JPH0726320A - Production of high strength press formed part - Google Patents

Abstract

PURPOSE:To produce a press formed part excellent in strength by press-forming an ultralow carbon steel plate of specific composition, applying a carbon- containing paint to a part, requiring high strength, of the resulting formed part, and irradiating this part with high density energy. CONSTITUTION:A steel plate, which has a composition containing, by weight, 0.0005-0.0080% C, 0.005-1.00% Si, 0.01-3.0% Mn, 0.001-0.150% P, 0.001-0.025% S, 0.005-0.100% Al, and 0.0005-0.01% N or further containing 0.005-0.060% Nb and/or 0.005-0.100% Ti and further 0.05-1.00% Mo and/or 0.0005-0.0050% B or further 0.10-2.0% Cu and/or 0.05-2.0% Ni, is press-formed. Subsequently, the part, requiring high strength, of the resulting formed part is subjected to application of a powder or paint containing 72wt.% C and then irradiated with high density energy such as laser to undergo melting and solidification. As a result, C is absorbed and the structure of the steel plate is transformed, by which the strength of the part can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength press-molded product used for automobile bodies and the like.

[0002]

2. Description of the Related Art A method is known in which, after press-forming a steel sheet, a required portion is irradiated with a high energy source such as a laser to increase the strength (for example, JP-A-4-72010).
Issue). In the above-mentioned conventional technique, the C content of the steel sheet is required to be 0.01% or more in order to obtain the required strength. That is, in order to utilize the transformation strengthening of steel as a mechanism for irradiating a high energy source to increase the strength, it is necessary that the C content be high to some extent. However, if the amount of C is high, it is difficult to secure moldability, and a press-formed product having a complicated shape cannot be obtained.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of increasing strength while ensuring high moldability.

[0004]

The gist of the present invention is C0.
When a press-formed product is formed by using steel containing 0005 to 0.0080% by weight, and at the time of increasing the strength by irradiating at least a site requiring strength with a high-density energy source, C is applied to at least one surface of the irradiation site. A method for producing a high-strength press-formed product is characterized in that a powder or paint containing 2% or more is coated.

As the steel of the present invention, in weight percent, C0.00
05-0.0080%, Si 0.005-1.00%,
Mn 0.01-3.0%, P 0.001-0.150
%, S 0.001 to 0.025%, Al 0.005
Steel containing 0.10% and N 0.0005 to 0.0100% (Steel 1), Nb 0.005 to 0.060 in the Steel 1
% And Ti 0.005 to 0.100% of one or two added steel (steel 2) and the composition of said steel 2 with Mo0.0
5 to 1.00% and B 0.0005 to 0.0050% 1
Steel with addition of one or two kinds (steel 3), and further steel 1 to steel 3 with Cu 0.10 to 2.0% and Ni 0.05 to
It is possible to use steel (steel 4) added with 2.0% of one or two kinds.

The present invention will be described in detail below. First,
In order to secure the press formability of the steel sheet, the amount of C as a component of the above steel needs to be 0.0080% or less. Further, in order to secure the strength after press molding, at least a portion of the molded product where strength is required is previously coated with a powder or paint containing 2% or more of C, and thereafter, a high density energy source is irradiated to the coated product. The penetration of C into the molten portion of the steel sheet at the energy irradiation portion promotes transformation strengthening.

Next, the reasons for limiting the components of steel will be described. If C is less than 0.0005%, the cost of producing steel increases, which is not economically suitable. Also, 0.0080
%, The formability of the steel sheet deteriorates and complicated press working is difficult, so the appropriate range is 0.0005-0.0.
080%. If Si, Mn, P, S, Al, and N are less than these lower limit values, the manufacturing cost of the steel sheet increases significantly, which is not economically suitable. Further, if the upper limit of these is exceeded (however, if S is 0.025% or more), the press formability deteriorates, so the range of the above components was limited.

Nb 0.005 to 0.060% and Ti 0.
One or two kinds of 005 to 0.100% may be added for improving moldability. If the Nb content is less than 0.005% and / or the Ti content is less than 0.005%, the desired effect of improving formability cannot be obtained. Nb and Ti are more than 0.060% Nb, Ti
If it exceeds 0.100%, the effect of improving the formability is saturated, and only the addition cost increases, which is not economical. Nb and Ti are C
In order to fix N and N, it is preferable to add an equivalent amount or more in terms of atomic weight ratio.
20 ppm may be left.

Mo is added to promote transformation strengthening when the amount of C is small. If it is less than 0.05%, the transformation strengthening effect is small, and if it exceeds 1.00%, the effect is saturated. Therefore, the appropriate range is 0.05% to 1.00%. B is added when secondary workability of the steel sheet is required. That is, if C is extremely reduced, secondary work cracks will occur when drawing is performed, so B is added to prevent this. If it is less than 0.0005%, the effect of preventing secondary work cracking is lost, so this is the lower limit,
If it exceeds 0.0050%, the workability will deteriorate, so
This is the upper limit.

Cu may be contained in an amount of 0.1 to 2.0% for promoting precipitation strengthening or transformation strengthening. If it is less than the lower limit, the desired effect cannot be obtained, and if it exceeds the upper limit, the effect is saturated, and it causes surface cracking during steel sheet production. Ni
Is 0 to promote transformation strengthening and prevent Cu surface cracking.
You may contain 05-2.0%. If it is less than the lower limit value, the desired effect cannot be obtained, and if it exceeds the upper limit value, the cost becomes the upper limit and the economic efficiency is impaired.

The steel sheet whose components have been adjusted as described above is press-formed, and at least a portion where strength improvement is desired is irradiated with a high-density energy source such as laser or plasma. At this time, powder or paint containing 2% or more of C is applied to the irradiation surface or the back surface of the steel sheet. The irradiation conditions are such that the molten portion penetrates from the irradiation surface of the steel sheet to the back surface. As a result, C of the powder or paint on the surface of the steel sheet is taken into the steel sheet from the molten portion, the transformation of the steel is promoted during cooling after irradiation, and the required strength can be obtained. At this time, the lower limit of the amount of C contained in the applied powder or paint is 2%. If it is less than 2%, the amount of C taken into the steel sheet will be small, and the effect of promoting the transformation of the steel will be lost, so that the desired strength cannot be obtained. The coating thickness of the paint or powder may be 2 μm or more. 2μ
If it is less than m, the amount of C taken into the steel will be small, and the effect of promoting the transformation of the steel will be small.

The steel sheet according to the present invention may be any of hot rolled steel sheet, cold rolled steel sheet and plated steel sheet. As the galvanized steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet,
Hot-dip zinc-aluminum plated steel sheet, electrogalvanized steel sheet, electroalloy plated steel sheet, alloyed electrogalvanized steel sheet,
Electric Fe-based alloy plating (F
e60 wt% or more, Fe-Zn alloy, Fe-P alloy, etc.)-coated steel sheet, aluminum-plated steel sheet, turn-plated steel sheet, colored powder powder coated steel sheet, coated steel sheet containing zinc powder, organic composite-plated steel sheet, collar-plated steel sheet But it's okay.

Further, the C-containing coating material coated on the front surface and / or the back surface of the irradiated portion of the molded product is taken into the molten portion of the steel sheet or vaporized after the irradiation with the high-density energy source, so that the remaining portion. The C-containing paint remains on the surface and does not cause a poor appearance.

[0014]

EXAMPLES The present invention will be further described below based on examples. Steels having the components shown in Table 1 were melted and subjected to continuous casting, hot rolling, pickling, cold rolling and annealing according to a conventional method to obtain cold rolled steel sheets. A part was further galvanized to form a plated steel sheet. Moreover, a part was used for hot rolling. The plate thickness is
It was 1.4 mm. However, Steel 2 is 2.0 mm, Steel 11 is
It is 3.5 mm. The obtained steel plate was processed into a model part as shown in FIG. At this time, the moldability was evaluated based on the height at which molding was possible without cracking, that is, the "molding height" shown in FIG.

[0015]

[Table 1]

This molded product was cut along the broken line in FIG.
As shown in FIG. 2, steel plates of the same type were joined by spot welding to manufacture a box-shaped part. A paint having the components shown in Table 2 was applied to the center of this part. After coating and drying the paint,
A paint containing 50% by weight C was used. For comparison, a product without coating was also prepared. Then, this part was irradiated with a 3 kw laser in a cross beam shape as shown in FIG. The number of irradiation is 5 in the direction perpendicular to the longitudinal direction of the part,
Irradiation was performed on the entire circumference of 20 pieces at intervals of about 20 mm in the longitudinal direction. The irradiation width was 1.4 mm, 2.0 mm, and 3.5 mm, which were the same as the plate thickness. Upon irradiation with the laser, the fusion zone was made to reach the back surface of the steel sheet.

Buckling strength was measured using the model parts prepared as described above. Buckling strength is measured at 50ton
The compression side of the tensile tester was used. The strength of the parts was evaluated by the magnitude of the initial buckling load. The results are shown in Table 2.

[0018]

[Table 2]

[0019]

[Table 3]

As is clear from Table 2, the molded product using the steel of the present invention has a higher molding height and is excellent in moldability as compared with the conventional molded product of steel having a high C. Further, it can be seen that when steel having a chemical composition within the scope of the present invention is used and the coating material is previously coated as in the present invention, the initial buckling load is higher than that of the comparative part. That is, the strength of the press-formed product is increased.

[0021]

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a molded product having good press moldability and capable of performing complicated press molding, and it is possible to contribute to weight reduction of the molded product along with the increase in strength. Various automobile parts can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a press-formed product.

FIG. 2 is a schematic view of an irradiation press-formed product and an explanatory view showing a strength loading method.

[Explanation of symbols]

 1 Press-formed product 2 Cutting position 3 Forming height 4 Bottom plate 5 Spot welding 6 High-density energy source irradiation position 7 Load application direction

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[Procedure amendment]

[Submission date] August 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

[0015]

[Table 1]

Claims (5)

[Claims] 1. A press-formed product is formed by using steel containing 0.0005 to 0.0080% by weight of C, and at the time of increasing the strength by irradiating at least a portion requiring strength with a high-density energy source, irradiation is performed. A method for producing a high-strength press-formed product, characterized in that at least one surface of a part is coated in advance with a powder or paint containing 2% or more of C. 2. The composition of the steel used for press forming is C0.0005-0.0080%, Si0.00 by weight%.
5 to 1.00%, Mn 0.01 to 3.0%, P0.00
1 to 0.150%, S0.001 to 0.025%, Al
0.005-0.100%, N 0.0005-0.01
The method for producing a high-strength press-formed product according to claim 1, wherein the balance is 00% and the balance is Fe and inevitable impurities. 3. The composition of the steel used for press forming is C0.0005-0.0080%, Si0.00 by weight%.
5 to 1.00%, Mn 0.01 to 3.0%, P0.00
1 to 0.150%, S0.001 to 0.025%, Al
0.005-0.100%, N 0.0005-0.01
00%, and Nb 0.005-0.060% and Ti
0.005 to 0.100% of 1 type or 2 types, the balance being Fe
The method for producing a high-strength press-formed product according to claim 1, wherein the high-strength press-formed product is an unavoidable impurity. 4. The composition of the steel used for press forming is C0.0005-0.0080% and Si0.00 by weight%.
5 to 1.00%, Mn 0.01 to 3.0%, P0.00
1 to 0.150%, S0.001 to 0.025%, Al
0.005-0.100%, N 0.0005-0.01
00%, Nb 0.005-0.060% and Ti 0.00
5 to 0.100% of 1 type or 2 types, and Mo0.05
The method for producing a high-strength press-formed product according to claim 1, wherein one or two of 1.00% and B0.0005 to 0.0050%, and the balance being Fe and inevitable impurities. 5. The steel used for press forming has the composition of the steel according to any one of claims 2 to 4 and further contains Cu 0.10-2.
The method for producing a high-strength press-formed product according to claim 1, characterized in that it contains one or two of 0% and Ni of 0.05 to 2.0%.