Mechanical properties of high-Si plate steel produced by the quenching and partitioning process

The microstructures and mechanical properties of a high-Si (1.5 wt.%) steel produced by a novel process of quenching and partitioning (Q&P) were compared with those obtained using traditional heat treatments (i.e. austempering, intercritical annealing for dual phase, quench and tempering). Plate steel was included for exploration of the Q&P process in applications requiring strength and toughness (such as an API line pipe), where retained austenite may contribute to the overall toughness via the TRIP phenomenon at a crack tip. The Q&P process is based on the partial transformation of austenite to martensite, followed by partitioning of carbon from martensite into austenite, which leads to an untypical microstructure. Retained austenite amounts up to 6 vol.% with a carbon content of up to 0.88 wt.% were achieved in 0.1 wt.% carbon steel using Q&P. Superior impact toughness at higher yield strength levels was found after Q&P compared to other traditional beat treatments with equivalent partitioning, austempering or tempering conditions.