Influence of cold rolling on the stability of retained austenite and mechanical properties of a Cu bearing low carbon low manganese steel

It was reported that the distribution and morphology of retained austenite were greatly affected by cold rolling prior to intercritical annealing and tempering in medium Mn steel, but the effects of cold rolling have not been well investigated in low Mn steel. In this report, the microstructure and mechanical properties of a low-carbon low manganese steel bearing 2 mass% Cu was investigated. The amount of reversed austenite was similar with or without cold rolling, but the morphology was very different, globular and lath-type respectively. Nearly half of reversed austenite transformed to martensite upon cooling to room temperature in the cold rolled steel while almost all reversed austenite was retained in the non-cold rolled steel. During tempering, 85 vol% of retained austenite transformed to bainite in the non-cold rolled steel while a major proportion of austenite remained after tempering probably due to further carbon enrichment during tempering in the cold-rolled steel. The tensile strength and uniform elongation increased from 1104 MPa and 8.5% without cold rolling to 1264 MPa and 23% in the cold rolled steel, which indicates that cold rolling prior to annealing is beneficial for improving mechanical properties.