A Comparative Study on the Tribological Properties of a Cobalt-Free Superaustenitic Stainless Steel at Elevated Temperature

The properties of a cobalt-free cast superaustenitic stainless steel (SASS) is investigated comparatively to the commercial high-cobalt alloyed GX15CrNiCo21-20-20 (1.4957, N-155) steel regarding its global hardness and wear resistance at elevated temperature by means of in situ hot hardness tests and cyclic abrasive sliding wear tests against an Al2O3 (corundum) counter-body at 600 °C. In the aged condition, results show that the 1.4957 steel suffers a higher material loss due to brittle failure initiated by coarse eutectic Cr-rich carbides which are incorporated into a mechanically mixed layer during abrasive loading. In contrast, within the Co-free steel eutectic M6(C,N) carbonitrides are distributed more homogeneously showing less tendency to form network structures. Due to the combination of primary Nb-rich globular-blocky MX-type carbonitrides and eutectic M6(C,N) carbonitrides dispersed within an Laves phase strengthened austenitic matrix, this steel provides comparable hardness and significantly improved wear resistance at elevated temperature. Thus, it may be an adequate alternative material to commercial SASS and offers the possibility to save cobalt for future applications.