JP2004124131A - High strength austenitic stainless steel strip having excellent bending workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength austenitic stainless steel strip which has excellent bending workability by clarifying indexes for satisfying high strength and high bending workability. <P>SOLUTION: In the high strength austenitic stainless steel strip having excellent bending workability, the crystal grain size after final recrystallization annealing is 1 to 10 μm, and the ratio (YS/Ms)between 0.2% yield stress (=YS (MPa)) and a martensite content (=Ms (%)) is ≥25. <P>COPYRIGHT: (C)2004,JPO

Description

【００１７】
表１の結果に見られるように、結晶粒１μｍ以上では，同じ加工度４０％で比較すると、本発明のほうが、比較例より強度が大きくなっている。例えば、発明例Ｎｏ．１、３、４と比較例Ｎｏ．９とを比べると発明例のほうが大きい。また，同じ加工度４０％の比較例Ｎｏ．１３では，強度は発明例よりも大きいが，結晶粒が１μｍ未満となっており，曲げ加工性が悪い。
また、曲げ加工性については発明例Ｎｏ．１〜Ｎｏ．７は０．２％耐力とマルテンサイト量の比率（ＹＳ／Ｍｓ）が２５以上であり、良好な値を示しているが、比較例では、Ｎｏ．９、１０、１２が２５未満のため、曲げ加工性が悪い。
また、強度について，発明例Ｎｏ．１〜Ｎｏ．７は０．２％耐力が１０００ＭＰａを大きく越えているが，比較例Ｎｏ．８、１１、１３は，加工度が０％であり，０．２％耐力が１０００ＭＰａより低い。さらに，比較例Ｎｏ．９，１４も０．２％耐力が１０００ＭＰａより低くなっており，これは，Ｎｏ．９では結晶粒が大きいため，Ｎｏ．１４では，結晶粒が微細になり過ぎたため，低加工度では十分な０．２％耐力の上昇が得られないためである。
【００１８】
【発明の効果】
オーステナイト系ステンレスを適正に圧延，再結晶焼鈍を組み合わせた加工した場合，高強度と高曲げ加工性を同時に満たすことができる。この範囲は，最終の再結晶焼鈍において結晶粒径を微細にしてマルテンサイト量と引張り強さの比率で規定することが可能である。
また、さらに０．２％耐力と引張強さの比率で規定することにより、高強度と高曲げ加工性の両立できる加工度が可能である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stainless steel strip for a spring, which is suitable for a component that requires spring property, such as a connector used for various electronic device components and a component used for a contact.
[0002]
[Prior art]
High strength and resiliency are required as basic characteristics of connectors used for various electronic equipment parts and parts used for contact points. Since the metal members such as terminals and connectors are remarkably thinned and severe and complicated bending is performed, materials having higher strength and good bending workability are desired.
[0003]
As one of the materials requiring high strength and bending workability, a work hardening type austenitic stainless steel such as SUS304 or SUS301 is used. These stainless steels exhibit an austenitic phase after solution treatment, and then form cold-rolled work-induced martensite to obtain high strength. Further, the austenite matrix is refined to 2 μm or less and transformed into a martensite phase by heat treatment to increase the strength. (For example, see Patent Document 1)
However, when austenitic stainless steel uses this mechanism, if the generation of martensite increases, the bending workability deteriorates, although high strength can be achieved. Therefore, in order to satisfy both the required properties of high strength and high bending workability, an index that satisfies both properties of high strength and high bending workability is required. Was unknown.
[0004]
[Patent Document 1]
JP-A-11-80906 [0005]
[Problems to be solved by the invention]
An object of the present invention is to clarify an index for satisfying high strength and high bending workability, and to provide a high-strength austenitic stainless steel strip excellent in bending workability.
[0006]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the conditions under which austenitic stainless steel satisfies high strength and high bending workability. As a result, the conditions satisfying high strength and high bending workability due to the relationship between 0.2% proof stress and the amount of martensite are obtained. Was found. Further, an austenitic stainless steel having high strength and high bending workability was found by combining grain refinement and 0.2% proof stress increase by work hardening with the above conditions.
[0007]
That is, according to the present invention, (1) the crystal grain size after the final recrystallization annealing is 1 to 10 μm, and the 0.2% proof stress (= YS (MPa)) and the amount of martensite (= Ms (%)) A high-strength austenitic stainless steel strip excellent in bending workability, wherein the ratio (YS / Ms) is 25 or more;
(2) In the material according to claim 1, the crystal grain size after the final recrystallization annealing is 1 to 10 μm, and the material is subjected to recrystallization annealing, cold rolling, or strain relief annealing after cold rolling. A high-strength austenitic stainless steel excellent in bending workability, characterized in that the ratio (YS / TS) of the tensile strength of the stainless steel strip to the 0.2% proof stress (= TS (MPa)) is 0.8 or more. Steel strip,
(3) A high-strength austenitic stainless steel strip excellent in bending workability used for the contact parts such as the connector or the switch according to the above (1) or (2).
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The reason for the limitation will be described below.
(1) Relationship between the amount of martensite formation and 0.2% proof stress Work-hardening austenitic stainless steel exhibits an austenite phase in a solution-treated state, and then forms work-induced martensite in the subsequent cold working to achieve high strength. Is obtained. The strength and the amount of martensite depend on the cold working. By performing the strong working, the amount of martens can be increased and a high strength can be obtained. However, when the amount of martensis is increased, bending workability is deteriorated. The rate of increase of the amount of martensite with respect to the degree of work is greater than the rate of increase of the degree of workability with 0.2% proof stress. Will decrease.
[0009]
If the amount of Ms is large and the ratio between the 0.2% proof stress and the amount of martensite (YS / Ms) is less than 25, good bending workability cannot be obtained.
Therefore, in order to obtain the ratio (YS / Ms) of 0.2% proof stress and the amount of martensite (YS / Ms) of 25 or more so as to obtain good bending workability, it is necessary to limit the generation of the amount of martensite (Ms) or It is conceivable to increase YS.
[0010]
As an index for judging the strength and bending workability, there is a degree of cold rolling, but the Ms amount is affected not only by the degree of cold rolling but also by the crystal grains. Therefore, the Ms amount cannot be uniquely determined. Therefore, although the working degree of cold rolling can be an index for evaluating strength and bending workability, it is not possible to judge whether high strength and bending workability are good. The ratio (YS / Ms) between the 0.2% proof stress and the amount of martensite of the present invention is evaluated by combining the crystal grain sizes described later to produce a material (stainless steel) having both high strength and bending workability. It is a good index.
[0011]
(2) A method of increasing the strength of a material other than the crystal grain processing includes grain refinement. By combining the refinement of crystal grains and the generation of work-induced martensite, it is possible to increase the strength while considering bending workability.
The crystal grains after the final recrystallization annealing are reduced to 10 μm or less in order to obtain a predetermined high strength. If the crystal grains after the final recrystallization annealing exceed 10 μm, the crystals become large, and the effect of high strength is reduced.
The reason for making the crystal grains after recrystallization annealing 1 μm or more is that if the crystal grains are less than 1 μm, the bendability deteriorates. If the crystal grains after the final recrystallization annealing are less than 1 μm, the proof stress and tensile strength will be high, but the bendability will be poor, and both high strength and high bendability cannot be achieved.
[0012]
(3) Relationship between crystal grains and Ms amount When the crystal grains are finer than 1 μm, the amount of work-induced martensite decreases, that is, the Ms amount hardly increases due to processing. Even when a material having crystal grains of less than 1 μm is processed and the 0.2% proof stress and the tensile strength are sufficiently increased, the Ms amount does not increase, and the ratio between the 0.2% proof stress and the amount of martensite (YS / Ms). However, since the bending property is poor, it is impossible to achieve both high strength and high bending property.
When the crystal grain size is 1 μm or more, the bendability due to processing is less reduced than when the crystal grain size is less than 1 μm, and high strength and high bendability are achieved by processing the material with an appropriate degree of processing. Can be compatible.
[0013]
(4) Relationship between tensile strength and 0.2% proof stress 0.2% proof stress is a characteristic value that indicates the strength of a material. When strictly considering strength, how much stress can be elastically deformed is determined. This becomes a problem, and it is necessary to provide not only 0.2% proof stress but also 0.05% proof stress or a proof stress value in a finer plastic region. Preferably, a more delicate index such as 0.01% proof stress is required, but it is also possible to simply obtain the ratio between 0.2% proof stress and tensile strength. That is, for a material having a large ratio between the 0.2% proof stress and the tensile strength, the value of the 0.2% proof stress is close to the tensile strength, and the elastic region is maintained at a high stress.
Making the ratio of 0.2% proof stress to tensile strength (YS / TS) 0.8 or more can be combined by selecting the processing conditions of rolling and recrystallization annealing. The ratio (YS / TS) of 0.2% proof stress and tensile strength can be 0.8 or more even by adjusting components and the like based on austenitic stainless steel.
Further, by combining the above-described (1) martensite content and the ratio of 0.2% proof stress and (2) grain refinement, it is possible to obtain an austenitic stainless steel having high strength and high bending workability. it can.
[0014]
【Example】
The austenitic stainless steel used in the examples is SUS301. A SUS301 ingot obtained by melting and casting in the range of components based on JIS is hot-rolled, and after solution treatment, cold rolling and recrystallization annealing are repeated, and a sheet thickness of 0.06-0. It was processed to 1 mm. The amount of martensite was adjusted by changing the working ratio of the final rolling. The size of crystal grains was adjusted by changing the annealing temperature in recrystallization annealing after rolling.
[0015]
The effect was evaluated by the following method.
(1) Amount of martensite The amount of martensite is determined by utilizing the fact that the austenite phase is non-magnetic while the martensite phase is paramagnetic, and the magnetic strength of the material is measured using a ferrite content meter (ferrite) by magnetic induction. (Also referred to as a scope) to obtain a transformation amount into a martensite phase, that is, a volume ratio.
(2) Bending workability (MBR / t)
It was measured by a general 90 ° W bending test. The radius (R) of the bent portion is reduced with respect to the radius (R) and the plate thickness (t) of the bent portion, and the minimum bent portion radius (MBR) at which no crack is seen in the bent portion is determined by the plate thickness ( The value divided by t) is defined as MBR / t. The measurement was performed in the Bad way direction in which the bending axis was parallel to the rolling direction.
[0016]
[Table 1]

[0017]
As can be seen from the results in Table 1, when the crystal grain size is 1 μm or more, the strength of the present invention is higher than that of the comparative example when compared at the same working ratio of 40%. For example, Invention Example No. Nos. 1, 3, and 4 and Comparative Example Nos. In comparison with No. 9, the invention example is larger. Also, in Comparative Example No. having the same working ratio of 40%. In No. 13, although the strength is higher than that of the invention example, the crystal grains are less than 1 μm, and the bending workability is poor.
Regarding bending workability, Invention Example No. 1 to No. No. 7 has a 0.2% proof stress and the ratio of martensite (YS / Ms) of 25 or more, indicating a good value. Since 9, 10, and 12 are less than 25, bending workability is poor.
In addition, regarding the strength, Invention Example No. 1 to No. In Comparative Example No. 7, the 0.2% proof stress greatly exceeded 1000 MPa. 8, 11, and 13 have a workability of 0% and a 0.2% proof stress lower than 1000 MPa. Furthermore, in Comparative Example No. In Examples 9 and 14, the 0.2% proof stress was lower than 1000 MPa. No. 9 has large crystal grains. In No. 14, since the crystal grains were too fine, a sufficient increase of 0.2% proof stress could not be obtained at a low workability.
[0018]
【The invention's effect】
When austenitic stainless steel is processed by combining rolling and recrystallization annealing properly, high strength and high bending workability can be satisfied at the same time. This range can be defined by the ratio of the amount of martensite to the tensile strength by reducing the crystal grain size in the final recrystallization annealing.
Further, by defining the ratio between the 0.2% proof stress and the tensile strength, it is possible to achieve a workability capable of achieving both high strength and high bending workability.

Claims (3)

The crystal grain size after the final recrystallization annealing is 1 to 10 μm, and the ratio (YS / Ms) between the 0.2% proof stress (= YS (MPa)) and the amount of martensite (= Ms (%)) is A high-strength austenitic stainless steel strip excellent in bending workability characterized by being 25 or more. 2. The stainless steel strip according to claim 1, wherein the grain size after the final recrystallization annealing is 1 to 10 μm, and the strain relief annealing is performed after recrystallization annealing, cold rolling, or cold rolling. A high-strength austenitic stainless steel strip excellent in bending workability, characterized in that the ratio (YS / TS) of tensile strength to 0.2% proof stress (= TS (MPa)) is 0.8 or more. A high-strength austenitic stainless steel strip excellent in bending workability used for a contact part such as a connector or a switch according to claim 1 or 2.