1Central Research Laboratory, Hitachi Ltd., Kokubunji
The present investigation was carried out to clarify the influence of cold reduction on the martensitic transformation of Fe-Cr-Ni stainless steel, and also to investigate the relation between some mechanical properties and cold reduction. The specimens were prepared from Fe-Cr-Ni stainless steel with various Ni equivalents, cold rolled by different reductions. Then, the saturation flux densities of these specimens were measured to estimate the amount of martensite. Furthermore, Federbiege Grenze and elongation were measured.
The results obtained are summarized as follows:
(1) In regard to martensitic transformation of Fe-Cr-Ni stainless steel, the chemical composition and cold reduction are substitutional with each other in terms of equivalency, and they are expressed universally by a modified Ni equivalent in consideration of the degree of cold reduction.
(2) During the cold working of Fe-Cr-Ni stainless steel with unstable austenite, the substantial strain of retained austenite is considerably smaller than that estimated from the ordinary reduction and it is considered that the applied stress due to cold working is also low on account of the occurrence of transformation-induced plasticity accompanied by the generation of strain-induced martensite. Therefore, the work done by transformation strain induced by the applied stress due to cold working becomes low, so that the influence of cold reduction on the progress of transformation is considerably smaller than that on the onset of transformation at which transformation-induced plasticity has not yet occurred.
(3) When Federbiege Grenze is modified according to a simple work hardening and the occurrence of transformation with increase of strength is adjusted by the application of a modified Ni equivalent, the relation between modified Federbiege Grenze and the modified Ni equivalent is represented by one curve.
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