(α+γ)二相ステンレス鋼の引張性質と破壊に及ぼす475℃時効および750℃時効の影響

概要

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The effects of ageing at 475℃ and 750℃ on tensile properties were studied using (α+γ) two-phase stainless steel having different duplex structures. The main results obtained are as follows ; (1) On ageing at 475℃, 0.2% proof stress and tensile strength increased remarkably and ductility did not decrease so much for the fine grained specimens. In the coarse grained ones, however, ductility decreased remarkably with the ageing. These results are closely related to the fact that α phase deformed by slip for the fine grained specimens irrespective of the ageing whereas deformation mode changed from slip to mechanical twin with the ageing for coarse grained ones and therefore each specimen showed the different fracture mechanism. (2) On ageing at 750℃, 0.2% proof stress and tensile strength increased and ductility decreased remarkably for the fine grained specimens while strength and ductility did not change so much for the coarse grained ones compared with the fine grained specimens. These results are quite different from the behaviors for the case of ageing at 475℃, that is, grain refinement did not improve the ductility of specimens when aged at 750℃. The results are related to the fact that the formation of σ phase from a phase during the aging at 750℃ was accelerated by the grain refinement and then the fracture process showed the initiation of cleavage cracks in σ phase followed by the coalescence of these cracks.
1992-06-15