Fatigue life improvement of AISI 304L cruciform welded joints by cryogenic treatment

Abstract

Existing theories and reported practical experience show that cryogenic processing greatly increases abrasion resistance and contact fatigue resistance of some metals and alloys. In the present work, an attempt has been made to investigate the effect of cryogenic treatment on the axial fatigue performance of fillet welded cruciform joints of AISI 304L stainless steel, which failed in the weld metal. Constant amplitude fatigue experiments with R=0 were carried out with a 100 kN servo-hydraulic DARTEC universal testing machine with frequency of 30 Hz. It has been observed that after the deep cryogenic treatment at liquid nitrogen temperature (−185 °C), the fatigue life improved almost by a factor of two. During the treatment the significant microstructural changes that occurred accounted for the improved fatigue performance. Strain induced martensitic transformation was observed. During this transformation, the weld metal tends to expand inducing compressive residual stresses in the weld metal.