Mechanical and microstructure characteristics of heat-treated of high-Cr WI and AISI4140 steel bimetal beams

Heat treatments are considered as one of the most important methods used to make significant changes in the microstructure of the metallic materials and their alloys, which makes it possible to change the external behavior and properties of these materials. The effect of heat treatment at 900 °C on the microstructure, hardness and flexural behavior of bimetal beams has been studied in the present work. The bimetal beams composed of a high-Cr WCI as a wear-resistant part and an AISI4140 steel as a ductile part were fabricated. The two parts of bimetal castings are joined together by means of dovetail joint and/or connector pins. The present experimental and numerical results revealed that all bimetal beams exhibited flexural strength, toughness and maximum deflection higher than those of high-Cr WI specimen and lower than those of AISI4140 specimen in heat treated conditions. Heat treatment of the bimetal casting beams produced significant improvements in both hardness and flexural strength of high-Cr WI and AISI4140 steel. This is due to the formation of secondary carbides in the martensitic matrix surrounded by a network of M7C3 carbides in high-Cr WI, and formation of fine pearlite with proeutectoid α at grain boundaries for AISI4140 steel as revealed by SEM and an optical metallography. Bimetal beam with 12-connector pins (BI12CONN) as a mechanical joint exhibited the highest flexural strength and toughness compared with the other bimetal beams after heat treatment.