Elevated temperature intergranular cracking in heat-resistant steels

It is confirmed that the time to intergranular failure t under tensile stress in heat-resistant steels can be expressed by t0σ−nexp(Q/RT) where n is the stress exponent, Q the activation energy, and t0 the proportional constant. It is also confirmed that, because the phosphorus segregation concentration is markedly higher at grain boundary/carbide interfaces than carbide-free grain boundary areas, the cracks initiate at the grain boundary/carbide interfaces and then propagate along the intergranular path. On the basis of the dependence of yield, grain boundary/carbide interface and carbide-free grain boundary area strengths on temperature, the intergranular stress relief or premature cracking occurring in the heat-affected zone and/or the weld metal is elucidated in detail, and the major factors for the intergranular cracking are clarified.