INFLUENCE OF POROSITY ON DEFORMATION AND FATIGUE BEHAVIOR OF P M AUSTENITIC STAINLESS-STEEL/

The monotonic and cyclic deformation response of powder metallurgy aus tenitic stainless steels resembling the commercial grade 3161 has been evaluated. Two porous steels at densities 6.9 and 7.2g/cm(3) respecti vely were studied and compared to a fully dense HIPed steel. Methods u sed were tensile and low cycle fatigue testing. Additionally, a study of short cracks that developed during low cycle fatigue was made with a replication technique and by optical microscopy of longitudinal sect ions. Stress and strain concentrations caused by the pores and the var iation in load-bearing area along the specimen originating from the po re structure, result in microplasticity (early deviation from elastic behavior) during monotonic tensile straining. Tensile behavior is depe ndent strongly on specimen dimensions. The porous steels showed pronou nced hardening during cyclic straining caused by the creation and expa nsion of plastic zones near pores. Surface fatigue cracks nucleate ear ly (similar to 10% of the lifetime) and grow continuously until failur e. Internal cracks were seldom found. Crack linking was observed in th e low density porous steel.