Effect of austenitising temperature on microstructure and mechanical properties of an ultrahigh strength high alloy G33 steel

The microstructures of ultrahigh strength high alloy G33 steels quenched at different austenitising temperatures in the range of 1000-1150°C and tempered at 260°C were characterised by optical microscopy, scanning electron microscopy and transmission electron microscopy. The quasi-static tensile, dynamic compression and impact properties were evaluated from the as tempered specimens. Results showed that the prior austenite grain size was enhanced as the austenitising temperatures increased, whereas the lenticular martensite and undissolved carbides decreased. The strength at both quasi-static and dynamic impacts varied little, while the quasi-static plasticity, dynamic plasticity and impact toughness increased with elevated austenitising temperatures. The undissolved carbides had an adverse effect on toughness and plasticity. A high austenitising temperature of 1100 and 1150°C was beneficial for G33 alloy to acquire both high strength and high toughness.