Modelling of phase transformations induced by thermo-mechanical loads considering stress-strain effects in hard milling of AISI H13 steel

Hard milling of difficult-to-machine materials has emerged as a popular manufacturing technology in the hot forging and mould manufacturing industries. Local phase transformation of steels often occurs under deeply coupled thermomechanical effects during the hard milling process. This work focuses on the prediction of phase transformations in hard milling of AISI H13 steel. First, a rapid heat phase transformation model that considers stress-strain effects is proposed and described based on phase transformation kinetics. Second, the proposed model is implemented into a validated finite element model (FEM) as a user subroutine of Abaqus/Explicit to describe phase transformations during chip formation in hard milling of AISI H13 steel. The predicted results indicate that martensite transforms into austenite in the chip back surface while no austenite is produced in the machined surface. The volume fraction of austenite in different zones increases when cutting speed is increased from 200 m/min to 400 m/min. Finally, the proposed metallo-thermomechanical coupled finite element model is verified by comparing the simulated results with experimental data. Good agreement is achieved, demonstrating that the proposed model can be used for prediction of phase transformations during hard milling of AISI H13 steel. The experimental and predicted results help to promote understanding of the phase transformations and microstructure evolution mechanisms of AISI H13 steel in hard milling processes. This study also contributes to optimizing the machining parameters to acquire the desired surface integrity in hard milling of AISI H13 steel.