Effect of copper addition on microstructure and mechanical properties of ultra high strength NiSiCrCoMo steel

Effect of copper addition on microstructure and mechanical properties of an ultra high strength low alloy NiSiCrCoMo steel is investigated in the present study. Fe-0.38C-3Ni-2Si-1Cr-<1 (Co+Mo), is selected as base steel for the present study. Copper modified base steel was further austenitised and quenched, followed by tempering in the temperature range of 200-750 °C. The effect of tempering temperature on mechanical properties along with detailed microstructure changes at low (200 °C) and high (750 °C) tempering temperature has been evaluated for these steels. An increase in strength due to copper addition has been observed at both low and high tempering temperature. The increase in strength is observed to be much sharper at high tempering temperature than that at low ones. The higher strength value along with low toughness in copper modified base steel has been attributed to ordered B2 domains along with lenticular precipitates.