Enhanced strain hardening capacity in a lean alloy steel treated by a disturbed bainitic austempering process

A disturbed bainitic austempering process (isothermal bainitic transformation in conjunction with quenching and partitioning) was employed in a Mn-Si-Cr-C low-alloyed steel to reduce the fraction and size of the blocky martensite/austenite (M/A) islands. The M/A islands formed during the conventional bainitic austempering process are coarse and undesirable for property optimization. Owing to the novel heat treatment, the strain hardening capacity of the steel is improved remarkably, leading to an excellent combination of strength and ductility (e.g. ultimate strength: 1515 MPa; total elongation: 31.2%). The improvement of mechanical properties is attributed to both the transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects provided by the refined filmy austenite constituent. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.