Pre-strain effect on fatigue strength characteristics of SUH660 plain specimens

• Precipitate cutting may affect the fatigue crack growth rate for SUH660 steel.
• A dislocation accumulation model is proposed for the crack tip in SUH660 steel.
• The model is based on back stress behavior.
• Buff-polish causes acceleration of crack growth for the non-strained specimens.
• Buff-polish enhances plasticity-induced crack closure for the pre-strained specimen.

Precipitation particles in precipitation-strengthened materials are considered to be cut by pre-strain treatment, which affects the fatigue strength. In this study, fatigue tests were performed on precipitation-strengthened stainless steel SUH660 to investigate the effect of pre-strain on fatigue crack initiation and propagation characteristics. Fatigue test results showed that pre-strained specimens have a shorter fatigue crack propagation life compared to non-strained specimens; this is the opposite of results observed in carbon steel. The accelerated fatigue crack growth observed in pre-strained specimens was first assumed to be caused by precipitate cutting. A dislocation accumulation model for the fatigue crack tip in the precipitation-strengthened material was then suggested. Buff-polished specimens were also used for the fatigue tests, and the results showed that the work-hardened layer had a significant impact on the fatigue strength and fatigue life.