EFFECT OF AGING ON HIGH-TEMPERATURE BRITTLE INTERGRANULAR FRACTURE INAUSTENITIC STAINLESS-STEELS

The present paper describes the effect of aging on clack growth at 550 -750 degrees C in a series of 316 and 347 based stainless steels. Clac k initiation parameters and crack growth rates have been measured, and detailed fractography and microstructural characterisation carried ou t. The study shows that the high temperature brittle intergranular fra cture mechanism operates in these alloys, as expected from incidences of cracking in austenitic stainless steels used in power plant. High t emperature brittle intergranular fracture leads to lower crack lip ope ning displacements at initiation, and slightly higher crack growth rat es than ductile intergranular failure. Susceptibility to high temperat ure brittle intergranular fracture is enhanced by aging. This increase d susceptibility is explained in terms of the increased hardness, the reduction in dissolved C, and grain boundary precipitation. The effect s of temperature, composition, and loading mode on the behaviour of th e aged alloys are determined.