Fracture toughness and microstructure of the heat-affected zone of a welded maraging steel

Abstract

The fracture toughness and microstructure of the heat-affected zone of welded 300 grade maraging steel have been studied. A wide range of welding processes has been covered using a thermal simulation technique. This approach has been justified by correlating real and simulated heat-affected zone properties and structures. Fracture toughness has been found to be a function of peak temperature, but independent of heating and cooling rates. Increases in fracture toughness were found and related to peak temperature, specific values being 75 MNm^−3/2; (67·8 ksi√in) at 650°C and 66–;77·5 MNm^−3/2 (59·6–70·1 ksi√in) over 12000–1400°C, as compared with the parent material value of 60 MNm^−3/2 (54·2 ksi√in). These increases inf racture toughness were accompanied by decreases in tensile strength in all cases. The metallographic, fractographic and fracture toughness results have been correlated to explain the observed changes in properties. It is shown that reverted austenite gives increased toughness at 650°C while acicular structures account for toughness increases over the 12000–1400°C range. Constitutional liquation of inclusions was detected at the higher temperatures but did not produce grain-boundary embrittlement in this material.