| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1988: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1987: ¥6,700,000 (Direct Cost: ¥6,700,000)
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| Research Abstract |
Investigators have already succeeded in super grain refining to 0.5mum of metastable austenitic stainless steels based of Fe-Cr-Ni system by martensite austenite reversion. The purpose of this present work is to found that three conditions should be satisfied for the grain super refining : (1) Austenite transforms to martensite almost all, by cold rolling. (2) The martensite perfectly reverses to austenite by annealing at relatively low temperature. (3) Ms temperature of the reversed austenite exist under the room temperature. Next purpose is to determine the suitable chemical composition for the high strength steel containing molybdenum and nitrogen. Lastly, using 370kg ingot, the thermo-mechanical treatments were carried out on the pilot line in steel works. And then, the tensile properties and press formabilities were examined. Results obtained were as follows;
1. Typical composition of ultrafine grain steel in Fe-Cr-Ni system was Fe-15.5%Cr-10%Ni. A specimen with 90% cold rolling prior to annealing of 600゜C-10min. has the ultrafine grain with the mean size of 0.5mum,giving 0.2% proof stress of about 70kgf/mm^2.
2. The strength of 13%Cr-10%Ni-2.5%Mo-0.12%N steel increased in comparison with 15.5%Cr-10%Ni steel. It is attributed to refining of austenite grain rather than solid soution hardening by molybdenum and nitrogen. After reversion treatment, this high strength steel has an austenite grain of 0.2mum, giving 0.2% proof stress of 100kgf/mm^2, a tensile strength of 120kgf/mm^2 and an elongation of 35% respectively.
3. The texture of this high strength steel was of {110} type. A deep drawability was not enough, because both values of n and r were relatively lower than 18-8 austenitic steel. Therefore,this steel will be able to used for the parts not required the severe forming, for example, austenitic stainless for railroad vihicles.
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