heating temperature.

One embodiment of the present invention includes the steps of introducing a blank on which a plating layer is formed on at least one surface of a base material into a heating furnace having a plurality of sections having different temperature increase rate ranges; and a step of heating the blank, wherein the heating time of the blank in the step of heating the blank satisfies the following equation.

<Equation>

(At this time, λ _n is the heating time (s), a _n is the heat loss correction coefficient by heating, T _n is the heating temperature (℃), b _n is the Ac3 temperature correction coefficient, t is the material thickness (mm), and c _n is the High temperature material thickness sensitivity correction coefficient)

In this embodiment, in the above equation, a _n is -0.60 or more and -0.55 or less, T _n is Ac3 or more and 1000°C or less, b _n is 700 or more and 900 or less, and t is 1 mm or more and 2.6 mm or less, c _n may be 0.7 or more and 0.9 or less.

In this embodiment, the heating time may be 100 s or more and 900 s or less.

In this embodiment, the step of heating the blank includes a multi-stage heating step of heating the blank in stages; and a crack heating step of heating the blank to a temperature of Ac3 to 1000°C.

In this embodiment, the plurality of sections include: a first heating section having a first average temperature increase rate change rate; After the first heating section, a second heating section having a second average temperature increase rate change rate that is different from the first average temperature increase rate change rate; And after the second heating section, a third heating section having a third average temperature increase rate change rate that is different from the first average temperature increase rate change rate and the second average temperature increase rate change rate, and the third average temperature increase rate change rate. may include a section that changes from a positive value to a negative value.

In this embodiment, between the first heating section and the second heating section, the final temperature increase rate defining the first average temperature increase rate change rate and the initial temperature increase rate defining the second average temperature increase rate change rate are different values. You can have

In this embodiment, the third heating section includes a 3-1 heating section having a 3-1 average temperature increase rate change rate and a 3-2 heating section having a 3-2 average temperature increase rate change rate, The 3-1 average temperature increase rate change rate has a positive value, the 3-2 average temperature increase rate change rate has a negative value, and the absolute value of the 3-1 average temperature increase rate change rate is the 3-2 average temperature increase rate change rate. It may be smaller than the absolute value of the temperature increase rate change rate.

In this embodiment, the first average temperature increase rate change rate and the second average temperature increase rate change rate each have a negative value, and the absolute value of the first average temperature increase rate change rate is the absolute value of the second average temperature increase rate change rate. It can be bigger than

In this embodiment, the plurality of sections are, after the third heating section, the first average temperature increase rate change rate, the second average temperature increase rate change rate, and the fourth average temperature increase rate change rate different from the third average temperature increase rate change rate. It further includes a fourth heating section having, wherein the absolute value of the fourth average temperature increase rate change rate is greater than the absolute value of each of the first average temperature increase rate change rate, the second average temperature increase rate change rate, and the third average temperature increase rate change rate. It can be small.

In this embodiment, the plating layer may be alloyed in the second heating section, and the base material may undergo a phase transformation in the third heating section.

In this embodiment, after heating the blank, transferring the heated blank from the heating furnace to the mold; Forming a molded body by pressing the transferred blank into the mold; and cooling the formed molded body.

In this embodiment, the air cooling time of the blank in the step of transferring the blank may be 5 s or more and 20 s or less.

In this embodiment, the step of cooling the molded body may be performed within the mold.

In this embodiment, the mold cooling time for cooling the molded body within the mold may be 6 s or more and 40 s or less.

In another embodiment of the present invention, a hot stamping part having a tensile strength of 1350 MPa or more and less than 2300 MPa is provided.

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 as described above, the quality of manufactured hot stamping parts can be improved by controlling the heating time in consideration of various parameters such as blank material, blank thickness, and heating temperature. Of course, the scope of the present invention is not limited by this effect.

1 is a flowchart schematically showing a method of manufacturing a hot stamping part according to an embodiment of the present invention.
Figure 2 is a flowchart specifically showing the heating step of the method for manufacturing hot stamping parts according to an embodiment of the present invention.
Figure 3 is a diagram illustrating a heating furnace having a plurality of sections in the heating step of the method for manufacturing hot stamping parts according to an embodiment of the present invention.
Figure 4 is a diagram showing the temperature increase rate change rate of a plurality of sections according to heating time in the method of manufacturing hot stamping parts according to an embodiment of the present invention.
Figure 5 is a cross-sectional view schematically showing a hot stamping part according to an embodiment of the present invention.
Figure 6 is a cross-sectional view schematically showing a hot stamping part according to a comparative example.
Figure 7 is a diagram showing heating time according to material thickness and heating time according to heating temperature.

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 following embodiments, when a part of a film, region, component, etc. is said to be on or on another part, it is not only the case where it is directly on top of the other part, but also when another film, region, component, etc. is interposed between them. Also includes cases where there are.

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 arbitrarily shown for convenience of explanation, so the present invention is not necessarily limited to what is shown.

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

In the following embodiments, the meaning of "extending in the first direction or the second direction" includes not only extending in a straight line, but also extending in a zigzag or curved line along the first or second direction. .

In the following embodiments, “on a plane” means when the target part is viewed from above, and “on a cross-section” means when a cross section of the target part is cut vertically and viewed from the side. In the following embodiments, when referring to “overlapping”, this includes “in-plane” and “in-cross-section” overlapping.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and when described with reference to the drawings, identical or corresponding components will be assigned the same reference numerals.

1 is a flowchart schematically showing a method of manufacturing a hot stamping part according to an embodiment of the present invention, and FIG. 2 is a detailed diagram showing the heating step of the method of manufacturing a hot stamping part according to an embodiment of the present invention. This is a flowchart. Hereinafter, a method of manufacturing hot stamping parts will be described with reference to FIGS. 1 and 2.

Referring to Figure 1, in one embodiment, the method of manufacturing a hot stamping part includes a blank input step (S100), a heating step (S200), a transfer step (S300), a forming step (S400), and a cooling step (S500). It can be included.

First, the blank input step (S100) may be a step of inputting a blank into a heating furnace having a plurality of sections with different temperature increase rate ranges. The blank may be provided with a plating layer formed on at least one side of the base material. The base material may be a steel sheet manufactured by performing a hot rolling process and/or a cold rolling process on a steel slab cast to contain a predetermined content of a predetermined alloy element.

In one embodiment, in the blank input step (S100), the blank input into the heating furnace may be mounted on a roller and then transported along the transport direction.

Referring to Figures 1 and 2, after the blank input step (S100), a heating step (S200) may be performed. In one embodiment, the heating step (S200) may include a multi-stage heating step (S210) and a crack heating step (S220). Therefore, after the blank input step (S100), the multi-stage heating step (S210) and the crack heating step (S220) may be performed. The multi-stage heating step (S210) and the crack heating step (S220) may be steps in which the blank is heated while passing through a plurality of sections provided in the heating furnace.

In one embodiment, the overall temperature of the furnace may be 680°C to 1000°C. Specifically, the overall temperature of the heating furnace where the multi-stage heating step (S210) and the crack heating step (S220) are performed may be 680°C to 1000°C. At this time, the temperature of the heating furnace where the multi-stage heating step (S210) is performed may be from 680°C to Ac3, and the temperature of the heating furnace where the crack heating step (S220) is performed may be from Ac3 to 1000°C.

Specifically, in the multi-stage heating step (S210), the temperature of the blank may be increased step by step as it passes through a plurality of sections provided in the heating furnace. Among the plurality of sections provided in the heating furnace, there may be a plurality of sections in which the multi-stage heating step (S210) is performed, and each section may be raised in the direction from the entrance of the heating furnace where the blank is input to the exit of the heating furnace from which the blank is taken out. The temperature is set so that the blank can be heated in stages.

A crack heating step (S220) may be performed after the multi-stage heating step (S210). In the crack heating step (S220), the multi-stage heated blank may be heat treated while passing through a section of the heating furnace set to a temperature of Ac3 to 1000°C. Preferably, in the crack heating step (S220), the multi-stage heated blank may be crack heated at a temperature of 830°C to 1000°C. Additionally, among a plurality of sections provided in the heating furnace, there may be at least one section where the crack heating step (S220) is performed.

FIG. 3 is a diagram illustrating a heating furnace having a plurality of sections in the heating step of a method of manufacturing a hot stamping part according to an embodiment.

Referring to FIG. 3, the heating furnace according to one embodiment may include a plurality of sections (P1, P2, P3, and P4) having different temperature ranges. More specifically, the heating furnace has a first heating section (P1) having a first temperature range (T1), a second heating section (P2) having a second temperature range (T2), and a third temperature range (T3). It may be provided with a third heating section (P3) and a fourth heating section (P4) having a fourth temperature range (T4). At this time, the third heating section P3 may include two sections having different temperature ranges. The third heating section (P3) is a 3-1 heating section (P3-1) having a 3-1 temperature range (T3-1) and a 3-2 having a 3-2 temperature range (T3-2). It may include a heating section (P3-2).

In one embodiment, the second heating section P2 may include a plurality of sections having different temperature ranges. For example, the second heating section (P2) is a 2-1 heating section (P2-1) having a 2-1 temperature range (T2-1) and a second heating section (P2-1) having a 2-2 temperature range (T2-2). -2 may include a heating section (P2-2). However, the present invention is not limited to this. The second heating section (P2) is a 2-1 heating section (P2-1) having a 2-1 temperature range (T2-1) to a 2-n having a 2-n temperature range (T2-n). It may include a heating section (P2-n). At this time, n may be a natural number of 2 or more.

In one embodiment, the first heating section P1 may also include a plurality of sections having different temperature ranges. For example, the first heating section (P1) is a 1-1 heating section (P1-1) having a 1-1 temperature range (T1-1) and a 1-1 heating section (P1-1) having a 1-2 temperature range (T1-2). -2 It may include a heating section (P1-2). However, the present invention is not limited to this. The first heating section (P1) is a 1-1 heating section (P1-1) having a 1-1 temperature range (T1-1) to a 1-n heating section (P1-1) having a 1-n temperature range (T1-n). It may include a heating section (P1-n). At this time, n may be a natural number of 2 or more.

In one embodiment, referring to FIGS. 2 and 3, in the multi-stage heating step (S210), the blank is heated in the first heating section (P1), the second heating section (P2), and the 3-1 heating defined in the heating furnace. It may be heated in stages (or multi-stage heated) while passing through the section (P3-1). Additionally, in the crack heating step (S220), the multi-stage heated blank may be crack heated while passing through the 3-2 heating section (P3-2) and the fourth heating section (P4). That is, the first heating section (P1), the second heating section (P2), and the 3-1 heating section (P3-1) correspond to sections in which the blank is heated in multiple stages, and the 3-2 heating section (P3- 2) and the fourth heating section (P4) correspond to a section in which the blank is cracked and heated.

In one embodiment, the fourth heating section P4 may include a plurality of sections. For example, the fourth heating section P4 may be provided as a plurality of sections, such as two sections or three sections. At this time, the temperature range (or temperature) of the plurality of sections provided in the fourth heating section P4 may be the same.

The first heating section (P1) to the fourth heating section (P4) may be sequentially disposed in the heating furnace. The first heating section P1 may be adjacent to the entrance of the heating furnace into which the blank is input, and the fourth heating section P4 may be adjacent to the outlet of the heating furnace into which the blank is discharged. Therefore, the first heating section (P1) having the first temperature range (T1) may be the first section of the heating furnace, and the fourth heating section (P4) having the fourth temperature range (T4) may be the last section of the heating furnace. It may be a section. As will be described later, among the plurality of sections of the heating furnace, the 3-2 heating section (P3-2) and the fourth heating section (P4) may be a section in which crack heating is performed rather than a section in which multi-stage heating is performed. .

The temperature of a plurality of sections provided in the heating furnace, for example, the temperature of the first heating section (P1) to the fourth heating section (P4), increases in the direction from the entrance of the heating furnace where the blank is input to the outlet of the heating furnace where the blank is taken out. can do. Additionally, the temperature difference between two adjacent sections among the plurality of sections provided in the heating furnace may be greater than 0°C and less than or equal to 100°C. For example, the temperature difference between the first heating section (P1) and the second heating section (P2) may be greater than 0°C and less than or equal to 100°C.

In one embodiment, the first temperature range T1 of the first heating section P1 may be 680°C to 870°C. The second temperature range (T2) of the second heating section (P2) may be 700°C to 930°C. The 3-1 temperature range (T3-1) of the 3-1 section (P3-1) may be 800°C to 950°C. The 3-2 temperature range (T3-2) of the 3-2 section (P3-2) may be AC3 to 1000°C. The fourth temperature range (T4) of the fourth heating section (P4) may be Ac3 to 1,000°C. Preferably, the fourth temperature range (T4) of the fourth heating section (P4) may be 830°C or more and 1,000°C or less. The 3-2 temperature range (T3-2) of the 3-2 heating section (P3-2) and the fourth temperature range (T4) of the fourth heating section (P4) may be the same.

In one embodiment, when the second heating section (P2) includes the 2-1 heating section (P2-1) and the 2-2 heating section (P2-2) having different temperature ranges described above, The 2-1 temperature range (T2-1) may be 700°C to 900°C, and the 2-2 temperature range (T2-2) of the 2-2 heating section (P2-2) may be 750°C to 930°C. You can.

Boundary values defining the plurality of sections described above will be described. The boundary values represent the heating time (s) as the horizontal axis of the graph. First, the first boundary value e1 located between the first heating section P1 and the second heating section P2 may be about 30 s to about 50 s, or about 40 s. The second boundary value e2 located between the second heating section P2 and the third heating section P3 may be about 80 s to about 130 s, and may be about 85 s. The third boundary value (e3) located between the 3-1st heating section (P3-1) and the 3-2nd heating section (P3-2) may be about 110s to about 180s, and may be about 120s. . The fourth boundary value e4 located between the 3-2 heating section P3-2 and the fourth heating section P4 may be about 140 s to about 230 s, and may be about 150 s.

In one embodiment, when the second heating section (P2) includes the 2-1 heating section (P2-1) and the 2-2 heating section (P2-2) having different temperature ranges described above, The 2-1 boundary value (e2') located between the 2-1 heating section (P2-1) and the 2-2 heating section (P2-2) may be about 50 s to about 110 s, and may be about 60 s. You can.

In Figure 3, the heating furnace according to an embodiment of the present invention is shown as typically having five sections (P1, P2, P3-1, P3-2, P4) having different temperature ranges, but the present invention This is not limited to this. There may be six, seven, or eight sections within the furnace having different temperature ranges.

In one embodiment, the furnace may have a length of 20 m to 40 m along the transport path of the blank. The heating furnace may be provided with a plurality of sections having different temperature ranges, and the ratio of the length of the section in which the blank is heated in multiple stages among the plurality of sections and the length of the section in which the blank is crack-heated among the plurality of sections is 1:1 to 4. :1 can be satisfied. When the length of the section where the blank is crack-heated increases within the heating furnace and the ratio of the length of the section where the blank is multi-stage heated and the length of the section where the blank is crack-heated exceeds 1:1, the amount of hydrogen infiltration into the blank from the crack-heated section As this increases, delayed rupture may increase. On the other hand, if the length of the section where the blank is crack-heated is reduced and the ratio of the length of the section where the blank is multi-stage heated to the length of the section where the blank is crack-heated is less than 4:1, the crack heating section (time) is not sufficiently secured. The strength of hot stamping parts manufactured by the hot stamping part manufacturing process may be uneven.

In one embodiment, the length of the uniform heating section among the plurality of sections provided in the heating furnace may be 20% to 50% of the total length of the heating furnace.

Figure 4 is a diagram showing the temperature increase rate change rate of a plurality of sections according to heating time in the method of manufacturing hot stamping parts according to an embodiment of the present invention. At this time, Figure 4 shows a graph of the temperature increase rate (°C/s) of the blank according to the heating time (s). The plurality of sections and boundary values shown in FIG. 4 are the same as those described above in FIG. 3 and the description may be simplified or omitted.

Referring to FIG. 4, the distribution of the temperature increase rate (°C/s) or temperature increase rate change rate (°C/s ² ) in a plurality of sections where multi-stage heating of the blank is performed is as described later. Hereinafter, the “temperature increase rate change rate” refers to the average slope of each section of the graph shown in FIG. 4, and can hereinafter be explained as the “average temperature increase rate change rate.” Figure 4 shows a first temperature increase rate control curve 410 according to an embodiment of the present invention and a second temperature increase rate control curve 420 according to a comparative example.

First, the temperature increase rate first control curve 410 according to an embodiment of the present invention will be described.

The first heating section (P1) may have a first average temperature increase rate change rate (r1). The second heating section (P2) located after the first heating section (P1) may have a second average temperature increase rate change rate (r2) that is different from the first average temperature increase rate change rate (r1). The third heating section (P3) located after the second heating section (P2) has a third average temperature increase rate change rate (r3) that is different from the first average temperature increase rate change rate (r1) and the second average temperature increase rate change rate (r2). You can have it. At this time, the third average temperature increase rate change rate (r3) may include a section that changes from a positive value to a negative value. The fourth heating section (P4) located after the third heating section (P3) includes the first average temperature increase rate change rate (r1), the second average temperature increase rate change rate (r2), and the third average temperature increase rate change rate (r3) It may have a different fourth average temperature increase rate change rate (r4).

The first heating section (P1) may be a general temperature increase section, and in the second heating section (P2), the temperature increase rate decreases gently compared to the first heating section (P1) ( ) Alloying of the plating layer can be performed. The third heating section (P3) is a phase transformation section in which the base material of the blank undergoes a phase transformation. The 3-1 heating section (P3-1) has a positive temperature increase rate change rate, and the 3-2 heating section (P3-1) has a positive temperature increase rate change rate. 2) may have a negative (-) temperature increase rate change rate. The fourth heating section P4 may be a stabilization section in which the blank is cracked and heated to a uniform temperature.

Referring to the first control curve 410, the first average temperature increase rate change rate (r1) and the second average temperature increase rate change rate (r2) each have negative values, and the absolute value of the first average temperature increase rate change rate (r1) may be greater than the absolute value of the second average temperature increase rate change rate (r2) ( ). In one embodiment, the first average temperature increase rate change rate (r1) may be about -0.5 °C/s ² or more and 0 or less. For example, the first average temperature increase rate change rate (r1) may be about -0.3 °C/s ² . In one embodiment, the second average temperature increase rate change rate (r2) may be about -0.25 °C/s ² or more and 0 or less. For example, the second average temperature increase rate change rate (r2) may be about -0.07°C/ ^s2 .

In one embodiment, between the first heating section (P1) and the second heating section (P2), that is, the second average temperature increasing rate change rate ( The change to r2) may be discontinuous. Specifically, the temperature increase rate (v1) at the first boundary value (e1) defining the first average temperature increase rate change rate (r1) in the first heating section (P1), and the second average temperature increase rate in the second heating section (P2) The temperature increase rate (v2) at the first boundary value (e1) defining the temperature increase rate change rate (r2) may have a different value. In other words, the final temperature increase rate (v1) of the first average temperature increase rate change rate (r1) and the initial temperature increase rate (v2) of the second average temperature increase rate change rate (r2) may be different values. When the temperature increase rate change rate changes discontinuously (r1 → r2) (410) around the first boundary value (e1), the weldability of hot stamping parts can be improved compared to the case where it changes continuously (420).

Because a lot of energy is required to change the plating layer, the average temperature increase rate change rate may change discontinuously between the first heating section (P1) and the second heating section (P2). In order for Fe from the base material to diffuse into the Al plating layer and for the Al-Fe phase to initially be created and grow within the plating layer, the necessary energy must be supplied. In addition, Fe diffused into the base material creates an Al-Fe-Si alloy layer over time. The more discontinuous the change in temperature increase rate around the first boundary value (e1) is, the more uniform the diffusion to the surface becomes. Therefore, good weldability can be obtained. On the other hand, when the change is continuous, diffusion of Al-Fe-Si occurs quickly and unevenly to the surface, so phases with high welding resistance exist on the surface, which may result in poor weldability.

In one embodiment, the third heating section (P3) includes a 3-1 heating section (P3-1) having a 3-1 temperature increase rate change rate (r3-1) and a 3-2 temperature increase rate change rate (r3-2). ) may include a 3-2 heating section (P3-2). The 3-1 average temperature increase rate change rate (r3-1) has a positive value, the 3-2 average temperature increase rate change rate (r3-2) has a negative value, and the 3rd average temperature increase rate change rate (r3) is It can have sections that change from positive to negative values. At this time, the absolute value of the 3-1 average temperature increase rate change rate (r3-1) may be smaller than the absolute value of the 3-2 average temperature increase rate change rate (r3-2) ( ). In one embodiment, the 3-1 average temperature increase rate change rate (r3-1) may be 0 or more and about 0.25° C./s ^{2 or} less. For example, the 3-1 average temperature increase rate change rate (r3-1) may be about 0.07°C/s ² . In one embodiment, the 3-2 average temperature increase rate change rate (r3-2) may be about -0.3°C/s ² or more and 0 or less. For example, the 3-2 average temperature increase rate change rate (r3-2) may be about -0.08°C/s ² .

The smaller the third average temperature increase rate change rate (r3-1) in the 3-1 heating section (P3-1), the gentler the slope of the first control curve 410 may be, and the slope of the first control curve 410 may be more gradual. As the is gentler, the amount of mixed hydrogen decreases, and hydrogen embrittlement can be improved accordingly. In contrast, the second control curve 420 has a form in which the temperature increase rate change rate increases rapidly or increases discontinuously in the 3-1 heating section (P3-1). In this case, the amount of mixed hydrogen increases and thus the hydrogen Brittleness can become inferior. As such, in the third heating section (P3), unlike between the first heating section (P1) and the second heating section (P2), in the section where the phase transformation of the base material is performed, if there is a sudden temperature change, hydrogen embrittlement, Since there may be problems such as delayed rupture, the lower the rate of change in temperature increase, the more advantageous it is.

Between the second heating section (P2) and the 3-1 heating section (P3-1), that is, the 3-1 average temperature increase rate change rate from the second average temperature increase rate change rate (r2) near the second boundary value (e2) A change to (r3-1) can change from a negative value to a positive value. In other words, as the temperature increase rate decreases and then increases, phase transformation of the base material may occur. For example, during the phase transformation of the base material, an endothermic reaction occurs when transformation into austenite occurs in this section, and energy supply is required for this, so the temperature increase rate must be increased again in the 3-1 heating section (P3-1) to achieve a reasonable level of conversion to austenite. Phase transformation can be induced.

Between the 3-1st heating section (P3-1) and the 3-2nd heating section (P3-2), that is, from the 3-1 average temperature increase rate change rate (r3-1) around the third boundary value (e3) The change in the 3-2 average temperature increase rate change rate (r3-2) may change from a positive value to a negative value. In other words, as the temperature increase rate increases and then decreases again, phase transformation of the base material may occur.

In one embodiment, the absolute value of the fourth average temperature increase rate change rate (r4) is the absolute value of each of the first average temperature increase rate change rate (r1), the second average temperature increase rate change rate (r2), and the third average temperature increase rate change rate (r3). It may be smaller than the value. For example, the fourth average temperature increase rate change rate (r4) is close to 0, and the fourth heating section (P4) may be a section in which crack heating is performed at a uniform temperature.

The time t4 for which the blank is heated in the third-second heating section P3-2 and the fourth heating section P4 may be about 50% or less of the total heating time t. This is compared to the time (t1) in which the blank is multistage heated in the first heating section (P1), the second heating section (P2), and the 3-1 heating section (P3-1) in the 3-2 heating section (P3-2). ) and the longer the crack heating time (t4) in the fourth heating section (P4), the longer the part characteristics such as weldability, hydrogen embrittlement, and bending performance may become inferior.

Hereinafter, the characteristics of the second control curve 420 compared to the above-described first control curve 410 will be described, focusing on differences from the first control curve 410. Referring to the second control curve 420, the first' average temperature increase rate change rate (r1') may change continuously between the first heating section (P1) and the second heating section (P2). Specifically, the temperature increase rate at the first boundary value (e1) defining the first' average temperature increase rate change rate (r1') in the first heating section (P1), and the first' average temperature increase rate in the second heating section (P2) The temperature increase rate (v1') at the first boundary value (e1) defining the temperature increase rate change rate (r1') may have the same value.

In one embodiment, the first' average temperature increase rate change rate (r1') may be about -0.26 °C/s ² or more and 0 or less. For example, the first' average temperature increase rate change rate (r1') may be about -0.2 °C/s ² .

The change characteristics of the temperature increase rate change rate (r3';r3-1',r3-2') in the third heating section (P3) of the second control curve 420 are the same as those described in the first control curve 410. You can have However, the 3-1' temperature increase rate change rate (r3-1') may have a discontinuous or unstable value compared to the 3-1 average temperature increase rate change rate (r3-1) of the first control curve 410. At this time, the 3-1' temperature increase rate change rate (r3-1') may mean the change rate at the front end where the temperature increase rate shows an increasing trend during the 3-1 heating section (P3-1). The 3-1' temperature increase rate change rate (r3-1') may be about 0.04 ℃/s ² or more and about 0.16 ℃/s ² or less. For example, the 3-1' temperature increase rate change rate (r3-1') may be about 0.1°C/s ² . The 3-2' temperature increase rate change rate (r3-2') may be about -0.16 ℃/s ² or more and about -0.04 ℃/s ² or less. For example, the 3-2' temperature increase rate change rate (r3-2') may be about -0.1 °C/s ² . Like the first control curve 410, the fourth heating section P4 of the second control curve 420 may be a crack heating section in which the fourth average temperature increase rate change rate r4 has a value close to 0.

As such, in the method of manufacturing hot stamping parts according to an embodiment of the present invention, the temperature increase rate change rate is controlled for each section according to the plurality of section characteristics as described above, thereby reducing the ultra-high strength characteristics, weldability, and hydrogen embrittlement of the hot stamping parts. , bending performance, etc. can be precisely controlled and improved. Part characteristics of hot stamping parts according to embodiments will be discussed in more detail in FIGS. 5 and 6 described later.

The relationship between the heating time (s) and boundary values shown on the horizontal axis of FIG. 4 is not limited to that shown in FIG. 4, and can be modified and applied in various ways within the scope of improving the component performance of the hot stamping part of the present disclosure. . In the above, the plurality of sections has been described as having five sections, but the plurality of sections may be divided differently depending on the distribution of the temperature increase rate change rate.

Figure 5 is a cross-sectional view schematically showing a hot stamping part according to an embodiment of the present invention. Specifically, Figure 5 is a scanning electron microscope (SEM) image showing a cross-section of a hot stamping part according to an embodiment of the present invention, and the hot stamping part according to Figure 5 is a hot stamping part according to an embodiment of the present invention described above. It may be a part manufactured by a manufacturing method (for example, curve 410 in FIG. 4).

Referring to FIG. 5, the hot stamping part 1 may include a base material 10 and a plating layer 20 including a plurality of layers 21, 22, 23, and 24 located on the base material 10. The base material 10 is a base steel sheet and may be a steel sheet manufactured by performing a hot rolling process and/or a cold rolling process on a steel slab cast to contain a predetermined content of a predetermined alloy element.

In one embodiment, the base steel sheet may contain carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), the balance iron (Fe), and other unavoidable impurities. Additionally, the base steel sheet may further include one or more of boron (B), titanium (Ti), niobium (Nb), chromium (Cr), molybdenum (Mo), and nickel (Ni). Specifically, the base steel sheet contains 0.2 wt% to 0.5 wt% of carbon (C), 0.1 wt% to 0.8 wt% of silicon (Si), 0.3 wt% to 2.0 wt% of manganese (Mn), and phosphorus (P ) It may contain more than 0.05% by weight or less, sulfur (S) more than 0.01% by weight or less, and the balance of iron (Fe) and other unavoidable impurities. In addition, the base steel sheet contains boron (B) from 0.001 weight% to 0.005 weight%, titanium (Ti) from 0.01 weight% to 0.1 weight%, niobium (Nb) from 0.01 weight% to 0.1 weight%, and chromium (Cr) from 0.01 weight% to 0.1 weight%. It may further include one or more components of 0.5 wt% or less, molybdenum (Mo) 0.01 wt% or more and 0.5 wt% or less, and nickel (Ni) 0.01 wt% or more and 1.0 wt% or less. For example, the base material 10 may have the ingredients and composition described above.

Carbon (C) is a major element that determines the strength and hardness of steel, and can be added for the purpose of securing the tensile strength of steel after the hot stamping (or hot pressing) process. Additionally, carbon may be added for the purpose of securing the hardenability properties of steel. In one embodiment, carbon may be included in an amount of 0.2% by weight or more and 0.5% by weight or less based on the total weight of the base steel sheet. If carbon is included in less than 0.2% by weight based on the total weight of the base steel sheet, it may be difficult to achieve the mechanical strength of the present invention. On the other hand, if carbon is included in an amount of more than 0.5% by weight based on the total weight of the base steel sheet, problems may occur in reducing the toughness of the steel or controlling the brittleness of the steel.

Silicon (Si) can act as a ferrite stabilizing element in the base steel sheet. Silicon improves ductility by purifying ferrite, and can improve carbon concentration in austenite by suppressing the formation of low-temperature carbides. Furthermore, silicon can be a key element in hot rolling, cold rolling, hot stamping tissue homogenization (pearlite, manganese segregation zone control) and ferrite fine dispersion. In one embodiment, silicon may be included in an amount of 0.1% by weight or more and 0.8% by weight or less based on the total weight of the base steel sheet. If silicon is included in less than 0.1% by weight based on the total weight of the base steel sheet, the above-mentioned functions may not be sufficiently performed. On the other hand, if silicon is included in more than 0.8% by weight based on the total weight of the base steel sheet, hot rolling and cold rolling loads increase, hot rolling red scale may become excessive, and jointability may deteriorate.

Manganese (Mn) may be added to increase hardenability and strength during heat treatment. In one embodiment, manganese may be included in an amount of 0.3% by weight or more and 2.0% by weight or less based on the total weight of the base steel sheet. If manganese is included in an amount of less than 0.3% by weight based on the total weight of the base steel sheet, there may be a high possibility that the material quality (lower hard phase fraction) will be insufficient after hot stamping due to insufficient hardenability. On the other hand, if manganese is contained in more than 2.0% by weight based on the total weight of the base steel sheet, ductility and toughness may be reduced due to manganese segregation or pearlite bands, and it may cause deterioration in bending performance and cause heterogeneous microstructure. You can.

Phosphorus (P) is an element that is prone to segregation and may be an element that inhibits the toughness of steel. In one embodiment, phosphorus (P) may be included in an amount greater than 0 and less than or equal to 0.05% by weight based on the total weight of the base steel sheet. When phosphorus is included in the above-mentioned range with respect to the total weight of the base steel plate, deterioration of the toughness of the steel can be prevented. On the other hand, if phosphorus is included in more than 0.05% by weight based on the total weight of the base steel sheet, cracks may occur during the process and iron phosphide compounds may be formed, which may reduce the toughness of the steel.

Sulfur (S) may be an element that inhibits processability and physical properties. In one embodiment, sulfur may be included in an amount greater than 0 and less than or equal to 0.01% by weight based on the total weight of the base steel sheet. If sulfur is included in more than 0.01% by weight based on the total weight of the base steel sheet, hot workability may be reduced and surface defects such as cracks may occur due to the creation of large inclusions.

Boron (B) is added for the purpose of securing the hardenability and strength of the steel by securing the martensite structure, and can have a grain refining effect by increasing the austenite grain growth temperature. In one embodiment, boron may be included in an amount of 0.001% by weight or more and 0.005% by weight or less based on the total weight of the base steel sheet. When boron is included in the above-mentioned range with respect to the total weight of the base steel sheet, hard phase grain boundary embrittlement can be prevented and high toughness and bendability can be secured.

Titanium (Ti) may be added to strengthen hardenability and improve material quality by forming precipitates after hot stamping heat treatment. In addition, titanium forms precipitated phases such as Ti(C,N) at high temperatures, which can effectively contribute to austenite grain refinement. In one embodiment, titanium may be included in an amount of 0.01% by weight or more and 0.1% by weight or less based on the total weight of the base steel plate. When titanium is included in the above-mentioned range relative to the total weight of the base steel plate, playing defects can be prevented, coarsening of precipitates can be prevented, the physical properties of the steel can be easily secured, and cracks cannot occur on the steel surface. can be prevented or minimized.

Niobium (Nb) can be added to increase strength and toughness as the martensite packet size decreases. In one embodiment, niobium may be included in an amount of 0.01% by weight or more and 0.1% by weight or less based on the total weight of the base steel sheet. When niobium is included in the above-mentioned range relative to the total weight of the base steel plate, the grain refining effect of the steel material is excellent in the hot rolling and cold rolling processes, and the occurrence of cracks in the slab and brittle fracture of the product during steelmaking/rolling are prevented. , the generation of steelmaking coarse precipitates can be minimized.

Chromium (Cr) can be added to improve the hardenability and strength of steel. In one embodiment, chromium may be included in an amount of 0.01% by weight or more and 0.5% by weight or less based on the total weight of the base steel sheet. When chromium is included in the above-mentioned range relative to the total weight of the base steel sheet, the hardenability and strength of the steel can be improved, and the increase in production costs and the decrease in toughness of the steel can be prevented.

Molybdenum (Mo) can contribute to improving strength by suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot stamping. Molybdenum (Mo) may be included in an amount of 0.01% by weight or more and 0.5% by weight or less based on the total weight of the base steel sheet. When molybdenum is included in the above-described range relative to the total weight of the base steel sheet, the effect of suppressing coarsening of precipitates and increasing hardenability during hot rolling and hot stamping can be excellent.

Nickel (Ni) may be added to ensure hardenability and strength. Additionally, nickel is an austenite stabilizing element and can contribute to improving elongation by controlling austenite transformation. In one embodiment, nickel may be included in an amount of 0.01% by weight or more and 1.0% by weight or less based on the total weight of the base steel sheet. If nickel is included in less than 0.01% by weight based on the total weight of the base steel sheet, it may be difficult to properly implement the above-described effect. If nickel is included in excess of 1.0% by weight based on the total weight of the base steel sheet, toughness may be reduced, cold workability may be reduced, and the manufacturing cost of the product may increase.

The plating layer 20 is an alloy layer and is formed on at least one surface of the base material 10, and may include aluminum (Al), iron (Fe), etc. The plating layer 20 may include a plurality of layers 21, 22, 23, and 24 sequentially stacked on the base material 10. In the hot stamping part according to an embodiment of the present invention, the plating layer 20 can be clearly divided into four layers, as shown in FIG. 5. In one embodiment, the plurality of layers 21, 22, 23, and 24 may sequentially have an α-Fe phase, Fe ₂ Al ₅ phase, AlFe phase, and Fe ₂ Al ₅ phase, but the composition of the plurality of layers is as follows. It is not limited. The hot stamping part 1 shown in FIG. 5 may have an amount of mixed hydrogen of 0 to 0.21 ppm, and a dynamic resistance value of 0 to 0.8 mΩ.

Figure 6 is a cross-sectional view schematically showing a hot stamping part according to a comparative example. Specifically, FIG. 6 is a scanning electron microscope (SEM) image showing a cross-section of a hot stamping part according to a comparative example, and FIG. 6 mainly explains the parts that are different from the cross-section of FIG. 5. The hot stamping part 1' according to FIG. 6 may be a part manufactured by the above-described hot stamping part manufacturing method (eg, curve 420 in FIG. 4).

The hot stamping part 1' shown in FIG. 6 may include a base material 10 and a plating layer 30 located on the base material 10. Unlike the plating layer 20 of FIG. 5, the plating layer 30 may be a single layer rather than a plurality of layers, and may be thinner than the plating layer 20. For example, even if the plating layer 30 includes a plurality of layers, its boundaries may be unclear. The plating layer 30 may include at least one element among Al, Fe, and Si. The hot stamping part 1' shown in FIG. 6 may have an amount of mixed hydrogen of 0 or more and less than 0.35 ppm, and a dynamic resistance value of 0.5 mΩ or more and 1.5 mΩ or less.

Hereinafter, the characteristics of the hot stamping parts according to FIGS. 5 and 6 described above will be compared and described using [Table 1]. The evaluation contents described in the table below may be relative comparison results.

Example (Figure 5) Comparative example (Figure 6) Plating layer thickness thick tenuity Amount of hydrogen mixed (hydrogen embrittlement) less
(predominance) plenty
(inferior) dynamic resistance Small (about 0.8 mΩ or less) greatness
(approximately 0.8 mΩ or more) weldability predominance inferior

The plating layer 20 of FIG. 5 is composed of a plurality of layers than the plating layer 30 of FIG. 6. At this time, the boundary between the plurality of layers may also be clear, and the thickness of the plating layer 20 may be thicker than the thickness of the plating layer 30. there is. Here, referring to FIG. 4 together, the thickness characteristics of the plating layer and the control characteristics of the first control curve 410 may be derived as a result of mutual influence. For example, if the plating layer is thick, when heating during the first heating section (P1) and the second heating section (P2), the temperature increase rate change rate may change discontinuously between the two sections (P1, P2), and the third heating section (P2) may change discontinuously. In the section P3, the slope of the first control curve 410 may be gentle, that is, the temperature increase rate change rate may be small.

On the other hand, the thicker the plating layer, the smaller the amount of hydrogen incorporated, and the better the hydrogen embrittlement of the blank. Since the thickness of the plating layer 20 in FIG. 5 is thick, as described above, the amount of hydrogen mixed in the part 1 of FIG. 5 (less than about 0.21 ppm) is higher than that of the part 1' of FIG. 6 (less than about 0.35 ppm). It is small, so hydrogen embrittlement is superior and the risk of hydrogen delayed rupture can be reduced.

Additionally, due to the thickness characteristics of the plating layer described above, the surface resistance of the component 1 of FIG. 5 may be lower than that of the component 1' of FIG. 6. In addition, the smaller the dynamic resistance, the better the weldability. As mentioned above, the dynamic resistance value of the component 1 of FIG. 5 (about 0.8 mΩ or less) is higher than that of the component 1' of FIG. 6 (about 0.8 mΩ or less). Since it is small, it can be confirmed that the part 1 of FIG. 5 is superior in weldability.

According to the method of manufacturing hot stamping parts according to an embodiment of the present invention, precise control of the parts is possible by controlling the rate of change of temperature rise for each plurality of sections, and as a result, the weldability, hydrogen embrittlement, and ultra-high strength of the hot stamping parts are improved. There is an advantage in improving component performance, such as characteristics.

Figure 7 is a diagram showing heating time according to material thickness and heating time according to heating temperature. Specifically, FIG. 7 is a graph shown to explain the minimum heating time according to material thickness and the minimum heating time according to heating temperature. In Figure 7, the heating temperature means the cracking temperature of the cracking heating step (S220), and the heating time means the total heating time of the heating step (S200).

Referring to Figures 1, 2, and 7, it can be seen that when the material thickness is the same, the minimum heating time increases as the heating temperature decreases. Additionally, when the heating temperature is the same, it can be seen that the minimum heating time increases as the material thickness increases.

If the heating time (eg, total heating time) for heating the blank in the heating step (S200) is short, sufficient phase transformation may not occur in the blank. On the other hand, if the heating time for heating the blank in the heating step (S200) is excessive, austenite grain coarsening and hydrogen embrittlement resistance may occur, and the thickness of the plating layer may become thick, thereby reducing weldability. Therefore, it is necessary to adjust the heating time in the heating step (S200). However, in order to adjust the heating time in the heating step (S200), not only the heating temperature and the thickness of the blank (e.g., the thickness of the material), but also the heat loss and heat loss in the heating furnace caused by the sealing degree of the heating furnace, atmosphere, heat source, etc. Various variables, such as the composition of the blank, must be considered.

Accordingly, the present inventor derived a mathematical equation that can easily control the heating time through excessively repeated experiments. In one embodiment, the heating time of the blank in the heating step (S200) may satisfy the following equation.

<Equation>

In the equation, λ _n is the heating time (s), a _n is the heat loss correction coefficient by heating, T _n is the heating temperature (℃), b _n is the Ac3 temperature correction coefficient, c _n is the high temperature material thickness sensitivity correction coefficient, and t is Material thickness (mm). At this time, the material may mean a blank, and the unit s of heating time may mean seconds.

Since different heat sources are used for each furnace type, heat loss occurring for each furnace type may also be different. a _n is a correction coefficient that considers the heat loss of the heating furnace, and can have a value of about -0.60 or more and about -0.55 or less. At this time, a _n may have the unit of s / (℃ x mm).

If the components of each material are different, the temperature at which phase transformation occurs may be different. b _n is a correction coefficient that takes into account the difference in Ac3 temperature depending on the material composition, and can have a value of about 700 or more and about 900 or less. At this time, b _n may have the unit of s/mm.

Depending on the thickness of the material, the heat conductivity transmitted inside the material may vary. c _n is a correction coefficient that takes into account the difference in thermal conductivity depending on the thickness of the material at high temperatures, and can have a value of about 0.7 or more and about 0.9 or less. At this time, high temperature may mean 600°C or higher. However, high temperature may mean 500℃ or higher, or may mean 700℃ or higher.

The heating temperature (T _n ) refers to the cracking temperature of the crack heating step (S220), and the heating temperature (T _n ) may have a value of about Ac3 or more and about 1000°C or less. Additionally, the material thickness (t) may have a value of approximately 1 mm or more and approximately 2.6 mm or less.

In one embodiment, the heating time (λ _n ) according to the equation may be about 100 s or more and about 900 s or less. If the heating time (λ _n ) is less than 100 s, sufficient phase transformation may not occur in the blank. On the other hand, when the heating time (λ _n ) is more than 900 s, not only austenite grain coarsening and hydrogen resistance decrease, but also the thickness of the plating layer becomes thick, which may reduce weldability. Therefore, when the heating time (λ _n ) satisfies the range of about 100 s to about 900 s, sufficient phase transformation can be achieved in the blank, austenite grain coarsening can be prevented or minimized, and hydrogen embrittlement resistance can be achieved. And/or deterioration of weldability can be prevented or minimized.

Referring again to FIG. 1, after the heating step (S200), a transfer step (S300), a forming step (S400), and a cooling step (S500) may be further performed.

In one embodiment, the transfer step (S300) may be a step of transferring the heated blank from the heating furnace to the mold. At this time, in the transfer step (S300), the heated blank may be cooled at atmospheric temperature (or room temperature) while being transferred to the mold. Heated blanks can be air-cooled during transport. If the heated blank is not cooled in air, the mold entry temperature (e.g., molding start temperature) may increase and wrinkles (or bends) may occur on the surface of the manufactured hot stamping part. Additionally, since the use of a coolant may affect the subsequent process (hot stamping), it may be desirable for the heated blank to be air-cooled during transport.

In one embodiment, the forming step (S400) may be a step of forming a molded body by hot stamping the transferred blank. Specifically, in the forming step (S400), a molded body may be formed by pressing the blank with a mold.

In one embodiment, the cooling step (S500) may be a step of cooling the molded body. The cooling step (S500) may be performed within the mold.

In one embodiment, the heated blank may be cooled to ambient temperature (or room temperature) in the transfer step (S300). Specifically, in the transfer step (S300), the blank heated through the heating step (S200) may be removed from the heating furnace and then cooled at ambient temperature (or room temperature) while being transferred to the mold. Thereafter, in the forming step (S400), forming of the blank cooled at ambient temperature (or room temperature) may begin. At this time, the temperature at which molding of the blank begins can be referred to as the molding start temperature. That is, in the transfer step (S300), the blank heated through the heating step (S200) may be cooled from the ambient temperature to the molding start temperature after being taken out of the heating furnace.

In one embodiment, the molding start temperature may be 500°C or more and 700°C or less. If the forming start temperature is less than 500°C, the forming start temperature is too low and the formability of the blank may deteriorate, and the manufactured hot stamping part may not have the target structure and physical properties. On the other hand, if the molding start temperature is greater than 700°C, wrinkles (or bends) may occur on the surface of the manufactured hot stamping part. Additionally, the plating layer of the blank may adhere to the mold. Therefore, when the forming start temperature is 500℃ or higher and 700℃ or lower, the formability of the blank can be improved, the manufactured hot stamping part can have the target structure and physical properties, and there are no wrinkles (or wrinkles) on the surface of the manufactured hot stamping part. , bending) can be prevented or minimized.

Thereafter, in one embodiment, the blank transferred to the mold through the transfer step (S300) in the molding step (S400) may be molded to form a molded body, and the molded body may be cooled in the cooling step (S500). At this time, the cooling step (S500) of cooling the molded body may be performed within the mold.

Specifically, the final product can be formed by cooling the molded body at the same time as molding it into the final part shape in a mold. The mold may be provided with cooling channels through which refrigerant circulates inside. The molded body can be rapidly cooled by circulation in the refrigerant supplied through the cooling channel provided in the mold. At this time, in order to prevent the spring back phenomenon of the plate and maintain the desired shape, rapid cooling can be performed while pressing while the mold is closed. When forming and cooling the molded body, the average cooling rate can be at least 10°C/s to the martensite end temperature.

In one embodiment, the mold cooling end temperature at which the cooling step (S500) ends may be about room temperature or higher and about 200°C or lower. If the mold cooling end temperature is below room temperature, the productivity of the manufacturing process may decrease. On the other hand, when the mold cooling end temperature exceeds 200°C, the manufactured hot stamping part is cooled in air at room temperature. At this time, distortion may occur in the hot stamping part, and it may be difficult to secure the target material. Therefore, when the mold cooling end temperature at which the cooling step (S500) is completed satisfies the range of room temperature to about 200°C, the productivity of the manufacturing process can be improved, and the manufactured hot stamping part is air cooled at room temperature to allow hot stamping. Distortion of parts can be prevented or minimized.

In one embodiment, the air cooling time for cooling the blank in the transfer step (S300) may be about 5 s or more and about 20 s or less. If the air cooling time is less than 5 s, the forming start temperature at which blank forming begins is too high, so the forming of the blank may proceed at a high temperature, causing wrinkles (or bends) to occur in the manufactured hot stamping parts, and air cooling for less than 5 s may occur in the equipment. Time can be difficult to implement. On the other hand, if the air cooling time is more than 20 s, not only does productivity decrease, but phase transformation may occur in the blank during the process of transporting the blank, which may reduce the formability of the blank and the manufactured hot stamping part may not have the target material. You can. Therefore, when the air cooling time satisfies the range of about 5 s or more and about 20 s or less, the formability of the blank and the productivity of the process can be improved, and the manufactured hot stamping parts can be made to have the target material.

In one embodiment, the mold cooling time in the cooling step (S500) may be about 6 s or more and about 40 s or less. If the mold cooling time is less than 6 s, the mold cooling may end at a high temperature, resulting in long air cooling, which may cause distortion in the manufactured hot stamping part and prevent the target dimensions from being secured. On the other hand, if the mold cooling time is longer than 40 s, productivity may decrease. Therefore, if the mold cooling time satisfies the range of about 6s or more and about 40s or less, mold cooling ends when the temperature of the blank is above room temperature and below 200°C, thereby preventing or minimizing distortion in the manufactured hot stamping parts. and the productivity of the manufacturing process can be improved.

In one embodiment, the hot stamping part (1, Figure 5) manufactured through one embodiment of the present invention may have a tensile strength of about 1350 MPa or more and less than about 2300 MPa. Preferably, the produced hot stamped part may have a tensile strength of greater than or equal to about 1350 MPa and less than about 1680 MPa. Alternatively, the manufactured hot stamped part may have a tensile strength of greater than or equal to about 1680 MPa and less than about 2300 MPa.

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 scope of technical protection of the present invention should be determined by the technical spirit of the attached patent claims.

Claims (15)

Injecting a blank with a plating layer formed on at least one surface of a base material into a heating furnace having a plurality of sections having different temperature increase rate ranges; and
heating the blank;
Including,
The heating time of the blank in the step of heating the blank satisfies the following equation,
<Equation>

In the above equation, λ _n is the heating time (s), a _n is the heating heat loss correction coefficient, T _n is the heating temperature (°C), b _n is the Ac3 temperature correction coefficient, and t is the material thickness (mm ), and c _n is the high temperature material thickness sensitivity correction coefficient,
a _n is -0.60 or more and -0.55 or less, T _n is Ac3 or more and 1000°C or less, b _n is 700 or more and 900 or less, t is 1 mm or more and 2.6 mm or less, and c _n is 0.7 or more and 0.9 Below,
A method of manufacturing a hot stamping part, wherein the heating time is 100 s or more and 900 s or less. delete delete According to paragraph 1,
The step of heating the blank is,
A multi-stage heating step of heating the blank in stages; and
A crack heating step of heating the blank to a temperature of Ac3 to 1000°C;
Method for manufacturing hot stamping parts, including. According to clause 4,
The plurality of sections are,
A first heating section having a first average temperature increase rate change rate;
After the first heating section, a second heating section having a second average temperature increase rate change rate that is different from the first average temperature increase rate change rate; and
After the second heating section, a third heating section having a third average temperature increase rate change rate that is different from the first average temperature increase rate change rate and the second average temperature increase rate change rate,
A method of manufacturing a hot stamping part, wherein the third average temperature increase rate change rate includes a section that changes from a positive value to a negative value. According to clause 5,
Between the first heating section and the second heating section, the final temperature increase rate defining the first average temperature increase rate change rate and the initial temperature increase rate defining the second average temperature increase rate change rate have different values, a hot stamping part. Manufacturing method. According to clause 5,
The third heating section includes a 3-1 heating section having a 3-1 average temperature increase rate change rate and a 3-2 heating section having a 3-2 average temperature increase rate change rate,
The 3-1 average temperature increase rate change rate has a positive value, and the 3-2 average temperature increase rate change rate has a negative value,
The method of manufacturing a hot stamping part, wherein the absolute value of the 3-1 average temperature increase rate change rate is smaller than the absolute value of the 3-2 average temperature increase rate change rate. According to clause 5,
The first average temperature increase rate change rate and the second average temperature increase rate change rate each have a negative value,
A method of manufacturing a hot stamping part, wherein the absolute value of the first average temperature increase rate change rate is greater than the absolute value of the second average temperature increase rate change rate. According to clause 8,
The plurality of sections are, after the third heating section,
It further includes a fourth heating section having a fourth average temperature increase rate change rate that is different from the first average temperature increase rate change rate, the second average temperature increase rate change rate, and the third average temperature increase rate change rate,
The absolute value of the fourth average temperature increase rate change rate is smaller than the absolute values of each of the first average temperature increase rate change rate, the second average temperature increase rate change rate, and the third average temperature increase rate change rate. According to clause 9,
The plating layer is alloyed in the second heating section,
A method of manufacturing a hot stamping part, wherein the base material undergoes a phase transformation in the third heating section. According to paragraph 1,
After heating the blank,
transferring the heated blank from the heating furnace to a mold;
Forming a molded body by pressing the transferred blank into the mold; and
Cooling the formed molded body;
A method for manufacturing hot stamping parts, further comprising: According to clause 11,
In the step of transferring the blank, the air cooling time of the blank is 5s or more and 20s or less. According to clause 11,
The step of cooling the molded body is,
A method of manufacturing hot stamping parts, which takes place in the mold. According to clause 13,
A method of manufacturing a hot stamping part, wherein the mold cooling time for cooling the molded body in the mold is 6s or more and 40s or less. delete

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