Effect of grain size on fatigue behavior of Type 301LN stainless steel

• Axial fatigue behavior and resistance of reversion-treated 301LN was studied.
• Fatigue damage occurred by grain boundary cracking in ultrafine-grained structures.
• No slip bands were seen on the surface as marks of dislocation activity.
• Grain boundary cracking took place also within recrystallized shear bands.
• Fatigue resistance was improved by the grain size refinement.

The effect of grain size and phase structure on fatigue behavior in Type 301LN austenitic stainless steel was preliminarily investigated. Various grain sizes from submicron to coarse ones were obtained by controlled reversion treatments. Axial tension–tension fatigue tests were carried out under load control. Cyclic hardening was observed to take place very early in cycling. Hardness increased about 29% and high fraction of martensite, up to 40%, was formed in ultrafine-grained structures. The fatigue damage occurred by grain boundary cracking in ultrafine-grained structures, where no slip bands were formed. Partly recrystallized shear bands were observed in cold-rolled austenite grains and grain boundary cracking took place within them as well. In the coarse-grained steel, intense slip bands were formed and crack nucleated and propagated along them and grain boundaries. Fatigue resistance was improved by the grain size refinement.