Effect of thermal treatment on structure of newly developed 47CrMoWVTiCeZr16-26-8 hot-work tool steel

This paper presents of the results on the heat treatment parameters influence on the structure of the newly developed complex hot-work tool steel 47CrMoWVTiCeZr16-26-8 in relation to standard hot-work tool steel X40CrMoV5-1. After soft annealing the examined steels indicate the alloy ferrite structure with the great number of the carbides of the type of M6C and MC (nearing VC, (Ti,V)C and ZrC) as well as M2C3 (nearing Ce2C3) in the 47CrMoWVTiCeZr16-26-8 steel and with the carbides of the type of M6C, MC, M23C6 as well as M7C3 in the X40CrMoV5-1 steel. The volume fraction of carbides in the 47CrMoWVTiCeZr16-26-8 steel amounts to 8.2% and is higher then in the X40CrMoV5-1 steel. After hardening from temperature of 970–1180 °C the 47CrMoWVTiCeZr16-26-8 and X40CrMoV5-1 steels obtain the lath martensitic structure, partially twinned with a small fraction of retained austenite and the carbides partially undissolved in solid solution of the type of MC (TiC and ZrC) as well as M2C3 in the 47CrMoWVTiCeZr16-26-8 steel and of the type of MC (VC) in the X40CrMoV5-1 steel. The 47CrMoWVTiCeZr16-26-8 steel characterises itself by the greater fraction of carbides partially undissolved in solid solution during austenitizing as well as by the greater resistance to the growth of primary austenite grains then the X40CrMoV5-1 steel. Tempering the examined steels within the range of temperatures between 450 and 540 °C results in starting the precipitation processes in martensite and the secondary hardness effect after tempering from temperature of 540 °C in the 47CrMoWVTiCeZr16-26-8 steel and from temperature of 510 °C for the X40CrMoV5-1 steel, which is caused by the carbides M4C3 and M7C3 in the 47CrMoWVTiCeZr16-26-8 steel and M7C3 in the X40CrMoV5-1 steel.