Surface integrity evaluation of high-strength steel with a TiCN-NbC composite coated tool by dry milling

Abstract

During high-speed machining (HSM) of high-strength steel, the poor surface integrity of workpiece affects its service performance. HSM of AISI 4340 steel is carried out by a TiCN-NbC composite coated tool in dry milling conditions. For the machined surface, the surface roughness, microstructure, residual stress and micro-hardness are measured to discuss the surface integrity evaluation. The minimum variation of surface roughness Ra with tool wear is obtained at vc = 350 m/min. The microstructure characteristics with twins, dislocations or their combination is also observed by using electron backscattered diffraction (EBSD) technique, which can result in the surface transformation and recrystallization. The appropriate plastic deformation causes the work hardening degree to be controlled within the range of 110%–120%. The compressive residual stress is achieved, which is benefit to seal the micro-cracks in the surface layer. The research results will be able to promote the high-quality processing of AISI 4340 steel parts.