Investigations of fracture surfaces of relaxation induced cracks

In this paper the effects of grain boundary segregations and the brittleness of two weldable steels were studied with creep tests followed by Auger analysis of fracture surfaces and electron microscopy of carbide morphology on precipitation. Reheat cracking of fine-grain steels has received considerable research attentions in recent years. It occurs if the postweld martensite or bainite is tempered in the vincinity of 600 degree C for few hours. In addition to the loss in toughness which is a result of tempering in this range, the fracture mode often changes from transgranular cleavage to brittle intergranular separation along the prior austenite grain boundaries. In this paper we report a study about the effects of phosphorous, sulphur and nitrogen in reheatcracking.