Вплив Q&P-обробки на мікроструктуру та механічні властивості низьковуглецевої TRIP-assisted сталі

Abstract

. The article describes the effect of heat treatment according the «Quenching and Partitioning» (Q&P) technology on the phase-structural status and mechanical properties of low-alloy 20Si2Mn2Nb steel. It is found that the standard heat treatment which is an isothermal annealing at 300°C (holding for 20 min) after heating in intercritical temperature range (ITR) provides a moderate complex of mechanical properties at low impact toughness. The heat treatment according to the ITR/Q&P scheme (austenitization in intercritical temperature range with a quenching cooling to 200°C and subsequent holding at 350-400°C for 5-20 min) significantly increases the ductile behavior of low carbon TRIP-assisted steels compared to its standard heat treatment. The positive effect of ITR/Q&P heat treatment on steel ductility was caused by the presence of high content of ductile ferrite (54,4 vol. %) in the steel structure. Heat treatment according to the FA/Q&P scheme (FA-full austenitization) with quenching cooling to 235°C and subsequent holding at 350-400°C for 5-20 minutes provided a considerable increase in the strength properties and impact toughness of steel. High strength level was ensured by the formation of a multiphase structure with a high volume fraction of hard martensite phase. The maximum combination of strength and ductility (PSE » 20 GPa·%) was provided by ITR/Q&P treatment conducted according to modes A770Q200P400(5 min) and A770Q200P400(20 min). The improvement in mechanical properties was associated with the formation of multiphase micro-structure which contains an increased amount of retained austenite. It is shown that Q&P treatment with heating in the intercritical temperature range notably improved a steel ability to work-hardening under cold plastic deformation