Enhancement of Superplastic Properties in Ultrahigh Carbon Steel through Silicon Addition

The superplastic behaviour of ultrahigh carbon steels (UHCS) has been greatly improved by silicon additions and thermomechanical processing. A UHC steel containing 3 wt% Si shows superplastic behaviour in a wide temperature range from 650 to 900 degrees C. This behaviour is observed even at high strain rates, i.e. 10(-2)s(-1), in the temperature range between 800 and 825 degrees C. Furthermore, the flow stress required for superplastic deformation is reduced drastically, i.e. sigma=12 MPa at a strain rate of 10(-4) s(-1). Finally, it is found that the flow stress at a given strain rate is relatively constant over a wide range of temperatures (750-900 degrees C) due to a unique transformation behaviour in the UHCS-3Si alloy.