Cutting Behavior of Steels Mixed with Martensite

Abstract

The cutting resistance value in turning decreased for the case hardening steel mixed with martensite in the ferrite matrix as compared with the normalized case hardening steel.
In the cutting at the low and intermediate speed, the micro-cracks were observed in chip of the steel mixed with martensite.It suggested that the cutting resistance value was decreased by the formation of the brittle fracture in the shear region of chip.
In the steel tempered for the softening of martensite, the cutting speed range where the built-up edge disappeared shifted to the high cutting speed side, and in this cutting speed range the side force increased.
In the cutting at the intermediate and high speed, the damaged layer (D₁) between the deformation flow layer (F_μ) and chip and the influence of the flow speed of chip (V_c) on the plasticity of F_μ, were important. The V_c and the difference of the hardness between D₁ and F_μ increased with an increase of shear angle of chip (φ) in the steel mixed with martensite more than the normalized steel.It was suggested that the cutting resistance value decreased with an increase of the plasticity in F_μ.Increase of the plasticity in F_μ resulted from the rise of the temperature due to the increase of theV_c and the hardness difference between D₁ and F_μ.