Further insight into the chip formation of ferritic-pearlitic steels: Microstructural evolutions and associated thermo-mechanical loadings

• Microstructural evolutions in the shear regions are highlighted by FESEM and EBSD analyses
• Grain size down to 200 nm are observed in the Secondary Shear Zone where the highest strains are reported.
• Cementite lamellae are found to be fragmented and decomposed due to the intensive strains
• Dynamic recrystallisation promoted by heat generation is taking place in the shear regions.
• Severe plastic strains and elevated temperatures are the main driving forces of this mechanism.

The main objective of this paper is to clarify the deformation mechanisms of ferritic-pearlitic steels in metal cutting and correlate them to the associated thermo-mechanical loadings. Dry orthogonal cutting tests have been performed on a normalised AISI 1045 steel with coated carbide tools. Experimental evidences of a drastic grain refinement process in the main deformation zones are advanced on the basis of optical microscope, Field Emission Scanning Electron Microscope (FESEM) and Electron BackScattered Diffraction (EBSD). Microstructural evolutions leading to a grain size down to 200 nm and fragmented cementite are especially emphasized. A numerical approach is further employed to target and quantify the loadings applied to the machined material and extract further information on the Secondary Shear Zone (SSZ). Strains amplitude appears to be the driving parameter of these evolutions via a dynamic recrystallisation process promoted by an intense and localised heat generation. The present contribution highlights that in-depth and microscale investigations of chip formation including microstructural aspects are still required.