| A new method for fatigue life extension has been proposed in this study. To confirm the effectiveness of the proposed method, an austenitic stainless(SUS304) steel(pre-strain : about 2%) was prepared. It was shown from transmission electron microscopy(TEM) observation that micro-sized α martensite particles (0.02∼0.1㎛ in diameter) were dispersed in the SUS304 steel by cooling at -78℃. No decrease in ductility was observed in tensile tests for the material with dispersed micro-sized martensite particles as compared to the as-received material. After tension-compression loading, dislocation structure and surface microstructure observations were carried out using a TEM and a laser microscope, respectively. It was found that the re-arrangement of dislocations and the formation of large α martensite, which may cause fatigue crack initiation, were suppressed in the material with dispersed micro-size α martensite particles as compared to the as-received material. Fatigue life of the material with dispersed micro-sized α martensite particles did not increase in a low cycle regime($lt; 10⁴cycles) as compared to the as-received material. However, in a high cycle regime( $gt; 10⁴cycles), the fatigue life of the material with dispersed micro-sized a martensite particles was much longer than that of the as-received material. |
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