1987 Volume 5 Issue 4 Pages 527-533
The effect of stress on the types of fracture surfaces of reheat cracking was investigated on three grades of heat resisting steels; 1Cr-1/2Mo, 2 1/4Cr-1Mo and 1/2Mo steels. The modified implant test method was employed for a constant load condition. Two types of fracture surfaces were recognized; an intergranular and a transgranular types, depending on the magniturd of the stress. When the restraint stress was high, the crack initiated at an earlier stage of reheating and the intergranular type appeared. At this stage, the prior-austenite grain boundaries were embrittled by the phosphorus segregation. When the stress was low, the crack initiated after a long lapse of time in the holding stage at 873K. In this stage, the percentage of intergranular fracture surface was decreased with increasing the lapse of time by the reason that phosphorus formerly segregated at the grain boundaries diffused back into the grain interior. The phosphorus concentration in the grain boundaries was increased by the stress in both the earlier stage of reheating and the holding stage at 873K.
