A. H. Heuer, N. Agarwal, K. F. Day, A. Avishai, H. Kahn, G. M. Michal, F. Ernst, Case Western Reserve University, Cleveland, OH
A novel low-temperature carburization process is reported that generates homogeneous, carbide-free solid solutions with up to 12 at% carbon various austenitic alloys, including 316L, 321, and 254SMO alloys. This process, based on carbon diffusion under paraequilibrium conditions, results in a carburized case that extends to a depth up to 50 µm and has a surface hardness 3 to 4 times that of the core, resulting in much improved wear resistance. After tensile testing, profuse slip traces are observed in the carburized surface. Fatigue lifetimes are significantly enhanced, apparently due to very large (~2 GPa) residual compressive stresses accompanying the high carbon concentration near the surface.
Summary: Low-temperature carburization of austenitic stainless steels, based on carbon diffusion under paraequilibrium conditions, results in a 50 µm carburized case with increased surface hardness and large residual compressive stresses. This leads to increased fatigue resistance and wear resistance with no loss of ductility.
