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Effects of Intercritical Quenching Temperature on Microstructural Evolution and Mechanical Properties of a New Type of Cryogenic Steel With Ni Replaced by Mn

Effects of intercritical quenching temperature on microstructural evolution and mechanical properties of a new type of cryogenic steel with Ni replaced by Mn were investigated by XRD, EBSD and TEM. The results show that the volume fraction of metastable austenite at room temperature decreases with the increase of intercritical quenching temperature. When interctritical quenching temperature is at 700 or 740??, metastable austenite mainly precipitates in the shape of thin film along the lath boundaries of tempered martensite, paralleling to the surrounding martensitic laths. This ??film-type?? metastable austenite is uniformly distributed and stable, with a thickness of about 100nm. When intercritical quenching temperature is 780??, the volume faction of ??film-type?? metastable austenite decreases, and large ??blocky-type?? metastable austenite appears at the junction of interface of tempered martensite. Analysis indicates that the differences on ??effective grain size?? of matrix, volume fraction of metastable austenite and its stability caused by different heat treatment process lead to the difference on low temperature toughness of the tested steel at different intercritical quenching temperature.