Two-body abrasion resistance of high-carbon high-silicon steel: Metastable austenite vs nanostructured bainite

In the current study, a high-carbon, high-silicon steel (1.21 wt% C, 2.56 wt% Mn, 1.59 wt% Si) was subjected to different heat treatments ((a) quenching from 800–1000 °C; (b) quenching from 800–1000 °C with further bainitizing at 250 °C for 8 days), resulting in microstructures consisting (a) of austenite and martensite (up to 94 vol% austenite) or (b) of austenite, nanobainite, and tempered martensite (up to 39 vol% nanobainite). The work is carried out using SEM, XRD, microhardness measurement, surface profile characterization, and two-body abrasion testing. It was found that steel wear behaviour is strongly dependent on austenite volume fraction and its metastability to mechanically-induced martensite transformation under wear. Austenite enrichment with carbon (upon carbides dissolution or bainite transformation) inhibits mechanically-induced transformation leading to decrease in microhardness increment after wear test and to an increase in wear rate. Specimens as-quenched from 900–1000 °C are found to have the highest wear resistance. This is attributed to the higher metastability of the retained austenite of these specimens. Nanobainite-containing specimens exhibit suppressed TRIP-effect under abrasion. The specimens containing 60–94 vol% of metastable austenite are by 1.5–1.8 times more wear resistant compared with the specimens consisting of 10–39 vol% nanobainite and 49–55 vol% of more stable austenite. Also, the relationship between wear behaviour and surface profile of the worn specimens is discussed.