Effect of early stage of κ-carbides precipitation on tensile properties and deformation mechanism in high Mn–Al–C austenitic low-density steel

Abstract

High Mn–Al–C austenitic low-density steels possess the great combination of strength and ductility due to their excellent strain hardening capability. At present, there is no consensus on the controlling factors of the deformation mechanism, of which κ-carbides may play an important role. Abundant literatures have investigated the influence of long-term or peak aging heat-treatment so far, while few reports have focused on the early stage of κ-carbides precipitation. In this study, samples characterized by short-range order (SRO) and early precipitation states of κ-carbides were processed by rapidly quenched (RQ) and water quenched (WQ) treatment, respectively. When the ordering process from SRO to ultrafine nano κ-carbides was stopped by the increase of cooling rate, the ultimate tensile strength of the alloy was significantly increased without a decrease in yield strength, which indicates a dramatic increase in the work hardening rate. TEM investigation clearly revealed that the precipitation of κ-carbides slowed down the evolution of microstructure, which is an essential factor for the deterioration of work hardening capability. Another interesting result was that although the stacking fault energy (SFE) of the alloy was high (∼108 mJ/m2), twinning phenomena was observed in the RQ sample, implying that SRO should assist the formation of deformation twins, which provided a novel example for the development of twins in high SFE alloys.