JP3398258B2 - Austenitic stainless steel for press forming with excellent abrasiveness - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel for press forming which has improved polishability for mirror finishing. Generally, stainless steel for mirror finishing is used for building materials, sinks, etc., but the quality characteristics required for this steel are that there is little unevenness on the surface, surface texture, that is, good gloss and high sharpness of the image. And that the press formability is good.

[0002]

2. Description of the Related Art Conventionally, austenitic stainless steels used for building materials, sinks, etc. have been mirror-finished before use, but the load of this process (mirror-polishing finish by lapping or grounding before this process) It was essential to reduce the grain size of steel in order to reduce the above. (See JP-A-3-169405) On the other hand, in order to improve press forming of this austenitic stainless steel, for example, as disclosed in JP-B-1-40102, Al and Cu are added in combination. The method of doing is proposed.

[0003]

However, it is well known that when the crystal grain size of austenitic stainless steel is reduced, the press formability, that is, the deep drawability and the bulging property generally deteriorate. Therefore, for a material such as austenitic stainless steel used for building materials and sinks, which is subjected to mirror-polished finishing after press working, it is not enough to simply improve the grindability. It is necessary to devise so as not to deteriorate drawability and overhang. That is, the object of the present invention is to
It has excellent deep drawability and overhang during press working, and
An object of the present invention is to provide stainless steel which is also excellent in polishability when mirror-finished.

[0004]

In order to achieve the above object, the inventors of the present invention designed a composition of metastable austenitic stainless steel by adding Al and Cu in combination and adding appropriate C and Ni. By delicately balancing the equivalent weight and the grain size, it was decided to simultaneously satisfy the two characteristics that are originally incompatible with each other. Further, the present invention proposes an austenitic stainless steel in which the addition of Mo to the steel improves the corrosion resistance and the addition of B improves the hot workability.

That is, according to the present invention, C: 0.01 to 0.10 wt.
%, Si: 1.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 ~
10.0 wt%, Cr: 15.0 to 19.0 wt%, Cu: 1.0 to 4.0 wt%,
Al: 0.2 to 2.5 wt% and N: 0.05 wt% or less, and the following Ni equivalent was adjusted to fall within the range of 21.0 to 22.5. Ni equivalent (wt%) = 12.6 (C + N) + 0. 35Si ＋ 1.05Mn ＋ Ni ＋ 0.65
We propose an austenitic stainless steel for press forming, which is excellent in polishability and is characterized in that Cr + 0.6Cu-0.4Al comprises balance iron and unavoidable impurities and has a grain size number (N) of 8 or more.

In addition, the present invention improves the corrosion resistance in addition to the polishing property and press formability by adding Mo in the range of 0.03 to 3.0 wt% to the above component composition. .

The present invention has the above-mentioned composition of components,
Further, by containing B in the range of 0.0010 to 0.020 wt%, the hot workability as well as the polishing property and the press formability are improved.

[0008]

Next, the reason why each chemical component of the present invention is limited as described above will be described. C: 0.01 to 0.10 wt% C is a strong austenite forming element and at the same time,
It is very effective in strengthening the austenite phase and the work-induced martensite phase, and is an essential component for improving the deep drawability and bulging property, and at least 0.01 wt%, preferably 0.03 wt% or more is required. However, if it exceeds 0.10 wt%, both the susceptibility to time cracking and the susceptibility to intergranular corrosion increase, so the upper limit is made 0.10 wt%, preferably 0.08 wt%.

Si: 1.0 wt% or less Si is an effective deoxidizing agent and is an essential component in the steelmaking process. However, if it exceeds 1.0 wt%, cracking tends to occur, so Si is 1.0 wt% or less. To do. The lower limit is preferably 0.05 wt% or more in order to ensure deoxidation during steelmaking work.

Mn: 3.0 wt% or less Mn is a component that acts as a deoxidizing agent and a desulfurizing agent and contributes to stabilization of the austenite phase. At least 0.1 wt% is necessary, but if it exceeds 3.0 wt%. Since the austenite phase becomes too stable and the deep drawability deteriorates, the content is set to 3.0 wt% or less.

Ni: 6.0-10.0 wt% When Ni is less than 6.0 wt%, δ ferrite is formed and hot workability is deteriorated, while when it exceeds 10.0 wt%, a martensite phase is formed during press working. 6.0-
Limit to the range of 10.0wt%.

Cr: 15.0 to 19.0 wt% When Cr is less than 15.0 wt%, corrosion resistance becomes insufficient, while when it exceeds 19.0 wt%, δ ferrite is formed and hot workability is deteriorated, so that 15.0 to 19.0 wt%. Limit to wt% range.

Cu: 1.0 to 4.0 wt% Cu is a component that cooperates with Al to improve the deep drawability of austenitic stainless steel. If it is less than 1.0 wt%, its effect is poor, while 4.0 wt% is If it exceeds, hot workability is impaired, so the content is limited to the range of 1.0 to 4.0 wt%.
The preferred range is 1.5 to 3.0 wt%.

Al: 0.2 to 2.5 wt% Al is a component which is not only effective for refining austenite grains but also cooperates with Cu to contribute to the improvement of deep drawability. This improvement in deep drawability is not recognized, and the susceptibility to time cracking is further increased. On the other hand, 2.5 wt%
Δ ferrite is formed, hot workability and deep drawability are deteriorated, so the content is limited to 0.2 to 2.5 wt%.
The deep drawability and the time crack resistance are most improved in the range of Al: 0.5 to 1.0 wt%.

N: 0.05 wt% or less N is an austenite-forming element and is effective in improving corrosion resistance. However, in a component system containing Al, N is 0.05 wt%.
If it exceeds 0.1%, a large amount of AlN precipitates, and the time cracking resistance and deep drawability deteriorate, so the content is made 0.05 wt% or less.

Mo: 0.03 to 3.0 wt% Mo is generally well known as an element for improving the corrosion resistance of stainless steel. Therefore, in the present invention,
We decided to improve corrosion resistance by using appropriate Mo. To improve this corrosion resistance, at least 0.03wt
% Needs to be added. However, if it exceeds 3.0 wt%, a large amount of δ-ferrite is generated and hot workability and deep drawability deteriorate. Therefore, Mo is 0.03
Limit to ~ 3.0 wt%. Preferably 0.1-1.0 wt
The range is%.

B: 0.0010 to 0.020 wt% B is an extremely effective component for improving the hot workability of steel containing Cu and Al.
If it is less than 0.020 wt%, the effect is poor, and if it exceeds 0.020 wt%, the corrosion resistance deteriorates, so the range is limited to 0.0010 to 0.020 wt%.

Next, in the present invention, the Ni equivalent (wt%) represented by the following formula is controlled as one means for simultaneously improving the deep drawing property, the overhanging property and the polishing property. this
The Ni equivalent is an index indicating the difficulty of occurrence of work-induced martensitic transformation, and if this Ni equivalent is high, the austenite phase becomes stable. If this Ni equivalent is less than 21.0 wt%, the martensite phase will already be generated in the solution heat treatment state, and both the deep drawability and the overhang property will deteriorate. On the other hand, when the Ni equivalent exceeds 22.5 wt%, the amount of work-induced martensite formed is reduced, and the deep drawing property and the projecting property when the grain size number (N) ≧ 8.0 is deteriorated.

FIG. 1 shows the relationship between the Ni equivalent and the forming height (mm). The Ni equivalent shows a high forming height within the range of 21.0 to 22.5%. Therefore, this Ni equivalent is 2
Within the range of 1.0 to 22.5%. Ni equivalent (%) = 12.6 (C + N) ＋ 0.35Si ＋ 1.05Mn ＋ Ni ＋ 0.65Cr
+ 0.98Mo + 0.6Cu-0.4Al The above Ni equivalent formula in the present invention is 30 in tensile test.
% Of the martensite of the test piece with elongation was calculated with a ferrite scope, and the terms of Cu and Al were added to the Ni equivalent formula of Hirayama, which is an index of austenite stability. is there.

Grain size (N): 8 or more Generally, in order to reduce the load in the mirror polishing step, it is necessary to set the surface roughness (Rmax) of the polishing material surface to 4 μm or less. On the other hand, as described above, in order to reduce the surface roughness (Rmax) of this polishing material (4 μm or less), the grain size must be reduced. Figure 2
Grain size (N) and surface roughness of deep drawn cup bottom (Rmax)
It shows that the surface roughness of the molded product becomes smaller as the crystal grain size becomes smaller. That is, the grain size number (N) specified in JIS G 0551
When the value is less than 8.0, the surface of the press-molded product becomes rough and the polishing property is significantly deteriorated. Therefore, in the present invention, the grain size number (N) needs to be 8.0 or more. However, in general, austenitic stainless steel tends to have a worse deep drawability as the grain size number (N) increases, that is, the grain size decreases.
As shown in, in order to maintain the formability in the region where the grain size number (N) is 8.0 or more, the range of components in the present invention must be limited, and the Ni equivalent of a certain range must be limited. The upper limit of the grain size number (N) is not specified, but the range obtained by solution heat treatment of the product is 11.0 or less.

In the present invention, the reduction ratio and the heat treatment conditions are mainly adjusted so that the grain size number (N) is 8 or more based on the steel having the above composition. That is,
Cold rolling reduction rate is 40% or more, and during cold-rolled sheet annealing,
It was carried out under the cooling condition of heating at a temperature of 1000 to 1100 ° C for 10 to 30 seconds and a cooling rate faster than air cooling (air cooling or water cooling).

[0022]

【Example】

Example 1 Austenitic stainless steel having the composition shown in Table 1 was melted, hot-rolled and cold-rolled by a method according to a conventional method to finish a 1.0 mm-thick sheet, and then 1000 to 1150 ° C. The grain size number (N) was adjusted by annealing for 10 to 60 seconds. From the thus obtained annealed plate, a cylindrical deep drawing test was performed using a 40 mmφ flat bottom punch. The deep drawability was evaluated for superiority or inferiority when the limit draw ratio (LDR) was 2.20 or less, and the overhang property was evaluated by the forming height at the draw ratio (DR) = 2.50. The smaller the surface roughness is, the better the polishing property is. Therefore, in this experiment, the surface roughness (Rmax) of the bottom of the cylindrical deep-drawing cup with a drawing ratio of 2.20 (the part with strong overhang deformation) was measured and Was used as an index of polishability.

[0023]

[Table 1]

[0024]

[Table 2]

The results are shown in Table 2. Nos. 1 to 8 using the steels (A to F) having the composition suitable for the present invention have a grain size number (N) of 8.0 or more, Good deep drawability, surface roughness (Rmax) of all 3.0μ or less,
A product having excellent press formability as well as polishing property is obtained. On the other hand, Comparative Steel No. 9 has a composition that is compatible with the present invention, but has a large crystal grain size and thus has poor abrasiveness. In addition, No. 10, 11 and Cu, Al using steels G and H with Ni equivalent
The results of Nos. 12 to 14 in which the content of No. 12 was out of the range of the present invention were all poor in deep drawability. Further, in No. 15 in which the C content was out of the range of the present invention, when LDR ≧ 2.20, time cracking occurred.

[002]

As described above, according to the present invention, Ni
Since the crystal grain size was finely controlled after finely controlling the component composition such as equivalent addition, Al and Cu composite addition, it is possible to provide building materials and austenitic stainless steel for sinks that are excellent in both abrasiveness and press formability. .

[Brief description of drawings]

FIG. 1 is a graph showing the effect of Ni equivalent on molding height.

FIG. 2 is a graph showing the relationship between crystal grain size and surface roughness of a molded product.

FIG. 3 is a graph showing the relationship between the grain size number and the height of a molded product.

Claims (3)

(57) [Claims] 1. C: 0.01 to 0.10 wt%, Si: 1.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, Cr: 15.0 to 19.0 wt%, Cu: 1.0 to 4.0 wt% , Al: 0.2 to 2.5 wt% and N: 0.05 wt% or less, and the following Ni equivalents are adjusted to fall within the range of 21.0 to 22.5, and Ni equivalent (wt%) = 12.6 (C + N) + 0. .35Si ＋ 1.05Mn ＋ Ni ＋ 0.65
Cr + 0.6Cu-0.4Al Austenitic stainless steel for press forming, which has excellent grindability and is characterized by a balance of iron and inevitable impurities, and having a grain size number (N) of 8 or more. 2. C: 0.01 to 0.10 wt%, Si: 1.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, Cr: 15.0 to 19.0 wt%, Mo: 0.03 to 3.0 wt% , Cu: 1.0 to 4.0 wt%, Al: 0.2 to 2.5 wt%, and N:
It contains 0.05wt% or less and is adjusted so that the Ni equivalent below falls within the range of 21.0 to 22.5. Ni equivalent (wt%) = 12.6 (C + N) + 0.35Si + 1.05Mn + Ni + 0.65
Cr + 0.98Mo + 0.6Cu-0.4Al Austenitic stainless steel for press forming, which is excellent in abradability and is characterized by having a balance of iron and unavoidable impurities and having a grain size number (N) of 8 or more. 3. C: 0.01 to 0.10 wt%, Si: 1.0 wt% or less, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, Cr: 15.0 to 19.0 wt%, Mo: 0.03 to 3.0 wt% , Cu: 1.0 to 4.0 wt%, Al: 0.2 to 2.5 wt%, N: 0.05 wt% or less and B: 0.0010 to 0.020 wt%, and adjusted so that the Ni equivalent below falls within the range of 21.0 to 22.5. Ni equivalent (wt%) = 12.6 (C + N) ＋ 0.35Si ＋ 1.05Mn ＋ Ni ＋ 0.65
Cr + 0.98Mo + 0.6Cu-0.4Al Austenitic stainless steel for press forming, which is excellent in abradability and is characterized by a balance of iron and unavoidable impurities and having a grain size number (N) of 8 or more.