Effect of thermomechanical treatment on structure and mechanical properties of Mo-bearing dual phase steel

Abstract

The effects of hot rolling of a dual phase steel in the (α+γ) range on microstructure and mechanical properties was investigated by using two thermomechanical (TMT) routes. The first consisted of heating Ac(3), soaking, cooling to deformation temperature in the (α+γ) range. The second comprises heating to deformation temperature in the (α+γ) range, followed by rolling and quenching. Parameters varied were temperature (with the first route) and extent of deformation (with the second). The microstructures were characterized by optical and transmission electron microscopy. The results indicate a distinct difference in the final structure and properties due to the two different TMT routes. The first TMT route resulted in a greater amount of ferrite, finer lath width of martensite, finer ferrite grain size and increased density of dislocations. The strength properties decreased, the YS/UTS ratio decreased and ductility increased with the increase in the extent and temperature of deformation. However, TMT route 2 resulted in an increase in the amount of martensite, finer ferrite grain size, decrease in the martensite lath width and increased dislocation density. The strength properties increased, YS/UTS ratio increased and ductility decreased with increase in the extent and temperature of deformation.