JPH0653892B2 - Method for producing high strength non-magnetic stainless steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing stainless steel having both high strength and non-magnetic properties.

2. Description of the Related Art In recent years, as electronic equipments, audio equipments, and video equipments have been miniaturized and have been improved in performance, materials used for these equipments are required to be nonmagnetic and have high strength.

Conventionally, SUS305J1 or SU has been used as a material for obtaining stable non-magnetism having a magnetic permeability of less than 1.01.
Although the material that has been subjected to the solution treatment of S316 or slightly processed thereafter has been used, these steel types have a drawback that high strength cannot be obtained. As a method of solving this drawback, high Mn steel represented by 18Mn-5Cr steel was often used. However, 18Mn-5Cr steel can obtain a Vickers hardness of 500 or more and a magnetic permeability of less than 1.01 by cold working, but has a drawback that it is significantly inferior in corrosion resistance to conventional stainless steel.
It was never widely used. A high Mn austenitic stainless steel typified by AISI 205 is a steel type that solves these drawbacks all at once, and is gradually being used in recent years. This steel type has a Vickers hardness of 470 to 500 and a magnetic permeability of less than 1.01 by cold working around 60%.
Moreover, it is characterized in that the same corrosion resistance as SUS304 can be obtained.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in order to obtain high strength, when 60% or more of cold working is applied, the magnetic permeability may be 1.01 or more,
In order to obtain a stable magnetic permeability of less than 1.01, the workability is 6
The Vickers hardness at this time is 470 to 500 at the highest, since it must be pressed down to about 0%. Therefore, it can be said that it is still insufficient for obtaining as high strength as possible, that is, Vickers hardness of 520 or more.

The present invention aims to solve these problems and provide a method for producing stainless steel having high strength and stable non-magnetic properties.

Means for Solving the Problems A feature of the method for producing a stainless steel having both high strength and non-magnetism in the present invention is that C0.05 to 0.25% in weight percent and Si 1.0% or less in weight percent. , Mn11 ~
16%, Cr 15 to 20%, Ni 0.2 to 4.0%, N0.
After high-Mn austenitic stainless steel containing 2 to 0.45% balance Fe and unavoidable impurities is drawn by 60% or more, preferably 75% or more, and then 500 ° C
By performing the heat treatment at a temperature of 650 ° C. or lower, a high-strength nonmagnetic stainless steel having a magnetic permeability of less than 1.01 and a Vickers hardness of 520 or more is obtained.

The 60% wire drawing is a process of giving plastic deformation by wire drawing until the cross section is reduced to 60%.

Hereinafter, a method for producing stainless steel having high strength and stable non-magnetic properties according to the present invention will be described in detail.

In the production of stainless steel having high strength and stable non-magnetic property according to the present invention, C0.05 to 0.25%, Si1.
00% or less, Mn 11 to 16%, Cr 15 to 20%, Ni 0.
It is applicable to a wide range of high Mn austenitic stainless steels containing 2 to 4%, N 0.2 to 0.45% balance Fe and unavoidable impurities. The reasons for limiting the components of the applicable material in the present invention will be described below.

C is an element that stabilizes the austenite phase and imparts high work hardenability. It is necessary to contain 0.05% or more to give high hardenability, but if it exceeds 0.25%, corrosion resistance deteriorates or weldability is impaired, so the lower limit is 0.05% and the upper limit. Was set to 0.25%.

Si is an element necessary as a deoxidizing agent, but even if 1.0% or more is added, the curing as a deoxidizing agent is similar to the case of 1.0%, so the upper limit was made 1.0%.

Mn stabilizes the austenite phase and gives high work hardenability. In the present invention, which requires a larger amount of solid solution of N, it is a main element. To obtain these effects, it is necessary to contain 11% or more, and the lower limit is 11%.
%. However, if the content exceeds 16%, the stability of the austenite phase becomes stronger, the work hardenability of the austenite phase becomes lower, and in order to stably obtain the Vickers hardness of 460 or more, the processing of 85% or more must be given. Since there are many industrial disadvantages such as increased manufacturing cost and limited manufacturing size, the upper limit was set to 16%.

Cr is an indispensable element that is necessary to give corrosion resistance and S
To obtain the same corrosion resistance as US304, it is necessary to contain 15% or more, and the lower limit is set to 15%. But,
If too much is added, δ ferrite precipitates in the austenite phase at high temperatures and hot workability is impaired, so the upper limit was made 20%.

Ni is an element that stabilizes the austenite phase and must be contained at least 0.2% or more, so the lower limit is 0.1.
It was set to 2%. However, if the content exceeds 4%, the work hardenability of the austenite phase deteriorates, and Vickers hardness after processing of 460 or more cannot be obtained, so the upper limit is 1.0.
%.

N is an element that stabilizes the austenite phase, enhances work hardenability, and imparts corrosion resistance. 1 more
Upon heat treatment at 20 ° C. or higher, there is fixation of mobile dislocations due to strain aging together with C, and hardening at higher temperature heat treatment forms fine precipitates and improves strength. In particular, N exhibits excellent softening resistance even in the heat treatment at 500 ° C. or higher and 650 ° C. or lower. Therefore, 0.2% or higher is required to maintain Vickers hardness of 520 or higher after the heat treatment at 500 ° C. or higher and 650 ° C. or lower. And its lower limit is 0.2
%. However, if the content exceeds 0.45%, the hot workability is significantly deteriorated, so the upper limit was made 0.45%.

In the method for producing a stainless steel having high strength and stable non-magnetic properties according to the present invention, a high content of the above-mentioned components is contained.
About 980-1200 Mn austenitic stainless steel
After the solution treatment is performed at a temperature of ℃, preferably at a temperature of about 1050 ℃ to obtain an austenite phase, wire drawing of 60% or more is performed. As a result, the Vickers hardness is 460 or more, but the magnetic permeability is often 1.01 or more.
Therefore, heat treatment is further performed at a temperature of 500 ° C. or more and 650 ° C. or less to improve the magnetic permeability to less than 1.01 and the Vickers hardness to 520 or more. The processing and heat treatment for obtaining a Vickers hardness of 520 or more and a magnetic permeability of less than 1.01 will be described below.

In the conventional manufacturing method of high Mn austenitic stainless steel, in the wire drawing process following the solution treatment, in order to reduce the magnetic permeability to less than 1.01, it must be around 60%, and therefore the Vickers hardness of the material is Is 460 to 500,
It was difficult to stably obtain a Vickers hardness of 520 or higher. In the present invention, as will be described later, even if the magnetic permeability increases to 1.01 or more in the wire drawing process following the solution heat treatment, the magnetic permeability can be decreased to less than 1.01 by the subsequent heat treatment. In the wire drawing work following the solution heat treatment, the wire drawing work can be carried out at any workability of 60% or more without being restricted by the magnetic permeability of less than 1.01, and the Vickers hardness is 46%.
It can be 0 or more. After the solution treatment of the high Mn austenitic stainless steel containing the component system of the present invention, 6
When 0% or more of wire drawing is applied to make the Vickers hardness 460 or more, the permeability exceeds 1.01 because it is a processing-induced martensite, and a slight amount of ferromagnetic α'martensite phase is generated. The conventional non-magnetic steel made of high-Mn austenitic stainless steel was intended to suppress the generation of this α ′ martensite phase as much as possible by devising the composition system, but the present invention is bound by such a concept. First, the heat treatment causes the α'martensite phase generated during processing to undergo reverse transformation to an austenite phase, thereby increasing the hardness and reducing the magnetic permeability to less than 1.01.

The degree of processing subsequent to the solution treatment in the present invention is not limited as described above, since the α ′ martensite phase generated by processing can be reverse transformed by heat treatment. Further, when the high Mn austenitic stainless steel was subjected to solution treatment and then processed so that the magnetic permeability was 1.01 or more, a heat treatment at 100 ° C. to 700 ° C. was applied, and its structure and characteristics were examined. The α ′ martensite generated by the processing starts reverse transformation at 500 ° C and finishes the transformation at 650 ° C, and the austenite phase of the mother phase is stable up to 600 ° C and the recovery phenomenon from around 650 ° C, 700 ° C. Then, it was found that the most crystallization occurs. From this, it is necessary to heat treat at 500 ° C. in order to reverse transform the α ′ martensite phase into the austenite phase.
The above heating is practically necessary, and heating above 650 ° C. causes recovery of the austenite phase and recrystallization, so the heat treatment temperature range must be 500 ° C. or more and 650 ° C. or less.

EXAMPLES Next, the features of the present invention will be clarified by examples in comparison with the conventional method and the comparative steel.

Table 1 shows the chemical composition of these test steels.
In Table 1, A to G steels are high Mn austenitic stainless steels which are objects of the present invention, H to J steels are comparative steels,
H steel is SUS304N1, I steel is SUS304, N2,
J steel corresponds to SUS304.

Table 2 shows the hardness and magnetic permeability when the A to J steels in Table 1 were subjected to the solution heat treatment and 60% and 75% wire drawing, and the hardness when these were further heat-treated at 600 ° C. for 20 minutes. And the magnetic permeability. The hardness was determined as an average value at 5 points on the cross section, and the magnetic permeability was determined as a value at 200 Oersted. The heat treatment was carried out in a non-oxidizing atmosphere. Some of the A to G steels have a magnetic permeability of less than 1.01 with 60% wire drawing, but the hardness cannot exceed Vickers hardness 520. Further, although there are some that have a Vickers hardness of more than 520 when the wire drawing process of 75% is left as it is, the magnetic permeability has exceeded 1.01. On the other hand, in the case where 75% wire drawing is applied and heat treatment is performed at 600 ° C. for 20 minutes,
All of the A to G steels have a Vickers hardness of 530 or more and a magnetic permeability of less than 1.01.

FIG. 1 shows the results of examination of changes in hardness and magnetic permeability of 75% drawn B and D steels as they are in the as-processed state and subjected to heat treatment up to 700 ° C. High-Mn austenitic stainless steel B and D steels have a magnetic permeability of less than 1.01 and a Vickers hardness of 5 by heat treatment at 500 ° C or higher and 650 ° C or lower.
30 or more is obtained.

Specific applications of the present invention include VTR microshafts in wire rods, various motor shafts, solenoid valve shafts,
Although there are coil springs, spring washers, etc., in these applications, wire-drawn wires are often further processed. In this case, the heat treatment in the present invention may be carried out immediately after the wire drawing, or may be carried out after the linear working or the spring forming, and the hardening of the present invention is effective. Further, according to the present invention, 500 ° C or higher 6
When heat treatment at 50 ° C. or lower is applied to high-Mn austenitic stainless steel, oxide scale is generated on the surface when treated in the atmosphere. The oxide scale itself has magnetism and an α'martensite phase may be formed very thinly just under the scale, which can be easily removed by chemical polishing or mechanical polishing.

Effect As described above, according to the present invention, C0.
05-0.25, Si1.0%, Mn11-16%, Cr15
~ 20%, Ni0.2-4.0%, N0.2-0.45%
For a wide range of high-Mn austenitic stainless steels containing Fe and the balance Fe and unavoidable impurities,
The Vickers hardness of 520 or more and the magnetic permeability of less than 1.01 can be obtained by working and heat treatment, and it has extremely high practicality as a method for producing high strength non-magnetic stainless steel.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of heat treatment on Vickers hardness and magnetic permeability.

Claims (1)

[Claims] 1. C0.05-0.25 in weight percent.
%, Si 1.00% or less, Mn 11 to 16%, Cr15
~ 20%, Ni0.2-4.0%, N0.2-0.45
%, And the balance is high Mn austenitic stainless steel consisting of iron and unavoidable impurities, after wire drawing of 60% or more, heat treatment at a temperature of 500 ° C. or more and 650 ° C. or less, A method for producing a high-strength nonmagnetic stainless steel, characterized by obtaining a high-strength nonmagnetic stainless steel having a Vickers hardness of 520 or more and less than 1.01.