Wear property of low-temperature bainite in the surface layer of a carburized low carbon steel

A process primarily based on carburization and successive low-temperature austempering, was proposed for the generation of low-temperature bainitic microstructure in the surface layer (∼2.5 mm in thickness) of low-carbon steel. For a potential use in the manufacture of heavy-duty gears, wear properties of this type of microstructure were studied. Comparisons were made with carburized commercial steel of 20CrMnTi subjected to quenching followed by tempering, which is widely used in the area of gear. The result showed that the experimental steel and the control steel present different wear mechanisms under the same sliding wear process. The low-temperature bainitic steel exhibits an excellent wear resistance as a consequence of the following three main factors: (i) high strength plus high toughness, (ii) carbon enriched austenite, and (iii) extremely fine α-phase microstructure. The low-temperature bainitic microstructure exhibits high strength and high toughness due to the refinement of the microstructure. Secondly, the film-like carbon enriched austenite (∼30 nm in thickness) uniformly distributed between the carbide-free bainitic ferrite plates can retard the crack propagation during sliding friction and play an advantageous role in wear resistance. Lastly, an extremely fine single α-phase microstructure was promptly induced in the dry sliding friction of the surface layer of the low-temperature bainitic steel; such fine refined microstructure lead to an increase in hardness, which can improve wear resistance.