Effect of thermomechanical processing on microstructural evolution in precipitation strengthened ferrite steel

Abstract

The present study is focused on processing simulation in Gleeble® to understand the effect of thermomechanical processing parameters, especially thin-slab casting rolling (TSCR) process, on the ferrite grain structure and precipitation in a nano-precipitation strengthened ferritic steel. The double-hit compression test confirmed that heavy deformation in the range of 900–850 °C can accumulate sufficient strain in deformed austenite that is required to achieve significant ferrite grain refinement. Subsequent simulation of conventional hot-strip mill processing route showed fully ferritic microstructure upon isothermal holding at and above 650 °C (for coiling simulation). Holding at lower temperatures (≤ 600 °C) generate pearlite and bainite, which are undesirable for formability. Finally a TSCR-type of processing schedule is applied maintaining a constant deformation temperature (870 °C) and isothermal holding temperature (650 °C) to understand the effect of equalization entry temperature (Teet). A low equalization entry temperature (900 °C) was found to be beneficial to generate fine ferrite grains with fine precipitates during processing by TSCR route which is a novel finding.