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 μm 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 10⁷ cycles) increased from about one-third to about one-half the yield stress (from ～200 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.