Two-step treatment carburizing followed by boriding on medium-carbon steel

Combined surface hardening with boron and carbon was used for medium-carbon 4lCr4 steel. The microstructure, carbon profiles and chosen properties of borided layers produced on the carburized 4lCr4 steel (similar in chemical composition as AISI 5140 steel) have been examined. This two-step treatment carburizing followed by boriding is termed borocarburizing. 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 + Fe2B) and a carburized layer. The depth (100- 125 mum) and microhardness (1450-1900 HV) of iron borides zone have been found. The carbon content (0.94-1.41 wt.%) and microhardness (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. The increase of distance from the surface is accompanied by the decrease of carbon content and n-ticrohardness in the carburized zone. The carbon and microhardness profiles of borided, carburized and borocarburized layers have been presented. A positive influence of borocarburizing on the wear resistance was determined. The wear resistance of the borocarburized layer was determined to be higher in comparison with that for borided or carburized layers. (C) 2003 Elsevier Science B.V. All rights reserved.