Effect of Quenching Temperature and Tempering Time on the Evolution of Microstructure in UNS S17400 Stainless Steel

In the present work, the effect of quenching temperature and tempering time on the evolution of microstructure in UNS S17400 precipitation-hardening (PH) stainless steel has been investigated. Two temperatures, 950 and 1050 °C, were selected for quenching followed by tempering at 620 °C for different times ranging from 15 min to 6 h. Optical microscope (OM), electron backscattered diffraction (EBSD) and scanning electron microscope (SEM) were used to obtain the microstructural information. Energy-dispersive spectrometer (EDS) attached to SEM was used to obtain the localized chemical composition of various phases/precipitates. X-ray diffraction (XRD) was used to quantify the reverted austenite, coherently diffracting domain size and lattice strain. There was little change in the grain size with the increase in quenching temperature. On the other hand, tempering resulted in formation of precipitates of various types, which increased (as expected) with increase in tempering time. Lower quenching temperature resulted in higher reverted austenite.