(α+α′) 2相ステンレス鋼の結晶粒微細化

Abstract

The microduplex process of a Fe-16%Cr-5%Mo-8%Co-2%Ni alloy has been investigated. The alloy used has a fully ferritic structure after quenching from 1573 K, and then austenite (followed by martensitic transformation during air cooling) decomposes from the ferrite during reheating up to the temperature range of (α+γ) tow phase.If the ferrite, however, was cold rolled about 90% prior to the reheating, strain induced precipitation of Laves phase occurs in the temperature range 850-950 K. On 923 K aging, the precipitates play an important role in the suppression of subgrain growth, resulting in the fine subgrain structure. It was also shown that austenite nucleates at the subgrain boundaries. On the other hand, in the temperature range 1000-1300 K, austenite immediately nucleates along slip bands and deformation twins, resulting in the microduplex structure of ferrite and martensite. At temperatures above 1300 K where the recrystallization of ferrite matrix can preferentially occur, however, a structure abruptly coarsened. Consequently, to obtain the microduplex structure, it is likely important that the nucleation of austenite should take place prior to the recrystallization of ferrite matrix.