Effect of laser direct metal deposition process on the microstructure and mechanical properties and temperature and stress fields of 24CrNiMo

We conducted a study to investigate the impact of the laser direct metal deposition (LMD) process on the microstructure, mechanical properties, temperature fields, and stress fields of 24CrNiMo steel in order to determine the optimal process parameters. The optimal parameters were determined to be a laser power of 1400 W, scanning speed of 7 mm/s, and powder feed rate of 8 g/min. When these optimal parameters were used, the formed specimens exhibited a high densely of up to 97.5 %. The microstructure of the specimens formed different parameters primarily consisted of bainite, martensite and ferrite. The specimens formed under various process conditions demonstrated good toughness, with a maximum tensile strength of 1131 +/- 20 MPa and an elongation of 16 +/- 1.8 %. Additionally, there was little difference in wear resistance and wear morphology among the specimens formed under different processes. The predominant wear mechanisms include abrasive wear, adhesive wearand oxidative wear. Increasing laser power and decreasing scanning speed resulted in a gradual increase in the temperature gradient gradually, leading to higher residual stresses in the formed specimens. Longitudinal stresses concentrated on both sides of the deposited layer, while the transverse stresses concentrated on one side of the deposited layer. The simulation results of the temperature field and stress field were consistent with the experimental results, with errors within the range of 10 %-20 %. This study demonstrated that the simulated models of temperature and stress fields effectively captured the fundamental phenomena in the LMD process, providing valuable tools for predicting and optimizing temperature distribution and stress in the LMD process. These findings contribute to the understanding and enhancement of the LMD process for 24CrNiMo steel, making it applicable for various applications requiring superior microstructure and mechanical properties.