It is important for the improvement of mechanical properties of quenching and partitioning (QP) steels to control the martensite transformation behavior and the stability of untransformed austenite. In this study, we evaluated the martensite transformation restart temperature (Mr) via a dilatometer during the reheat austempering pattern. This heat pattern corresponding to the typical heat treatment for QP steel involves quenching to TQ, a temperature between the martensite transformation start temperature (Ms) and the finish temperature, and austempering above Ms. In Fe-8Ni-0.2C alloy, Mr equals TQ, regardless of the progress of bainite transformation during austempering at 673 K (400 °C). In Fe-8Ni-1Si-0.2C alloy, Mr decreases parabolically from TQ with the progress of bainite transformation, and this behavior corresponds to the assumed carbon concentration by bainite transformation. These results indicate that the self-stabilization of the entire untransformed austenite during the first quench from Ms to TQ was preserved, regardless the bainite transformation. Moreover, the stabilization by the carbon concentration in untransformed austenite was added to this self-stabilization.
|ジャーナル||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|出版ステータス||出版済み - 4月 2021|
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