Enhanced fatigue resistance in 316L austenitic stainless steel due to low-temperature paraequilibrium carburization

Fully reversed fatigue tests have been performed on wrought 316L stainless steel samples after low-temperature carburization. The resulting 25 mu m case depth, with a surface hardness three times that of the core and a surface compressive stress greater than 2 GPa, leads to significantly enhanced fatigue performance. The so-called endurance limit (defined as the stress at which the fatigue life is 10(7) cycles) increased from about one-third to about one-half the yield stress (from similar to 200 to similar to 325 MPa). Fractographic investigations reveal that the surface stresses change the preferred site of fatigue crack nucleation from the surface for noncarburized samples to the interior for carburized samples. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.