The surface integrity of AISI 1010 and AISI 4340 steels subjected to face milling

Similar to other metal cutting operations, milling can substantially affect the surface integrity of metallic components. Nevertheless, in contrast to its counterparts, milling possesses peculiarities, especially the variable thermal and mechanical loadings, which may affect the performance of the finished part in a unique manner. Additionally, considering that published literature is not consensual with regard to the influence of cutting parameters on induced residual stresses, the aim of this work is to investigate the influence of the principal milling parameters (cutting speed, feed rate, axial depth of cut and cutting fluid usage) on the induced residual stresses and subsurface microhardness distribution of AISI 1010 and AISI 4340 steels. Moreover, owing to the difference between the carbon content of these steels, one can estimate the contribution of martensite (which may be formed in AISI 4340 steel when austenitization temperature is reached) to residual stress and microhardness variation. The results showed that when cutting speed is elevated, the tensile stresses induced in AISI 4340 steel shifted to slightly compressive values (phenomenon not observed in AISI 1010 steel), thus suggesting that martensite formation may have contributed to the inducement of more compressive residual stresses in the former steel. The elevation of feed per tooth caused tensile stresses to shift into slightly compressive in AISI 1010 steel. Changing axial depth of cut did not affect the residual stresses distribution and the application of cutting fluid led to a slight reduction in the magnitude of the tensile residual stresses for both materials. Finally, the subsurface microhardness profile of AISI 1010 steel was not affected when the cutting parameters were altered, whereas slightly higher values were recorded near the surface of AISI 4340 steel when cutting speed and feed per tooth were elevated.