高Mnオーステナイト鋼の恒温変態に伴う組織変化

抄録

Microstructural change during isothermal aging has been investigated in 13%Mn-0.9%C and 22%Mn-0:6%C steels by means of optical and electron microscopy and X-ray diffractometry.
High manganese austenitic steels undergo three kinds of reactions during isothermal aging ;(1) grain boundary precipitation of carbide, (2)precipitation of platelet carbide within austenite(γ) grains and (3)formation of lamellar structure through eutectoid transformation (γ→ferrite(α)+carbide).In 13%Mn-0.9%C steel, all of the reactions occur and the carbide concerning the reactions is M₃C in any case. On the other hand, in 22%Mn-0.6%C steel, only two of them occur ; grain boundary precipitation of M₂₃C₆ carbide (not M₃C) and the eutectoid transformation (γ→α+M₃C). Besides, both of the two reactions in 22%Mn-0.6%C steel were effectively suppressed due to the chemical composition ; high Mn and low C content.
Eutectoid transformation proceeds by being supplied carbon from untransformedγ, so that this results in the shortage of carbon in untransformedγduring isothermal aging and theγphase undergoesγ→ε(hcp) martensitic transformation on the following cooling.