MICROSTRUCTURAL ALTERATION AND MICROHARDNESS AT NEAR-SURFACE OF AISI H13 STEEL BY HARD MILLING

In the present research, the microstructural alteration and microhardness at near-surface of AISI H13 steel by hard milling under different cutting parameters with coated cutting tools have been investigated. Very thin white layer forms or even no obvious microstructural alteration layer appears at the near-surface. It is reasonable that the formation of the very thin white layer is primarily due to mechanical effect (severe plastic deformation) rather than thermal effect (rapid heating and quenching). The 'hook' shape of the microhardness profile indicates that the highest microhardness appears on the very top surface; while the smallest microhardness occurs at the depth of 25 mu m below the machined surface. Moreover, the microhardness profiles below the machined surfaces well correlate with the microstructural change of the machined near-surface. It is expected that the experimental results will provide a useful guide to control or minimize the white layer formation and, more significantly, to promote the application of hard milling technique in die and mold industry.