Surface hardening and wear performance of ausferritic silicon steels

A special microstructure called ausferrite, consisting of ferrite laths surrounded by carbon supersaturated retained austenite can be created in steels containing more than about 1.5 % silicon. This structure, which is achieved by means of an austempering treatment, is fine-grained and free of carbides, presenting a good combination of properties such as high strength, good ductility, high toughness and excellent wear and fatigue resistance. This project examines the effect of the surface hardening on the microstructure and mechanical properties as wear resistance of silicon alloyed steels. 55Si7 steel specimens have been austempered, hardened by YAG high power laser, and subjected to tempering resistance tests. Afterwards rolling/sliding wear performance of 55Si7 steel, with surface treated and untreated conditions, was tested, and compared with 50CrV4 chromium steel, by means of twin disc machine. Results analysis has been assessed by optical and SEM microscopy, XRD analysis, wear measurements, microhardness tests, and optical surface profiles. Results show that ausferritic structure has an excellent tempering resistance, and that laser hardening treatment greatly improves wear resistance of ausferritic steels. However wear performance of the untreated ausferritic structure was close to that of laser treated specimens. After wear tests, both of silicon steel specimens, with treated and untreated surface, presented an excellent contact fatigue resistance, opposite to chromium steels which showed cracking in the worn subsurface.Validerat; 20101217 (root