Influence of multiple quenching treatment on microstructure and tensile property of AISI M50 steel

Abstract

Microstructure and tensile property of AISI M50 under a series of multiple quenching treatments is studied in this paper. With quenching number increasing from 1 to 3, the grain size increases from 15.06 μm to 60.16 μm and the morphology of martensite transforms from cryptocrystalline type into plate type. The volume fraction of retained austenite decreases quickly from 21 % to 8 % when quenching number increases from 1 to 2, and keeps at a stable level of 4 % under triple quenching. The ultimate tensile strength peaks at 2834 MPa under double quenching, and lowers down to 2715–2730 MPa with quenching time increasing from 2 to 4. A 2.8GPa AISI M50 steel with elongation rate of 2.4 % is obtained under double quenching, which indicates that multiple quenching is promising in the strengthening of high carbon steels.