Surface hardening and wear performance of ausferritic
silicon steels

Abstract: 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.