Superplastic characteristic of Mn-Si-Cr alloyed ultrahigh carbon steel realized through a novel process

A novel process based on simple heat treatment was developed in order to explore the superplastic characteristic of Mn-Si-Cr alloyed ultrahigh carbon steel. After austenitizmg at A(1)-A(cm) and slow cooling, a microstructure with superplastic "potential" was obtained. The microstructure with superplastic "potential", mainly composed of inartensite and spherical carbides, could transform to a fine (austenite + ferrite + spherical carbides) microstructure beneficial for superplasticity during subsequent warm deformation at Just below A(1). The superplastic characteristic during warm deformation is as follows: flow stress stays at 30-50 M Pa and the in value reaches 0 4-0.5 at a strain rate of 10(-4)-2 x 10(-4) s(-1) The novel process has two advantages: ultrahigh strength (HRC52) and excellent ductility (the reduction of area similar to 45%) are ensured after superplastic forming without the need of supplementary heat treatment; internal stress in the microstructure obtained after superplastic forming can be avoided to a great extent. (C) 2010 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved.