Development of a Fatigue Life Extension Method by Dispersing Micro-sized Matensite Particles in Austenitic Stainless Steel - (I) Cyclic Plastic Deformation Behaviour

摘要

A new method for fatigue life extension has been proposed inthis study. To confirm the effectiveness of the proposed method, an austeniticstainless(SUS304) steel(pre-strain: about 2percent) was prepared. It wasshown from transmission electron microscopy (TEM) observation that micro-sized #alpha# martensite particles (0.02~0.1 #mu#m in diameter) weredispersed in the 5U5304 steel by cooling at -780C. No decrease in ductilitywas observed in tensile tests for the material with dispersed micro-sizedmartensite particles as compared to the as-received material. After tension-compression loading, dislocation structure and surface microstructureobservations were carried out using a TEM and a laser microscope,respectively. It was found that the re-arrangement of dislocations and theformation of large #alpha# martensite, which may cause fatigue crackinitiation, were suppressed in the material with dispersed micro-sized #alpha#martensite particles as compared to the as-received material. Fatigue life ofthe material with dispersed micro-sized #alpha# martensite particles did notincrease in a low cycle regime( < 10~4 cycles) as compared to the as-receivedmaterial. However, in a high cycle regime(>10~4 cycles), the fatigue life of thematerial with dispersed micro-sized #alpha# martensite particles was muchlonger than that of the as-received material.