Enhanced carbon enrichment in austenite through introducing pre-existing austenite as a ‘carbon container’ in 0.2C-2Mn steel: The significant impact on microstructure and mechanical properties

Abstract

We describe here a novel approach of increasing the carbon in austenite via intercritical annealing and consequently derive the benefit of obtaining the desired microstructure and mechanical properties in a low carbon low manganese steel. The reversed austenite obtained by pre-annealing acted as a “carbon container”, and received carbon from cementite dissolved during pre-annealing. The reversed austenite was partly retained at room temperature and the retained austenite could further absorb carbon from martensite. As a result, the precipitation of cementite was significantly reduced during subsequent intercritical annealing and austenite was enriched with more carbon compared to the situation without pre-annealing. The morphology of reversed austenite changed from granular in the absence of pre-annealing to lath-like in pre-annealed steel. In addition, the size of retained austenite was refined by pre-annealing, which enhanced the stability of austenite and contributed to superior ductility of steel.