Effect of long time isothermal after deformation on tempering microstructure and nanometer precipitation in Nb-bearing micro-alloyed steel

摘要

Thermo-simulation test, measurement of hardness and transmission electron microscopy (TEM) were applied to investigate the variation of microstructure along with precipitation behavior during tempering at 525 °C after long time isothemal in deformed Nb-bearing micro-alloyed steel. The results indicate that the microstructure remains nearly unchanged until 1200 min. The hardness decreases gradually after water-quenching tempering for 120 min, and then increases continuously until 1200 min. The coarsened strain-induced nanometer precipitates formed in deformed austenite almost in the same size even tempering for long time. While the further precipitates, which nucleate in a phase, contribute to the increasing of hardness curves.