Prediction of hardness and deformation using a 3-D thermal analysis in laser hardening of AISI H13 tool steel

In this study, a 3-D thermal analysis assisted by a systematic experimental study using a 2 kW multi-mode fiber laser was employed to develop predictive models for hardness and thermal deformation in laser transformation hardening of AISI H13 tool steel. Using the thermal model, temperature histories were obtained, which then were processed to compute the effective carbon diffusion time (ECDT) and the effective cooling time (ECT), the two concepts recently proposed by Ki and So [1]. Carefully observing the extensive hardness and deformation measurement data, it was revealed that ECDT is a parameter that correlates well with hardness, and ECT, when extended to the plastic deformation region, shows a strong correlation with deflection angle for both plastic deformation and solid-state phase transformation regions. By finding the minimum specimen thickness that preserves the hardening characteristics of thick steel plates, we were able to increase the deflection angle to ∼ 0.8°, and, after laser hardening, hardness values of up to ∼ 800 Hv were obtained. In this study, ECDT and ECT maps for AISI H13 tool steel were computed along with the hardening process window (or heat treatable region), and using the thermal model and experimental data, the minimum specimen thickness that preserves the hardening characteristics of thick plates was determined. This study shows that hardness distributions and thermal deformation behavior can be effectively predicted from a 3-D thermal analysis.