Thermal stability of metastable austenite in rapidly solidified chromium–molybdenum–vanadium tool steel powder

Thermal stability of metastable austenite in a Cr–Mo–V tool steel of ledeburite type was investigated by tempering rapidly solidified (RS) particles at temperatures from 100 up to 700°C and by continuous heating during differential thermal analysis. A rapid increase in microhardness was observed after the tempering at temperatures over 400°C. According to Mössbauer effect measurements, only non-magnetic phases were observed in the RS particles after atomization, as well as after the tempering at temperatures below 540°C. Above this temperature, the metastable austenite gradually transformed into martensite during cooling from the tempering temperature. The secondary hardening peak corresponding to 1220HV appears at 600°C. This temperature is higher than the temperature of the secondary hardening peak for this steel after conventional heat treatment. The thermal stability of austenite was determined and the mechanisms of phase transformations responsible for the achievement of secondary hardness in this steel following rapid solidification are described.