Comprehensive Study of the Single High-Energy Laser Pulse Effect on the Wear Resistance of R6M5 Steel

Abstract— Research on microstructure changes and structural defects (using the example of dislocation density) of samples made of high-speed steel R6M5 and irradiated with a single high-energy laser pulse as well as the effect of these changes on the abrasive wear resistance of the studied material is presented in the article. It was found that the proposed laser treatment significantly affects the microstructure of the irradiated samples. This is expressed in the almost complete disappearance of the banded distribution of carbides in the samples, which indicates a partial redistribution and dissolution of “heavy” carbides of the Me6C type containing tungsten and molybdenum in the material matrix (martensite). In this case, the configuration of heavy Me6C carbides is located between the formulas Fe3(W,Mo)3C–Fe4(W,Mo)2C. Also, exposure to a high-energy laser pulse leads to an increase in the quantity and size of secondary carbides in the alloy matrix, significantly enriched in tungsten and molybdenum. In addition, there is a change in the type of vanadium carbides from Me2C to VC, accompanied by a significant decrease in the amount of molybdenum and tungsten in it. Using the Thixomet image analysis program, it was determined that the number of grains of heavy Me6C carbides in terms of volume decreased by 1.30–1.58 times, depending on the distance from the point of interest to the irradiation place of the sample. At the same time, the average size and direction (anisotropy) of the material grains has not changed. The results of X-ray phase analysis showed that after treatment, the number of main phases of the samples remained practically unchanged in distribution, but there was an increase in the responses intensity. Based on the above, the change in the structure defectiveness was determined using the example of dislocation density. The results of abrasive wear tests showed that there is an increase in the wear resistance of irradiated samples by 1.58–2.48 times, depending on the distance from the point of interest to the irradiation place of the sample. In this case, the value of the greatest wear resistance (2.48 times) is achieved with the greatest microstructure changes and structure defectiveness, which corresponds to the distance from the point of interest to the irradiation place of the sample equal to 20 mm. The obtained results allow us to recommend the use of the microstructural analysis method for assigning optimal modes of laser hardening of materials.