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ABSTRACT
Surface and subsurface microstructure evolution are particularly highlighted in dry machining of hard-to-cut materials. In this research, a user-defined subroutine integrated into an established finite element (FE) cutting model for AISI H13 steel was developed to simulate dynamic recrystallization (DRX) and surface microhardness variation in the hard milling process. At first, the hierarchical structure of tempered martensite transformed from prior-austenite was analyzed and the initial effective grain size was identified. Secondly, the material sub-model used for DRX and microhardness prediction on the basis of empirical formulas of Zener-Hollomon (Z-H) and Hall-Petch (H-P) was presented. Then, the user-defined subroutine programmed in software FORTRAN adapted from the proposed sub-model was incorporated into a verified 2D cutting simulation model to explore the effects of cutting parameters. Finally, hard milling experiments and corresponding microstructure characterization were performed to verify the grain size changes and microhardness variation. Comparison results confirmed the validity of the presented sub-model for microstructure characteristics prediction aiming at grain size and microhardness.