Microstructure and Properties of Surface Layer of Carburized 38CrAlMo6-10 Steel Subjected to Nanostructurization by a Heat Treatment Process/ Struktura I Właściwości Warstwy Naweglanej Na Stali 38Cralmo6-10 Po Procesie Nanostrukturyzacji W Warunkach Obróbki Cieplnej

Abstract

Abstract The aim of the study was to produce and characterize a nanobainitic microstructure in surface layers of carburized 38CrAlMo6-10 structural steel. Steel contained 1.% Al and 0.3% Si - elements hindering the cementite precipitation, which was considered to be adequate for obtaining a carbide free bainite. Steel samples were subjected to two different vacuum carburizing processes in order to obtain two different contents of carbon in surface layer. To produce a nanobainitic microstructure a heat treatment consisting of austempering at temperature slightly higher than the martensite start temperature (Ms) of the layer was applied after each carburization process. It was found, that the obtained microstructure of carburized layer depends strongly on carbon content. In steel with surface layer containing lower carbon content a nanobainitic microstructure with carbon-enriched residual austenite was formed. In case of surface layer containing higher carbon content the ultra-fine grained lower bainite was obtained.