Super strength of 65Mn spring steel obtained by appropriate quenching and tempering in an ultrafine grain condition

The effect of austenitizing and tempering temperature on the microstructure and mechanical properties of 65Mn spring steel refined by Tempforming (tempering and deforming of a quenched steel) process was investigated. The martensite substructure of ultrafine grain is composed of high density dislocations and a few twins, but the quantity of twins increases in normal grain martensite steel. Super strength (2220 MPa) and good ductility (8.6%) are achieved at grain size of 5.6 μm when austenitized at 790 °C and tempered at 250 °C. However, contrasted 65Mn steel with normal grain (18.7 μm) displayed almost no any ductility when processed at identical temperature parameters. Accordingly, the tempforming preprocessing contributes to the decrease in grain size and formation of crystallographic texture, which is beneficial for eventual grain refinement after subjected to reheat treatment. By appropriate quenching and tempering treatment after tempforming process, 65Mn spring steel achieved ultrafine grain and super strength and good ductility.