Microstructure and hardness of adiabatic shear bands formed during orthogonal cutting of high strength steel

To study the influence of cutting speed and workpiece hardness on the microstructure and microhardness of the adiabatic shear bands, microstructure observation and microhardness measurement were performed on the adiabatic shear bands in the sawtooth chips formed during orthogonal cutting of two tempering hardness of 30CrNi3MoV high strength steel under different cutting speeds by optical microscope, SEM, TEM and microhardness tester. Results show that two types of adiabatic shear bands, i.e., deformed band with heavy elongated microstructure and transformed band with fine grains, are formed as cutting speed increases. The increase of the workpiece hardness promotes the formation of the transformed band. The increases of the cutting speed and workpiece hardness have little influence on the microhardness values in the transformed bands, but rapidly raise hardness in the deformed bands.