FRICTION AND WEAR BEHAVIOR OF HIGH SILICON BAINITIC STRUCTURES IN AUSTEMPERED CAST-IRON AND STEEL

The sliding wear behavior of various microstructural combinations obtained by austempering ductile cast iron (3.7 wt.% C, 2.54 wt.% Si, 0.45 wt.% Mn) in the upper bainitic temperature range of 370 °C as a function of time was investigated. The wear behavior of high silicon steel (2.5 wt.% Si, 1 wt.% Ni) austempered at 420 °C for various times was also studied. Sliding wear tests were performed in a pin-on-disk wear tester with the test material rubbing under dry atmospheric conditions against a flat hardened toolsteel disk at a speed of 1.15 m s-1 and loaded with normal loads of 10.5 and 19.6 N. It was found that the wear resistance of austempered steel was much higher than that of austempered cast iron. The effect of graphite on friction and wear was studied using the high silicon steel austempered to provide the same microstructures as in ductile cast iron with the exception of graphite. The increased wear rate of cast iron was attributed to the surface-weakening produced by the presence of graphite. The effect of retained austenite on wear behavior was investigated in terms of work hardening and the deformation-induced transformation of retained austenite to martensite. The worn surfaces of austempered cast iron and steel were studied by scanning electron microscopy. Surface cracks and extensive deformation were observed on the worn surfaces of austempered cast iron but there was no indication of cracking on the austempered steel surfaces. © 1990.