Study on W-Mo-Y multi-elements alloying and plasma nitriding on Q235 steel

Using plasma alloying technique, Q235 steel was firstly treated by W-Mo-Y Multi-elements alloying followed by plasma nitriding process. The effects of process parameters on alloying layer were studied. The structure, composition, phase and micro-hardness of alloying layer were analyzed by metalloscope, XRD, SEM and microhardness tester. Results show that the microstructure of W-Mo-Y alloying layer is columnar crystal, and W, Mo contents decrease from the outside to the inside. The element Y is distributed mainly at the grain boundaries. The phase of alloying layer consisted of Fe, Fe3Mo, Fe17Y2 and the solid solution of (W, Mo, Y) in alpha-Fe. After plasma nitriding process, the co-diffusion layer is strengthened and large amounts of nitrides form and dispersedly distribute in the alloying layer. The phase of alloying layer consist of Fe4N, Fe3Mo, Fe, MoN, Mo2N, W2N, WN. The average micro-hardness of alloying layer is 850HV(0.05). And then the wear tests were conducted. Compared with untreated samples, the wear resistance of alloying layer is improved by 2 times under abrasive wear conditions.