Mold and method for manufacturing a hot press formed product

Abstract

A mold is provided that can be used to manufacture thermoformed articles with excellent impact absorption capabilities. The mold (10) of this disclosure comprises: an upper mold (11) having a first forming surface (110); and a lower mold (12) having a second forming surface (120). The first forming surface (110) includes a first slow-cooling region (113) having a plurality of first ribs (111) and a plurality of first grooves (112). The width of the first ribs (111) is narrower than the width of the first grooves (112). The second forming surface (120) includes a second slow-cooling region (123) having a plurality of second ribs (121) and a plurality of second grooves (122). The width of the second ribs (121) is narrower than the width of the second grooves (122). During hot pressing, when viewed from the normal direction of the first slow cooling region (113) and the second slow cooling region (123), the first rib (111) and the second rib (121) at least partially overlap.

Description

Technical Field

[0001] This disclosure relates to a mold and a method for manufacturing a thermoformed article using the mold. Background Technology

[0002] In the automotive industry, lightweighting of the vehicle body is required to improve fuel economy. Furthermore, improved crash safety is also essential to protect occupants during collisions. For lightweighting the vehicle body, reducing the wall thickness of structural components is effective. To achieve both thinner structural components and improved crash safety, the raw materials used in these components must possess high strength. However, high-strength raw materials have lower formability during stamping. If high-strength raw materials are cold-worked during stamping, cracks may occur, or elastic deformation (springback) may occur due to stress generated during stamping. Therefore, hot pressing has been proposed as a method for forming structural components using such high-strength raw materials.

[0003] In hot pressing, the raw material is heated to a temperature range where the microstructure becomes a single phase of austenite. Then, the heated raw material is hot-pressed using a hot pressing device equipped with a die. During hot pressing, the raw material softens due to heating. Therefore, the raw material in hot pressing has high formability. In hot pressing, the raw material also comes into contact with almost the entire forming surface of the die. At this time, the raw material is quenched by heat dissipation from the die in contact with the raw material. Thus, in hot pressing, the raw material is quenched simultaneously with hot pressing. Therefore, high-strength hot-pressed articles can be easily manufactured.

[0004] However, for impact-absorbing components, which are structural parts of automobiles, excellent impact absorption capacity is required. Therefore, Patent Document 1 (Japanese Patent Application Publication No. 2014-79790) discloses a mold for hot pressing to form impact-absorbing components.

[0005] In the hot pressing process disclosed in Patent Document 1, a mold is used to hot press a heated raw material. During hot pressing, refrigerant is also locally quenched by flowing into the gap between the mold and the raw material. Specifically, the mold in Patent Document 1 has a refrigerant supply port on its surface for supplying refrigerant from the refrigerant path inside the mold to the outside of the mold. The mold in Patent Document 1 also has a protrusion that contacts the interface between the high-strength and low-strength portions of the raw material. During hot pressing, refrigerant is supplied from the supply port into the gap between the high-strength portion and the mold. On the other hand, refrigerant is not supplied into the gap between the low-strength portion and the mold. The protrusion that contacts the interface between the high-strength and low-strength portions intercepts the refrigerant. Therefore, the refrigerant filling the gap between the high-strength portion and the mold does not flow into the gap between the low-strength portion and the mold. As a result, a hot-pressed product (impact-absorbing member) with excellent impact absorption capacity in the low-strength portion can be manufactured.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-79790 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The mold disclosed in Patent Document 1 can be used to manufacture a hot-pressed article with a low-strength portion that has excellent impact absorption capabilities. However, it is also possible to manufacture a hot-pressed article with excellent impact absorption capabilities using other technologies different from those described in Patent Document 1.

[0011] The purpose of this disclosure is to provide a mold for manufacturing thermoformed articles with excellent impact absorption capabilities using thermoforming and a method for manufacturing thermoformed articles using the mold.

[0012] Solution for solving the problem

[0013] The mold disclosed herein is a mold used for hot pressing and forming raw materials.

[0014] The mold has an upper mold and a lower mold. The upper mold has a first forming surface. The lower mold has a second forming surface. The second forming surface is positioned opposite to the first forming surface during hot pressing, and together with the first forming surface, the raw material is hot pressed.

[0015] The first forming surface includes a first slow cooling region. The first slow cooling region has a plurality of first ribs and a plurality of first grooves. The plurality of first ribs are arranged in the width direction of the first ribs. The plurality of first grooves are arranged in the width direction of the first grooves. The first ribs are formed between adjacent first grooves. The width of the first rib is narrower than the width of the first groove.

[0016] The second forming surface includes a second slow cooling region. The second slow cooling region has a plurality of second ribs and a plurality of second grooves. The plurality of second ribs are arranged in the width direction of the second ribs. The plurality of second grooves are arranged in the width direction of the second grooves. The second ribs are formed between adjacent second grooves. The width of the second ribs is narrower than the width of the second grooves.

[0017] During hot pressing, when the first and second slow cooling regions are viewed from the normal direction of the first slow cooling region, the first rib and the second rib at least partially overlap.

[0018] The method for manufacturing hot-pressed articles disclosed herein includes the following steps: a step of preparing raw materials; heating the prepared raw materials to A c3 The process of heating the raw material to a temperature above a certain point; the process of hot pressing the heated raw material using the aforementioned mold; and the process of demolding the hot-pressed raw material from the mold to manufacture a hot-pressed product.

[0019] The effects of the invention

[0020] The mold disclosed herein can be used to manufacture thermoformed articles with excellent impact absorption capabilities using hot pressing. The method for manufacturing thermoformed articles disclosed herein can manufacture thermoformed articles with excellent impact absorption capabilities. Attached Figure Description

[0021] Figure 1 This is a front view showing an example of a hot pressing apparatus for hot pressing.

[0022] Figure 2 This is a perspective view showing an example of the mold used in this embodiment.

[0023] Figure 3 This is a cross-sectional view showing the state of the mold and raw material during hot pressing in a slow cooling zone, representing an example of the mold in this embodiment.

[0024] Figure 4 This is a cross-sectional view showing the state of the mold and raw material during hot pressing in the quenching zone of an example mold of this embodiment.

[0025] Figure 5A It is magnification Figure 3 A schematic diagram of region 100.

[0026] Figure 5B It indicates the removal during hot pressing. Figure 5A A schematic diagram of raw material B.

[0027] Figure 5C Is with Figure 5A as well as Figure 5B A cross-sectional view of the first or second rib of different shapes, perpendicular to the direction of extension.

[0028] Figure 5D Is with Figures 5A to 5C A cross-sectional view of the first or second rib of different shapes, perpendicular to the direction of extension.

[0029] Figure 6 This is observed from above (the normal direction of the first and second slow-cooling regions). Figure 3 A schematic diagram of region 100.

[0030] Figure 7 It is magnification Figure 4 A schematic diagram of region 200.

[0031] Figure 8 This is a graph showing the relationship between Fn1 and the temperature deviation ΔT (°C) in the first and second slow cooling regions.

[0032] Figure 9 It is used for making Figure 8 A schematic diagram of the heat conduction model used in the two-dimensional heat transfer simulation.

[0033] Figure 10 This is a graph showing the relationship between Fn2 and the cooling rate V (°C / second) of the raw material B during hot pressing.

[0034] Figure 11 This refers to the mold in this embodiment. Figure 2 A 3D diagram of another different example.

[0035] Figure 12 This refers to the mold in this embodiment. Figure 2 , Figure 11 A 3D diagram of another different example.

[0036] Figure 13 This refers to the mold in this embodiment. Figure 2 , Figure 11 as well as Figure 12 A 3D diagram of another different example.

[0037] Figure 14 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A Another different example.

[0038] Figure 15 yes Figure 14 A cross-sectional view of line segment XV-XV.

[0039] Figure 16 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A , Figure 14 Another different example.

[0040] Figure 17 Viewed from the normal direction of the first slow-cooling region Figure 16 The diagram only shows a schematic representation of the ribs in area 100.

[0041] Figure 18 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A , Figure 14 as well as Figure 16 Another different example.

[0042] Figure 19 Viewed from the normal direction of the first slow-cooling region Figure 18 The diagram only shows a schematic representation of the ribs in area 100. Detailed Implementation

[0043] As mentioned above, in the impact-absorbing components of automotive structural members, it is required to improve the ability to absorb impact energy during a collision, i.e., the impact absorption capacity. Structural components absorb impact energy through plastic deformation. Therefore, in order to improve impact absorption capacity, it is effective to ensure excellent plastic deformation capacity even under high stress.

[0044] The inventors believe that if the cooling rate of the raw material during hot pressing can be reduced, excellent plastic deformation capacity can be achieved even when the raw material is subjected to high stress. Therefore, the inventors studied the surface shape of the forming surface of the mold. As a result, the inventors believe that if a slow-cooling region including multiple ribs and multiple grooves is formed on the forming surface, the cooling rate of the raw material during hot pressing can be reduced.

[0045] In the forming surface, the ribs extend in a specified direction, and the cross-section perpendicular to the extension direction has a convex shape. In the forming surface, the grooves extend along the extension direction of the ribs, and the cross-section perpendicular to the extension direction has a concave shape. Multiple ribs and multiple grooves are formed alternately.

[0046] During hot pressing, in the slow cooling zone, the ribs directly contact the raw material to dissipate heat. On the other hand, the grooves do not directly contact the raw material. Therefore, if the forming surface includes multiple ribs and multiple grooves, the contact area between the die and the raw material during hot pressing can be reduced. This allows for a decrease in the cooling rate of the raw material during quenching.

[0047] Based on the above insights, the inventors conducted further detailed research focusing on the widths of the ribs and grooves in the slow-cooling region of the forming surface of the mold. As a result, the inventors obtained the following insights: if the width of the ribs is narrower than the width of the grooves, heat dissipation from the raw material during hot pressing can be effectively reduced, thus lowering the cooling rate. Slowing down the cooling rate of the raw material during hot pressing can suppress the high-strength development of the raw material and improve impact absorption capacity.

[0048] If the width of the rib in the slow cooling region is narrower than the width of the groove, it is possible to form at least locally a reduced-strength impact buffer region in the hot-pressed article. However, when the width of the rib is narrower than the width of the groove, a wavy deformation occurs on the surface of the hot-pressed article, resulting in reduced dimensional accuracy. Therefore, the inventors investigated the cause of this problem. As a result, the inventors obtained the following insights.

[0049] During hot pressing, sometimes ribs formed in the slow cooling zone of the forming surface of one of a pair of molds (upper mold and lower mold) may enter grooves formed in the slow cooling zone of the forming surface of the other mold. In this case, the aforementioned wavy deformation occurs on the surface of the hot-pressed article.

[0050] Based on the above insights, the inventors conceived of a method during hot pressing where ribs formed in a slow-cooling region of one mold overlap with ribs formed in a slow-cooling region of another mold when viewed from the normal direction of the slow-cooling region. If at least a portion of the ribs formed in the slow-cooling region of one mold overlaps with ribs formed in the slow-cooling region of another mold, it is possible to prevent the ribs from entering the groove.

[0051] In the mold of this embodiment, during hot pressing, when the slow cooling region is viewed from the normal direction of the slow cooling region, the ribs formed in one slow cooling region at least partially overlap with the ribs formed in the other slow cooling region. As a result, the aforementioned wavy deformation caused by the ribs being narrower than the grooves can be suppressed.

[0052] Based on the above insights, the mold of this embodiment and the method for manufacturing a thermoformed article using the mold of this embodiment have the following configuration.

[0053] [1] A mold for hot pressing raw materials, wherein,

[0054] The mold has the following features:

[0055] The upper mold has a first forming surface;

[0056] The lower mold has a second forming surface, which is configured opposite to the first forming surface during hot pressing, and together with the first forming surface, hot presses the raw material.

[0057] The first forming surface includes a first slow-cooling region, which has multiple first ribs and multiple first grooves.

[0058] The plurality of the first ribs are arranged in the width direction of the first ribs.

[0059] The plurality of the first groove portions are arranged in the width direction of the first groove portion.

[0060] The first rib is formed between adjacent first grooves.

[0061] The width of the first rib is narrower than the width of the first groove.

[0062] The second forming surface includes a second slow-cooling region, which has multiple second ribs and multiple second grooves.

[0063] The plurality of said second ribs are arranged in the width direction of the second ribs.

[0064] The plurality of said second groove portions are arranged in the width direction of the second groove portions.

[0065] The second rib is formed between adjacent second grooves.

[0066] The width of the second rib is narrower than the width of the second groove.

[0067] During hot pressing, when viewing the first slow cooling region and the second slow cooling region from the normal direction of the first slow cooling region,

[0068] The first rib and the second rib at least partially overlap.

[0069] [1] The mold can be used to manufacture thermoformed products with excellent impact absorption capabilities by thermoforming.

[0070] [2] According to the mold described in [1], wherein,

[0071] During hot pressing, when viewing the first slow cooling region and the second slow cooling region from the normal direction of the first slow cooling region,

[0072] The first rib and the second rib extend in the same direction.

[0073] The first groove and the second groove extend in the same direction.

[0074] [2] The mold can improve the accuracy of simulating heat transfer in raw materials during hot pressing.

[0075] [3] According to the mold described in [1] or [2], wherein,

[0076] The width of the first rib is 10% to 50% of the width of the first groove.

[0077] The width of the second rib is 10% to 50% of the width of the second groove.

[0078] If it is a mold of [3], the cooling rate can be slowed down during hot pressing. If the cooling rate can be slowed down, it is easy to stop the cooling at the desired raw material temperature. For example, the cooling can be stopped between the Mf point and the Ms point during hot pressing, and then the heat holding process discussed later can be performed to adjust the amount of martensite and retained austenite in the microstructure of the raw material. Alternatively, the cooling can be stopped at a temperature between the Ms point and 500°C during hot pressing, and then the heat holding process discussed later can be performed to make the microstructure of the raw material a bainite-based structure.

[0079] [4] The mold according to any one of [1] to [3], wherein,

[0080] At least a portion of the first slow-cooling region,

[0081] The width of the first rib is 1.0 mm to 8.0 mm.

[0082] The height of the first rib is 0.2mm to 5.0mm.

[0083] At least in a portion of the second slow-cooling region,

[0084] The width of the second rib is 1.0 mm to 8.0 mm.

[0085] The height of the second rib is 0.2mm to 5.0mm.

[0086] [4] The mold can suppress the temperature deviation of the raw materials during hot pressing.

[0087] [5] According to the mold described in [2], wherein,

[0088] The width of the first rib is 10% to 50% of the width of the first groove.

[0089] The width of the second rib is 10% to 50% of the width of the second groove.

[0090] The width of each of the first rib and the second rib is 1.0 mm to 8.0 mm.

[0091] The height of the first rib and the second rib is 0.2 mm to 5.0 mm respectively.

[0092] Fn1, as defined by equation (1), is 14 or less.

[0093] Fn1=Wr 0.9 / P0 0.8 +0.05Hr (1)

[0094] In formula (1), Wr is the width (mm) of the first rib and the second rib, P0 = Wr / Ws, Ws is the width (mm) of the first groove and the second groove, and Hr is the height (mm) of the first rib and the second rib.

[0095] In the mold of [5], the temperature deviation of the raw materials during hot pressing can be further suppressed.

[0096] [6] According to the mold described in [2] or [5], wherein,

[0097] The width of the first rib is 10% to 50% of the width of the first groove.

[0098] The width of the second rib is 10% to 50% of the width of the second groove.

[0099] The width of each of the first rib and the second rib is 1.0 mm to 8.0 mm.

[0100] The height of the first rib and the second rib is 0.2 mm to 5.0 mm respectively.

[0101] Fn2, as defined by equation (2), is 30 or higher.

[0102] Fn2=Ws 2 ×Hr 0.4 / Wr (2)

[0103] In formula (2), Ws is the width (mm) of the first groove and the second groove, Wr is the width (mm) of the first rib and the second rib, and Hr is the height (mm) of the first rib and the second rib.

[0104] In the mold of [6], the cooling rate of the raw material can be further slowed down. If the cooling rate can be slowed down, it is easier to stop the cooling at the desired raw material temperature. For example, the cooling can be stopped between the Mf point and the Ms point during hot pressing, and then the heat holding process discussed later can be performed to adjust the amount of martensite and retained austenite in the microstructure of the raw material. Alternatively, the cooling can be stopped at a temperature between the Ms point and 500°C during hot pressing, and then the heat holding process discussed later can be performed to make the microstructure of the raw material a bainite-based structure.

[0105] [7] The mold according to any one of [4] to [6], wherein,

[0106] At least a portion of the first slow-cooling region,

[0107] The width of the first rib is 1.0 mm to 4.0 mm, and is 10% to 30% of the width of the first groove.

[0108] At least in a portion of the second slow-cooling region,

[0109] The width of the second rib is 1.0 mm to 4.0 mm, and is 10% to 30% of the width of the second groove.

[0110] [7] The mold can further suppress the temperature deviation of raw materials during hot pressing.

[0111] [8] A method for manufacturing a hot-pressed article, comprising the following steps:

[0112] The process of preparing raw materials;

[0113] Heat the prepared raw materials to A c3 Processes involving temperatures above a certain point;

[0114] The process of hot pressing the heated raw material using any one of the molds described in [1] to [7]; and

[0115] The process of manufacturing a thermoformed article by demolding the raw material that has been thermoformed from the mold.

[0116] [8] The hot-pressed molding method can produce hot-pressed molded articles with excellent impact absorption capabilities.

[0117] [9] According to the method for manufacturing hot-pressed articles described in [8], wherein,

[0118] The method for manufacturing the hot-pressed article further includes a step of holding the hot-pressed article at a temperature of 100°C to 500°C after demolding from the mold.

[0119] Hereinafter, the mold of this embodiment and the manufacturing method of the hot-pressed molded article using the mold of this embodiment will be described with reference to the accompanying drawings. Furthermore, the same reference numerals will be used to denote the same or equivalent structures in each of the drawings, and the same descriptions will not be repeated.

[0120] [Structure of hot pressing device 1]

[0121] Figure 1 This is a front view showing an example of a hot pressing apparatus 1 for hot pressing. (Refer to...) Figure 1 The hot pressing device 1, except for the mold 10 of this embodiment, has a structure substantially the same as that of a known hot pressing device. The hot pressing device 1 includes a frame 2, a slider 3, a pad 4, and a mold 10 (upper mold 11 and lower mold 12). In the following description, the vertical (up and down) direction of the hot pressing device 1 will be referred to as the V direction, the width direction of the hot pressing device 1 will be referred to as the W direction, and the direction perpendicular to the V direction and the W direction will be referred to as the L direction.

[0122] Reference Figure 1 A frame 2 is positioned above the hot press device 1. The frame 2 supports a slider 3 positioned below it, allowing it to be raised and lowered. The frame 2 has a drive mechanism (not shown) for raising and lowering the slider 3. The drive mechanism can be either mechanical or hydraulic. The slider 3 is mounted on the frame 2 and can be raised and lowered in the vertical direction using the drive mechanism provided by the frame 2. An upper mold 11 is mounted on the lower surface of the slider 3. A pad 4 is positioned below the slider 3. The upper surface of the pad 4 is opposite to the lower surface of the slider 3. A lower mold 12 is mounted on the upper surface of the pad 4. At this time, the lower mold 12 is positioned below the upper mold 11.

[0123] The mold 10 includes the aforementioned upper mold 11 and lower mold 12. The upper mold 11 and lower mold 12 are located in... Figure 1 Extending in the L direction. Hereinafter, for the hot pressing device 1 and the mold 10, the direction in which the upper mold 11 and the lower mold 12 extend will also be referred to as the "length direction (L direction) of the mold 10". For the mold 10, the direction will also be related to the L direction and... Figure 1 The direction perpendicular to the V direction is called the "width direction (W direction) of mold 10".

[0124] As described above, the upper mold 11 is fixed to the lower surface of the slider 3, and the lower mold 12 is fixed to the upper surface of the pad 4. Furthermore, the lower mold 12 is positioned below the upper mold 11. During hot pressing, the heated raw material (blank) is first placed on the lower mold 12. After the raw material is placed, the upper mold 11 slides relative to the lower mold 12 in the V direction, contacting the raw material while applying external force. In other words, the upper mold 11 and the lower mold 12 hot press the raw material. This shapes the raw material into the desired form. Moreover, during hot pressing, the forming surfaces of the upper mold 11 and the lower mold 12 contact the raw material, causing the upper mold 11 and the lower mold 12 to dissipate heat from the raw material, thereby quenching it. Therefore, a hot-pressed product with the desired shape and improved strength can be manufactured.

[0125] The hot pressing device 1 may also include (not shown) Figure 1 The structure is as follows. The hot pressing apparatus 1 may also include a cooling device for cooling the mold 10. In this case, for example, a flow path for the cooling medium is provided inside the mold 10. Furthermore, a pump is provided for supplying the cooling medium into the mold 10. Alternatively, the hot pressing apparatus 1 may also include a conveying mechanism for conveying raw materials to the hot pressing apparatus 1. The hot pressing apparatus 1 may also include a structure not shown. Figure 1 The structure is that of a well-known hot pressing device.

[0126] [Structure of mold 10]

[0127] Further details Figure 1 The structure of mold 10 in the middle.

[0128] Figure 2 yes Figure 1 A three-dimensional view of mold 10. (Refer to...) Figure 2 The upper mold 11 has a first forming surface 110. The first forming surface 110 is disposed on the lower surface of the upper mold 11. Figure 2 In the middle, the first forming surface 110 includes a recess extending in the L direction at its central portion in the W direction.

[0129] The lower mold 12 has a second forming surface 120. The second forming surface 120 is disposed on the upper surface of the lower mold 12. Figure 2 In this process, the second forming surface 120 includes a protrusion extending in the L direction at its central portion in the W direction. During hot pressing, the second forming surface 120 is disposed opposite to the first forming surface 110. Furthermore, the second forming surface 120 and the first forming surface 110 together contact the raw material (blank) to perform hot pressing on the raw material.

[0130] [Structure of the first forming surface 110 and the second forming surface 120]

[0131] The first forming surface 110 includes a first slow cooling region 113, indicated by a diagonal line. Figure 2 In this process, the first slow-cooling region 113 is formed in a portion of the first forming surface 110. Figure 2 In the first forming surface 110, there are a first slow cooling region 113 and a first rapid cooling region 114.

[0132] Similarly, the second forming surface 120 includes a second slow-cooling region 123, indicated by a diagonal line. Figure 2 In this process, the second slow-cooling region 123 is formed in a portion of the second forming surface 120. Figure 2 In the middle, the second forming surface 120 includes a second slow cooling region 123 and a second rapid cooling region 124.

[0133] During hot pressing, the first quenching region 114 is opposite to the second quenching region 124. The first quenching region 114 and the second quenching region 124 form a high-strength region with high strength in the raw material (hot-pressed product) after hot pressing.

[0134] During hot pressing, the first slow cooling region 113 is opposite to the second slow cooling region 123. The first slow cooling region 113 and the second slow cooling region 123 form an impact buffer region in the raw material (hot pressed product) after hot pressing, which has lower strength than the high-strength region and is easy to plastically deform.

[0135] Figure 3 It is a cross-sectional view including the V and W directions, showing the state of the mold 10 and the raw material (blank) B in the first slow cooling zone 113 and the second slow cooling zone 123 during hot pressing. Figure 4 It is a cross-sectional view including the V and W directions, showing the state of the mold 10 and the raw material B in the first quenching zone 114 and the second quenching zone 124 during hot pressing. Figure 3 and Figure 4 This indicates that the upper mold 11 has reached its lower stop point and the mold 10 is closed. In other words, Figure 3 and Figure 4 This indicates that approximately the entire first forming surface 110 of the upper mold 11 and approximately the entire second forming surface 120 of the lower mold 12 are in contact with the raw material B, thus applying an external force to the raw material B.

[0136] Reference Figures 2-4 During hot pressing, raw material B is sandwiched between upper mold 11 and lower mold 12. At this time, the protrusion of the second forming surface 120 is fitted into the recess of the first forming surface 110. As a result, raw material B is formed into a cap-shaped hot-pressed article.

[0137] Figure 2The mold 10 also includes slow cooling regions (113 and 123) and rapid cooling regions (114 and 124). In the first forming surface 110 of the upper mold 11, the surface structure of the first slow cooling region 113, which forms the impact buffer region of the hot-pressed article, differs from the surface structure of the first rapid cooling region 114, which forms the high-strength region of the hot-pressed article. Similarly, in the second forming surface 120 of the lower mold 12, the surface structure of the second slow cooling region 123, which forms the impact buffer region of the hot-pressed article, differs from the surface structure of the second rapid cooling region 124, which forms the high-strength region of the hot-pressed article. The surface structures of the first forming surface 110 and the second forming surface 120 will be further described below.

[0138] [Structure of the first forming surface 110]

[0139] [Structure of the first slow cooling zone 113]

[0140] Figure 5A yes Figure 3 An enlarged view of region 100 within the first slow cooling region 113 of the first forming surface 110. (Refer to...) Figure 5A The first slow cooling region 113 of the first forming surface 110 of the upper mold 11 has a plurality of first ribs 111 and a plurality of first grooves 112. Figure 6 This is observed from above (the normal direction of the first slow cooling region 113 and the second slow cooling region 123). Figure 3 A schematic diagram of region 100. (Refer to...) Figure 5A and Figure 6 Multiple first ribs 111 extend in a prescribed direction. Figure 5A and Figure 6 In the example, multiple first ribs 111 extend in the L direction. However, the direction of extension of the multiple first ribs 111 is not limited to the L direction.

[0141] Multiple first ribs 111 are arranged in the width direction of the first ribs 111. The width direction of the first ribs 111 refers to the direction perpendicular to the extending direction of the first ribs 111. Figure 5A In this embodiment, the width direction of the first rib 111 is the W direction. However, the width direction of the first rib 111 is not limited to the W direction. In this embodiment, each first rib 111 extends in the L direction and is arranged in the W direction.

[0142] Reference Figure 5A A plurality of first grooves 112 are arranged in the width direction of the first grooves 112, and first ribs 111 are formed between adjacent first grooves 112. Figure 5A In this configuration, the first groove 112 and the first rib 111 both extend in the L direction and are arranged in the W direction. Furthermore, the first rib 111 is formed between two adjacent first grooves 112. Figure 5A In the middle, multiple first grooves 112 and multiple first ribs 111 extend in the L direction, and the first grooves 112 and first ribs 111 are arranged alternately in the W direction.

[0143] Reference Figure 5A The width of the first rib 111 is narrower than the width of the first groove 112. As described above, the width of the first rib 111 refers to the width of the first rib 111 in a cross-section perpendicular to its extending direction. Figure 5A In this context, the width of the first rib 111 refers to its width in the W direction. Similarly, the width of the first groove 112 refers to the width of the first groove 112 in a cross-section perpendicular to its extending direction. Figure 5A In this context, the width of the first groove 112 means the width of the first groove 112 in the W direction. The widths of the first rib 111 and the first groove 112 can be easily determined, for example, using a vernier caliper.

[0144] Reference Figure 5A In this embodiment, the width of the first rib 111 is narrower than the width of the first groove 112. When the first slow cooling region 113 comes into contact with the raw material B during hot pressing, the heat dissipation at the first groove 112 is less than the heat dissipation at the first rib 111. Since the width of the first rib 111 is narrower than the width of the first groove 112, the heat dissipation at the first rib 111 can be suppressed even less. Therefore, in the first slow cooling region 113, the cooling rate of the raw material B can be slowed down compared to the first rapid cooling region 114. Therefore, when hot pressing is performed using the mold 10, the degree of quenching in the region of the raw material B that comes into contact with the first slow cooling region 113 can be reduced. As a result, an impact-buffered region with suppressed strength can be formed in the raw material B (hot-pressed product) after hot pressing.

[0145] [Structure of the first quenching region 114]

[0146] Figure 7 yes Figure 4 An enlarged view of region 200 in the first quenching region 114 of the first forming surface 110. (Refer to...) Figure 7The first rib 111 and the first groove 112 are not formed in the first quenching region 114 of the first forming surface 110 of the upper die 11. In other words, the first quenching region 114 of the first forming surface 110 is a smooth surface. Therefore, during hot pressing, approximately the entire first quenching region 114 is in contact with the raw material B. Therefore, compared with the first slow cooling region 113, the cooling rate of the raw material B can be accelerated in the first quenching region 114. Therefore, when hot pressing is performed using the die 10, the degree of hardening of the area of ​​the raw material B in contact with the first quenching region 114 can be improved. As a result, a high-strength region with higher strength than the impact buffer region can be formed in the raw material B (hot-pressed product) after hot pressing.

[0147] [Structure of the second forming surface 120]

[0148] [Structure of the second slow-cooling zone 123]

[0149] Reference Figure 5A The second slow cooling region 123 of the second forming surface 120 of the lower mold 12 has a plurality of second ribs 121 and a plurality of second grooves 122. (Refer to...) Figure 5A and Figure 6 Multiple second ribs 121 extend in a prescribed direction. Figure 5A and Figure 6 In the middle, a plurality of second ribs 121 extend in the L direction. However, the extension direction of the plurality of second ribs 121 is not limited to the L direction.

[0150] Multiple second ribs 121 are arranged in the width direction of the second ribs 121. The width direction of the second ribs 121 refers to the direction perpendicular to the extending direction of the second ribs 121. Figure 5A In this embodiment, the width direction of the second rib 121 is the W direction. However, the width direction of the second rib 121 is not limited to the W direction. In this embodiment, each second rib 121 extends in the L direction and is arranged in the W direction.

[0151] Reference Figure 5A Multiple second grooves 122 are arranged in the width direction of the second grooves 122, and second ribs 121 are formed between adjacent second grooves 122. Figure 5A In this configuration, the second groove 122 and the second rib 121 both extend in the L direction and are arranged in the W direction. Furthermore, the second rib 121 is formed between two adjacent second grooves 122. Figure 5A In the middle, multiple second grooves 122 and multiple second ribs 121 extend in the L direction, and the second grooves 122 and second ribs 121 are arranged alternately in the W direction.

[0152] Reference Figure 5AFurthermore, the width of the second rib 121 is narrower than the width of the second groove 122. As described above, the width directions of the second rib 121 and the second groove 122 correspond to the width direction (W direction) of the mold 10. Therefore, in Figure 5A In the cross-section shown, the width of the second rib 121 means the width of the second rib 121 in the W direction, and the width of the second groove 122 means the width of the second groove 122 in the W direction. The widths of the second rib 121 and the second groove 122 can be determined, for example, using vernier calipers.

[0153] Reference Figure 5A The width of the second rib 121 is narrower than the width of the second groove 122. As described above, the width of the second rib 121 refers to the width of the second rib 121 in a cross-section perpendicular to the extending direction of the second rib 121. Therefore, the same effect as the relationship between the width of the first rib 111 and the width of the first groove 112 described above can be obtained. Specifically, when the second slow cooling region 123 comes into contact with the raw material B during hot pressing, the heat dissipation at the second groove 122 is less than the heat dissipation at the second rib 121. Since the width of the second rib 121 is narrower than the width of the second groove 122, the heat dissipation at the second rib 121 can be suppressed even less. Therefore, in the second slow cooling region 123, compared with the second rapid cooling region 124 discussed later, the cooling rate of the raw material B can be slowed down. Therefore, when hot pressing is performed using mold 10, the degree of quenching in the region of raw material B that comes into contact with the second slow cooling region 123 can be reduced. As a result, an impact-buffered region with suppressed strength can be formed in the raw material B (hot-pressed product) after hot pressing.

[0154] [Structure of the second quenching region 124]

[0155] Reference Figure 7 The second rib 121 and the second groove 122 are not formed in the second quenching region 124 of the second forming surface 120 of the lower die 12. That is, the second quenching region 124 of the second forming surface 120 is a smooth surface. Therefore, during hot pressing, approximately the entire second quenching region 124 is in contact with the raw material B. Therefore, compared with the second slow cooling region 123, the cooling rate of the raw material B can be accelerated in the second quenching region 124. Therefore, when hot pressing is performed using the die 10, the degree of hardening of the area of ​​the raw material B in contact with the second quenching region 124 can be improved. As a result, a high-strength region with higher strength than the impact buffer region can be formed in the raw material B (hot-pressed product) after hot pressing.

[0156] [The relationship between the first rib 111 and the second rib 121]

[0157] In the mold 10, and during hot pressing, when the first slow cooling region 113 of the first forming surface 110 and the second slow cooling region 123 of the second forming surface 120 are viewed from the normal direction of the first slow cooling region 113, the first rib 111 and the second rib 121 at least partially overlap. Here, "during hot pressing" means the state in which approximately the entire forming surface 110 of the upper mold 11 and approximately the entire forming surface 120 of the lower mold 12 are in contact with the raw material B and exert external force on the raw material B, and the state in which the mold 10 is closed, and the upper mold 11 is held at the lower dead center, while the raw material B is cooled by the mold 10.

[0158] In this case, such as Figure 5A As shown, during hot pressing, the first rib 111 will not enter the second groove 122, and the second rib 121 will not enter the first groove 112. Therefore, it is possible to prevent the raw material B from deforming into a wavy shape during hot pressing, where the first rib 111 enters the second groove 122 or the second rib 121 enters the first groove 112.

[0159] [Features of mold 10]

[0160] As described above, in the mold 10 of this embodiment, the width of the first rib 111 of the first slow cooling region 113 is narrower than the width of the first groove 112. Furthermore, the width of the second rib 121 of the second slow cooling region 123 is narrower than the width of the second groove 122. Therefore, when hot pressing is performed using the mold 10, the cooling rate of the raw material B is suppressed in the region sandwiched between the first slow cooling region 113 and the second slow cooling region 123. Therefore, it is possible to form an impact buffer region with suppressed strength and a high-strength region with higher strength than the impact buffer region within the hot-pressed article. Moreover, during hot pressing, when the first slow cooling region 113 and the second slow cooling region 123 are viewed from the normal direction of the first slow cooling region 113, the first rib 111 and the second rib 121 at least partially overlap. Therefore, in the impact buffer region, it is possible to suppress the deformation of the raw material B into a wavy shape.

[0161] [Preferred configuration for mold 10]

[0162] In the first slow-cooling region 113 and the second slow-cooling region 123, preferably, the first rib 111 and the second rib 121 extend in the same direction. Furthermore, the first groove 112 and the second groove 122 extend in the same direction. Figure 5A and Figure 6 In the middle, the first rib 111 and the second rib 121 extend in the L direction, and the first groove 112 and the second groove 122 extend in the L direction.

[0163] As described above, when the first rib 111, the first groove 112, the second rib 121, and the second groove 122 all extend in the same direction, a two-dimensional simulation is sufficient for simulating the heat transfer of raw material B. That is, only a cross-section perpendicular to the extending directions of the first rib 111, the first groove 112, the second rib 121, and the second groove 122 needs to be implemented (i.e., Figure 5A The results of a two-dimensional simulation (shown in the cross-section) are essentially the same as those obtained using a three-dimensional simulation. Therefore, there is no need to perform a three-dimensional simulation. Consequently, the heat transfer of raw material B can be simulated more easily and accurately. That is, the cooling rate can be controlled more easily and accurately. In this case, by using simulation, the chemical composition of raw material B can be controlled to achieve the desired microstructure.

[0164] For example, if raw material B is steel, and the hot-pressed product has a microstructure containing not only a hard phase but also retained austenite, its impact absorption capacity will be further improved. The hard phase consists of martensite and / or bainite.

[0165] [The preferred relationship between the first rib 111 and the first groove 112 and the preferred relationship between the second rib 121 and the second groove 122]

[0166] Preferably, the width of the first rib 111 formed in the slow cooling region 113 is 10% to 50% of the width of the first groove 112, and the width of the second rib 121 formed in the slow cooling region 123 is 10% to 50% of the width of the second groove 122.

[0167] If the width of the first rib 111 is more than 10% of the width of the first groove 112, the first rib 111 will properly dissipate heat from the raw material B. In this case, the cooling rate of the raw material B can be prevented from becoming too slow. Therefore, the formation of ferrite and pearlite in the microstructure of the raw material B can be suppressed, and the formation of hard phase, or hard phase and retained austenite, can be promoted. As a result, the impact absorption capacity of the hot-pressed article is improved.

[0168] On the other hand, if the width of the first rib 111 is less than 50% of the width of the first groove 112, the cooling rate can be slowed down during hot pressing. If the cooling rate can be slowed down, it is easier to stop cooling at the desired raw material temperature. For example, cooling can be stopped between the Mf point and the Ms point to adjust the amount of martensite and retained austenite formed. For example, cooling can be stopped at a temperature higher than the Ms point to make the microstructure of the raw material predominantly bainite.

[0169] Therefore, preferably, the width of the first rib portion 111 is 10% to 50% of the width of the first groove portion 112.

[0170] A further preferred upper limit of the ratio of the width of the first rib portion 111 to the width of the first groove portion 112 is 45%, more preferably 40%, and even more preferably 35%.

[0171] A further preferred lower limit of the ratio of the width of the first rib portion 111 to the width of the first groove portion 112 is 12%, more preferably 14%.

[0172] Figure 5B It is a schematic diagram of the raw material B after removing Figure 5A during hot pressing. Among them, the width of the first rib portion 111 is defined as follows. The surface of the first rib portion 111 that faces the second forming surface 120 is defined as the top surface of the first rib portion 111. That is, the surface of the first rib portion 111 that contacts the raw material B during hot pressing is defined as the "top surface". As Figure 5B shown, in the cross-section perpendicular to the extending direction of the first rib portion 111, the width W 111P of the top surface 111P is defined as the width of the first rib portion 111. The width W 111P of the top surface 111P, that is, is equivalent to the length of the top surface 111P in the direction perpendicular to the extending direction of the first rib portion 111 and the normal direction of the top surface 111P (in Figure 5B it is the W direction).

[0173] The height of the first rib portion 111 is defined as follows. In Figure 5B it, the height H 111P from the top surface 111P of the first rib portion 111 to the bottom of the first groove portion 112 is defined as the height of the first rib portion 111. In other words, the length in the normal direction of the top surface 111P (in Figure 5B it is the V direction) from the top surface 111P of the first rib portion 111 to the bottom of the first groove portion 112 is defined as the height H 111P of the first rib portion 111.

[0174] The width of the first groove portion 112 is defined as follows. As Figure 5B shown, in the cross-section perpendicular to the extending direction of the first rib portion 111, the width W 112P of the gap between the end points of one top surface 111P and the end points of the other top surface 111P of adjacent first rib portions 111 is defined as the width of the first groove portion 112.

[0175] The width of the second rib 121 is defined as follows: The surface of the second rib 121 that faces the first forming surface 110 is defined as the top surface of the second rib 121. That is, the surface of the second rib 121 that contacts the raw material B during hot pressing is defined as the "top surface". Figure 5B As shown, in a section perpendicular to the extending direction of the second rib 121, the width W of the top surface 121P is... 121P Defined as the width of the second rib 121. The width W of the top surface 121P. 121P That is, the direction perpendicular to the extension direction of the second rib 121 and the normal direction of the top surface 121P (in Figure 5B The length of the top surface 121P in the W direction is in the middle.

[0176] The height of the second rib 121 is defined as follows. Figure 5B In the middle, the height H from the top surface 121P of the second rib 121 to the bottom 122P of the second groove 122 is... 121P Defined as the height of the second rib 121. In other words, it is the normal direction of the top surface 121P from the top surface 121P of the second rib 121 to the bottom surface 122P of the second groove 122 (in... Figure 5B The length in the V direction is defined as the height of the second rib 121.

[0177] The width of the second groove 122 is defined as follows. For example... Figure 5B As shown, in a cross-section perpendicular to the extending direction of the second rib 121, the width W of the gap between the endpoints of one top surface 121P and the endpoints of the other top surface 121P of adjacent second ribs 121 is... 122P Defined as the width of the second groove 122.

[0178] Furthermore, the shape of the cross-section of the first rib 111 or the second rib 121 perpendicular to the extending direction can be as follows: Figure 5A and Figure 5B This is a rectangular shape, as shown. Figure 5C As shown, it can also be a trapezoidal shape with its width narrowing towards the top surface 111P or the top surface 121P. Additionally, in the first rib 111 or the second rib 121, as... Figure 5D As shown, the corners of the top surface 111P or the top surface 121P can also be chamfered, or the root of the first rib 111 or the second rib 121 can be chamfered. Alternatively, the corners of the top surface 111P or the top surface 121P can be rounded (that is, rounded), or the root of the first rib 111 or the second rib 121 can be rounded (that is, rounded).

[0179] Furthermore, if the top surface (111P or 121P) has been chamfered or rounded, the width of the top surface (111P or 121P) is set to the width of the portion of the top surface (111P and 121P) that has not been chamfered or rounded.

[0180] As described above, the mold 10 in this embodiment is a mold for hot pressing. During hot pressing, the temperature of the raw material B is A. c3 The temperature is higher than that of hot pressing. Therefore, the raw material B used in hot pressing has lower hardness and better processability compared to the raw material used in warm pressing. Therefore, the surface pressure applied to the raw material B during hot pressing is lower than the surface pressure applied during warm pressing. Therefore, even if the width of the first rib 111 is less than 50% of the width of the first groove 112, it is difficult to damage the surface of the raw material B.

[0181] Similarly to the relationship between the first rib 111 and the first groove 112, if the width of the second rib 121 is more than 10% of the width of the second groove 122, excessive reduction in the cooling rate of the raw material B can be suppressed. Therefore, the impact absorption capacity of the hot-pressed article is improved.

[0182] On the other hand, if the width of the second rib 121 is less than 50% of the width of the second groove 122, the cooling rate of the raw material B can be moderately slowed down. Therefore, during hot pressing, it is easy to adjust the cooling stop temperature (that is, the temperature of the raw material B when the mold 10 is separated from the raw material B). For example, it is easy to adjust the cooling stop temperature to a temperature higher than the Ms point, or it is easy to adjust the cooling stop temperature to a temperature between the Mf point and the Ms point, or it is easy to adjust the cooling stop temperature to a temperature between the Ms point and 500°C.

[0183] Therefore, the width of the second rib 121 is 10% to 50% of the width of the second groove 122.

[0184] The preferred upper limit of the ratio of the width of the second rib 121 to the width of the second groove 122 is 45%, more preferably 40%, and even more preferably 35%.

[0185] A further preferred lower limit for the ratio of the width of the second rib 121 to the width of the second groove 122 is 12%, and even more preferred is 14%.

[0186] Similarly to the relationship between the width of the first rib 111 and the width of the first groove 112 mentioned above, even if the width of the second rib 121 is less than 50% of the width of the second groove 122, it is difficult to damage the surface of the raw material B.

[0187] [Preferred width and preferred height of the first rib 111, preferred width and preferred height of the second rib 121]

[0188] Preferably, in at least a portion of the first slow cooling region 113, the width of the first rib 111 is 1.0 mm to 8.0 mm, and the height of the first rib 111 is 0.2 mm to 5.0 mm; in at least a portion of the second slow cooling region 123, the width of the second rib 121 is 1.0 mm to 8.0 mm, and the height of the second rib 121 is 0.2 mm to 5.0 mm. The height of the first rib 111 corresponds to the depth of the first groove 112. Similarly, the height of the second rib 121 corresponds to the depth of the second groove 122.

[0189] If the width of the first rib 111 or the width of the second rib 121 is set to 8.0 mm or less, the temperature deviation in the width direction of the first rib 111 or the second rib 121 in the raw material B can be reduced. Therefore, during hot pressing, the fluctuation of cooling rate originating from the temperature deviation of the raw material B can be reduced.

[0190] On the other hand, if the width of the first rib 111 or the width of the second rib 121 is set to 1.0 mm or more, the first rib 111 or the second rib 121 will be difficult to bend during hot pressing, thus increasing productivity. Therefore, the preferred width of the first rib 111 is 1.0 mm to 8.0 mm. The preferred width of the second rib 121 is 1.0 mm to 8.0 mm.

[0191] A further preferred lower limit for the width of the first rib 111 is 1.8 mm, and even more preferably 2.0 mm. A further preferred lower limit for the width of the second rib 121 is 1.8 mm, and even more preferably 2.0 mm. In this case, the first rib 111 and the second rib 121 are more difficult to bend. In addition, the dimensional accuracy of the first rib 111 and the second rib 121 is relaxed, thus making them easier to process.

[0192] If the height of the first rib 111 or the height of the second rib 121 is set to 0.2 mm or more, heat dissipation from the raw material B in the first groove 112 or the second groove 122 can be suppressed. On the other hand, if the height of the first rib 111 or the height of the second rib 121 is set to 5.0 mm or less, the first rib 111 or the second rib 121 is less prone to bending during hot pressing, thus improving productivity. Therefore, the preferred height of the first rib 111 is 0.2 mm to 5.0 mm. The preferred height of the second rib 121 is 0.2 mm to 5.0 mm.

[0193] Furthermore, in at least a portion of the first slow-cooling region 113 and the second slow-cooling region 123, the aforementioned preferred effect can be obtained in at least a portion of the aforementioned regions simply by adjusting the width or height of the first rib 111 or the second rib 121 as described above. Therefore, in this embodiment, in at least a portion of the first slow-cooling region 113 and the second slow-cooling region 123, the width or height of the first rib 111 or the second rib 121 can be adjusted as described above. Preferably, in the entire first slow-cooling region 113, the width of the first rib 111 is 1.0 mm to 8.0 mm, and the height is 0.2 mm to 5.0 mm; in the entire second slow-cooling region 123, the width of the second rib 121 is 1.0 mm to 8.0 mm, and the height is 0.2 mm to 5.0 mm.

[0194] Further preferably, in at least a portion of the first slow cooling region 113, the width of the first rib 111 is 1.0 mm to 4.0 mm, and is 10% to 30% of the width of the first groove 112; and in at least a portion of the second slow cooling region 123, the width of the second rib 121 is 1.0 mm to 4.0 mm, and is 10% to 30% of the width of the second groove 122. In this case, the cooling rate of the raw material B can be further slowed down. Therefore, it is easier to adjust the cooling stop temperature to the desired temperature. Moreover, the temperature deviation of the raw material B during hot pressing can be reduced.

[0195] [Regarding Fn1]

[0196] In mold 10, the following situation is envisioned: the first rib 111 and the second rib 121 extend in the same direction, the first groove 112 and the second groove 122 extend in the same direction, the width of the first rib 111 is 10% to 50% of the width of the first groove 112, the width of the second rib 121 is 10% to 50% of the width of the second groove 122, the width of the first rib 111 and the second rib 121 is 1.0 mm to 8.0 mm, and the height of the first rib 111 and the second rib 121 is 0.2 mm to 5.0 mm.

[0197] In this case, it is preferable that Fn1, as defined by equation (1), is 14 or less.

[0198] Fn1=Wr 0.9 / P0 0.8 +0.05Hr (1)

[0199] Wherein, Wr is the width (mm) of the first rib 111 and the second rib 121. P0 = Wr / Ws, where Ws is the width (mm) of the first groove 112 and the second groove 122. Hr is the height (mm) of the first rib 111 and the second rib 121. Fn1 will be explained below.

[0200] Figure 8 This is a graph showing the relationship between Fn1 and the temperature deviation ΔT (°C) in the first slow cooling region 113 and the second slow cooling region 123. Figure 8 The results were obtained through a two-dimensional heat transfer simulation as shown below. Specifically, the simulation utilized a hypothetical... Figure 9 The finite difference method of the thermal conductivity model shown simulates the temperature distribution of raw material B during hot pressing and the change of this temperature distribution over time.

[0201] Figure 9 This is a cross-sectional view along the width direction of the first rib 111 and the second rib 121 in the first slow cooling region 113 and the second slow cooling region 123. The raw material B is divided into multiple elements E with a width D0 = 1 mm, a thickness D1 = the plate thickness of raw material B (assumed to be 1.4 mm), and a unit length in the L direction. The heat gain / loss Q (W / m²) per unit time (1 second) at the i-th (i is a natural number) element E due to heat conduction and heat transfer is... 2 It is represented by the following formula.

[0202] Q = (Q²i) - (Q²i + 1) - 2Q¹

[0203] The terms of this expression are defined by the following formula.

[0204] (The situation where element E is in contact with the first rib 111 and the second rib 121)

[0205] Q1: The heat transfer per unit time from element E to the mold caused by the contact heat transfer between raw material B and ribs (111 or 121) (W / m) 2 )

[0206] Q1 = -h(Tr - Tbi)

[0207] Heat transfer coefficient h = 2000 W / m 2 ·K

[0208] Mold temperature Tr = 100℃

[0209] Tbi: Temperature of the i-th element E in raw material B

[0210] (The case where element E does not contact the first rib 111 and the second rib 121)

[0211] Q1: The amount of heat transferred from element E to the mold per unit time (W / m) due to heat conduction through the air at the groove (112 or 122). 2 )

[0212] Q1=-λa(Tr-Tbi) / Hr

[0213] λa: Thermal conductivity of air = 0.04 W / m·K

[0214] Q2i: The movement of heat per unit time from element E (i-1) to the adjacent element E (i) due to thermal conduction within raw material B (W / m) 2 )

[0215] Q2i=-λb(Tbi-Tbi-1) / Δx

[0216] λb: Thermal conductivity of raw material B = 50 W / m·K

[0217] Tbi: Temperature of the i-th element E (raw material B)

[0218] Tbi-1: The temperature of the (i-1)th element E adjacent to the i-th element E.

[0219] Δx: Distance between adjacent feature E = 1 mm

[0220] In addition, the temperature change ΔTb (°C) of the element E per unit time resulting from the heat gain or loss Q is expressed by the following formula.

[0221] ΔTb=Q / (c·ρ·D0·D1)

[0222] c: Specific heat of raw material B = 0.435 J / (g·K)

[0223] ρ: Density of raw material B = 7.8 × 10 3 (g / m 3 )

[0224] In the above heat conduction model, the first rib 111 and the second rib 121 are assumed to extend in the same direction, and the first groove 112 and the second groove 122 are assumed to extend in the same direction. Furthermore, the width of the first rib 111 is assumed to be the same as the width of the second rib 121, and the height of the first rib 111 is assumed to be the same as the height of the second rib 121. Similarly, the width of the first groove 112 is assumed to be the same as the width of the second groove 122. Moreover, as... Figure 9 As shown, it is configured such that during hot pressing, the entire top surface of the first rib 111 overlaps with the entire top surface of the second rib 121. Furthermore, the cross-sectional shape of the ribs (111 and 121) perpendicular to their extending direction is rectangular.

[0225] As an initial condition, the temperature Tbi of element E at time 0 (seconds) is set to 622℃. Furthermore, it is set as follows: [The text abruptly ends here, so the translation stops as well.] Figure 9Within a 500mm to 1000mm interval to the right and left, element E contacts the first rib 111 and the second rib 121 (that is, the above interval is designated as the slow cooling region 113 and the slow cooling region 123), as boundary conditions, respectively in... Figure 9 The thermal conductivity of raw material B within element E at locations 1000 mm to the right and left is assumed to be adiabatic. Furthermore, the temperature change ΔTb of element E is calculated successively at time intervals of 0.01 seconds, thereby simulating the temperature distribution of raw material B and its change over time.

[0226] By varying the width and height of the ribs (111 and 121) and the width of the grooves (112 and 122), respectively... Figure 9 The difference between the maximum and minimum values ​​of Tbi, Tbimax and Tbimin, within a 250mm interval to the right and left of the material, Tbimax-Tbimin, is defined as the temperature deviation ΔT (°C) in raw material B. The calculated ΔT was used to produce... Figure 8 .

[0227] Reference Figure 8 When Fn1 is higher than 14, ΔT decreases rapidly along with the decrease in Fn1. Furthermore, when Fn1 falls below 14, the decrease in ΔT due to the decrease in Fn1 becomes more gradual. When Fn1 falls below 10, the decrease in ΔT due to the decrease in Fn1 becomes even more gradual. Therefore, in Figure 8 In the chart, there are inflection points near Fn1=14 and near Fn1=10.

[0228] Therefore, the preferred upper limit for Fn1 is 14, and more preferably 10. As long as Fn1 is 14 or less, for example, the temperature deviation ΔT of raw material B becomes 110°C or less. In addition, as long as Fn1 is 10 or less, for example, the temperature deviation ΔT of raw material B becomes 40°C or less.

[0229] [Regarding Fn2]

[0230] In mold 10, the following situation is envisioned: the first rib 111 and the second rib 121 extend in the same direction, the first groove 112 and the second groove 122 extend in the same direction, the width of the first rib 111 is 10% to 50% of the width of the first groove 112, the width of the second rib 121 is 10% to 50% of the width of the second groove 122, the width of the first rib 111 and the second rib 121 is 1.0 mm to 8.0 mm, and the height of the first rib 111 and the second rib 121 is 0.2 mm to 5.0 mm.

[0231] In this case, it is preferable that Fn2, as defined by equation (2), is 30 or more.

[0232] Fn2=Ws 2 ×Hr 0.4 / Wr (2)

[0233] Wherein, Ws is the width (mm) of the first groove 112 and the second groove 122. Wr is the width (mm) of the first rib 111 and the second rib 121. Hr is the height (mm) of the first rib 111 and the second rib 121.

[0234] Figure 10 This is a graph showing the relationship between Fn2 and the cooling rate V (°C / second) of the raw material B during hot pressing. Figure 10 By using Figure 9 The heat transfer model shown above was obtained from a two-dimensional heat transfer simulation. Furthermore, in the heat transfer simulation, the cooling rate V was calculated by averaging the temperature change of element E per unit time from time 0 to the moment when the temperature of element E reaches 400°C. Here, the element E used for calculating the cooling rate is assumed to be an element whose temperature Tbi is Tbimax.

[0235] Reference Figure 10 As Fn2 increases, the cooling rate V of raw material B decreases rapidly, and then the rate of decrease in cooling rate V becomes gradual. Therefore, the preferred lower limit of Fn2 is 30, more preferably 45, and even more preferably 90. As long as Fn2 is 30 or higher, for example, the cooling rate V of raw material B becomes 80°C / second or lower. Therefore, during hot pressing, it is easy to adjust the cooling stop temperature (that is, the temperature of raw material B when the mold 10 separates from raw material B) to the desired temperature. As long as Fn2 is 45 or higher, for example, the cooling rate of raw material B becomes 70°C / second or lower. Therefore, it is easier to adjust the cooling stop temperature to the desired temperature. As long as Fn2 is 90 or higher, for example, the cooling rate V of raw material B becomes 50°C / second or lower. Therefore, it is easier to adjust the cooling stop temperature to the desired temperature.

[0236] In mold 10, it is further preferred that Fn1 is 14 or less and Fn2 is 30 or more. In this case, the temperature deviation ΔT of the raw material B can be further suppressed, and it is easier to adjust the cooling stop temperature to the desired temperature.

[0237] Further preferably, in the mold 10, the first rib 111 and the second rib 121 extend in the same direction, and the first groove 112 and the second groove 122 extend in the same direction. The width of the first rib 111 is 1.0 mm to 4.0 mm and is 10% to 30% of the width of the first groove 112. Similarly, the width of the second rib 121 is 1.0 mm to 4.0 mm and is 10% to 30% of the width of the second groove 122. Fn1 is 14 or less, and / or Fn2 is 30 or more. In this case, the cooling rate of the raw material B can be further slowed down. Therefore, it is easier to adjust the cooling stop temperature to the desired temperature. Furthermore, the temperature deviation of the raw material B during hot pressing can be reduced.

[0238] [Other forms of the mold 10 in this embodiment]

[0239] [Regarding the shapes of the first forming surface 110 and the second forming surface 120 of the mold 10]

[0240] The mold 10 in this embodiment is not limited to the structure described above. For example, the mold 10 is not limited to... Figure 2 The shapes shown are as follows. The first forming surface 110 and the second forming surface 120 of the mold 10 can also be bent in the length direction. In addition, the cross-sectional shape of the first forming surface 110 of the upper mold 11 of the mold 10, which is perpendicular to the length direction (L direction), is not limited to a concave shape. The cross-sectional shape of the second forming surface 120 of the lower mold 12, which is perpendicular to the length direction (L direction), is not limited to a convex shape. As long as the first forming surface 110 of the upper mold 11 and the second forming surface 120 of the lower mold 12 are fitted together, the shapes of the first forming surface 110 and the second forming surface 120 are not particularly limited.

[0241] [Regarding the configuration of the first slow-cooling region 113 of the first forming surface 110 and the second slow-cooling region 123 of the second forming surface 120]

[0242] Furthermore, the configuration of the first slow cooling region 113 of the first forming surface 110 is not particularly limited. Similarly, the configuration of the second slow cooling region 123 of the second forming surface 120 is not particularly limited. The first forming surface 110 may include the first slow cooling region 113, and the second forming surface 120 may include the second slow cooling region 123.

[0243] For example, the first slow cooling region 113 and the second slow cooling region 123 are not limited to Figure 2 The shape shown. Figure 11 This refers to the mold 10 in this embodiment and... Figure 2 A 3D diagram of another different example. For example... Figure 11As shown, a first slow cooling region 113 may also be provided on the entire bottom surface of the recess of the first forming surface 110 of the upper mold 11 of the mold 10. A second slow cooling region 123 may also be provided on the entire upper surface of the protrusion of the second forming surface 120 of the lower mold 12 of the mold 10.

[0244] Figure 12 This refers to the mold 10 in this embodiment and... Figure 2 , Figure 11 A 3D diagram of another different example. For example... Figure 12 As shown, a first slow cooling region 113 may also be partially provided on the side of the concave portion of the first forming surface 110 of the upper mold 11 of the mold 10. A second slow cooling region 123 may also be partially provided on the side of the convex portion of the second forming surface 120 of the lower mold 12 of the mold 10.

[0245] Figure 13 This refers to the mold 10 in this embodiment and... Figure 2 , Figure 11 as well as Figure 12 A 3D view of another different example. Figure 2 , Figure 11 as well as Figure 12 In this process, the first forming surface 110 includes a first slow cooling region 113 and a first rapid cooling region 114. Furthermore, the second forming surface 120 includes a second slow cooling region 123 and a second rapid cooling region 124. In contrast, Figure 13 As shown, the entire first forming surface 110 may be a first slow cooling region 113. Alternatively, the entire second forming surface 120 may be a second slow cooling region 123.

[0246] As described above, as long as the first forming surface 110 includes a first slow cooling region 113 and the second forming surface 120 includes a second slow cooling region 123, the positions of the first slow cooling region 113 in the first forming surface 110 and the second slow cooling region 123 in the second forming surface 120 are not particularly limited. However, when the upper die 11 and the lower die 12 are in contact with the raw material B during hot pressing and are stamping the raw material B, at least a portion of the first slow cooling region 113 and at least a portion of the second slow cooling region 123 are arranged opposite to each other.

[0247] In this embodiment, the first slow-cooling region 113 can also be defined as a portion of the region where the first rib 111 and the first groove 112 are formed. Similarly, the second slow-cooling region 123 can also be defined as a portion of the region where the second rib 121 and the second groove 122 are formed. In summary, in this embodiment, in at least a portion of the first forming surface 110, the width of the first rib 111 is narrower than the width of the first groove 112, and in at least a portion of the second forming surface 120, the width of the second rib 121 is narrower than the width of the second groove 122.

[0248] [Regarding the extending direction of the first rib 111 and the second rib 121]

[0249] In this embodiment, the extending directions of the first rib 111 and the second rib 121 are not particularly limited. For example, the first rib 111 and the second rib 121 may not be... Figure 5A and Figure 6 It extends in the L direction as shown. Figure 14 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A Another different example. Figure 15 yes Figure 14 A cross-sectional view at line segment XV-XV. (Refer to...) Figure 14 and Figure 15 In this embodiment, the first rib 111, the first groove 112, the second rib 121, and the second groove 122 all extend in the W direction and are arranged in the L direction. In this case, the width of the first rib 111, the width of the first groove 112, the width of the second rib 121, and the width of the second groove 122 all represent the width of the mold 10 in the L direction.

[0250] In hot pressing, the upper die 11 moves together with the slider 3 in the V direction. As a result, the raw material B is hot pressed by the first forming surface 110 of the upper die 11 and the second forming surface 120 of the lower die 12. The first forming surface 110 and the second forming surface 120 have... Figure 2 In the case of the shape shown, due to hot pressing, the metal flow of raw material B occurs in the W direction. That is, in region 100, raw material B slides in the W direction relative to the first forming surface 110 and the second forming surface 120.

[0251] like Figure 14 and Figure 15As shown, when the first rib 111, the first groove 112, the second rib 121, and the second groove 122 all extend in the W direction, the raw material B is less likely to experience frictional resistance from the first rib 111 and / or the second rib 121, and the raw material B is more likely to slide relative to the first rib 111 and / or the second rib 121. Therefore, it is possible to suppress the formation of defects on the surface of the raw material B.

[0252] Thus, when the first rib 111, the first groove 112, the second rib 121, and the second groove 122 extend in the sliding direction of the raw material B during the hot pressing process, it is possible to suppress the formation of defects on the surface of the raw material B during the hot pressing process.

[0253] [Regarding the configuration relationship between the first rib 111 and the second rib 121]

[0254] In this embodiment, the arrangement of the first rib 111 and the second rib 121 may also be different. Figure 5A and Figure 6 As shown, they completely overlap when the mold 10 is closed. Figure 16 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A , Figure 14 Another different example. Figure 17 Viewed from the normal direction of the first slow-cooling region 113 Figure 16 Region 100 is shown only as a schematic diagram of the ribs. For example, refer to Figure 16 and Figure 17 Alternatively, with the mold 10 closed, the first rib 111 and the second rib 121 can be arranged parallel to each other and overlapped in a staggered manner. In this way, the first rib 111 and the second rib 121 only need to overlap at least partially.

[0255] In this embodiment, the arrangement of the first rib 111 and the second rib 121 may also be different. Figure 5A and Figure 16 They extend in the same direction as shown. Figure 18 It is magnification Figure 3 In the schematic diagram of area 100, and... Figure 5A , Figure 14 as well as Figure 16 Another different example. Figure 19 Viewed from the normal direction of the first slow-cooling region Figure 18 Region 100 is shown only as a schematic diagram of the ribs. For example, as... Figure 18 and Figure 19As shown, alternatively, multiple first grooves 112 and multiple first ribs 111 may extend in the L direction, and multiple second grooves 122 and multiple second ribs 121 may extend in the W direction. Even in this case, referring to... Figure 19 When the mold 10 is closed, the first rib 111 also overlaps at least partially with the second rib 121.

[0256] [For the first slow cooling zone 113 and the second slow cooling zone 123]

[0257] In this embodiment, the first slow-cooling region 113 and the second slow-cooling region 123 preferably do not have supply ports for supplying cooling medium to the surfaces of the first slow-cooling region 113 and the second slow-cooling region 123. Assuming that the first slow-cooling region 113 and the second slow-cooling region 123 have supply ports, in the portions of the first slow-cooling region 113 and the second slow-cooling region 123 with supply ports, the raw material B is prone to excessive heat dissipation due to air trapped in the piping inside the mold 10 (upper mold 11, lower mold 12) communicating with the supply ports. Therefore, there is a possibility of contributing to temperature deviations in the raw material B.

[0258] On the other hand, the upper mold 11 and the lower mold 12 may also have internal cooling paths for the flow of cooling medium. In this case, the temperature of the upper mold 11 and the lower mold 12 during hot pressing can be kept sufficiently low.

[0259] [Manufacturing method of thermoformed article using mold 10]

[0260] A method for manufacturing a thermoformed article using mold 10 based on thermoforming will be described. The method for manufacturing a thermoformed article according to this embodiment includes the following steps.

[0261] Preparation process

[0262] Heating process

[0263] Hot pressing process

[0264] Demolding process

[0265] The following is a description of each process.

[0266] [Preparation Process]

[0267] In the preparation process, raw material B with the desired chemical composition is prepared. In this embodiment, raw material B is not particularly limited. Raw material B is, for example, a steel plate. When raw material B is a steel plate, the type of steel plate is not particularly limited. Raw material B can be, for example, a steel plate that has undergone surface treatment such as plating, or a steel plate that has not undergone surface treatment such as plating (so-called bare material). When plating is performed, the plating treatment can be hot-dip galvanizing, alloyed hot-dip galvanizing, or aluminizing.

[0268] As mentioned above, the chemical composition of the base steel plate of raw material B is not particularly limited. The base steel plate of raw material B may, for example, have the following chemical composition by mass percent: C: 0.10% to 0.60%, Si: 0 to 5.0%, Mn: 0 to 5.0%, P: less than 0.100%, S: less than 0.100%, N: less than 0.100%, O: less than 0.100%, Al: 0 to 1.0%, Cr: 0 to 3.0%, Mo: 0 to 5.0%, V: 0 to 2.0%, Nb: 0 to 1.0%, Ti: 0 to 1.0%, B: 0 to 1.0%, Ca: 0 to 1.0%, Mg: 0 to 1.0%, Zr: 0 to 1.0%, rare earth elements: 0 to 1.0%, Co: 0 to 5.0%, W: 0 to 5.0%, Ni: 0 to 3.0%, Cu: 0 to 3.0%, and the remainder consisting of Fe and impurities. Impurities refer to elements that are introduced during the industrial manufacturing of steel from raw materials such as ore, waste, or the manufacturing environment, and are permissible within a range that will not adversely affect the hot-pressed product of this embodiment.

[0269] The thickness of raw material B is not particularly limited and can be selected according to the characteristics of the thermoformed product to be obtained. For example, the thickness of raw material B can be 0.6 mm to 3.2 mm. The mechanical properties of raw material B are also not particularly limited. The mechanical properties of raw material B can be appropriately selected according to the characteristics of the thermoformed product to be obtained. For example, the tensile strength of raw material B can also be 400 MPa or higher.

[0270] There are no particular limitations on the method for preparing raw material B. For example, raw material B can be manufactured from molten steel having the aforementioned chemical composition using known manufacturing methods. Alternatively, it can be prepared by purchasing raw material B manufactured by a third party.

[0271] [Heating Process]

[0272] In the heating process, the prepared raw material B is heated to A. c3 Temperatures above point A. If the heating temperature is less than A... c3If the temperature is A, then raw material B will not become a single austenitic phase. In this case, when raw material B is cooled during the hot pressing process, the formation of the hard phase (martensite and / or bainite) in the region of raw material B sandwiched between the first quenching region 114 and the second quenching region 124 becomes insufficient. Therefore, there is a possibility of not obtaining sufficient strength. If the heating temperature is A c3 Above a certain point, the raw material B before the hot pressing process becomes an austenitic single phase. Therefore, when the raw material B is cooled in the hot pressing process, a hard phase is sufficiently formed in the region of the raw material B sandwiched between the first quenching region 114 and the second quenching region 124. As a result, the strength of this region can be improved.

[0273] Preferably, the heating temperature is set to less than 950°C. In this case, the heating time of raw material B can be shortened, thereby increasing productivity. Moreover, the fuel and electricity required for heating can be reduced, thus suppressing manufacturing costs.

[0274] In the heating process, there are no particular limitations on the method used to heat raw material B. For example, an electric furnace, a gas furnace, a far-infrared heating furnace, or a near-infrared heating furnace can also be used to heat raw material B. Additionally, electrically powered heating devices or high-frequency induction heating devices can also be used. There are no limitations on the method used to heat raw material B in the heating process; any known heating method can be appropriately selected.

[0275] [Hot pressing process]

[0276] In the hot pressing process, the aforementioned mold 10 is used to heat the material to A. c3 The raw material B above the specified point is hot-pressed. In the hot-pressing process, the raw material B, which has been heated in the heating process, is placed on the second forming surface 120 of the lower mold 12. Then, as... Figure 3 As shown, the upper mold 11 is brought relatively close to the lower mold 12, thereby closing the mold 10. At this time, the raw material B comes into contact with the first forming surface 110 of the upper mold 11 and the second forming surface 120 of the lower mold 12. In other words, the raw material B is sandwiched between the first forming surface 110 of the upper mold 11 and the second forming surface 120 of the lower mold 12. The raw material B is thermoformed using the upper mold 11 and the lower mold 12.

[0277] Furthermore, in the hot pressing process of this embodiment, no cooling medium is used to cool the raw material B during hot pressing. Instead, the mold 10, which is in contact with the raw material B during hot pressing, dissipates heat from the raw material B. When the mold 10 is closed, in the first slow cooling zone 113, the first rib 111 of the first forming surface 110 of the upper mold 11 contacts the raw material B. Moreover, in the second slow cooling zone 123, the second rib 121 of the second forming surface 120 of the lower mold 12 contacts the raw material B. At this time, the temperature of the upper mold 11 and the lower mold 12 is sufficiently lower than that of the raw material B. Therefore, the raw material B dissipates heat through the first rib 111 and the second rib 121. The temperature of the upper mold 11 and the lower mold 12 is, for example, room temperature (20±15°C) to 200°C.

[0278] [Demolding process]

[0279] In the demolding process, the raw material B, which has undergone hot pressing, is demolded from the mold 10 to manufacture a hot-pressed article. The temperature of the raw material B (hot-pressed article) when demolded from the mold 10 is defined as the cooling stop temperature. For example, if the cooling stop temperature is between the Mf point and Ms point of the hot-pressed article, or between the Ms point and 500°C, the microstructure of the hot-pressed article will be composed of a hard phase, or a hard phase and retained austenite. In this case, the obtained hot-pressed article has excellent impact absorption capacity. Therefore, it is preferable that, in the demolding process of this embodiment, the raw material B is demolded from the mold 10 when the temperature of the region of the raw material B sandwiched between the Mf point and Ms point determined according to the chemical composition of the raw material B, or between the Ms point and 500°C.

[0280] Furthermore, the Ms point and Mf point of raw material B differ depending on the chemical composition of raw material B. Therefore, in raw material B, the preferred cooling stop temperature varies depending on the chemical composition of raw material B, depending on whether a microstructure composed of a hard phase or a microstructure composed of a hard phase and retained austenite is desired. However, according to the manufacturing method of hot-pressed articles using mold 10, the cooling rate, temperature change over time in the region of raw material B sandwiched between the first slow-cooling region 113 and the second slow-cooling region 123 can be determined using heat transfer simulation based on the width and height of the first rib 111, the first groove 112, the second rib 121, and the second groove 122 formed in the first slow-cooling region 113 and the second slow-cooling region 123, and the chemical composition of raw material B. Therefore, the preferred cooling stop temperature or the time from the start of hot pressing to demolding can be determined using these heat transfer simulations. Therefore, according to the mold 10 of this embodiment, a hot-pressed product having a structure composed of a hard phase or a structure composed of a hard phase and retained austenite can be manufactured by hot pressing based on the chemical composition of the raw material B.

[0281] [Other processes]

[0282] Alternatively, the method for manufacturing a hot-pressed molded article according to this embodiment may also include other manufacturing steps besides those described above. For example, the method for manufacturing a hot-pressed molded article according to this embodiment may also include a heating and holding process at a temperature range of 500°C or below after the demolding process.

[0283] In the heat-holding process, the hot-pressed article after the demolding process is heat-held within a temperature range of 500°C or lower. Specifically, the hot-pressed article formed by demolding from mold 10 is held at a heating temperature of 100°C to 500°C. In this case, heat-holding can be used to distribute carbon from the hard phase in the microstructure of the hot-pressed article to the retained austenite. The carbon in the retained austenite becomes more concentrated, thus promoting the formation of retained austenite. As a result, the proportion of retained austenite in the hot-pressed article increases. In this case, the retained austenite phase transforms into martensite during impact deformation, thereby improving the ductility of the hot-pressed article (the so-called TRIP (Transformation Induced Plasticity) effect). As a result, the impact absorption capacity of the hot-pressed article is further improved.

[0284] The preferred upper limit for the heating and holding temperature is 400°C. Furthermore, the heating and holding temperature is preferably set above Ms point -209°C. In this case, the impact absorption capacity of the hot-pressed article is stable and further improved. Therefore, when Ms point -209°C exceeds 100°C, the preferred lower limit for the heating and holding temperature is Ms point -209°C. The heating and holding time is not particularly limited. The holding time at the heating and holding temperature is preferably set, for example, from 5 seconds to 30 minutes (1800 seconds).

[0285] The embodiments of this disclosure have been described above. However, the above embodiments are merely illustrative examples for implementing this disclosure. Therefore, this disclosure is not limited to the above embodiments, and can be implemented by appropriately modifying the above embodiments without departing from its spirit.

[0286] Explanation of reference numerals in the attached figures

[0287] 1. Hot pressing device; 10. Mold; 11. Upper mold; 110. First forming surface; 111. First rib; 112. First groove; 113. First slow cooling zone; 12. Lower mold; 120. Second forming surface; 121. Second rib; 122. Second groove; 123. Second slow cooling zone.

Claims

1. A mold for hot pressing raw materials, wherein, The mold has the following features: Upper mold, having a first forming surface; and The lower mold has a second forming surface, which is positioned opposite to the first forming surface during hot pressing, and together with the first forming surface, hot presses the raw material. The first forming surface includes a first slow-cooling region, which has multiple first ribs and multiple first grooves. The plurality of the first ribs are arranged in the width direction of the first ribs. The plurality of the first groove portions are arranged in the width direction of the first groove portion. The first rib is formed between adjacent first grooves. The width of the first rib is narrower than the width of the first groove. The second forming surface includes a second slow-cooling region, which has multiple second ribs and multiple second grooves. The plurality of said second ribs are arranged in the width direction of the second ribs. The plurality of said second groove portions are arranged in the width direction of the second groove portions. The second rib is formed between adjacent second grooves. The width of the second rib is narrower than the width of the second groove. During hot pressing, when viewing the first slow cooling region and the second slow cooling region from the normal direction of the first slow cooling region, The first rib and the second rib at least partially overlap.

2. The mold according to claim 1, wherein, During hot pressing, when viewing the first slow cooling region and the second slow cooling region from the normal direction of the first slow cooling region, The first rib and the second rib extend in the same direction. The first groove and the second groove extend in the same direction.

3. The mold according to claim 1 or 2, wherein, The width of the first rib is 10% to 50% of the width of the first groove. The width of the second rib is 10% to 50% of the width of the second groove.

4. The mold according to claim 1, wherein, At least a portion of the first slow-cooling region, The width of the first rib is 1.0mm to 8.0mm. The height of the first rib is 0.2mm to 5.0mm. At least in a portion of the second slow-cooling region, The width of the second rib is 1.0mm to 8.0mm. The height of the second rib is 0.2mm to 5.0mm.

5. The mold according to claim 2, wherein, The width of the first rib is 10% to 50% of the width of the first groove. The width of the second rib is 10% to 50% of the width of the second groove. The width of the first rib and the second rib is 1.0 mm to 8.0 mm respectively. The height of the first rib and the second rib is each 0.2mm to 5.0mm. Fn1, as defined by equation (1), is 14 or less. Fn1=Wr 0.9 / P0 0.8 +0.05Hr (1) In formula (1), Wr is the width of the first rib and the second rib in mm, P0 = Wr / Ws, Ws is the width of the first groove and the second groove in mm, and Hr is the height of the first rib and the second rib in mm.

6. The mold according to claim 2 or 5, wherein, The width of the first rib is 10% to 50% of the width of the first groove. The width of the second rib is 10% to 50% of the width of the second groove. The width of the first rib and the second rib is 1.0 mm to 8.0 mm respectively. The height of the first rib and the second rib is each 0.2mm to 5.0mm. Fn2, as defined by equation (2), is 30 or higher. Fn2=Ws 2 ×Hr 0.4 / Wr (2) In formula (2), Ws is the width of the first groove and the second groove in mm, Wr is the width of the first rib and the second rib in mm, and Hr is the height of the first rib and the second rib in mm.

7. The mold according to claim 4 or 5, wherein, At least a portion of the first slow-cooling region, The width of the first rib is 1.0mm to 4.0mm, and is 10% to 30% of the width of the first groove. At least in a portion of the second slow-cooling region, The width of the second rib is 1.0 mm to 4.0 mm, and is 10% to 30% of the width of the second groove.

8. A method for manufacturing a hot-pressed article, wherein, The manufacturing method of this hot-pressed product includes the following steps: The process of preparing raw materials; Heat the prepared raw materials to A c3 Processes involving temperatures above a certain point; The process of hot pressing the heated raw material using the mold according to any one of claims 1 to 7; and The process of manufacturing a thermoformed article by demolding the raw material that has been thermoformed from the mold.

9. The method for manufacturing a hot-pressed article according to claim 8, wherein, The method for manufacturing the hot-pressed article further includes a step of maintaining the hot-pressed article at a temperature of 100°C to 500°C after demolding from the mold.

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