JPH0726181B2 - High strength, high corrosion resistance austenitic stainless steel - 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 having high strength and high corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, work hardening type austenitic stainless steel represented by SUS301 and SUS304 has been used as a spring material which requires corrosion resistance and high strength. However, these steels have a Vickers hardness HV of at most 50 even when subjected to aging treatment in addition to cold working.
It is about 0 to 550, and there is a limit in achieving high strength.

Further, regarding the corrosion resistance, there is a problem of rusting, and SUS304 may be insufficient depending on the application, so that the application is limited.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an austenitic stainless steel which has higher strength than conventional steel grades, especially SUS301, and is excellent in corrosion resistance.

[0005]

The present inventors have conducted various studies on the relationship between the alloy composition of austenitic stainless steel, strength, corrosion resistance, and spring property. As a result, Si lowers the stability of the austenite phase and accelerates the generation of the work-induced martensite phase during cold working,
It was found that it contributes to higher strength. Further, they have found that the combined addition of Mo and Mo significantly improves the corrosion resistance, leading to the present invention.

The gist of the present invention is that C% < 0.15% by weight.
%, Si 3.2 to 4.5%, Mn < 2.0%, P < 0.
040%, S < 0.030%, Cr 13.0 to 17.0
%, Ni 6.0 to 7.8%, Mo 0.8 to 2.0%, N
< 0.10%, with the balance being Fe and unavoidable impurities, a high strength, high corrosion resistant austenitic stainless steel.

[0007]

The features of the present invention will be specifically described below together with the action thereof. First, the reason for limiting the essential components in the steel of the present invention is as follows.

C: C is an austenite forming element,
It has the function of stabilizing the austenite phase, but on the other hand, it is extremely effective in strengthening the martensite phase induced by cold working. However, if the content exceeds 0.15%, carbides are likely to precipitate at the crystal grain boundaries, resulting in deterioration of corrosion resistance and workability. Therefore, C is 0.15
% Or less.

Si: Si is an essential element for realizing high strength and high corrosion resistance, which are the characteristics of the steel of the present invention. To exhibit these characteristics, Si must be 3.2% or more. However, excessive addition of more than 4.5% is disadvantageous for stabilizing the austenite structure, impairs hot workability, and unfavorably increases the tendency of sigma phase formation, so its upper limit is set to 4.5. %.

Mn: Mn is an austenite-forming element and is effective in stabilizing the austenite structure. However, if the Mn content exceeds 2.0%, the work-induced martensitic transformation due to cold rolling is suppressed, so the upper limit was made 2.0%.

P: If P exceeds 0.04%, corrosion resistance and hot workability deteriorate, so the upper limit was made 0.04%.

S: If S exceeds 0.03%, inclusions increase and rust resistance decreases, and cracking susceptibility during hot working remarkably increases. Therefore, the upper limit is 0.0.
It was 3%.

Cr: Cr is a basic component of stainless steel, and it is necessary to add 13.0% or more in order to obtain good corrosion resistance. However, Cr is a ferrite forming element, and in the steel of the present invention having a high Si content, if it exceeds 17.0%, the hot workability is deteriorated, which is not preferable. Therefore, the upper limit of Cr is set to 17.0% and the lower limit is set to 13.0%.

Ni: Ni is a typical element of austenite forming elements, and is at least 6.0% in order to stabilize the austenite structure and to obtain good hot workability and cold formability.
The above is necessary. However, excessive addition exceeding 7.8% suppresses work-induced martensitic transformation due to cold rolling. Therefore, the upper limit of the amount of Ni added is 7.8% and the lower limit is 6.0%.

N: N, like C, contributes to solid solution strengthening, but if it exceeds 0.1%, blowholes are formed and a sound steel ingot cannot be obtained, so 0.1% was made the upper limit.

Mo: Mo is effective in improving the corrosion resistance, but at least 0.8% or more is necessary to sufficiently bring out the effect. On the other hand, if the content exceeds 2.0%, a large amount of delta ferrite is produced and the hot workability is deteriorated. Therefore, the upper limit of the added amount of Mo is set to 2.0% and the lower limit is set to 0.8%.

[0017]

EXAMPLES Table 1 shows each component of the steels of the present invention (No. 1 to No. 5) and the comparative steels (No. 6 to No. 11).
No. No. 6 is an excessive Si additive, No. 6 No. 7 is an excessive additive material of Ni, No. 7 No. 8 is a material with insufficient addition of Ni. No. 9,
10 and 11 are comparative steels, SUS301 and SUS30, respectively.
4 and SUS316. Each of these test materials is a steel ingot with a thickness of 2 m obtained by hot rolling a 5 Kg steel ingot by high frequency melting.
m, which was annealed at 1050 ° C. and cold-rolled to a maximum of 50% was subjected to a work hardening test. Further, a plate having a thickness of 0.5 mm by cold rolling, and 105
Those annealed at 0 ° C. were subjected to various accuracy tests. The results were as follows.

[0018]

[Table 1]

Hot workability Each sample steel ingot was heated to 1200 ° C. for a predetermined time and then tested for 4
It was made into 2 mm by hot rolling with a High rolling mill.
The results are shown in Table 2. Comparative steel No. which is steel with excessive Si addition.
No. 6 with insufficient addition of Ni. Except for No. 8, good rolling results were shown.

[0020]

[Table 2]

Mechanical Properties As a representative example of the steel of the present invention, Sample No. 2 and No. 3 is shown in Table 3 and FIG. The steel of the present invention showed higher work hardenability and higher strength than SUS301. In addition, the amount of Ni is
If it exceeds 7.8%, the work hardenability is insufficient and high strength cannot be obtained.

[0022]

[Table 3]

Corrosion resistance Sample No. 2 and No. A corrosion resistance test was conducted on No. 3 and showed a corrosion resistance superior to SUS304.

Spring Property (FIGS. 2 and 3) The low temperature annealing significantly improves the spring limit value Kb and the Vickers hardness HV. No. 4 by heat treatment at 450 ° C. for 30 minutes. 2 and No. Kb = 17 in the sample of 3
It reaches 5 Kg / mm ² , HV = 710.

[0025]

INDUSTRIAL APPLICABILITY The present invention realizes an austenitic stainless steel having higher strength than SUS301 and excellent corrosion resistance than SUS304. The industrial value thereof is extremely high as a stainless steel material having high strength and high corrosion resistance used for various thin leaf springs, blades, cutter core materials and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between hardness and reduction ratio of the steel of the present invention.

FIG. 2 is a diagram showing a relationship between an aging temperature and a Kb value of the steel of the present invention.

FIG. 3 is a diagram showing a relationship between hardness and aging temperature of the steel of the present invention.

[Explanation of sign] None

Claims (1)

[Claims] 1. C in wt%<0.15%, Si 3.2-
4.5%, Mn<2.0%, P<0.040%, S<
0.030%, Ni 6.0-7.8%, Cr 13.0-
17.0%, Mo 0.8-2.0%, N<0.10%
In particular, the balance consists of Fe and unavoidable impurities.
High strength, high corrosion resistance austenitic stainless steel
steel.