JPS62130263A - Precipitation strengthened stainless steel superior in cold workability - Google Patents

Abstract

PURPOSE:To facilitate cold working and to improve strength and corrosion resistance, by regulating a total content of N and C and an N content to specified ranges in Fe-Cr-Ni-Cu precipitation strengthened stainless steel. CONSTITUTION:In Fe-Cr-Ni-Cu precipitation strengthened stainless steel contg. by weight <1.0% Si, 0.5-2.0% Mn, 4.5-6.5% Ni, 14.5-17.5% Cr, 1.0-2.5% Cu, 1.0-2.5% Mo, <0.5% V and the balance Fe or further one or 2 kinds among 0.05-0.2% Ti, 0.2-1.0% Nb, the total content of C and N is regulated to 0.06-0.10% range, and the N content is to <=0.005%. Since the stainless steel is easily softened by soln. heat treatment, a large capacity pressing machine is not required, cracks due to cold working are not caused, high strength and superior corrosion resistance are obtd. by deep subzero heat treatment and aging heat treatment thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a FeCr-NiCu precipitation-strengthened stainless steel.

[Conventional technology]

Fe-Cr-Ni-Cu precipitation-strengthened stainless steel has high strength and excellent corrosion resistance, so it is often used in structures that are subject to high stress and require weight reduction.

Among Fe-Cr-Ni-Cu precipitation-strengthened stainless steels, those whose martensitic transformation point (Ms point) is below room temperature are soft because the structure after solution heat treatment is usually austenite. For this reason, the conventional method was to form the material by cold working while still solution heat treated, and then perform deep cooling (sub-zero) heat treatment followed by aging heat treatment to obtain high strength.

Therefore, although this conventional precipitation-strengthened stainless steel is remarkable in that it can be cold-worked and has high strength, it often does not soften even after solution treatment; It required a large-capacity press for processing, resulting in enormous equipment costs, and it also had drawbacks such as cracks often occurring during cold working.

[Problem that the invention seeks to solve]

In view of this, the present invention has been developed so that it is easily softened by solution heat treatment, does not require a large-capacity press, does not cause cracking during cold working, and is further developed by deep cold heat treatment after cold working. The purpose of this project is to develop materials that can obtain high strength through aging heat treatment.

[Means for solving problems]

The present inventors investigated the cold workability and aging heat treatment FI of FeCrNi-Cu precipitation strengthened stainless steel! As a result of a detailed study of the tensile properties, it was discovered that by specifying the amounts of (c+N) and N, a steel capable of achieving the above objectives could be obtained. That is, in the present invention, (C+N) is 0.06 to 0.10% by weight and N 0.0
05% or more, 8110% or less, Mn0.5-2.0%,
Ni 4.5-6.5%, Cr 14.5-17.5%,
Cu1.0-2.5%, Mo1.0-2.5%, V0.
5% or less, with the remainder being Fe and unavoidable impurities, and having excellent cold workability and precipitation strength 1H type stainless steel.

The present invention further includes 0.05 to 0.2% Ti in the above composition.
Precipitation-strengthened stainless steel with excellent cold workability contains one or two types of Nb in an amount of 0.2 to 1.0%.

(effect) Next, the reasons for limiting each component are shown below.

From the figure obtained based on the results of tensile tests and tests of steels with compositions shown in Table 1, cracks occur when cold working is applied to solution-treated materials in the region where C+N is lower than 0.06%. .

Further, in a region where C0N exceeds 0.10%, the increase in yield strength and tensile strength is not so large even though aging heat treatment is performed after cryogenic heat treatment. Furthermore, if the N content is 0°005%, the austenite cannot be sufficiently stabilized. Therefore, for the above-mentioned reason, the C+N content is 0.06%.
~0.10%, and the N content was limited to 0.005% or more.

(I-, Si: 1.0%r Si has the effect of stabilizing the austenite phase, but if its content exceeds 1.0%, it will precipitate as inclusions, resulting in a decrease in cleanliness and toughness.

Manganese (Mn: 0.5-2.0% Mn also has the effect of stabilizing the austenite phase, but the effect is small when the content is less than 0.5%. On the other hand, when the content is less than 2.0%, If it is exceeded, the tensile strength decreases.

Nickel Ni: 4.5 to 6.59' Ni stabilizes the austenite phase and works synergistically with Cu to bring about precipitation hardening, but if the content is less than 4.5%, the effect is small; If it exceeds 5%, the tensile strength will decrease.

Chromium Cr: 14.5+-17.5% Cr is also an essential element from the viewpoint of stabilizing the austenite phase and corrosion resistance, but if its content is less than 145%, these effects will be small; If it exceeds 17.5%, the tensile strength after aging will decrease.

Cu: 1.0 to 2.5% Copper is important as a precipitation hardening element, but its effect is small if the content is less than 1.0%.
If it exceeds 5%, hot workability decreases.

Moly boon MO=1.0~2,5/Mo has the effect of increasing strength, but 1,0:'
If it is less than 6, the effect will be small, while if it exceeds 25%, hot workability will deteriorate.

Vanadium V: 0.551 V fixes C and causes further precipitation hardening, but 0.5
If the content exceeds %, the toughness will decrease.

Nib Nb, 0.2-1.0% Nb has the effect of fixing C and N, but if the content is less than 0.2%, the effect is small, while if it exceeds 1.0%, inclusions It exists as a substance, impairs cleanliness and reduces toughness.

Tan Ti: 0.05-0.2% Ti has the effect of fixing C and N, but 0.05%
If the content is less than 0.02%, the effect will be small, while if it exceeds 0.02%, it will exist as inclusions, resulting in poor cleanliness and reduced toughness.

〔Example〕

In order to demonstrate the effects of the present invention, as shown in Table 2, the present invention materials and conventional materials were used as comparison materials, and these materials were subjected to a bending test at room temperature in the state 1 after solution heat treatment at 0.1035°C. (2) A tensile test was conducted after deep cooling heat treatment at -10°C followed by aging heat treatment. The test results are shown in Table 3.

As can be seen from Tables 2 and 3, the material of the present invention does not crack even during cold bending, and has a sufficiently high 0.2% yield strength and tensile strength after deep cooling treatment and aging heat treatment. I am gaining strength.

〔Effect of the invention〕

By using the material according to the present invention, a stable soft state can be obtained after 1 ft of solution heat treatment, so (1) cold working becomes easy, the capacity of the press can be small, and equipment costs can be significantly reduced.

■Cracks no longer occur during cold working.

Furthermore, due to aging heat treatment after cold working, a sufficiently high 0.2
% proof stress and tensile strength could be obtained.

[Brief explanation of drawings]

The figure shows the relationship between Cfi, N content, cold workability, tensile strength, and yield strength. C amount (Imperial amount %J

Claims (1)

[Claims] 1. (C+N) 0.06 to 0.10% by weight
And N0.005% or more, Si1.0% or less, Mn0
．． 5-2.0%, Ni4.5-6.5%, Cr14.5
~17.5%, Cu1.0~2.5%, Mo1.0~2
．． Precipitation-strengthened stainless steel with excellent cold workability, containing 0.5% or less of V and 0.5% or less of V, with the remainder consisting of Fe and unavoidable impurities. 2. (C+N) 0.06-0.10% by weight
And N0.005% or more, Si1.0% or less, Mn0
．． 5-2.0%, Ni4.5-6.5%, Cr14.5
~17.5%, Cu1.0~2.5%, Mo1.0~2
．． 5%, V0.5% or less, and Ti0.05~
A precipitation-strengthened stainless steel with excellent cold workability, containing one or two of 0.2% and 0.2 to 1.0% of Nb, with the balance being Fe and unavoidable impurities.