Laser Harding And Nitriding Composite Treatment Of High Speed Steel And Nitriding Steel

Nitriding treatment is a widely used surface chemistry-heat treatment technology; it has simple process operation, low cost, convenient for mass production, and many other advantages; it is a commonly used method of the surface strengthening of nitriding steel and high speed steel. However, conventional nitriding treatment technology will lead to shallow nitriding layer, nitriding time getting too long and the surface will easily form a brittle continuous e phase contained nitriding layer after nitriding treatment. Trying to join the laser surface modification technology and nitriding surface modification technology together, on one hand, using the fine grains function of laser surface modification to form a high volume fraction of the interface to providing an ideal channel for the spread of nitrogen element; On the other hand, due to the high heating and cooling speed of laser surface modification, it will lead to microscopic defect such as large dislocations, twin crystals and spaces formed in the hardening layer, speed up the spread of dynamical process significantly, make the value of nitrogen compounds potential threshold reduce, thus increasing nitriding efficiency, and improve the distribution of the nitriding uniformly.The laser hardening and nitriding composite surface modification technology was used to treat the W9Mo3Cr4V high speed steel and38CrMoAl steel in this paper. X-ray diffraction, scanning electron microscope, electron probe micro-analyzer, Vickers hardness tester and friction wear testing machine were respectively used to study the changing rules of the microstructure, composition and properties of the composite treatment layer along with change of the technological parameter, at the same time laser hardening and nitriding experiment are carried to make contrast and analysis.It is shown that the composite modification layer of W9Mo3Cr4V high speed steel is mainly composed of tempered martensite, retained austenite, Fe3N, O7C3and M2C type carbide. Along with the increase of the laser scanning velocity, tempered martensite, Fe3N and the number of CT7C3increases gradually, and the number of retained austenite gradually reduced. At the same time, because of grain refinement and microscopic defect density gradually increased the depth of nitriding layer increases, the distribution of nitrogen compounds get uniformly. It is the changes above that lead to the hardness of the hardening layer, friction resistance and wear resistance increase with the scanning velocity keep increasing, and compared with simple laser hardening and nitriding technology composite modification process can effectively improve the hardness and wear resistance of high speed steel. Because of the differences in composition between W9Mo3Cr4V high speed steel and38CrMoAl steel, the composite modification layer of38CrMoAI steel is mainly composed of4N, Fe3N, a-Fe, O23C6, Cr2N and AlN. When the laser scanning velocity and laser power increase respectively, the number of Fe3N phase in the composite modification layer gradually reduced, and the number of Fe4N phase increase gradually, the whole depth of the nitriding layer increases. Affected by the grains refinement and the growing number of nitriding compounds, the hardness of the composite modification layer increases with the laser scanning velocity and laser power increasing respectively, while friction resistance and wear resistance firstly increase then decrease with the laser scanning velocity and laser power keeping increasing respectively.