過時効残留オーステナイトのマルテンサイト変態

抄録

The martensite transformation of over-aged retained austenite was investigated using nickel steels. The martensite transformation showed the complicated changes by aging. These changes consist of four stages (see Fig. 1). The lowering of Ms′ point in the 1st stage is caused by the stabilization of retained austenite. The rising of Ms′ point in the 2nd stage is caused by the stress relaxation due to martensite decomposition during aging. The lowering of Ms′ point in the 3rd stage is caused by the increase in the martensite-austenite interfacial free energy because of the lowering of carbon content in martensite and the concentration of these partial carbon atoms at the martenite-austensite interface during aging. The lowering of Ms′ point in 4th stage is caused by the stabilization of retained austenite due to partial transformation to martensite during cooling from the aging temperature.