In situ observation of high temperature microstructure and reverted austenite evolution in 13Cr supermartensitic stainless steel

Abstract

In situ observation of high-temperature microstructure in 13Cr supermartensitic stainless steel was investigated by the high temperature laser scanning confocal microscopy (LSCM), and the effects of tempering temperature and tempering cooling rate on the morphology and contents of reverted austenite were characterized via transmission electron microscopy (TEM), x-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The results indicate that only α phase appeared in the XRD diffraction pattern after quenching at 1050 °C, there was no retained austenite in the quenched microstructure. The martensite transformation starting temperature (Ms) was around 177.6 °C according to the results of LSCM. The amount of reverted austenite increased first and then decreased with the tempering temperature increasing, and it reached a maximum value when the sample tempered at 620 °C. With the cooling rate increasing, the amount of reverted austenite showed a sharp decrease after tempering at 620 °C. The reverted austenite precipitated on martensite laths, blocks and prior austenite grain boundaries, while the misorientation angles ranged from 0° to 60° in the tempered martensite structure.