Improved process prediction of laser surface hardening on basis of experimental in-situ data

• Applicants: Dr. Felix Beckmann; Dr.-Ing. Jens Gibmeier
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275300507

In industry laser surface hardening is a well-established technique for local surface hardening of steel components. The process is characterized by a local austenitization of a component by means of a focused laser beam and the martensitic hardening through self-quenching that occurs subsequent to the local short time heat treatment. This is accompanied by the improvement of the wear resistance, the oxidation resistance and the fatigue strength through a significant hardness increase and through the formation of beneficial compressive residual stresses. A large number of process parameters and a complex interaction between individual process variables affect the resulting hardness and hamper the prediction via process simulations. The aim of the continuation of the project is unchanged the significant improvement of the laser surface line hardening by means of FEM simulations. Basis for the approach are still real time insights into the rapid local heat treatment process through in-situ synchrotron X-ray diffraction experiments using a well-established and continuously improved measuring and evaluation strategy for local, temporal resolved analyses of the phase transformation kinetics and the stress evolution. As presented in the mid-term report, a considerable improvement regarding the process prediction of laser surface line hardening was already achieved within the scope of the first funding period. However, the results have indicated that the determination of the stress component in longitudinal direction of the laser path is mandatory that also in this direction a better agreement for the prediction of the final residual stress distributions can be achieved. This requires a modification of the instrumentation of the in-situ experiment, which will be realized within the scope of the project continuation. Finally, the temporal evolution of the stresses in longitudinal direction of the laser track will be determined in a further synchrotron beamtime. These data will be applied together with the already existing experimental data for the further improvement of the simulation model. Furthermore the throughput time of the simulation will be significantly reduced and the reachable measuring frequencies of the in-situ measuring series will be further increased by using refractive X-ray lenses. Regarding the experimentally determined residual stress depth distribution the redistributions of the residual stress states that result from the successive local, electrochemical sub-layer removal will be calculated numerically. Using these results the residual stress distribution determined in defined depths by X-ray diffraction will be effectively corrected. By this means, finally the validation of the laser surface line hardening simulations can be additionally done on basis of the depth resolved experimental results.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Fabian Wilde