Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1991-03-15
1993-01-12
Dean, R.
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148605, 148607, 148608, 148622, 148326, 148328, C21D 802, C21D 902, C21D 946
Patent
active
051786931
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a commercial process for the production of a high strength stainless steel strip of a duplex structure essentially consisting of ferrite and martensite, which has an excellent spring limit value. The product of the process according to the invention is a novel stainless steel strip which is mainly suitable for use in the production of springs such as thin plate spring and windup spring. The product is commercially produced in the form of a strip, and is delivered to a market in the form of a strip as produced (a coiled strip) or in the form of plates cut therefrom. Since these strip and plates already have necessary spring characteristics for end use, springs formed therefrom need no special heat treatment.
BACKGROUND OF THE INVENTION
Japanese Industrial Standards JIS G 4313 standardizes 4 types of stainless steel strips for spring. They are austenitic SUS301-CSP, austenitic SUS304-CSP, martensitic SUS420J2-CSP and precipitation hardenable SUS631-CSP.
The austenitic stainless steel strips, SUS301-CSP and SUS304-CSP, are to be work hardened by cold rolling to increase strength, and depending upon the degree of the temper rolling (% rolling reduction) there are standardized 4 species of SUS301-CSP and three species of SUS304-CSP. Such austenitic stainless steel strips for spring are delivered in the cold rolled condition from a steel maker to a spring maker, where they are formed into desired shapes of springs, and thereafter when further enhancement of spring characteristics are desired they are subjected to aging of the order of 400.degree. C., 1 hour
The martensitic stainless steel strips, SUS420J2-CSP, are to be quenched and tempered to increase hardness (strength) thereby achieving spring characteristics. In many cases, such martensitic stainless steel for spring are delivered in the cold rolled and annealed condition from a steel maker to a spring maker, where they are formed into desired shapes of springs, and thereafter subjected to quenching and tempering treatment.
The precipitation hardenable stainless steel strips, SUS631-CSP, except for those of SUS631-CSP-0 which are delivered from a steel maker in the solution treated condition, are delivered in the cold rolled condition from a steel maker to a spring maker, as is the case with the austenitic strips, and by the spring maker they are formed into desired shapes of springs, and thereafter subjected to precipitation hardening to enhance spring characteristics. Incidentally, various precipitation hardenable stainless steel strips for spring, other than SUS631-CSP according to JIS, are commercially available.
Problems the Invention Aims to Solve
With the austenitic and precipitation hardenable stainless steels for spring, as the temper rolling reduction is increased the hardness and spring limit value are improved. Furthermore, the higher the % temper rolling reduction, the higher the hardness and spring limit value attainable after the aging or precipitation hardening.
Accordingly, in order to enhance the spring characteristics it is necessary to use an increased % temper rolling reduction. The increase in the spring limit value by cold rolling is, however, greater in the direction of rolling (LD) of the strip than in the direction perpendicular thereto (TD), and there is posed a problem of anisotropy in that the difference in the spring limit value between both the directions is intolerably increased as the % temper rolling reduction is increased, frequently limiting the direction in which springs are taken from the strip.
Moreover, in cases wherein ultrathin plates of a thickness of not in excess of 0.3 mm having a high spring limit value are required, it is necessary to prepare such ultrathin plates with a very high rolling reduction. It is not technically easy, however, to prepare broad and ultrathin steel strips of a good shape by cold rolling with highly work-hardenable materials as SUS301-CSP, SUS304-CSP or SUS631-CSP.
With the martensitic stainless steel strips for spring there
REFERENCES:
patent: 4812176 (1989-03-01), Tanaka et al.
patent: 5019181 (1991-05-01), Yazawa et al.
Fujimoto Hiroshi
Miyakusu Katsuhisa
Tanaka Teruo
Toyokihara Chizui
Dean R.
Ip Sikyin
Nisshin Steel Co. Ltd.
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