Strength-toughness improvement of martensite-austenite dual phase deposited metals after austenite reversed treatment with short holding time

Abstract

To obtain a better strength-toughness balance of martensite-austenite dual phase deposited metals, an austenite reversed treatment (ART) with short holding time (namely S-ART), combining with the advantage of quenching & partitioning (Q&P) is proposed. The dual phase deposited metal is heated to the intercritical region (620 °C) for austenite reversion with a short holding time of 0.5 h. Compared to the conventional ART (C-ART) with the holding time of 2.0 h, S-ART provides significant improvement in yield strength, elongation and impact toughness. Due to the stronger partitioning effect of carbon, the carbon concentration of the retained austenite (RA) during S-ART is higher than that of C-ART and as-welded. Therefore, the stability of the RA in S-ART state increases dramatically and induces sustained transformation induced plasticity (TRIP) effect, which contributes to the enhancement of yield strength, ductility and toughness. Moreover, after S-ART, the volume fraction of RA increases and the dislocation density in martensite decreases significantly, further improving the ductility and toughness.