Influence of cutting condition on white layer induced by high speed machining of hardened steel

White layer formed on machined surface during dry and hard high speed machining has great influence on workpiece performance. Studying machined surface white layer is significant to improve the machinability and surface quality of workpiece. Experiments of dry and hard high speed machining of GCr15 bearing steel and 40CrNiMoA alloy steel were carried out with PCBN inserts, the phase composition and the thickness of white layer were studied experimentally; the formation mechanism of the white layer were studied; effects of cutting parameters, carbon content of substrate material on white layer thickness were analyzed; effects of cutting speed on retained austenite content in machined surface were also summarized. Results show that the microstructure of white layer consists of cryptocrystalline martensite, retained austenite and carbide; the white layer is formed by martensitic transformation; the white layer thickness and the retained austenite content of machined surface increase firstly and then decrease with cutting speed; the white layer thickness increases with flank wear and carbon content.