CN116783012A

CN116783012A - Method for producing press-molded article

Info

Publication number: CN116783012A
Application number: CN202280010150.3A
Authority: CN
Inventors: 伊藤泰弘; 田畑亮
Original assignee: Nippon Steel and Sumitomo Metal Corp
Current assignee: Nippon Steel Corp
Priority date: 2021-04-09
Filing date: 2022-03-09
Publication date: 2023-09-19
Also published as: JPWO2022215425A1; WO2022215425A1; JP7477810B2

Abstract

The method for manufacturing the pressed molded product comprises the following steps: overlapping at least one of the steel plates (10, 20) having a plating layer on the surface thereof so that the plating layer is disposed between the steel plates (10, 20); pressing the overlapped steel plates (10, 20) along the thickness direction to make them closely contact; and heating the closely-adhered steel plates (10, 20) to a temperature equal to or higher than the melting point of the plating layer.

Description

Method for producing press-molded article

Technical Field

The present disclosure relates to a method for producing a press-molded article.

Background

Conventionally, press-molded articles have been widely used as members constituting automobile bodies. The press-formed product is produced by, for example, hot pressing (hot stamping) a steel plate as a blank. In recent years, in order to reduce the weight of a vehicle body and improve the collision safety, a poor steel plate is sometimes used as a blank for a press-formed product. The differential steel plate is, for example, a splice plate formed by overlapping a plurality of steel plates. In the splice plate, the position and the range of the thick region, the plate thickness difference between the thick region and the thin region, and the like can be freely designed.

In the splice plate, the overlapped steel plates are joined by spot welding, for example. In this case, the effect of integrating the steel sheets tends to be insufficient, and it is difficult to make the stacked steel sheets function as a single thick-walled material. Therefore, in the press-formed product produced from such a splice plate, it is difficult to significantly improve the rigidity of the overlapped surface between steel plates. In order to enhance the integration effect between steel plates, it is conceivable to expand the joint area between steel plates by using laser welding, brazing, or the like, for example. However, the larger the joining area, the more labor is required for the joining operation between the steel plates.

In contrast, patent document 1 discloses a technique for joining steel plates to each other by a plating layer between the steel plates. In patent document 1, when a press-formed article is produced, steel sheets having zinc or aluminum plating layers on both surfaces are stacked on each other and fed into a heating furnace to be heated. By this heating, the plating layer melts. Next, the steel sheets in the overlapped state are taken out from the heating furnace, and these steel sheets are molded into a predetermined shape by a mold and cooled. Patent document 1 describes that the molten plating layer is solidified by cooling a mold, and steel plates are welded to each other.

Prior art literature

Patent literature

Patent document 1 Japanese patent application laid-open No. 2014-124673

Disclosure of Invention

Problems to be solved by the invention

In patent document 1, steel sheets in a simple stacked state are heated to melt a plating layer, and then the plating layer is solidified. However, if only the steel plates are simply overlapped with each other, microscopic gaps exist between the steel plates. If the air entering the gap is heated to a high temperature by the heating of the steel sheets, the air expands, and the overlapping steel sheets may be peeled off. Therefore, in the technique of patent document 1, the overlapped steel plates are difficult to fix due to the resolidification of the plating layers, and the joining between the steel plates becomes insufficient.

The technical problem of the present disclosure is that, in a method of manufacturing a press-formed article using a plurality of steel sheets, overlapped steel sheets are simply and well joined to each other.

Solution for solving the problem

The manufacturing method according to the present disclosure is a manufacturing method of a press-molded article. The manufacturing method includes the following (a) to (c).

(a) The 1 st steel plate with a coating layer on the surface is overlapped with the 2 nd steel plate in a way that the coating layer is arranged between the 1 st steel plate and the 2 nd steel plate

(b) The 1 st steel plate and the 2 nd steel plate which are overlapped are pressed along the thickness direction to be closely contacted

(c) Heating the 1 st steel plate and the 2 nd steel plate which are closely connected to each other to a temperature higher than the melting point of the coating

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, in a method of manufacturing a press-formed article using a plurality of steel sheets, overlapped steel sheets can be simply and well joined to each other.

Drawings

Fig. 1 is a flowchart of a method for manufacturing a press-molded article according to an embodiment.

Fig. 2 is a schematic diagram for explaining the preparation steps included in the manufacturing method according to the embodiment.

Fig. 3 is a schematic diagram for explaining a pressurizing step included in the manufacturing method according to the embodiment.

Fig. 4 is another schematic diagram for explaining a pressurizing step included in the manufacturing method according to the embodiment.

Fig. 5 is a schematic diagram for explaining a molding step included in the manufacturing method according to the embodiment.

Fig. 6 is another schematic diagram for explaining a molding step included in the manufacturing method according to the embodiment.

Fig. 7 is a perspective view of a press-molded article manufactured by the manufacturing method according to the embodiment.

Fig. 8 is a photograph showing the surface of each of the peeled steel sheets of the examples and the comparative examples.

Fig. 9 is an observation image of the surface of the steel sheet shown in fig. 8.

Detailed Description

The manufacturing method according to the embodiment is a manufacturing method of a press-molded article. The manufacturing method includes the following (a) to (c) (first configuration).

In the manufacturing method of the first configuration, the 1 st steel sheet and the 2 nd steel sheet which are overlapped are pressurized in advance. Accordingly, the 1 st steel plate and the 2 nd steel plate are closely adhered, and microscopic gaps between the 1 st steel plate and the 2 nd steel plate can be reduced or substantially eliminated. That is, since air can be prevented from entering between the 1 st and 2 nd steel plates which are overlapped, expansion between the 1 st and 2 nd steel plates and pushing away of the molten coating layer can be suppressed when the 1 st and 2 nd steel plates which are in close contact are heated to a temperature equal to or higher than the melting point of the coating layer. As a result, it is difficult to prevent the fixation due to the resolidification of the plating layer generated between the 1 st steel sheet and the 2 nd steel sheet. Therefore, the 1 st steel sheet and the 2 nd steel sheet can be joined favorably over a large area by the fixation due to the resolidification of the plating layer. Further, by utilizing the fixation by resolidification of the plating layer, the 1 st steel sheet and the 2 nd steel sheet can be joined easily without performing joining work such as brazing.

In the above (b), the adhesion between the 1 st steel plate and the 2 nd steel plate is preferably pressure-bonded (second configuration). This makes it possible to make the 1 st steel sheet and the 2 nd steel sheet difficult to peel after pressurization.

The plating layer may be a zinc-based plating layer or an aluminum-based plating layer (third composition).

The 2 nd steel sheet may have a plating layer on the surface. In this case, the 1 st steel sheet and the 2 nd steel sheet may be superimposed so that the plating layers face each other (fourth configuration).

The plating layer of the 2 nd steel sheet may be the same kind of plating layer as the plating layer of the 1 st steel sheet (fifth constitution).

Embodiments of the present disclosure will be described below with reference to the drawings. In the drawings, the same or corresponding structures are denoted by the same reference numerals, and the same description is not repeated.

[ method for producing compression molded article ]

The manufacturing method according to the present embodiment is a method for manufacturing a press-molded article by hot press working (hot stamping). The press-molded article is used, for example, as a structural member constituting a part of an automobile body. Structural components are, for example, a-pillar reinforcements, B-pillar reinforcements, bumper reinforcements, tunnel reinforcements, side sill reinforcements, roof reinforcements, floor cross members, and the like.

Fig. 1 is a flowchart of a method for manufacturing a press-molded article according to the present embodiment. As shown in fig. 1, the manufacturing method according to the present embodiment includes a preparation step S1, a pressurizing step S2, a heating step S3, and a molding step S4. Hereinafter, each step will be specifically described.

(preparation step)

Fig. 2 is a schematic diagram for explaining the preparation step S1. Referring to fig. 2, in a preparation step S1, a plurality of steel sheets 10, 20 to be blanks of press-molded articles are prepared. In the present embodiment, 2 steel plates 10 and 20 are prepared. In the example shown in fig. 2, the surface of the steel sheet 20 (the surface substantially perpendicular to the plate thickness direction) has a smaller area than the surface of the steel sheet 10 (the surface substantially perpendicular to the plate thickness direction). The thickness of the steel sheet 20 may be the same as or different from the thickness of the steel sheet 10.

The surface of at least one of the steel sheet 10 and the steel sheet 20 is provided with a plating layer. Alternatively, each of the steel plates 10, 20 has a plating layer on at least one surface. That is, at least one of the steel plates 10, 20 is a plated steel plate. In the case where the steel sheet 10 is a plated steel sheet, the steel sheet 20 may be a plated steel sheet or a so-called bare (steel sheet without a plating layer). Similarly, in the case where the steel sheet 20 is a plated steel sheet, the steel sheet 10 may be a plated steel sheet or a bare steel sheet.

The materials of the steel plates 10 and 20 as the base material may be the same or different. The materials of the steel plates 10, 20 are not particularly limited, and may be appropriately selected. The plating layer can be zinc plating layer or aluminum plating layer.

The zinc-based plating layer is, for example, a zinc plating layer or a zinc alloy plating layer. The zinc plating layer is a plating layer containing zinc (Zn) as a main component. The zinc alloy plating layer is a plating layer mainly composed of a zinc alloy, for example, a Zn-Fe-based plating layer, a Zn-Al-based plating layer, a Zn-Mg-based plating layer, a Zn-Ni-based plating layer, a Zn-Al-Mg-based plating layer, or the like. More specifically, examples of the zinc-based plating layer include hot dip Zn-plating, alloying hot dip Zn (e.g., zn-10% fe), hot dip Zn-55% al-1.6% si, hot dip Zn-11% al-3% mg, hot dip Zn-6% al-3% mg, hot dip Zn-11% al-3% mg-0.2% si, zn-plating, zn-Ni plating, zn-Co plating, and the like (% by mass). The zinc-based plating layer may be formed by vapor deposition having the same composition as any of these plating layers.

The aluminum-based plating layer is, for example, an aluminum plating layer or an aluminum alloy plating layer. The aluminum plating layer is a plating layer containing aluminum (Al) as a main component, and the aluminum alloy plating layer is a plating layer containing an aluminum alloy as a main component. The aluminum-based plating layer may have the following chemical composition. Specifically, the aluminum-based plating layer contains, for example, si:0.05 to 15.00 percent of Zn: 0-30.00%, mg:0 to 5.00 percent of Fe: 0-10.00% and Ca:0 to 3.00 percent, and the balance of Al and less than 1 percent of impurities. In this chemical composition, the Mg content is preferably 3.00% or less, and the Si content is preferably 5.00% or more.

The aluminum-based plating layer having the above-described basic chemical composition may optionally further contain Sb in mass%: 0 to 0.50 percent of Pb:0 to 0.50 percent of Cu:0 to 1.00 percent of Sn:0 to 1.00 percent of Ti:0 to 1.00 percent of Sr:0 to 0.50 percent of Cr:0 to 1.00 percent of Ni:0 to 1.00% and Mn:0 to 1.00% of 1 or more than 2 kinds. The total content of these optional additives is preferably 5.00% or less, more preferably 2.00% or less.

The content of each of Sb and Pb in the above-mentioned optional additive elements is preferably 0.20% or less. The content of each of Cu, sn, and Ti is preferably 0.80% or less, more preferably 0.50% or less. Sb, pb, cu, sn and Ti may be 0.01% or more, respectively. The Sr content is preferably 0.30% or less, more preferably 0.10% or less. The Sr content may be 0.01% or more. The content of each of Cr, ni, and Mn is preferably 0.50% or less, more preferably 0.10% or less. The contents of Cr, ni and Mn are each preferably 0.01% or more.

The chemical composition (average composition) of the plating layer can be obtained, for example, by dissolving the plating layer in an acid solution to which an inhibitor for corrosion of the steel base material is added, and measuring the obtained solution by ICP (high frequency inductively coupled plasma) emission spectrometry.

(pressurizing step)

Fig. 3 and 4 are schematic diagrams for explaining the pressurizing step S2. In the pressurizing step S2, the stacked steel plates 10, 20 are pressurized in the plate thickness direction to be closely adhered. The pressurization of the plate assembly 30 may be performed, for example, using a known press 40.

Referring to fig. 3, when the pressurizing step S2 is performed, first, the steel plates 10 and 20 are overlapped. For example, the steel plates 10, 20 are overlapped such that the entire surface 21 of the steel plate 20 is in contact with the surface 11 of the steel plate 10. In the following description, the steel sheets 10 and 20 in a superimposed state are sometimes referred to as a sheet assembly 30.

The steel plates 10, 20 are overlapped such that the plating layer is disposed between the steel plates 10, 20. In the case where the steel sheet 10 has a plating layer, the surface 11 of the steel sheet 10 opposite to the steel sheet 20 is preferably covered with the plating layer. On the other hand, the surface 12 of the steel sheet 10 disposed on the opposite side to the steel sheet 20 may be covered with a plating layer or may not be covered with a plating layer.

In the case where the steel sheet 20 has a plating layer in addition to the steel sheet 10, the steel sheets 10, 20 are preferably overlapped in such a manner that the plating layers face each other. That is, when the surface 11 of the steel sheet 10 is coated with the plating layer, the surface 21 of the steel sheet 20 facing the steel sheet 10 is preferably also coated with the plating layer. In this case, the plating layer of the steel sheet 20 may be the same kind of plating layer as that of the steel sheet 10. The same kind of plating means that the main metal in one plating layer is the same as the main metal in the other plating layer. For example, in the case where the plating layer of the steel sheet 10 is a zinc-based plating layer, the plating layer of the steel sheet 20 may be a zinc-based plating layer. In addition, for example, in the case where the plating layer of the steel sheet 10 is an aluminum-based plating layer, the plating layer of the steel sheet 20 may be an aluminum-based plating layer. The coating of the steel sheet 20 may be a different type of coating from that of the steel sheet 10.

In the case where the steel sheet 10 has a plating layer, the steel sheet 20 may not have a plating layer. That is, in the case where the surface 11 of the steel sheet 10 is coated with the coating layer, the surface 21 of the steel sheet 20 is not necessarily coated with the coating layer. On the other hand, in the case where the surface 11 of the steel sheet 10 is not covered with the plating layer, the surface 21 of the steel sheet 20 is covered with the plating layer. The surface 22 of the steel sheet 20 disposed on the opposite side to the steel sheet 10 may be coated with a plating layer or may not be coated with a plating layer.

The total weight per unit area of the plating layer between the steel sheet 10 and the steel sheet 20 may be appropriately determined, and may be 30g/m, for example ² The above. In the case where the plating layers are formed on both the surface 11 of the steel sheet 10 and the surface 21 of the steel sheet 20, the sum of the weight per unit area of the plating layer in the surface 11 of the steel sheet 10 and the weight per unit area of the plating layer in the surface 21 of the steel sheet 20 may be set to 30g/m ² The above. In the case where the plating layer is formed only on one of the surface 11 of the steel sheet 10 and the surface 21 of the steel sheet 20, the weight per unit area of the plating layer in the surface 11 or the surface 21 may be set to 30g/m ² The above.

As shown in fig. 3, a die 41 including an upper die 411 and a lower die 412 is provided in the press 40 for performing the pressurizing step S2. The upper die 411 is fixed to a slider 42 that can be lifted and lowered relative to a main body frame (not shown) of the press 40. The lower die 412 is disposed below the upper die 411. The upper die 411 and the lower die 412 have, for example, solid rectangular parallelepiped shapes, respectively. In the pressurizing step S2, the plate assembly 30 is placed on the lower die 412.

In the pressurizing step S2, the steel sheets 10 and 20 stacked in the sheet assembly 30 may be conveyed to the press 40, or the steel sheets 10 and 20 may be conveyed to the press 40, respectively. When the steel plates 10 and 20 are conveyed to the press 40, the steel plates 10 and 20 are overlapped on the lower die 412 to form the plate assembly 30. In the example shown in fig. 3, a steel sheet 10 is disposed on the lower die 412 side, and a steel sheet 20 is superimposed on the steel sheet 10. However, the steel plate 20 may be disposed on the lower die 412 side, and the steel plate 10 may be superimposed on the steel plate 20.

As shown in fig. 4, the upper die 411 is lowered to contact the plate assembly 30 on the lower die 412 by lowering the slide 42 of the press 40. As the upper die 411 descends, the plate assembly 30 is pressurized in the plate thickness direction of the steel plates 10, 20 between the upper die 411 and the lower die 412. The plate assembly 30 is preferably pressurized in its entirety by an upper mold 411 and a lower mold 412. At this time, the average pressure applied to the plate assembly 30 is, for example, 20MPa or more and 200MPa or less. The time for pressurizing the plate assembly 30 may be, for example, 1 second or more and 60 seconds or less.

Such a pressurizing step S2 may be performed in a cold state. That is, the steel plates 10, 20 or the plate assembly 30 may not be actively heated at high temperature before the pressurizing process S2 or during the pressurizing process S2. In the pressurizing step S2, for example, pressure can be applied to the normal-temperature plate assembly 30 from both sides in the plate thickness direction. By pressing the plate assembly 30 in the plate thickness direction, the minute gap between the steel plates 10, 20 is reduced or eliminated, and the steel plates 10, 20 are closely adhered.

The pressing of the plate assembly 30 is completed after the steel plates 10, 20 are pressed together. That is, the upper die 411 is raised together with the slider 42, whereby the pressurization of the plate assembly 30 is released. The plate assembly 30 having the steel plates 10, 20 in the close contact state is taken out from between the upper die 411 and the lower die 412, and is supplied to the subsequent heating step S3. After the pressurizing step S2, when the plate assembly 30 is conveyed in order to perform the heating step S3, the place where the heating step S3 is performed is preferably in the vicinity of the place where the pressurizing step S2 is performed in order to prevent the separation of the steel plates 10, 20 due to vibration, tilting, or the like.

Here, the adhesion of the steel plates 10, 20 includes the adhesion of the steel plates 10, 20 and the pressure bonding of the steel plates 10, 20. The steel plates 10, 20 are adsorbed by overlapping the steel plates 10, 20 and pressurizing to exclude air between the steel plates 10, 20. In the manufacturing method according to the present embodiment, the adsorbed steel sheets 10, 20 may be subjected to hot stamping. In the case where the steel plates 10, 20 are adsorbed, if at least one of the steel plates 10, 20 is deformed, air intrudes between the steel plates 10, 20 and the steel plates 10, 20 may be peeled off. In addition, if the shape and surface roughness of the steel plates 10, 20 are not properly managed, the steel plates 10, 20 may not be well adsorbed. Therefore, in the pressurizing step S2, the steel plates 10 and 20 are preferably pressure-bonded. The press-bonding of the steel plates 10 and 20 means that the steel plates 10 and 20 are fixed by being pressed. Only by crimping, the coating neither melts nor resolidifies.

(heating step)

The heating step S3 is a step of heating the plate assembly 30 after the pressurization of the plate assembly 30 is completed. In the heating step S3, the board assembly 30 may be heated by a heating device (not shown). The heating device is, for example, a step-wise or intermittent heating furnace. The heating mode of the heating furnace may be a combustion type or an electric type. The heating device used in the heating step S3 is not limited to a heating furnace. Instead of the heating furnace, an electric heating device, a high-frequency heating device, or the like may be used.

When the plate assembly 30 is heated by the heating furnace, the pressurizing step S2 is completed, and the plate assembly 30 in the state where the pressurization is released is fed into the heating furnace. The steel sheets 10 and 20 closely adhered by pressurization are heated to a temperature equal to or higher than the melting point of the coating layer between the steel sheets 10 and 20 by a heating furnace. The plate assembly 30 may be heated by a furnace to a temperature suitable for hot stamping. The plate package 30 is heated, for example, to a temperature above 750 ℃. The heating temperature of the plate assembly 30 is preferably a of the steel plates 10, 20 _c3 Above the point. The heating temperature of the plate assembly 30 is, for example, a of the steel plates 10, 20 _c3 The temperature is below +200℃. The holding time of the plate assembly 30 in the heating furnace may be set to 60 seconds or more and 360 seconds or less. The heating of such a plate assembly 30 is preferably performed in a reducing atmosphere. That is, when a heating furnace is used in the heating step S3, it is preferable to heat the board assembly 30 in the heating furnace in which a reducing atmosphere is formed using, for example, hydrogen gas or the like.

The melting point of the coating is below the heating temperature of the plate assembly 30. The coating may, for example, have a melting point that is more than 50 ℃ lower than the heating temperature of the plate assembly 30. Therefore, the coating layer between the steel sheet 10 and the steel sheet 20 is melted by heating in the heating step S3.

The plate assembly 30 is heated at a predetermined heating temperature and holding time, and then taken out of the heating furnace. Then, the plate assembly 30 is supplied to the molding process S4.

(molding step)

Fig. 5 and 6 are schematic views for explaining the molding step S4. In the molding step S4, the plate assembly 30 heated to a temperature equal to or higher than the melting point of the plating layer in the heating step S3 is subjected to hot stamping. The hot stamping may be performed using a known press 50, for example. The heated plate assembly 30 is transported from the furnace to the press 50, for example, by a conveyor belt or the like.

A die 51 is provided in the press 50. The mold 51 includes an upper mold 511 and a lower mold 512. A molding surface having the shape of the target press-molded article is formed on the upper die 511 and the lower die 512. In the example of the present embodiment, the upper die 511 is a female die, and has a concave molding surface. In the example of the present embodiment, the lower die 512 is a male die paired with a female die, and has a convex molding surface corresponding to the concave molding surface of the upper die 511. The upper die 511 is fixed to a slider 52 having a vertically movable structure with respect to a main body frame (not shown) of the press 50. The lower die 512 is disposed below the upper die 511. As in the example shown in fig. 5, holders 513 having a vertically movable structure may be disposed on both sides of the lower die 512.

In the molding process S4, the plate assembly 30 is placed on the lower die 512. In the example shown in fig. 5, the plate assembly 30 is placed on the lower die 512 in such a manner that the steel plate 20 is opposite to the lower die 512. As shown in fig. 6, by lowering the slide 52 of the press 50, the upper die 511 is lowered toward the plate assembly 30 together with the slide 52. When the upper die 511 is brought to the bottom dead center, the plate assembly 30 is molded into the press-molded article 60 by the concave molding surface of the upper die 511 and the convex molding surface of the lower die 512.

The heated plate assembly 30 is molded into a press-molded article 60 by the mold 51, and is cooled (quenched) by contact with the mold 51. The coating melted between the steel sheet 10 and the steel sheet 20 is solidified by cooling the sheet assembly 30 by the mold 51. Thereby, the steel plates 10, 20 are surface-joined. The press-molded article 60 is sufficiently cooled by the mold 51 and then taken out of the press 50.

(compression molded article)

Fig. 7 is a perspective view of a press-molded article 60 manufactured by the manufacturing method according to the present embodiment. As shown in fig. 7, the steel sheet 10 constitutes the main body of the press-formed product 60. The steel sheet 10 is formed into a substantially hat shape as viewed in the longitudinal direction of the press-formed article 60. On the other hand, the steel sheet 20 constitutes a reinforcing member that locally reinforces the main body of the press-molded article 60. The steel plate 20 is formed into a substantially U-shape as viewed in the longitudinal direction of the press-formed product 60. The steel plate 20 is disposed inside the hat-shaped steel plate 10. The steel sheet 20 is joined to the steel sheet 10 by fixation by resolidification of the plating layer. The press-formed product 60 is locally thickened by the steel plate 20.

[ Effect ]

In the manufacturing method according to the present embodiment, in the pressing step S2, the plate assembly 30, which is a blank of the press-molded product 60, is pressed in advance, and the steel plates 10, 20 included in the plate assembly 30 are brought into close contact with each other. Therefore, microscopic gaps between the steel plates 10 and 20 can be reduced or substantially eliminated. Thus, when the sheet member 30 is heated in the subsequent heating step S3 and the sheet member 30 is molded and cooled in the subsequent molding step S4, it is difficult to prevent fixation due to resolidification of the plating layer between the steel sheets 10, 20. Accordingly, the steel sheets 10 and 20 can be favorably joined to each other over a large area by the fixation due to the resolidification of the plating layer. Further, by utilizing the fixation by resolidification of the plating layer, the steel plates 10, 20 can be simply joined to each other without performing a joining operation such as brazing.

For example, when welding overlapping steel plates 10 and 20, gaps are likely to occur between the steel plates 10 and 20 around the welded portions due to deformation around the welded portions, and the steel plates 10 and 20 do not closely adhere to each other. However, in the present embodiment, the steel sheets 10 and 20 are brought into close contact (adsorbed or pressure-bonded) by pressurizing in the sheet thickness direction so that air does not enter between the steel sheets 10 and 20, and the steel sheets 10 and 20 are heated while maintaining the close contact state, whereby the plating layer between the steel sheets 10 and 20 is melted. Therefore, the air between the steel plates 10, 20 can be prevented from expanding at a high temperature to push away the plating layer between the steel plates 10, 20. Therefore, the plating layer between the steel plates 10, 20 is easily resolidified and fixed to the steel plates 10, 20, and the steel plates 10, 20 can be joined well.

In the manufacturing method according to the present embodiment, the plate package 30 is pressurized to reduce or eliminate microscopic gaps between the steel plates 10, 20, whereby the plating layer is effectively resolidified and fixed to the steel plates 10, 20. Therefore, the steel sheets 10 and 20 can be favorably ground-joined to each other, and the effect of integrating the steel sheet 10 and the steel sheet 20 in the press-formed product 60 can be improved. This can make the steel plates 10, 20 function substantially as one sheet material, and can improve the rigidity of the overlapped surface between the steel plates 10, 20 in the press-molded product 60. In addition, the effective width of the press-formed product 60 can be enlarged. The effective width is, for example, a width of a portion that can be compressively deformed by a load in the longitudinal direction when the load is input to the press-molded product 60, and is generally expressed by a ratio to a width of an arbitrary surface included in the press-molded product 60 (for example, a width of a top plate, a width (height) of one vertical wall).

In the manufacturing method according to the present embodiment, the heating step S3 is performed after the pressurizing step S2 is completed. Therefore, only the plate assembly 30 can be fed to the heating device (heating furnace) in a state where the pressurization of the mold 41 is released, and only the plate assembly 30 can be removed from the heating device. That is, the mold 41 and the like do not need to be moved together with the plate assembly 30. Therefore, the manufacturing equipment of the press-molded product 60, the work accompanying the manufacture of the press-molded product 60, and the like can be simplified.

In the manufacturing method according to the present embodiment, the steel plates 10 and 20 are pressed and the steel plates 10 and 20 are closely adhered to each other before the heating step S3. The steel plates 10, 20 may be adsorbed by pressurization, but preferably by crimping. By pressure-bonding the steel plates 10, 20, the steel plates 10, 20 can be made less likely to peel than by suction.

In the manufacturing method according to the present embodiment, the plate assembly 30 can be heated in a reducing atmosphere in the heating step S3. Thus, when the plate assembly 30 is heated, oxides are less likely to be generated on the surface of the plating layer. Therefore, fixation due to resolidification of the plating layer generated between the steel plates 10, 20 is more difficult to be hindered. Therefore, the steel plates 10, 20 can be better joined to each other.

The embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above embodiments, and various modifications may be made without departing from the gist thereof.

For example, in the above embodiment, the heating step S3 is performed immediately after the pressurizing step S2. However, a step of simply joining the steel plates 10, 20 may be performed between the pressurizing step S2 and the heating step S3. That is, the steel plates 10 and 20 may be joined by, for example, spot welding after the pressurizing step S2 is completed and before the heating step S3 is started. The simple joining step of the steel plates 10, 20 may be performed before the pressurizing step S2.

However, as described in the above embodiment, the steel sheets 10 and 20 are surface-joined by fixation by resolidification of the plating layer generated through the heating step S3 and the forming step S4. Therefore, in the case of performing a simple joining process between the pressurizing process S2 and the heating process S3 or before the pressurizing process S2, the steel plates 10, 20 are joined only in a small area so that the burden of the joining operation does not become large.

In the above embodiment, in the pressurizing step S2, the press 40 is used for pressurizing the plate assembly 30. However, in the pressurizing step S2, the press 40 is not necessarily required. Other machines such as rolling mills or clamps may be used instead of the press 40 if the plate assembly 30 can be pressurized.

In the above embodiment, in the press-formed product 60, the steel sheet 20 as the reinforcing member is disposed inside the steel sheet 10 as the main body. However, in contrast, the steel plate 20 may be disposed outside the steel plate 10. The position and the range of the steel sheet 20 with respect to the steel sheet 10 are not limited to those in the above embodiment, and may be appropriately changed. The overall shape of the press-molded product 60 is not limited to the example of the embodiment described above, and may be changed as appropriate.

In the example of the embodiment described above, the steel sheet 20 as the reinforcing member is overlapped with the steel sheet 10 as the main body in such a manner that the entire surface 21 thereof is in contact with the surface 11 of the steel sheet 10. However, the manner of overlapping the steel plates 10, 20 is not limited thereto. For example, the steel sheet 20 may be partially overlapped with the steel sheet 10.

In the example of the embodiment described above, the steel sheet 10 constituting the main body of the press-formed product 60 may be a steel sheet having a uniform plate thickness and uniform material. The steel sheet 10 may be a steel sheet having at least one of a plate thickness and a material different from each other. That is, the steel sheet 10 may be a continuous variable cross-section (TRB) sheet in which the sheet thickness is varied for each portion by rolling, or may be a Tailor Welded Blank (TWB) sheet in which a plurality of steel sheets are butt welded. In the case where the steel sheet 10 is a TWB, the steel sheet 20 may be disposed across the weld line of the TWB.

In the above embodiment, the plate assembly 30, which is a blank of the press-formed product 60, is composed of two steel plates 10, 20. However, the plate assembly 30 may include 3 or more steel plates. For example, 3 or more steel plates may be stacked in this order in the plate assembly 30, or a plurality of steel plates may be arranged in a staggered position on 1 steel plate. In this case, if the plating layer is disposed between adjacent steel plates in the plate thickness direction and the steel plates are brought into close contact with each other by performing the pressurizing step S2 before the heating step S3, the steel plates can be surface-joined to each other by the fixation due to resolidification of the plating layer.

In the above embodiment, the steel sheets 10 and 20 that are pressed and bonded together are formed into the press-formed product 60 by hot pressing (hot stamping). However, the method of forming the steel plates 10, 20 is not limited thereto. The steel sheets 10 and 20 may be cooled while being kept in close contact after being heated to a temperature equal to or higher than the melting point of the plating layer. The steel sheets 10 and 20 are joined by fixation by resolidification of the plating layers as in the above embodiments. Cold press forming may be performed on the joined steel plates 10 and 20.

Examples

The present disclosure is further described in detail below by way of examples. Wherein the present disclosure is not limited to the following examples.

Example (example)

In order to confirm the effects of the present disclosure, experiments were performed to manufacture press-molded articles in the same manner as the methods according to the above embodiments. In this experiment, 2 steel sheets having aluminum-based plating layers (Al plating layers) on both sides were stacked to form a sheet assembly before hot stamping, and the sheet assembly was pressed in the sheet thickness direction by a known press to be closely contacted (press-contacted) (pressing step). Each steel plateThe weight per unit area of the Al plating layer in the (B) was 80g/m ² . The pressurization of the plate assembly was performed under cold conditions (normal temperature) with a load (pressure) of about 40 tons (about 80 MPa) and a pressurization time of 1 second.

Next, the plate assembly after the completion of the pressurization was heated to 950 ℃ in a heating furnace and held for 240 seconds (heating step). Then, the heated plate assembly is molded into a press-molded article by a predetermined mold (molding step).

Comparative example

For comparison, an experiment for manufacturing a press-molded article was performed under the same conditions as in the above examples, except that the pressing step was not performed before the hot stamping.

(evaluation)

In the example in which the pressing process was performed, 2 steel plates were firmly joined to such an extent that the peeling was not easy by manpower. In the examples, 2 steel plates were finally peeled off by using a tool. On the other hand, in the comparative example in which the pressurizing step was not performed, 2 steel sheets could be easily peeled off by manpower without using any tool.

Fig. 8 is a photograph showing the surface (overlapped surface) of each of the peeled steel sheets of the examples and the comparative examples. Fig. 9 is an observation image (scanning electron microscope image) of the surface of the peeled steel sheet.

As shown in fig. 8, in the example in which the pressing step is performed, a glossy portion is generated on the surface of the steel sheet. The glossy portion is present so as to spread on the surface of the steel sheet. As shown in fig. 9, the glossy portion is a brittle fracture that breaks and becomes flat when the 2 steel sheets are peeled off, and is a portion where the plating layer is melted and resolidified after being crimped and fixed.

On the other hand, in the comparative example in which the pressurizing step was not performed, as shown in fig. 8, the surface of the steel sheet had no glossy portion and only gray portion. As shown in fig. 9, the gray portion is a concave-convex surface generated by fe—al alloying at the boundary between the steel sheet and the plating layer, and is an unfixed portion caused by the melting and resolidification of the plating layer without being pressed against the steel sheet.

From these experiments, it was confirmed that the steel sheets were adhered to each other by performing the pressing step before hot stamping, and that fixation due to resolidification of the plating layer occurred in a planar shape for the overlapped steel sheets. As a result, it was confirmed that the steel plates were well joined to each other.

Description of the reference numerals

10. 20: steel plate

11. 12, 21, 22: surface of the body

51: mould

60: press-formed article

Claims

1. A method for producing a press-molded article, comprising the steps of:

overlapping a 1 st steel sheet having a plating layer on a surface thereof with a 2 nd steel sheet in such a manner that the plating layer is arranged between the 1 st steel sheet and the 2 nd steel sheet;

pressurizing the overlapped 1 st steel plate and 2 nd steel plate along the thickness direction to make them closely contact; the method comprises the steps of,

and heating the 1 st steel plate and the 2 nd steel plate which are closely connected to each other to a temperature higher than the melting point of the coating.

2. The method for producing a press-molded article according to claim 1, wherein the bonding is pressure bonding.

3. The method for producing a press-formed article according to claim 1 or 2, wherein the plating layer is a zinc-based plating layer or an aluminum-based plating layer.

4. The method for producing a press-molded article according to any one of claim 1 to 3, wherein,

the 2 nd steel plate is provided with a plating layer on the surface,

the 1 st steel sheet and the 2 nd steel sheet are overlapped in such a manner that the plating layers face each other.

5. The method for producing a press-formed article according to claim 4, wherein the plating layer of the 2 nd steel sheet is the same kind of plating layer as the plating layer of the 1 st steel sheet.