Characterization of complex (B + C) diffusion layers formed on chromium and nickel-based low-carbon steel

Abstract

Combined surface hardening with boron and carbon was used for low-carbon chromium and nickel-based steels. The microstructure, boron contents, carbon profiles and chosen properties of borided layers produced on the carburized steels have been examined. These complex (B+C) layers are termed borocarburized layers. The microhardness profiles and wear resistance of these layers have been studied. In the microstructure of the borocarburized layer two zones have been observed: iron borides (FeB+Fe 2B) and a carburized layer. The depth (70–125 μm) and microhardness (1500–1800 HV) of iron borides zone have been found. The carbon content (1.2–1.94 wt.%) and microhardness (700–950 HV) beneath iron borides zone have been determined. The microhardness gradient in borocarburized layer has been reduced in comparison with the only borided layer. An increase of distance from the surface is accompanied by a decrease of carbon content and microhardness in the carburized zone. The carbon and microhardness profiles of borided, carburized and borocarburized layers have been presented. A positive influence of complex layers (B+C) on the wear resistance was determined. The wear resistance of the borocarburized layer was determined to be greater in comparison with that for only borided or only carburized layers.