抄録
The effect of sulphur and phosphorus content on the toughness of carburized SCM420 steel was studied. At first, charpy impact test was conducted using 0.8%C-1%Cr-0.2%Mo steels which simulate the case of carburized SCM420 steel to evaluate the crack initiation resistance.
With increasing phosphorus content, charpy impact energy decreases, which is associated with the increase in intergranular fracture ratio. Auger electron analysis showed that phosphorus segregated to prior austenite grain boundaries in phosphorus doped steels. Furthermore, sulphur forms manganese sulphides elongated in the forging direction and deteriorates the toughness in the transverse direction.
Next, charpy impact tests for hardened and tempered SCM420 steel were carried out to estimate the crack propagation resistance of core. It was revealed that only sulphur reduces charpy impact energy. It was further shown through charpy impact test for carburized SCM420 steel that phosphorus deteriorates the toughness of the case whereas sulphur reduces that of the core.
