WO2010150683A1

WO2010150683A1 - Hot press-forming method for steel sheets, hot press-forming device for steel sheets, and steel formed member

Info

Publication number: WO2010150683A1
Application number: PCT/JP2010/060127
Authority: WO
Inventors: 裕一石森; 弘福地; 哲男嶋
Original assignee: 新日本製鐵株式会社
Priority date: 2009-06-22
Filing date: 2010-06-15
Publication date: 2010-12-29
Also published as: CN102458708B; JPWO2010150683A1; JP4795486B2; CN102458708A

Abstract

Before hot press-forming a flat plated steel sheet (K) that has been uniformly heated to a temperature equal to or greater than an A₁ transformation point, a partial rapid cooling stage (11) rapidly cools a prescribed region of the plated steel sheet (K) to a temperature equal to or less than the martensite start (Ms) temperature, and then the rapidly cooled region of the plated steel sheet (K) is reheated to a temperature greater than the martensite start (Ms) temperature. After the plated steel sheet (K) is reheated, a forming/rapid-cooling stage (13) simultaneously forms the plated steel sheet (K) and rapidly cools same to a temperature equal to or less than the martensite finish (Mf) temperature.

Description

Steel plate hot press forming method, steel plate hot press forming apparatus, and steel forming member

The present invention relates to a forming method, a forming apparatus, and a forming member that facilitate processing of a part in a subsequent process by forming a structure including tempered martensite in an arbitrary part of a steel sheet in hot press forming. Is.

In recent years, hot press forming, which has been increasingly used as a steel plate forming means for automobile parts using high-tensile steel plate, forms a steel plate at a higher temperature than cold press forming. When hot press forming is performed, the deformation resistance of the steel sheet during press forming is reduced, and due to this reduction in deformation resistance, the desired shape can be obtained without causing molding defects such as press cracks and wrinkles, and the mold It can be press-molded into a shape conforming to the shape.

In the hot press forming method, the punch is lowered to the bottom dead center in a state where a steel plate that has been heated to a predetermined temperature in a heating furnace is placed on the die of the molding die, and the state is maintained while maintaining the state. The steel sheet is rapidly cooled for a certain period of time by supplying a coolant into the mold. This quenching by quenching changes the structure of the steel sheet to martensite, thereby increasing the hardness of the steel sheet and greatly improving the strength of the molded product.

However, if the steel sheet is cooled rapidly over the entire steel sheet, depending on the part, the hardness of the molded product may increase, which may be undesirable. For example, the bending strength around the welded joint area is reduced, the joint strength is reduced, the processing of the molded product is difficult in the subsequent processes such as drilling and shearing, and the life of the processing tool is reduced. Or For this reason, in Patent Document 1, a steel plate is not quenched by providing a gap in a mold so that a portion that requires machining in a subsequent process of hot press molding does not contact the molding die. It has been proposed to do. Patent Document 1 also proposes that a heating element is pressed against a portion that requires machining in a subsequent process. In Patent Document 1, by adopting these methods, it is said that the cooling rate can be reduced, that is, the hardness of the part can be reduced, and the machining of the steel sheet can be facilitated in the subsequent process.

Moreover, in patent document 2, by suppressing the temperature rise of a steel plate by heating in a state where a heat insulating material is attached to a part of the steel sheet, quenching to the part where the heat insulating material is attached is suppressed, and the workability is applied to the part. A method for forming a soft part with good quality has been proposed.

JP 2003-328031 A JP 2009-61473 A

However, in the method disclosed in Patent Document 1, in which a gap is provided in a mold, for example, a portion whose hardness is to be reduced does not contact the mold. For this reason, when the site | part which wants to reduce hardness and the site | part to which a bending process is given by press molding overlap, there exists a problem that a steel plate cannot be shape | molded with high precision. In addition, if the portion where the hardness is desired to be lowered and the portion where the bending process is performed by press molding are not overlapped, a restriction is imposed on the portion where the hardness is desired to be reduced, so that the degree of freedom in design is reduced. is there. Further, in the method of providing a gap in a mold disclosed in Patent Document 1, a mold that performs hot pressing (molding and quenching at the same time depending on the size and location of a part that needs to be machined in a later process is performed. You have to prepare a mold to do). There is a problem in that a large amount of cost is required for manufacturing the mold. Further, in the method of pressing the heating element disclosed in Patent Document 1, the heating element is brought into contact with the steel plate in the vertical direction, so that, for example, a portion where the hardness is desired to be reduced can be formed on the side surface of the molded product. However, there was a problem in terms of design freedom.

In general, when a steel sheet is heated in a heating furnace for hot press forming, scale is generated on the surface of the steel sheet. Since this scale adversely affects a post-process after molding, for example, a coating process, it is preferable to prevent the scale from being generated as much as possible. Therefore, in order to suppress the generation of scale, a steel plate having a surface plated is usually used. In a plated steel plate, alloying between the steel plate and the plating layer proceeds by heating. The degree of alloying between the plating and the steel sheet affects the corrosion resistance, paintability, weldability, etc. of the molded product. For this reason, it is extremely important in terms of product quality to make the thermal history of the steel sheet uniform during heating and to uniformize the degree of alloying between the steel sheet and the plating layer over the entire surface of the steel sheet.

However, in the method disclosed in Patent Document 2, the temperature history of the steel sheet during heating is different between the place where the heat insulating material of the steel sheet is attached and the place where it is not attached. For this reason, there has been a problem that the degree of alloying between the steel sheet and the plating layer cannot be made uniform over the entire steel sheet, affecting the quality of the product. Thus, preventing the temperature history during heating from being different depending on the location is important not only for plated steel sheets but also for bare steel sheets from the viewpoint of ensuring stable quality.

The present invention has been made in view of such points, and when performing hot press forming on a steel sheet, the hardness of a predetermined part is set to be higher than that of other parts without changing the maximum temperature at the time of heating depending on the part. The purpose is to lower.

Hot press forming method of the steel sheet of the present invention for achieving the above objects, in hot press forming of a steel sheet forming is carried out and hardening of the steel sheet is heated to a temperature not lower than the A ₁ transformation point at the same time, A ₁ A partial quenching step of rapidly cooling a predetermined portion of the steel sheet to a martensitic transformation start temperature (Ms point) or lower before forming a flat steel sheet uniformly heated to a temperature equal to or higher than the transformation point; After the recooling step of returning the rapidly cooled predetermined part to a temperature higher than the start temperature (Ms point) of martensite transformation, and after reheating the steel plate, the forming of the steel plate and the end temperature of martensite transformation (Mf) Point) It has the shaping | molding rapid cooling process which performs rapid cooling to the following simultaneously, It is characterized by having.

According to the present invention, prior to forming the steel sheet is heated to a temperature not lower than the A ₁ transformation point, subjected to rapid cooling and recuperation at the predetermined site of the steel sheet is performed thereafter, a rapid cooling and shaping of the steel sheet at the same time . Therefore, the reheated part can be made into a structure containing tempered martensite, and the other parts can be made into a martensite structure. For this reason, the site | part which requires machining in a post process, or the site | part which welds can be made into the structure | tissue containing tempered martensite. Therefore, it is possible to form a molded product that ensures the workability in the subsequent process, the strength of the welded joint, and the like while maintaining the necessary strength as the entire molded product. In addition, since the steel sheet partial quenching step and the recuperation step are performed in a plate-like state, for example, a position where bending is performed by press forming, a position that becomes a vertical surface after forming, etc. A structure containing tempered martensite can be produced. Therefore, the degree of freedom in design is great. Furthermore, since the steel plate is uniformly heated to a predetermined temperature in advance, even when a plated steel plate is used as the steel plate, the degree of alloying of the plating can be made uniform over the entire surface of the steel plate.

Here, in the partial quenching step, the upper cooling body is brought into contact with the predetermined portion of the steel plate from above, and the lower cooling body is brought into contact with the predetermined portion of the steel plate from below, The steel plate and the upper cooling body or the lower cooling body are formed by unevenness formed on one or both of the contact surface of the upper cooling body with the steel plate and the contact surface of the lower cooling body with the steel plate. You may make it eject a refrigerant | coolant to the clearance gap formed in between. Further, the jetted refrigerant may be sucked and discharged from a refrigerant suction port formed in a cooling body in which unevenness is formed on a contact surface with the steel plate.

The forming and quenching step uses a punch and a die to press the steel plate from above and below, and the steel plate and the die are formed by unevenness formed on one or both of the forming surface of the punch and the forming surface of the die. The refrigerant may be ejected into a gap formed between the punch or the die. In addition, the jetted refrigerant may be sucked and discharged from a refrigerant suction port formed in a mold having irregularities formed on the contact surface with the steel plate.

Further, the time required in the partial quenching step, the recuperation step, and the molding quenching step may be the same.

The recuperation step may be performed by placing the steel plate at a predetermined processing position for a predetermined time. At this time, the required time in the partial quenching step, the recuperation step, and the forming quenching step can be made the same based on at least the amount of the refrigerant ejected from the steel plate. Moreover, the steel plate placed at the predetermined processing position may be heated by a non-contact heating device. In addition, a non-contact heating apparatus refers to what can heat the said heating target object, without contacting with a heating target object, such as the heating by a near-infrared lamp, the heating by a laser, and induction heating, for example. When a non-contact heating device is used in this way, at least the time required for the partial quenching step, the recuperation step, and the molding quenching step is the same based on the amount of heating by the non-contact heating device. can do.

Furthermore, the predetermined portion where the steel sheet is rapidly cooled may be a continuous region around the region where the steel plate is not rapidly cooled.

Further, the hot press forming apparatus of the steel sheet of the present invention, the lower cooling with respect to a predetermined portion of the uniformly heated flat plate-like steel sheet to a temperature above the A ₁ transformation point, contacting the upper cooling body from above The body is brought into contact with the bottom, a partial quenching stage for rapidly cooling a predetermined portion of the steel sheet to a martensitic transformation start temperature (Ms point) or less, and the steel plate with the predetermined portion rapidly cooled to a predetermined processing position. The predetermined cooling unit comprising a die and a punch, and a recuperation stage that reheats a predetermined portion of the steel sheet that has been rapidly cooled to a temperature higher than a martensitic transformation start temperature (Ms point), Forming a quenching stage that simultaneously performs forming of the steel sheet after reheating of the part and quenching to a martensitic transformation end temperature (Mf point) or lower, and the steel sheet from the partial quenching stage to the recuperating stage, in front And a transport mechanism that sequentially transports from the regenerative heat stage to the molding quenching stage.

Here, a refrigerant supply source that supplies the refrigerant to the steel plate, a suction mechanism that sucks and discharges the supplied refrigerant, and a contact surface of the upper cooling body with the steel plate, and the lower portion Either or both of the contact surface with the steel plate of the cooling body, unevenness, a refrigerant supply port serving as a refrigerant outlet for the steel plate, a refrigerant suction port serving as a suction and discharge port for the jetted refrigerant, Is formed on one or both of the molding surface of the punch and the molding surface of the die, and a refrigerant supply port serving as a refrigerant outlet for the steel plate, and a refrigerant suction serving as a suction port for the jetted refrigerant. And a discharge port, and the refrigerant supply source may eject the refrigerant into a gap formed by the irregularities. Moreover, you may make it provide the non-contact heating apparatus which heats the predetermined | prescribed site | part rapidly cooled by the said partial quenching stage in the said recuperation stage.

The steel forming member of the present invention is a steel forming member formed by a hot press forming method of the steel plate, and the hardness of the predetermined part after the forming is higher than the hardness of other parts. It is characterized by being 20 or more smaller.

According to the present invention, when hot press forming is performed on a steel sheet, the hardness of a predetermined part can be reduced as compared with other parts without changing the maximum temperature during heating depending on the part.

FIG. 1 is a side view showing an outline of a configuration of a hot press molding apparatus according to the present embodiment. FIG. 2 is a plan view showing an outline of the configuration of the hot press forming apparatus according to the present embodiment. FIG. 3 is an explanatory diagram showing an outline of the configuration of the partial quenching stage. FIG. 4 is an explanatory diagram showing an outline of the configuration of the partial quenching stage. FIG. 5 is an enlarged view of the die surface of the quenching mold to which the present invention is applied. FIG. 6 is an explanatory view of a die of a quenching mold to which the present invention is applied. FIG. 7 is an explanatory view showing a state in which concentric partial quenching portions are formed on the plated steel sheet. FIG. 8 is an explanatory diagram when the hot press molding apparatus according to the present embodiment is applied to a transfer press. FIG. 9 is an explanatory diagram of a plated steel sheet used in the examples.

Hereinafter, embodiments of the present invention will be described. FIG. 1 is a side view showing an outline of the configuration of a hot press forming apparatus 1 according to an embodiment. FIG. 2 is a plan view schematically showing the configuration of the hot press molding apparatus 1 according to the embodiment.

The hot press molding apparatus 1 includes a charging stage (stage) 10, a partial quenching stage (stage) 11, a recuperation stage (stage) 12, a molding quenching stage (stage) 13, and a transport mechanism 14. is doing.
The input stage (stage) 10 is a stage (stage) into which a flat steel plate (here, plated steel plate K) heated to a predetermined temperature by a heating device (not shown) is input. The partial quenching stage (stage) 11 is a stage (stage) for rapidly cooling a predetermined portion of the plated steel sheet K conveyed from the charging stage (stage) 10. The recuperation stage (stage) 12 is a stage (stage) that performs so-called recuperation in which a predetermined portion of the plated steel sheet K rapidly cooled in the partial quenching stage (stage) 11 is returned to a temperature higher than a predetermined temperature. The forming and quenching stage (stage) 13 is a stage (stage) that simultaneously forms and quenches the plated steel sheet K reheated by the recuperating stage (stage) 12. The conveyance mechanism 14 conveys the plated steel plate K in the hot press forming apparatus 1. The charging stage 10, the partial quenching stage 11, the recuperation stage 12, and the forming quenching stage 13 are provided on the upper surface of the base 15 in the flow direction H of the plated steel plate K (the positive direction of the X axis in FIG. 1 (arrow direction)). Are arranged at equal intervals in order. An upper support 16 is provided above the base 15. The upper support 16 supports an upper stamp 37 and a punch 62 described later.

The plated steel plate K in the present embodiment is, for example, in mass% C: 0.05 to 0.7%, Si: 0.1 to 1%, Mn: 0.7 to 2%, P: 0.003. A steel sheet containing steel containing 0.1 to 0.1% and S: 0.003 to 0.1% and plated mainly with Al having a plating layer thickness of 30 μm or less. The target temperature for heating the steel sheet before hot pressing is 850 ° C. or higher and 1000 ° C. or lower. The plated steel plate K, the entire surface of which is uniformly heated to such a temperature range, is conveyed to the charging stage 10.

The input stage 10 has a pair of support bases 20, and positioning pins 21 for positioning between pre-pierce holes P previously formed on the plated steel plate K on the upper surface of each support base 20. A support pin 22 that supports the plated steel plate K is provided at its upper end. The support base 20 is formed in a rectangular shape in plan view, for example, and is arranged on the base 15 so that the longitudinal direction thereof coincides with the flow direction H of the plated steel plate K.

The positioning pin 21 is provided at the center position of the support base 20, for example. The support pins 22 are provided on both sides of the positioning pins 21 along the longitudinal direction of the support base 20. In FIG. 2, two support pins 22 are depicted for one support base 20, but the number and arrangement of the positioning pins 21 and the support pins 22 are not limited to the present embodiment. The upper end of the support pin 22 is in point contact with the back surface of the plated steel plate K so that the contact area between the support pin 22 and the plated steel plate K is reduced and heat transfer is minimized. Therefore, the upper end of the support pin 22 is formed in a spherical shape, for example.

The partial quenching stage 11 includes a pair of support tables 30 and a quenching stamp 31 as a cooling body that rapidly cools a predetermined portion of the plated steel plate K by contacting the predetermined portion of the plated steel plate K in the same manner as the charging stage 10; have. Positioning pins 32 and support pins 33 having the same shape as the support table 20 are provided on the upper surface of the support table 30. On the lower surfaces of the pair of support bases 30, a pedestal 34, which is a substantially rectangular plate partially recessed in a substantially U shape in plan view, is provided. Between the pedestal 34 and the base 15, there is provided a spring body 35 that can expand and contract in the vertical direction by a load. On both sides of the support base 30 in the longitudinal direction and on the upper surface of the pedestal 34, round bar-shaped push rods 36 extending vertically upward are provided. The push rod 36 is formed such that its upper end is lower than the upper end of the support pin 33.

The quenching stamp 31 has an upper stamp 37 and a lower stamp 38. The upper surface 38a of the lower stamp 38 is formed in a substantially disk shape, for example. The upper surface 38 a of the lower stamp 38 is parallel to the lower surface of the plated steel plate K placed on the support pin 33 and is located at a position lower than the upper end of the support pin 33. As a result, when the plated steel plate K is placed on the support pins 33, the plated steel plate K and the upper surface 38a of the lower stamp 38 do not come into contact with each other as shown in FIG. For this reason, in the state in which the plated steel plate K is placed on the support pins 33, the plated steel plate K is not cooled by the rapid cooling stamp 31. The lower stamp 38 is disposed directly on the upper surface of the base 15 inside the U-shaped depression of the base 34, for example.

The upper stamp 37 is provided vertically above the lower stamp 38, and the lower surface 37a has the same shape as the lower stamp 38. The lower surface 37 a of the upper stamp 37 is parallel to the upper surface of the plated steel plate K placed on the support pin 33. The upper portion of the upper stamp 37 is supported by the upper support 16. The upper stamp 37 can be moved up and down by moving the upper support 16 up and down in the vertical direction (positive and negative directions of the Y axis in FIG. 1) by an elevating mechanism (not shown).

An upper push rod 36a is provided extending downward in the vertical direction at a position corresponding to the push rod 36 on the lower surface of the upper support 16. The spring body 35 can be bent and the pedestal 34 can be pushed downward by lowering the upper support 16 and pressing the push rod 36 vertically downward by the upper push rod 36a. The length of the upper push rod 36 a in the extending direction is such that when the upper support 16 is lowered, the upper stamp 37 contacts the upper end of the push rod 36 before contacting the upper surface of the plated steel plate K on the support pin 33. It has become. For this reason, when the upper support 16 is lowered, first, the upper push rod 36a presses the push rod 36 to push down the pedestal 34, and the plated steel plate K placed on the support pin 33 is pushed down together with the pedestal 34. The plated steel plate K descends relative to the lower stamp 38. When the lowering of the upper support 16 is continued, the plated steel plate K on the support pin 33 is transferred to the upper surface 38a of the lower stamp 38, and then the lower surface 37a of the upper stamp 37 and the plated steel plate K as shown in FIG. In contact with the top surface. In this embodiment, the pedestal 34 is a substantially rectangular plate that is recessed in a substantially U-shape, but the pedestal 34 can be moved up and down without interfering with the lower stamp 38. However, the present invention is not limited to this embodiment.

On the upper surface 38a of the lower stamp 38, for example, as shown in FIGS. 5 and 6, a refrigerant supply port 40 for supplying a refrigerant to the plated steel plate K, and a refrigerant suction port 41 for sucking and discharging the supplied refrigerant. And are provided. The refrigerant suction port 41 is connected to a suction mechanism 47. The refrigerant supply port 40 communicates with a refrigerant flow path 42 provided inside the lower stamp 38. A refrigerant supply pipe 43 is connected to the flow path 42, and a refrigerant is supplied from the refrigerant supply source 46 to the plated steel plate K by opening a supply valve 44 provided in the refrigerant supply pipe 43. In addition, a plurality of independent convex portions 38 b having a certain height are formed on the upper surface 38 a of the lower stamp 38. As a result, when the lower surface 37a of the upper stamp 37 is lowered to a position in contact with the plated steel plate K, the upper surface 38a of the lower stamp 38 and the plated steel plate are formed by the concave portions between the plurality of convex portions 38b, that is, the plurality of convex portions 38b. The refrigerant supplied from the refrigerant supply port 40 can flow through the gap formed between the refrigerant and the K. Therefore, the predetermined part of the plated steel plate K can be cooled in a short time, that is, rapidly cooled. The refrigerant supplied from the refrigerant supply port 40 is sucked from the refrigerant suction port 41 and discharged to the outside of the lower stamp 38. In addition, as a refrigerant | coolant of this Embodiment, water etc. can be used, for example.

Inside the upper stamp 37, for example, as shown in FIGS. 3 and 4, a cooling pipe 45 for cooling the lower surface 37a of the upper stamp 37 is provided. When the lower surface 37a of the upper stamp 37 is brought into contact with the plated steel plate K, the plated steel plate K can be cooled by supplying a coolant to the cooling pipe 45.

The recuperation stage 12 has the same configuration as the charging stage 10, and includes a pair of support bases 50, positioning pins 51 and support pins 52 provided on the upper surface of the support base 50.

The forming and quenching stage 13 has a quenching mold 60 for simultaneously forming and quenching the plated steel plate K. The quenching mold 60 has a die 61 that is a lower mold and a punch 62 that is an upper mold. The die 61 has the same configuration as the lower stamp 38 shown in FIGS. That is, the die 61 is connected to the coolant supply port 63, the coolant suction port 64 that sucks and discharges the coolant supplied from the coolant supply port 63, the flow path 65 communicating with the coolant supply port 63, and the flow path 65. The refrigerant supply pipe 66 and a supply valve 67 provided in the refrigerant supply pipe 66 are provided.
The coolant supply port 63 supplies the coolant to the plated steel plate K when the punch 62 is lowered to the bottom dead center and the plated steel plate K is hot press formed. The refrigerant suction port 64 is connected to the suction mechanism 81 similarly to the refrigerant suction port 41 of the lower stamp 38. On the molding surface 61a of the die 61, like the upper surface 38a of the lower stamp 38, a plurality of independent convex portions 61b having a certain height are formed. The coolant supplied from the coolant supply source 82 via the coolant supply port 63 is caused to flow through the gap formed between the forming surface 61a of the die 61 and the plated steel plate K by the plurality of convex portions 61b, and the plated steel plate K Cool quickly. In FIG. 5, the lower stamp 38 and the die 61 are shown as being exactly the same for convenience of description, but in actuality, their shapes and sizes are different.

In the punch 62, a cooling pipe (not shown) for cooling the molding surface 62a of the punch 62 is provided in the same manner as the upper stamp 37. When the forming surface 62a of the punch 62 is brought into contact with the plated steel plate K, the plated steel plate K can be cooled by supplying a coolant to a cooling pipe (not shown). Similar to the upper stamp 37, the upper portion of the punch 62 is supported by the upper support 16. The punch 62 is also moved up and down by moving the upper support 16 up and down in the vertical direction by a lifting mechanism (not shown). For this reason, the upper stamp 37 and the punch 62 are configured to move up and down in synchronization with the upper support 16 moving up and down.

The die 61 is provided with a positioning pin 68 that penetrates the inside of the die 61 and projects vertically upward, and is slidable with respect to the die 61. The positioning pin 68 is supported on the upper surface of the base 15 via a spring (not shown). When the punch 62 is lowered and presses the positioning pin 68, the plated steel plate K is pushed down together with the positioning pin 68, and the plated steel plate K is formed by the rapid cooling mold 60.

As shown in FIG. 2, the transport mechanism 14 includes a gripping portion 70 that grips the plated steel plate K and a pair of transport supports 71. A pair of conveyance support bodies 71 support the grip part 70, and follow a horizontal direction (vertical direction toward FIG. 2) perpendicular to the flow direction H of the plated steel plate K and the flow direction H by a drive mechanism (not shown). And reciprocally movable. The conveyance support body 71 is disposed so as to face the insertion stage 10 and the molding quenching stage 13. The gripping part 70 has, for example, three gripping

parts

70a, 70b, and 70c. The three

gripping portions

70 a, 70 b, and 70 c are provided at equal intervals in order along the flow direction H of the plated steel plate K on each of the pair of transport supports 71. For this reason, the gripping portion 70a is moved from the charging stage 10 to the partial quenching stage 11 and the gripping portion 70b is moved to the partial quenching stage by reciprocating the transport support 71 in parallel with the flow direction H of the plated steel plate K by a drive mechanism (not shown). 11 to the recuperation stage 12, and the gripping portion 710 c can simultaneously convey a plurality of plated steel plates K from the recuperation stage 12 to the forming and quenching stage 13.

The hot press molding apparatus 1 according to the present embodiment is configured as described above, and the principle of the hot press molding of the present invention will be briefly described below.

The steel material is heated to an A ₁ transformation point (A ₁ transformation point; in the case of the embodiment of the present invention, 690 to 720 [° C.]) or more, and the formation of the austenite phase begins, and the A ₃ transformation point (the embodiment of the present invention). In this case, an austenite single phase structure is obtained by heating to 730 to 890 [° C.] or higher. By performing so-called quenching, in which the austenite is rapidly cooled to a temperature below the starting temperature Ms (Martensite-transformation Starting Point) of transformation to martensite, a martensite structure having high hardness is generated in the steel material. On the other hand, for example, the temperature of the steel product A ₁ transformation point or more, or from A ₃ transformation point or higher, after lowering to the Ms point or lower, by heating the steel material raises the temperature of the steel material to more than Ms point, the so-called recuperation And then quenching again to bring the temperature of the steel below the martensite transformation end point Mf (Martensite-transformation finishing point), so-called tempering, so that the steel has a lower hardness than the martensite structure. The structure contains tempered martensite.

Therefore, in the present embodiment, in the process of hot press forming, a part of the steel sheet, for example, a part that requires machining in a subsequent process or a part to be welded is selectively tempered, and tempered martensite. To form a tissue. In this way, for example, a product (steel molded member) having the required hardness for the other parts while ensuring the workability of the parts that need to be machined in the post-process and the strength of the welded joints. be able to. Next, an example of the method of hot press forming of the plated steel plate K by the hot press forming apparatus 1 according to the present embodiment will be described.

First, in advance A ₁ transformation point or above by the heating device, uniformly heated plated steel sheet K over the entire surface is placed on the support pins 22 of input stage 10 by a not shown transfer device. When the sensor provided on the support base 20 detects that the plated steel plate K is placed on the support pins 22, the transport mechanism 14 starts operating. The plated steel plate K placed on the charging stage 10 is gripped by the gripping portion 70 a of the transport mechanism 14, transported to the partial quenching stage 11, and placed on the support pin 33. At this time, as shown in FIG. 3, the positioning pin 32 is inserted into the prepierce hole P of the plated steel plate K placed on the support pin 33, and the relative positional relationship between the plated steel plate K and the quenching stamp 31 is present. It is set by the prepierce hole P and the positioning pin 32.

When the plated steel plate K is conveyed to the partial quenching stage 11, a partial quenching process is performed in which, for example, the central portion of the plated steel plate K is rapidly cooled. In the partial quenching step, first, the upper stamp 37 and the upper push rod 36a are lowered together with the upper support 16, and the upper push rod 36a and the push rod 36 are in contact with each other as shown in FIG. At this time, the lower surface 37a of the upper stamp 37 and the upper surface of the plated steel plate K are separated from each other by a predetermined distance. The upper support 16 continues to descend from this state, moves the plated steel plate K placed on the support pin 33 downward via the push rod 36 and the base 34, and lowers the plated steel plate K on the support pin 33. Transfer to the upper surface 38 a of the stamp 38.

Thereafter, the upper support 16 is further lowered, and the state where the upper surface of the plated steel plate K is pressed by the lower surface 37a of the upper stamp 37 is maintained for a predetermined time as shown in FIG. That is, the upper stamp 37 is held for a predetermined time at the position of the bottom dead center of the upper stamp 37. At the same time that the plated steel plate K is pressed by the upper stamp 37, the supply valve 44 is opened, and the coolant is supplied to the plated steel plate K from the coolant supply port 40 of the lower stamp 38. Note that the coolant is constantly supplied to the cooling pipe 45 inside the upper stamp 37. Thereby, the site | part which contacts the upper stamp 37 and the lower stamp 38 of the plated steel plate K is rapidly cooled, and it becomes the partial quenching part Kc. On the other hand, a portion that is not in contact with the upper stamp 37 and the lower stamp 38 is maintained as a high temperature portion Ka that maintains a high temperature.

In the partial quenching stage 11, when the predetermined portion of the plated steel plate K (the portion that contacts the upper stamp 37 and the lower stamp 38) is rapidly cooled for a predetermined time, the upper stamp 37 rises to the top dead center together with the upper support 16. The partial quenching process ends. When the partial quenching step is finished, the plated steel plate K is gripped by the gripping portion 70b of the transport mechanism 14 and transported from the partial quenching stage 11 to the recuperation stage 12. At the same time, the second plated steel plate K on the charging stage 10 is conveyed to the partial quenching stage 11 and the third plated steel plate K is placed on the charging stage 10.

When the plated steel plate K is conveyed onto the support pin 52 of the recuperation stage 12, a recuperation step is performed in which the temperature of the partially quenched portion Kc of the plated steel plate K is reheated to a temperature equal to or higher than the Ms point. In the recuperation step, the recuperation stage is performed for a predetermined time, that is, a time in which the upper support 16 reciprocates once between the top dead center and the bottom dead center with the plated steel plate K placed on the support pins 52. Twelve. At this time, the temperature of the partially quenched portion Kc of the plated steel plate K rises due to heat transfer from a portion that is not rapidly cooled in the partially quenched process and maintains a high temperature, and is reheated to a temperature equal to or higher than the Ms point.

When the recuperation process is completed in the recuperation stage 12, the plated steel plate K is held by the holding portion 70 c of the transfer mechanism 14 and transferred from the reheat stage 12 to the forming and quenching stage 13.

When the plated steel plate K is conveyed to the forming and quenching stage 13, first, the plated steel plate K is positioned by the prepierce hole P of the plated steel plate K and the positioning pin 68 of the die 61, and the plated steel plate K is placed on the die 61. Placed. Next, the punch 62 descends to the bottom dead center, and the plated steel plate K is formed. Simultaneously with the formation of the plated steel plate K, the supply valve 67 of the coolant supply pipe 66 is opened, and the coolant is supplied from the coolant supply port 63 to the plated steel plate K. A refrigerant is always supplied to a cooling pipe (not shown) inside the punch 62. Thereby, the plated steel plate K is rapidly cooled over the entire surface. When the plated steel plate K is rapidly cooled for a predetermined time and the temperature of the plated steel plate K becomes equal to or lower than the Mf point, the punch 62 rises to the top dead center together with the upper support 16, and the forming and quenching process ends.

When the forming and quenching process is completed, the formed plated steel sheet K is removed from the die 61 by, for example, an unillustrated unloading device and unloaded from the hot press forming device 1. This series of hot press molding is repeated.

According to the above embodiment, partial quenching the predetermined portion of the plated steel sheet K preheated to A ₁ transformation point or above the temperature, and quenched to the starting temperature (Ms point) below the temperature of the transformation to martensite Part Kc is formed. Thereafter, in the recuperation stage 12, the partially quenched portion Kc is reheated to a temperature higher than the start temperature (Ms point) of transformation to martensite. After this, the forming of the plated steel sheet K and the rapid cooling of the entire forming surface (rapid cooling to a temperature not higher than the end temperature (Mf point) of transformation into martensite) are performed simultaneously. Therefore, the reheated part can be made into a structure containing tempered martensite, and the other part of the molding surface can be made into a martensite structure. For this reason, a part that does not require machining in the subsequent process after molding is formed into a martensite structure. For example, a part that requires machining in the subsequent process or a part that requires welding in the subsequent process is tempered martensite. It can be set as the organization containing. Therefore, it is possible to form a molded product that ensures the workability in the subsequent process while maintaining the necessary strength as a product. Moreover, since the plated steel plate K is uniformly heated over the entire surface in advance, the highest temperature achieved when the plated steel plate K is heated can be made uniform over the entire surface of the plated steel plate K. Therefore, the degree of alloying of plating can be made uniform over the entire surface of the steel sheet. Furthermore, the partial rapid cooling process and the recuperation process of the plated steel plate K are performed in a state where the plated steel plate K is in a flat plate shape. Therefore, for example, a structure containing tempered martensite can be generated at an arbitrary position such as a part that is subjected to bending in the forming and quenching process or a part that becomes a vertical surface after forming. Therefore, the degree of freedom in design is great.

In the partial quenching stage 11, the plated steel plate K is positioned by the prepierce hole P and the positioning pin 32. In the forming quenching stage 13, the plated steel plate K is positioned by the prepierce hole P and the positioning pin 68 of the die 61. Therefore, in the partial quenching stage 11 and the forming quenching stage 13, the relative positional relationship between the plated steel plate K and the positioning pins 32 and 68, that is, the relative relationship between the quenched stamp 31 and the quenching mold 60 and the plated steel plate K. The positional relationship does not shift. Therefore, a structure including tempered martensite can be generated very accurately at a predetermined position of the molded product. Thereby, for example, the arrangement of the plated steel plate K on the die 61 is deviated for some reason, and press forming in the deviated state can be reliably prevented. Therefore, it is possible to reliably prevent a structure containing tempered martensite from being generated at a site where machining or welding is performed in a subsequent process. Therefore, troubles such as hindrance to machining in the subsequent process and insufficient joint strength of welding can be avoided.

Further, according to the above embodiment, the

convex portions

38b and 61b are formed on the upper surface 38a and the forming surface 61a which are the contact surfaces of the lower stamp 38 and the die 61 with the plated steel plate K. For this reason, in the partial quenching process and the forming quenching process, the plated steel sheet K can be rapidly cooled in a short time by ejecting the coolant from the

coolant supply ports

40 and 63 to the plated steel sheet K. Therefore, the productivity of hot press molding can be improved.

In the above embodiment, the means for rapidly cooling the plated steel plate K, such as the

convex portions

38b and 61b, the

refrigerant supply ports

40 and 63, and the

refrigerant suction ports

41 and 64, is a lower stamp 38 or die that is an example of a lower cooling body. Although provided on the 61 side, the means may be provided on the upper stamp 37 or the punch 62 side which is an example of the upper cooling body. The means may be provided on both the lower stamp 38 and the die 61 side which are examples of the lower cooling body, and the means may be provided on both the upper stamp 37 and the punch 62 side which are examples of the upper cooling body. .

In the above embodiment, the shape of the partial quenching portion Kc is substantially a plate shape. However, for example, by changing the shape of the quenching stamp 31 in accordance with the content of machining in a later process, any other shape is possible. It is good. In this case, the quenching stamp 31 forming the partial quenching portion Kc and the quenching mold 60 are provided independently. For this reason, for example, when forming a molded product having the same shape but different only in the machining part in the subsequent process, it is possible to cope with the problem by simply changing the shape and arrangement of the quench stamp 31, for example. . Therefore, it is not necessary to replace the quenching mold 60 having a large mass.

Further, in a subsequent process, when a concentric hole is drilled in a predetermined portion of the plated steel plate K, for example, a high temperature portion Ka portion that is maintained at a high temperature without quenching in the region of the partial quench portion Kc. May be set. Specifically, as shown in FIG. 7, for example, a partially quenched portion Kc is formed in an annular shape on a plated steel plate K, and is maintained at a high temperature in a region surrounded by the annular partially quenched portion Kc. You may make it leave the high temperature part Ka. As described above, by leaving the high temperature portion Ka in the region of the partial quenching portion Kc, heat transfer is performed between the partial quenching portion Kc and the high temperature portion Ka, that is, between the partial quenching portion Kc and the high temperature portion Ka. The area to be increased. Further, by selectively quenching only the part to be processed, that is, the annular partial quenching portion Kc in FIG. 7 and reducing the range of the partial quenching portion Kc, the heat capacity required for recuperation is reduced. Therefore, it is possible to efficiently recover the partial quenching portion Kc.

In the above embodiment, one sheet of plated steel sheet K is processed in the hot press forming apparatus 1, but, for example, a plurality of plated sheet steels K may be processed simultaneously. In that case, for example, the time required for the partial quenching process including the vertical movement of the upper stamp 37 in the partial quenching stage 11 and the time required for the molding rapid cooling process including the vertical movement of the punch 62 in the molding quench stage 13, so-called tact. If the time is the same, the efficiency is good. The tact time is determined after obtaining the optimum condition for the holding time at the bottom dead center of the punch 62 necessary for satisfying the quality of the molded product by obtaining an optimum condition by a test or the like in advance. However, when the upper stamp 37 is reciprocated in synchronization with the punch 62 and the upper support 16, there may be a case where the rapid cooling of the plated steel plate K becomes insufficient in the partial quenching process. In that case, for example, the required cooling can be performed by adjusting the amount of the refrigerant supplied from the refrigerant supply port 40. Thus, by matching the tact times of the partial quenching stage 11 and the forming quenching stage 13, a plurality of plated steel plates K can be processed simultaneously.

When processing a plurality of, for example, plated steel plates K1 to K5 simultaneously, the plated steel plate K1 is transferred from the charging stage 10 to the partial quenching stage 11, and at the same time, a new plated steel plate K2 is charged to the charging stage 10. Next, the partial quenching of the plated steel plate K1 is finished, and the plated steel plate K1 is transferred from the partial quenching stage 11 to the recuperation stage 12, and at the same time, a new plated steel plate K3 is charged and the plated steel plate K2 charging stage 10 is moved to the partial rapid cooling stage 11. Is carried out. Next, when the reheating of the plated steel plate K1 is completed and transported to the forming and quenching stage 13, the plated steel plate K2 quenched in the partial quenching stage 11 is returned from the partial quenching stage 11 by the gripping portion 70b. The plated steel plate K3 of the charging stage 10 is transported to the partial quenching stage 11, and a new plated steel plate K4 is charged to the charging stage 10. As shown in FIG. 8, when the forming and quenching process of the plated steel plate K <b> 1 is completed, the formed plated steel plate K <b> 1 is removed from the die 61 and carried out from the hot press forming apparatus 1. At the same time, the plated steel plates K2, K3, and K4 are transported and a new plated steel plate K5 is charged, and this series of hot press forming is repeated. Thus, by adjusting the tact time in each process, the hot press molding apparatus 1 of the present embodiment is a so-called transfer press (a press method for forming a press molded part through a plurality of processes, It is possible to apply to a pressing method in which a steel plate is conveyed to the next step every time the press machine makes one stroke, and the productivity of the product can be improved. As described above, in the partial quenching step and the forming quenching step, the plated steel plate K can be rapidly cooled in a short time, so that the tact time can be shortened. Therefore, in recuperation process, (to a temperature lower than the A ₁ transformation point) temperature of the high temperature portion Ka is plated steel sheet K can be reliably achieved a decrease.

Moreover, in the above embodiment, the recuperation after the partial quenching of the plated steel plate K is performed for a predetermined time, for example, a hot press forming apparatus, with the plated steel plate K placed on the support pins 52 of the recuperation stage 12. It is performed by keeping it on the recuperation stage 12 for only one tact time. However, for example, when a time required for recuperation of the plated steel plate K is confirmed to be longer than the tact time by a preliminary test, for example, between the partial quenching stage 11 and the recuperation stage 12 or the recuperation stage 12. A new recuperation stage 12 may be further provided between the molding and quenching stage 13. On the other hand, when it is confirmed that the plated steel plate K is sufficiently reheated only by the time when the plated steel plate K is transported from the partial quenching stage 11 to the recuperation stage 12 by the transport mechanism 14, the recuperation stage 12 is not provided. A molding quenching stage 13 may be arranged next to the partial quenching stage 11.

In addition, when the recuperation stage 12 is further provided, the entire hot press molding apparatus 1 is increased in size, and a larger installation area is required. In this case, for example, as shown by a broken line in FIG. 1, the recuperating stage 12 is provided with a non-contact heating device 80 for heating the partially quenched portion Kc of the plated steel plate K, and the recuperating stage 12 Heating may be performed. If it does in this way, it will become unnecessary to install the new recuperation stage 12 further, and it can prevent that hot press molding device 1 enlarges. In this case, also in the recuperation stage 12, the relative positional relationship between the plated steel plate K and the heating device 80 is maintained by the prepierce hole P of the plated steel plate K and the positioning pin 51 of the recuperated stage 12. The apparatus 80 can accurately recover the partial quenching portion Kc. In addition, when the heating device 80 is provided, the amount of heat held by the plated steel plate K is not sufficient, and when the reheat of the plated steel plate K cannot be sufficiently performed only by adding the recuperation stage 12, specifically, the plated steel plate K. It is possible to cope with the case where the thickness of the plate is small. The heating device 80 is preferably a near-infrared lamp that can be heated in a short time, but any heating method can be used as long as it is a non-contact heating method. For example, laser heating or induction heating can be used. The tact time in each step can be adjusted by changing at least the heating amount of the plated steel plate K by the heating device 80 or the supply amount of the refrigerant in at least one of the lower stamp 38 and the die 61.

Also, the time and heat capacity required for recuperation of the partial quenching portion Kc, that is, the number of recuperation stages 12 required for recuperation (the number of stages), the necessity of the heating device 80 and the heat capacity are determined. As a method to do this, in addition to a test performed in advance, it is also possible to obtain by calculation.

A method for obtaining by calculation will be briefly described. For example, as shown in FIG. 9, it is assumed that a partially quenched portion Kc is formed in a rectangular region having a width δ at the center of a flat plate-like steel plate K having a length A, a width B, and a thickness t. In this case, the initial temperature of the plated steel plate K is Ti, the temperature of the partial quenching portion Kc in the partial quenching step is Tc1, and the highest temperature at the time of recuperation of the partial quenching portion Kc is Tc2. Then, the heat capacity Qr [J] required to reheat to Tc2 after the temperature of the partial quenching portion Kc is once quenched to Tc1 can be obtained from the following equation (1).
Qr = (Tc2−Tc1) · ρ · Cm · δ · t · A · B (1)
Where ρ is the specific gravity [kg / m ³ ] of the plated steel plate K, Cm is the specific heat [J / kg · K] of the plated steel plate K, Ti is the temperature above the A1 transformation point [K], and Tc1 is the temperature below the Ms point. [K] and Tc2 are temperatures [K] higher than the Ms point. As described above, A, B, t, and δ are the length [m], the width [m], the thickness [m], and the width [m] of the partially quenched portion Kc, respectively.

On the other hand, after the partial quenching portion Kc is once cooled to Tc1, the heat quantity Qλ [J] used for recuperation of the partial quenching portion Kc by heat transfer from a high temperature portion other than the partial quenching portion Kc is (2 ) Is expressed as the formula
Qλ = f (λ, Ti1, Tc1, δ, Sr) (2)
Where λ is the thermal conductivity [W / m · K] of the plated steel plate K, Ti1 is the temperature around the partially quenched portion Kc [K] when the temperature of the partially quenched portion Kc is changed from Ti to Tc1, and Sr. Is the time [sec] required to reheat to Tc2 after the temperature of the plated steel plate K is once cooled to Tc1.

At this time, Sr is expressed as the following equation (3).
Sr = (St−Sh) + N · St (3)
However, St is the tact time [sec] of the hot press molding apparatus 1, Sh is the bottom dead center holding time [sec] in the partial quenching stage 11 and the molding quenching stage 13, and N is the number of stages of the recuperation stage 12 [-]. It is.

Here, in order to reheat the temperature of the partial quenching portion Kc to Tc2 or more, Ti1, δ, and Sr that satisfy the relationship of the following expression (4) may be selected.
Qr ≦ Qλ (4)

Further, when the recuperation stage 12 is provided with a heating device 80 and recuperation of the plated steel plate K is performed in combination with heat transfer from a portion other than the partial quenching portion Kc, the heating device 80 supplies the partial cooling portion Kc. The heat input amount QL can be obtained from the following equation (5). Further, in order to reheat the temperature of the partial quenching portion Kc to Tc2 or higher, QL may be set so as to satisfy the following expression (6).
QL = f (qL, C, N, SL) (5)
Qr ≦ Qλ + QL (6)
However, qL is the heat input density [W / m ² ] of the heating device 80, C is the heating width [m] of the heating device 80, and SL is the heating time [sec] by the heating device 80.

The above calculation method has been described with reference to the case where the partial quenching portion Kc is rectangular, but the same calculation method is applied even if the partial quenching portion Kc has another arbitrary shape such as a circle or a concentric circle. be able to. In that case, Qr, Qλ, and QL may be obtained according to the size and shape of the partial quenching portion Kc.

As an example, hot press forming was performed on the plated steel sheet K using the hot press forming apparatus 1, and a retest temperature and hardness confirmation test was performed. The results of the confirmation test are shown in Table 1. Here, a confirmation test is performed by changing the width δ of the partial quenching portion Kc, the thickness t of the plated steel plate K, the number N of the recuperation stages 12, and the presence or absence of heating by the heating device 80 in the recuperation stage 12. It was. A steel plate containing 0.2% by mass of C and a small amount of Mn, B, and Si, plated with 80 g / m ² of Al as a main component as a relatively low hardness plated steel plate K ( Examples 1 to 6) were used. Moreover, as a steel plate K having relatively high hardness, steel containing 0.3% by mass of C and a small amount of Mn, B, and Si was plated mainly with 80 g / m ² of Al. (Examples 7 to 11) were used. The initial temperature Ti of the plated steel plate K is 950 ° C., the temperature Tc 1 at the time of quenching of the partial cooling part Kc is less than 400 ° C., and the temperature around the partial quenching part Kc when the temperature of the partial quenching part Kc is changed from Ti to Tc 1. The temperature Ti1 was set to 800 ° C. As the heating device 80, a near infrared heating lamp was used.

As shown in Table 1, the bottom dead center retention time was 2 seconds and the tact time was 5 seconds. When the recuperation of the partial cooling section Kc is appropriately performed, that is, when the temperature of the partial quenching section Kc returns to a temperature higher than the martensitic transformation start temperature Ms, enter a circle in the recuperation temperature column, Otherwise, x was entered in the recuperation temperature column. In addition, the hardness of the high temperature portion Ka other than the partially quenched portion Kc is 450 Hv, and the hardness of the partially quenched portion Kc is softer (smaller) by 20 Hv or more than the hardness of the high temperature portion Ka. ○ was entered, otherwise it was judged as defective, and x was entered in the hardness evaluation column.

In addition, as a comparative prior art, a confirmation test of the recuperation temperature and hardness was also performed in the case where the molding quenching step was performed without performing the recuperation after the partial quenching step. Specifically, the related art A shows the result of the confirmation test when the number of stages of the recuperation stage 12 is zero, that is, when a hot press molding apparatus having no recuperation stage is used. On the other hand, the prior art B shows the result of the confirmation test in the case where the hot press forming apparatus 1 is used to hot press form a plated steel plate K having a thin plate thickness t. In the conventional techniques A and B, as in Examples 1 to 6, the steel sheet containing 0.2% by mass of C and trace amounts of Mn, B, and Si as the plated steel sheet K was added to 80 g / m ² of Al. The one with plating mainly composed of was used.

In the prior art, since the reheat of the plated steel plate K is not sufficiently performed, the hardness of the partially quenched portion Kc is not lowered to a desired value. In the prior art A, since the recuperation stage 12 is not provided, the recuperation of the partial quenching portion Kc becomes insufficient. As a result, the temperature of the partial quenching portion Kc does not return to a temperature higher than the Ms point, that is, the tempering of the entire plated steel plate K including the partial quenching portion Kc in the forming quenching stage 13 without tempering the partial quenching portion Kc. Rapid cooling is performed. For this reason, quenching is performed over the entire plated steel plate K. For this reason, the difference between the hardness of the partially quenched portion Kc and the hardness of the high temperature portion Ka is less than 20 in Hv. In the prior art B, since the thickness t of the plated steel plate K is thin, the amount of heat held by the plated steel plate K is not sufficient, and the reheating of the plated steel plate K is sufficient only by placing the plated steel plate K on the recuperation stage 12. I can not do it. For this reason, the difference between the hardness of the partially quenched portion Kc and the hardness of the high temperature portion Ka is less than 20 in Hv.

On the other hand, in Examples 1 to 3, the partial quenching portion Kc was reliably tempered in the recuperation stage 12, and as a result, good results were obtained (the hardness of the partial quenching portion Kc). Can be reduced to a value 20 or more smaller in Hv than the hardness of the high temperature portion Ka). On the other hand, in Example 4, the plate thickness t is reduced as in the case of the prior art B. However, by providing the heating device 80 in the recuperation stage 12, the recuperation of the partial quenching portion Kc is sufficiently performed. become. For this reason, it has confirmed that the hardness of the partial quenching part Kc could be made into a desired value (The value smaller by 20 or more in Hv than the hardness of the high temperature part Ka).

Further, Example 5 is based on a hot press molding apparatus that does not have the recuperation stage 12 as in the case of the prior art A, but in Example 5, the width of the partially quenched portion Kc as compared with the prior art A is shown. Since δ is small, the time required for recuperation is short. Therefore, in Example 5, the partial quenching portion Kc is reheated while the plated steel plate K is transported from the partial quenching stage 11 to the forming quenching stage 13 by the transport mechanism 14, and the hardness of the partial quenching portion Kc is desired. The value could be Further, in Example 6, good results were obtained even when the plate thickness t was increased (the hardness of the partially quenched portion Kc was able to be 20 or more smaller in Hv than the hardness of the high temperature portion Ka). ).

Examples 7 to 11 correspond to Examples 1 to 5, respectively. Even if the content of C in the steel was increased to increase (increase) the hardness of the plated steel plate K, good results were obtained (the hardness of the partially quenched portion Kc is 20 or more smaller in Hv than the hardness of the high temperature portion Ka) Value).

The present invention is useful when continuously hot pressing a steel sheet.

Claims

In the hot press forming of a steel sheet forming is carried out and hardening of the steel sheet heated to A 1 transformation point or above the temperature at the same time,
Before forming the uniformly heated flat plate-like steel sheet to a temperature above the A 1 transformation point, and portions quenching step of quenching the predetermined portion of the steel sheet below the starting temperature of martensitic transformation,
A recuperation step of returning the rapidly cooled predetermined portion of the steel sheet to a temperature higher than the start temperature of the martensitic transformation;
A hot press forming method for a steel sheet, comprising: a forming and quenching step in which after the reheating of the steel sheet, the forming of the steel sheet and the rapid cooling to a temperature below the end temperature of the martensite transformation are simultaneously performed.
In the partial quenching step, the upper cooling body is brought into contact with the predetermined part of the steel plate from above, and the lower cooling body is brought into contact with the predetermined part of the steel plate from below, so that the upper cooling is performed. Formed between the steel plate and the upper cooling body or the lower cooling body by unevenness formed on one or both of the contact surface of the body with the steel plate and the contact surface of the lower cooling body with the steel plate The hot press forming method for a steel sheet according to claim 1, wherein a refrigerant is jetted into the formed gap.
The partial quenching step sucks out the jetted refrigerant from a refrigerant suction port formed in a cooling body in which irregularities are formed on the contact surface with the steel plate among the upper cooling body and the lower cooling body, The hot press forming method for a steel sheet according to claim 2, wherein the steel sheet is discharged.
The forming and quenching step uses a punch and a die to press the steel plate from above and below, and the steel plate and the die are formed by unevenness formed on one or both of the forming surface of the punch and the forming surface of the die. The hot press forming method for a steel sheet according to claim 3, wherein the coolant is ejected into a gap formed between the punch or the die.
The forming and quenching step sucks and discharges the jetted refrigerant from a refrigerant suction port formed in a mold in which unevenness is formed on a contact surface with the steel plate of the punch and the die. The hot press forming method for a steel sheet according to claim 4, characterized in that it is characterized in that
The method for hot press forming a steel sheet according to claim 5, wherein the time required in the partial quenching step, the recuperating step, and the forming quenching step is the same.
In the recuperation step, the steel plate is placed in a predetermined processing position for a predetermined time to return a predetermined portion of the steel plate that has been rapidly cooled to a temperature higher than the start temperature of the martensitic transformation. Item 7. A method for hot press forming a steel sheet according to Item 6.
The time required for the partial quenching step, the recuperation step, and the forming quenching step is set to be the same based on at least the amount of the refrigerant jetted onto the steel plate. Hot press molding method.
The method of hot press forming a steel plate according to claim 7, wherein the recuperating step heats the steel plate placed at the predetermined processing position for a predetermined time by a non-contact heating device.
The steel sheet according to claim 9, wherein the time required in the partial quenching step, the recuperation step, and the forming quenching step is made the same based on at least the amount of heating by the non-contact heating device. Hot press molding method.
2. The method of hot press forming a steel sheet according to claim 1, wherein the predetermined portion of the steel plate that is rapidly cooled is a continuous region surrounding a region that is not rapidly cooled inside thereof.
For a given site of the uniformly heated flat plate-like steel sheet to a temperature above the A 1 transformation point, contacting the lower cooling member from below with contacting the upper cooling body from above, a predetermined portion of the steel plate A partial quenching stage that rapidly cools the martensite transformation below the start temperature,
A recuperation stage that places the steel sheet that has been rapidly cooled in the predetermined part at a predetermined processing position, and reheats the predetermined part that has been rapidly cooled in the steel sheet to a temperature higher than the start temperature of martensitic transformation,
A forming and quenching stage that simultaneously performs forming of the steel sheet after the predetermined portion is reheated and quenching to a temperature not higher than the end temperature of the martensite transformation by a quenching mold including a die and a punch, and
An apparatus for hot press forming a steel sheet, comprising: a transport mechanism that sequentially transports the steel sheet from the partial quenching stage to the recuperation stage and from the recuperation stage to the forming quenching stage.
A refrigerant supply source for supplying refrigerant to the steel plate;
A suction mechanism that sucks and discharges the supplied refrigerant, and
Either or both of the contact surface of the upper cooling body with the steel plate and the contact surface of the lower cooling body with the steel plate, unevenness, a refrigerant supply port serving as a refrigerant outlet for the steel plate, A refrigerant suction port serving as a suction and discharge port for the refrigerant formed,
On either or both of the molding surface of the punch and the molding surface of the die, a concavity and convexity, a refrigerant supply port serving as a refrigerant ejection port for the steel plate, and a refrigerant suction port serving as a suction and discharge port for the ejected refrigerant Formed,
The hot press forming apparatus for a steel sheet according to claim 12, wherein the refrigerant supply source ejects the refrigerant into a gap formed by the unevenness.
14. The hot-press forming apparatus for steel sheet according to claim 13, wherein the recuperation stage is provided with a non-contact heating device for heating a predetermined portion that has been quenched by the partial quenching stage. .
A steel forming member formed by the hot press forming method of a steel sheet according to claim 1,
The steel molded member according to claim 1, wherein the hardness of the predetermined part after the molding is 20 or less in Hv than the hardness of other parts.