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MM: Fachverband Metall- und Materialphysik

MM 20: Poster Session I

MM 20.10: Poster

Dienstag, 24. März 2009, 14:45–16:30, P4

X-ray Diffraction Analysis and Metal Physics Modeling of Static Strain Aging and Thermal Dislocation Recovery in the Mechanically Affected Zone of Surface Finished Hardened Steel — •Jürgen Gegner — SKF GmbH, Dept. of Material Physics, Ernst-Sachs-Strasse 5, 97424 Schweinfurt, Germany

After heat treatment, finish machining of the hardened steel represents the last manufacturing step of machine elements. The practically most important operation of grinding is applied to achieve edge zone compressive residual stresses, best surface quality and dimensional accuracy. Metal removal involves high plastic deformation work. Glide and intersection processes raise the density and produce lower energy substructures of dislocations. The temperature and time behavior of post-machining thermal treatment is analyzed on ground and honed martensitic SAE 52100 rolling bearing steel. Microstructure stabilization is reflected in a large XRD line width decrease on the surface. The kinetics is modeled by rate-controlling carbide dissolution as the carbon source for Cottrell-type segregation at dislocations. This static strain aging is verified by the formation of a slight white etching surface layer. The metal physics model is extended to also consider superimposed thermal dislocation recovery. Both effects are separable. In rolling contact fatigue tests under mixed friction running conditions, air reheating of the samples below the tempering temperature, which avoids hardness loss, leads to a significant lifetime increase. Thermal post-treatment after cold working results in similar changes of the XRD line width in the larger mechanically affected edge zone.