JPH0510417B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a steel plate for laser processing that has excellent stretch flanging properties. (Prior Art) Press-formed products of various steel sheets with excellent cold workability have been put into practical use as automobile parts, construction parts, and the like. Conventionally, when manufacturing such press-formed products, the material steel plate for press-forming is obtained by press punching from a hot-rolled steel plate or cold-rolled steel plate, and then the required press-forming is performed. When necessary, punching is often used. Press forming of such press forming material steel sheets and punched holes often involves stretch flange processing. By reducing the amount of C and the amount of non-metallic inclusions such as MnS,
Alternatively, by controlling the shape of nonmetallic inclusions, a steel plate is made to have good stretch flanging properties. However, in recent years, with the development of numerical control technology and laser cutting technology in machining, it has become possible to laser cut steel plates with complex shapes to produce raw steel plates for press forming, and also to drill holes after press forming. A method using laser processing has been proposed, and some have been put into practical use. Various studies have been conducted on the stretch flanging properties of the mechanically punched materials mentioned above.
The above laser processing technology is fundamentally different from conventional mechanical shearing technology, and is thought to have a large impact on the stretch-flange formability of steel sheets, but so far, little metallurgical research has been conducted. . (Purpose of the Invention) Therefore, as a result of intensive research on the stretch flange workability of laser cut steel sheets in comparison with conventional punching, the present inventors found that by giving the steel sheet a predetermined chemical composition, The inventors have discovered that it is possible to obtain a steel plate for laser machining that has extremely excellent stretch flanging properties at the laser cut portion, and has thus arrived at the present invention. That is, an object of the present invention is to provide a steel plate for laser processing which has excellent stretch flange workability at the laser cut portion. Hereinafter, in the present invention, when referring to a steel plate for laser processing with excellent stretch flangeability, this refers to:
As mentioned above, this refers to a steel plate for laser processing that has excellent stretch flanging properties at the laser cut portion. (Structure of the Invention) The steel plate for laser processing with excellent stretch flanging property according to the present invention has the following properties in terms of weight percentage: C 0.03 to 0.25%, Si 2.5% or less, Mn 0.1 to 2.5%, P 0.15% or less, S 0.020% or less. , and has Al 0.1% or less, the balance consists of iron and unavoidable impurities, and the formula value K = C + Si / 25 + Mn / 10 + P / 10 + 10 S + Cu / 15
It is characterized by satisfying 0.14≦K≦0.50 when +Ni/50+Cr/20 +Mo/20+2Nb+V/10+5B. First, the reason for limiting the chemical components in the steel sheet of the present invention will be explained. The steel sheet of the present invention is particularly suitable for cold working applications, and in this case, the smaller the amount of C added, the more preferable it is. It is necessary to add at least 0.03% in order to obtain a steel plate with a For example, in the case of ultra-low carbon steel with a C content of about 0.01%, a steel plate for laser processing with excellent stretch flangeability can be obtained even if the predetermined formula value is within the range according to the present invention, as described later. I can't. On the other hand, when adding too much C,
Although it can ensure excellent stretch flange workability of the laser cut section, the upper limit of the amount of C added is
The rate shall be 0.25%. Adding Si helps improve the stretch flange workability of the laser cut section, but adding too much Si can cause surface flaws in the steel plate and increase manufacturing costs.
The upper limit of the amount added is 2.5%. It is necessary to add at least 0.1% of Mn in order to prevent hot cracking due to FeS formation during hot rolling of steel. However, when adding too much, it impairs the cold workability of the steel plate.
The upper limit of the amount added is 2.5%. The smaller the content of P, the more preferable it is from the viewpoint of cold workability of the steel sheet, but in the present invention,
It may be added as a steel strengthening element if necessary. However, when adding a large amount exceeding 0.15%, the embrittlement of the steel becomes significant, so the addition amount is 0.15%.
The following shall apply. The lower the content of S is, the more preferable it is for the stretch-flange workability of punched materials, but in the case of laser processed materials, the amount of S does not have a large effect.
However, if the content is too high, the cleanliness of the steel plate will deteriorate and defects will increase in the steel, so the content should be 0.020% or less. Although the present invention can also be applied to rimmed steel,
In the case of killed steel, Al
The amount added shall be 0.1% or less. In the present invention, the steel plate has, as a chemical component,
It may contain at least one element selected from the group consisting of Cu, Ni, Cr, Mo, Nb, V and B. Cu is effective in improving the stretch flange workability of the laser cut section, but when added in excess, it causes surface flaws in the steel plate, so the amount added is limited to 1% or less. Ni has the effect of refining the microstructure of the laser-cut portion, and is effective in improving the stretch flange workability of high-strength steel sheets. However, even if the amount added exceeds 1%, the above effects are saturated and this is not preferable from an economic point of view, so the amount added is set to 1% or less. As mentioned above, when adding a large amount of Cu,
In particular, Cu should be added to 0.4
When adding % or more, as a composite addition with Ni,
It is preferable to try to improve this. Cr and Mo, like Cu, are effective in improving the stretch flange workability of laser cut parts, but adding large amounts impairs economic efficiency, so the amount of addition should be 2.5% or less for Cr and 0.5% for Mo. % or less. Both Nb and V are effective in improving the stretch flange workability of laser cut parts, but due to material strength design, this effect is saturated when the amount exceeds 0.1%, so the upper limit of the amount added is 0.1% for each. %. When B is added in combination with C and Mn, it is effective in improving the stretch flange workability of the laser cut portion. However, even if added in large amounts exceeding 0.01%,
Since the effect reaches saturation, the upper limit of the amount added is set at 0.01%. The steel plate according to the present invention has the chemical composition described above, and the formula value K=C+Si/25+Mn/10+P/10+10S+Cu/15
+Ni/50+Cr/20 +Mo/20+2Nb+V/10+5B, it is necessary to satisfy 0.14≦K≦0.50. The reason is explained below. The drawings show the results of hole expansion tests conducted on steel plates with various chemical compositions and strengths. That is, holes with a diameter of 10 mm were cut in steel plates having various chemical compositions and therefore various formula values K by laser cutting or punch punching, and a hole expansion test was conducted. As a result, the ratio of the hole expansion rate of the hole formed by laser processing to the hole expansion rate of the hole formed by punching increases as the formula value K increases. However, as mentioned above, for ultra-low carbon steel, even if the formula value is within the specified range, the effect of improving stretch flange formability cannot be obtained;
When it is smaller than 0.14, the effect of improving stretch flangeability cannot be obtained. On the other hand, when the formula value exceeds 0.50, the hardening of the laser-cut portion of the steel plate becomes extremely high, and in some cases, localized quench cracks are likely to occur, resulting in poor stretchability and stretch flange processing of the steel plate base material. Various problems occur in addition to deterioration in press formability such as hardness, ductility of hardened parts, and weldability such as under-bead cracking in thick materials. In this way, when the formula value exceeds 0.50, the obtained steel plate is practically
Since cold workability and weldability will be significantly deteriorated and it will become unsuitable for practical use, in the present invention, the range of the above formula value is set to 0.14 or more and 0.50 or less, preferably,
Must be 0.20 or more and 0.50 or less. Therefore, according to the present invention, even if the strength and S content are the same, the chemical composition is set within a predetermined range according to the present invention, and the above formula values defined by the amounts of these alloying elements are By regulating it within a predetermined range, it is possible to obtain a steel plate for laser machining that has excellent stretch flange workability at the laser cut portion. Note that the steel plate according to the present invention can be manufactured by any method including a plate mill, a hot rolling mill, and a cold rolling mill. (Effects of the Invention) As described above, the steel plate according to the present invention has a predetermined chemical composition and the above-mentioned formula values are adjusted to a predetermined range, and the stretch flange processability of the laser cut portion is improved significantly. A steel plate for laser processing can be obtained. (Example) The present invention will be described below with reference to Examples. Example A steel plate having the chemical composition and formula value K shown in the table was manufactured using either a plate mill, a hot rolling mill, or a cold rolling mill. A 10 mm diameter hole was cut into these steel plates by laser cutting or punch punching, and a hole expansion test was performed. The relationship between the formula value K and the ratio of the expansion rate of the hole by laser machining to the expansion rate of the hole by punch punching is shown in the drawing. According to the steel plate for laser processing according to the present invention, it is clear that the holes formed by laser cutting have excellent stretch flanging properties compared to the holes formed by punching.

【table】

【table】 [Brief explanation of drawings]

The drawing shows the hole expansion rate of the hole by the laser cutting method compared to the hole expansion rate of the hole by the punch punching method when a 10 mm diameter hole was cut in a steel plate using the laser cutting method and the punch punching method and a hole expansion test was performed. It is a graph showing the relationship between the ratio and the formula value K.

Claims (1)

[Claims] 1% by weight: C 0.03-0.25%, Si 2.5% or less, Mn 0.1-2.5%, P 0.15% or less, S 0.020% or less, and Al 0.1% or less, with the balance being iron and unavoidable. and the formula value K=C+Si/25+Mn/10+P/10+10S+Cu/15
A steel plate for laser processing with excellent stretch flangeability, which satisfies 0.14≦K≦0.50 when +Ni/50+Cr/20 +Mo/20+2Nb+V/10+5B. 2. Contains (a) C 0.03 to 0.25%, Si 2.5% or less, Mn 0.1 to 2.5%, P 0.15% or less, S 0.020% or less, and Al 0.1% or less, and (b) Cu 1% Contains at least one element selected from the group consisting of: Ni 1% or less, Cr 2.5% or less, Mo 0.5% or less, Nb 0.1% or less, V 0.1% or less, and B 0.01% or less, the balance being iron. and unavoidable impurities, and the formula value K=C+Si/25+Mn/10+P/10+10S+Cu/15
A steel plate for laser processing with excellent stretch flangeability, which satisfies 0.14≦K≦0.50 when +Ni/50+Cr/20 +Mo/20+2Nb+V/10+5B.