JPH08269634A - Austenitic stainless steel for press forming excellent in deep drawability and bulging property - Google Patents

Abstract

PURPOSE: To improve the deep drawability and bulging properties of a stainless steel by incorporating specified amounts of C, Si, Mn, Ni, Cr, Cu, Al, N and Fe therein. CONSTITUTION: The compsn. of this stainless steel is constituted of the one contg., by weight, 0.03 to 0.1% C, 0.5 to 1% Si, <=3% Mn, 6 to 10% Ni, 15 to 19% Cr, 1 to 4% Cu, 0.45 to 2% Al and <=0.05% N, furthermore satisfying (C+N)>=0.04 and 21 to <22.8 Ni equivalent, and the balance substantial Fe: Ni equivalent=12.6(C+N)+9.35Si+1.05Mn+Ni+0.65Cr+0.6Cu-0.4Al. In the case the Ni equivalent is less than 21%, a martensitic phase is already formed in the state of being subjected to solid solution heat treatment to deteriorate both of its deep drawability and bulging properties. In the case the Ni equivalent exceeds 22.8%, the amt. of strain induced martensite to be formed is made small, and its ultradeep drawability can not be obtd. Both of C and N strengthen the martensitic phase formed at the time of press working in the state of solid solution to improve the deep drawability and bulging properties.

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 is obtained mainly by controlling the (C + N) amount and the Ni equivalent and has an excellent super deep drawing property and a good overhang property. Is.

Conventionally, as austenitic stainless steels used for severe deep drawing, SUS 301 and SUS 304 have been used.
and so on. Strain-induced martensite is formed in these stainless steels by cold working, and marked work hardening occurs. Therefore, the overhanging property in the press working is remarkably excellent, but there is a problem that a product left after deep drawing is cracked, that is, a so-called cracking occurs.

[0003]

In order to solve this problem, for example, in Japanese Patent Publication No. 51-29854, Si, Mn and Cu are added in appropriate amounts to enhance work hardenability, and further the amount of solid solution carbon and the amount of solid solution nitrogen are increased. It has been proposed that austenitic stainless steels having a reduced susceptibility to time cracking by making the total of less than 0.04wt% be less. In addition, Japanese Patent Publication No. 1-40102 discloses that
An austenitic stainless steel with very good deep drawability, which has further improved deep drawability due to the combined addition of Cu and the reduction of Si content, has been proposed.
% Or less, Si: less than 0.5 wt%, Mn: 3.0 wt% or less, Cr: 1
5.0 to 19.0 wt%, Ni: 6.0 to 9.0 wt%, Cu: 3.0 wt% or less and Al: 0.5 to 3.0 wt%, with the balance substantially consisting of iron.

[0004]

However, in the stainless steel disclosed in Japanese Patent Publication No. 1-40102, the deep drawing property and the overhanging property are not sufficient in the severe press working with a complicated shape, and In the stainless steel disclosed in JP-A-51-29854, the total amount of solute C and solute N is 0.
Although it is less than 04 wt%, the deep-drawability itself is inferior at this level although it has excellent resistance to time cracking. Therefore, in the case of complicated and severe press working, this conventional technique has a problem that intermediate heat treatment is indispensable. It was Under such a background, in recent years, from the viewpoint of dealing with economical and complicated surface properties, it is possible to press work into various shapes without the need for intermediate heat treatment, which is excellent in so-called deep drawability and However, there has been a strong demand for the development of austenitic stainless steel having excellent bulging properties.

Therefore, an object of the present invention is to provide austenitic stainless steels which have been known in the past, and among them, Japanese Patent Publication No.
An object of the present invention is to provide an austenitic stainless steel for press forming in which the deep drawing property and the overhanging property of the stainless steel disclosed in Japanese Patent Publication No. 29854 are significantly improved.

[0006]

Means for Solving the Problems The inventors have studied in detail the influence of the composition of the stainless steel on the deep drawability and swelling property of the austenitic stainless steel, and have studied the effects of the austenitic stainless steel that can achieve the above object. The composition of ingredients has been reached. That is, when the (C + N) amount and the Ni equivalent amount are properly controlled, it is newly found that the austenitic stainless steel becomes a steel excellent in both deep drawing property and overhanging property, and the present invention has been completed. It was. Also, the present invention
It was developed with the aim of further improving corrosion resistance by adding Mo and improving hot workability by adding B.

The present invention developed on the basis of such knowledge is (1) C: 0.03 to 0.10 wt%, Si: 0.5 to 1.0 wt%, 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: 0.45 to 2.0 wt% and N: 0.05 wt% or less, and C + N ≧ 0.04 wt% is satisfied, and the following Ni equivalent (wt%) is 21 to less than 22.8. Within the range, Ni equivalent (wt%) = 12.6 (C + N) ＋ 0.35Si ＋ 1.05Mn ＋ Ni ＋ 0.65
Cr + 0.6Cu-0.4Al This is an austenitic stainless steel for press forming, which has excellent deep drawability and bulging properties, with the balance being iron and inevitable impurities. (2) Further, in the present invention, C: 0.03 to 0.10 wt%, Si: 0.5 to
1.0 wt%, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, C
r: 15.0 to 19.0 wt%, Mo: 0.05 to 3.0 wt%, Cu: 1.0 to
4.0 wt%, Al: 0.45 to 2.0 wt%, and N: 0.05 wt% or less and satisfy C + N ≧ 0.04 wt%, and the following Ni equivalent (wt%) is in the range of 21 to less than 22.8, Ni equivalent (wt%) = 12.6 (C + N) ＋ 0.35Si ＋ 1.05Mn ＋ Ni ＋ 0.65
Cr + 0.98Mo + 0.6Cu-0.4Al This is an austenitic stainless steel for press forming which has excellent deep drawability and bulging properties, with the balance being iron and inevitable impurities. (3) Regarding the above stainless steel, B: 0.0010-0.
It may contain 020 wt%.

The composition of the above stainless steel is as follows: C: 0.04 to 0.08 wt%, Al: 0.5 to 1.5 wt%, N:
Less than 0.025 wt%, especially less than 0.020 wt%, Ni equivalent 21 ~ 2
It is preferable that the composition is within the range of 2.7 or less.

[0009]

Next, the reasons for limiting the chemical components of the present invention will be described. C: 0.03 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 deep drawability and bulging property, and at least 0.03 wt%, preferably 0.04 wt% is necessary. 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: 0.5 to 1.0 wt% Si is an effective deoxidizing agent and is an essential component in the steelmaking process. The higher the content, the higher the work hardenability of the austenite phase itself. Especially in the component system containing Al and Cu, it is an element that is effective in improving the overhanging property, and 0.5 wt%
The above additions are necessary. On the other hand, when Si exceeds 1.0 wt%, δ ferrite is generated and the hot workability is impaired, high temperature cracking occurs and time cracking easily occurs.
It should be 1.0 wt% or less.

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, and preferably 0.1 wt% or more, but 3.0 wt% is required. If it exceeds, the austenite phase becomes too stable and the deep drawability deteriorates, so the content is made 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. On the other hand, when it exceeds 10.0 wt%, martensite phase is formed during press working. Because it is difficult to generate,
It is limited to the range of 6.0-10.0wt%.

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.

Mo: 0.05 to 3.0 wt% Mo is well known as an element for improving the corrosion resistance of stainless steel. Therefore, in the present invention, proper Mo
By using, it is possible to improve the corrosion resistance. To improve this corrosion resistance, at least 0.05 wt% is added. On the other hand, if it exceeds 3.0 wt%, a large amount of δ-ferrite is generated and the hot workability and the deep drawability are deteriorated, so Mo is limited to the range of 0.05 to 3.0 wt%.

Cu: 1.0 to 4.0 wt% Cu: is a component that significantly improves the deep drawability of austenitic stainless steel, and if it is less than 1.0 wt%, its effect is poor. On the other hand, if it exceeds 4.0 wt%, the hot workability is impaired, so the range is limited to 1.0 to 4.0 wt%. Preferably, the range of 1.0 to 3.0 wt% is desired.

Al: 0.45 to 2.0 wt% Al is a component that contributes to the improvement of deep drawability, and is 0.45 wt%
If the amount is smaller, the deep drawability is not improved, and the susceptibility to time cracking is further increased. On the other hand, if it exceeds 2.0 wt%, δ-ferrite is generated and the hot workability and deep drawability are deteriorated, so the content is limited to 0.45 to 2.0 wt%. The preferable range for improving both the deep drawability and the time crack resistance is:
Al: 0.50 to 2.0 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 0.05 wt% or less, preferably 0.
It is less than 025 wt%. In particular, it is preferably less than 0.020 wt%.

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%, the effect is poor, while if it exceeds 0.020 wt%, the corrosion resistance deteriorates, so the range is limited to 0.0010 to 0.020 wt%.

Further, in the steel according to the present invention, it is important to control the total amount of C and N in order to improve the deep drawing property and the overhanging property at the same time with the above-mentioned composition. Become. That is, both C and N strengthen the martensite phase generated during press working in the solid solution state, and therefore, deep drawability and overhanging property are remarkably improved. Therefore, in the present invention, the total amount of substantially solid solution C and solid solution N is set to 0.04 wt% or more. A preferable lower limit is 0.05 wt%.

Next, in the present invention, the Ni equivalent represented by the following formula is used as a means for improving the deep drawing property and the overhanging property.
(wt%) is controlled. This Ni equivalent is an index showing 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 wt%, the martensite phase will already be formed in the solution heat treatment state, and both the deep drawability and the bulging property will deteriorate. On the other hand, this Ni equivalent is 22.8
If it exceeds wt%, the amount of processing-induced martensite produced is small, and ultra-deep drawability cannot be obtained. Therefore, the Ni equivalent is in the range of 21 to less than 22.8%, preferably 21.0 to 22.7 (wt.
%). Modified Ni equivalent (%) = 12.6 (C + N) ＋ 0.35Si ＋ 1.05Mn ＋ Ni ＋ 0.
65Cr + 0.98Mo + 0.6Cu-0.4Al Note that the above Ni equivalent formula in the present invention is 30
% The amount of martensite of the test piece to which the elongation is added is calculated with a ferrite scope, and the terms Cu and Al are added to the Ni equivalent formula of Hirayama, which is an index of austenite stability. .

From the above results, by adding Al and Cu in combination to the metastable austenitic stainless steel, and further adjusting the C content and the Ni equivalent, an austenitic stainless steel excellent in both deep drawability and bulging property was obtained. You can see that

[0022]

【Example】

Example 1 Austenitic stainless steel having the composition shown in Table 1 (inventive steel) and Table 2 (comparative steel) was melted and finished to a thickness of 1.0 mm by ordinary hot rolling and cold rolling, and then 1100. ℃ ×
Annealed for 30 seconds. From the annealed plate thus obtained, 40
A cylindrical deep drawing test was performed using a mmφ flat bottom punch. The deep drawability is evaluated as superior or inferior based on the critical draw ratio (LDR) of 2.20 or more, and the overhanging property is the limit forming height when the draw ratio is 2.50 (the cup height when the deep draw cup breaks). ). The time cracking was evaluated by the presence or absence of cracking when a cup with a drawing ratio of 2.20 was left at room temperature for 100 hours.

[0023]

[Table 1]

[0024]

[Table 2]

From Table 1, all of the invention steels (No. 1 to 17) show LDR ≧ 2.20 and are excellent in deep drawability, and cracks do not occur even if left for 100 hours, so that they are resistant to time cracking. It turns out that it is excellent. The molding height was 26 mm or more, and the overhanging property was good.

On the other hand, in the case of the comparative steels (No. 18 to 27), those with C + N deviated (No. 21) and those with Ni equivalent deviated (N
o.18, 22) both have LDR less than 2.20 and poor deep drawability, and those with C, Si outside the upper limits (No. 21, 24) have cracks when left for 100 hours and have high Al content. LDR for .26 steel
Less than 2.20 showed poor results.

FIG. 1 shows the limiting drawing ratio (LD) of the steel containing Cu and Al (No. 4, 5, 6, 7, 8, 20, 21) with the Ni equivalent kept constant at 22%.
It is a graph which shows the relationship between R) and C amount. C content is 0.03wt%
As described above, the LDR was 2.20, which was a very good deep drawability. On the other hand, when C = 0.12 wt%, cracking occurred. From this figure, to obtain ultra-deep drawing (LDR ≧ 2.20),
It has been found that 0.03 wt% or more is required, and C ≧ 0.04 wt% is desirable.

FIG. 2 is a graph showing the relationship between the Ni equivalent and the limit forming height of the Cu / Al-containing steel (No. 1, 2, 3, 18, 19) with C = 0.04 wt%. A limit forming height of 26 mm or more is obtained when the Ni equivalent is in the range of 21.0 to 22.8 wt%. Therefore, it was found that it is necessary to control the Ni equivalent within the above range in order to obtain good overhanging property.

Example 2 Steels No. 2, No. 16 and No. 17 shown in Table 1 were melted and then continuously cast into a slab, which was then heated to 1250 ° C. and then hot-rolled. Then, the occurrence of ear cracks was investigated when a hot rolled steel strip having a thickness of 4 mm and a width of 1050 mm was manufactured. The results are shown in Table 3.
Shown in As shown in Table 3, the No. 16 steel containing B and the No. 17 steel containing Mo and B did not cause edge cracking, and therefore the yield was improved, which was economically advantageous. .

[0030]

[Table 3]

Example 3 No. 2, No. 15 (containing Mo) and No. 17 steels (Mo
+ B) was continuously cast into a steel slab, and the steel slab was processed by a conventional method including hot rolling, cold rolling and necessary annealing to obtain a product plate having a thickness of 0.6 mm. And
A corrosion resistance test was conducted on the obtained product plate. In this test, the corrosion resistance test was performed according to JIS G 0577 (Stainless steel pitting potential measurement method). The results of this test are shown in Figure 3.
As shown in Table 1, the stainless steels containing Mo and B (Nos. 15 and 17) all showed high pitting corrosion resistance.

[0032]

As described above, according to the present invention, it is possible to provide an austenitic stainless steel for press forming which is excellent in deep drawability and overhanging property, and it is possible to further widen the versatility of the austenitic stainless steel. .

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a C amount and a limit aperture ratio.

FIG. 2 is a diagram showing a relationship between a Ni equivalent and a limit forming height.

FIG. 3 is a graph of measurement results of pitting potential of stainless steel containing Mo and B.

Claims (3)

[Claims] 1. C: 0.03-0.10 wt%, Si: 0.5-1.0 wt
%, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, Cr: 1
5.0 to 19.0 wt%, Cu: 1.0 to 4.0 wt%, Al: 0.45 to 2.0 w
t% and N: Includes 0.05 wt% or less, and C + N ≧ 0.04w
t% is satisfied, the following Ni equivalent (wt%) is within the range of 21 to less than 22.8, 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 that has excellent deep drawability and bulging properties, with the balance being iron and inevitable impurities. 2. C: 0.03-0.10 wt%, Si: 0.5-1.0 wt
%, Mn: 3.0 wt% or less, Ni: 6.0 to 10.0 wt%, Cr: 1
5.0 to 19.0 wt%, Mo: 0.05 to 3.0 wt%, Cu: 1.0 to 4.0 w
t%, Al: 0.45 to 2.0 wt%, and N: 0.05 wt% or less, and C + N ≧ 0.04 wt% are satisfied, and the following Ni equivalent (wt
%) Is within the range of 21 to less than 22.8, and 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 that has excellent deep drawability and bulging properties with the balance being iron and inevitable impurities. 3. The steel according to claim 1 or 2, wherein the balance of the composition of the steel is replaced with iron, and B:
Austenitic stainless steel for press forming with excellent deep drawability and bulging characteristics, characterized by containing 0.0010 to 0.020 wt%.