Influence of Tempering Transformation Induced Plasticity (T-TRIP) on the Evolution of Residual Stresses in Laser Heat Treated 50CrMo4 Steel

Wednesday, May 7, 2025: 4:30 PM
Room 19 (Vancouver Convention Centre)
Ms. Niki Nouri , Karlsruhe Institute of Technology (KIT), Karlsruhe, Baden-Württemberg, Germany
Dr. Pierre Lapouge , Arts et Métiers, CNAM, CNRS UMR 8006, Paris, Île-de-France, France
Dr. Justin Dirrenberger , Arts et Métiers, CNAM, CNRS UMR 8006, Paris, Île-de-France, France
Dr. Stefan Dietrich , Karlsruhe Institute of Technology (KIT), Karlsruhe, Baden-Württemberg, Germany
Prof. Volker Schulze , Karlsruhe Institute of Technology (KIT), Karlsruhe, Baden-Württemberg, Germany
Laser hardening is a widely used and adaptable heat treatment technique, valued to its flexibility regarding the position of the laser. However, this method induces significant temperature gradients at the material's surface, leading to the formation of residual stresses. During the process, tempering may occur either intentionally, to modify material properties, or unintentionally, as a result of overlapping laser tracks. This tempering triggers the occurrence of tempering transformation induced plasticity (T-TRIP) due to the precipitation of cementite under stress, thereby altering the mechanical characteristics of the material.

Previous dilatometric studies have confirmed the presence of T-TRIP in quenched and tempered steels, highlighting its influence on the distribution of residual stresses after heat treatment. Therefore, for accurate prediction of the material state, it is essential to gain a deeper understanding of the interactions during laser heat treatment, especially between T-TRIP and the development of residual stresses.

In this study, the behavior of residual stresses in laser heat treated 50CrMo4 steel was analyzed before and after tempering. Different initial material states, heat treatment parameters, and laser configurations, such as single laser, double laser, and multi-line laser treatments, were examined. The investigation involved comprehensive measurements of hardness and residual stress in these samples. The experimental data obtained from these studies were compared with laser heat treatment simulations, allowing for an in-depth evaluation of the effects of various laser parameters on residual stress distribution and material hardness.

The findings offer critical insights into optimizing laser heat treatment parameters to control residual stresses and improve material properties, demonstrating the significance of T-TRIP in influencing the outcomes of laser tempering processes in industrial applications. Furthermore, the improved simulation would allow better prediction of the material state after heat treatment, facilitating the control over mechanical performance.

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