Metallurgical Microstructure and Properties of High Speed Steel Cementaion Layer Prepared by W-Mo Plasma Surface Co-cementation Using Pulse Single Power Source

Q195 steel was treated by plasma W and Mo co-cementation process using pulse single power source and followed by carburizing, quenching and tempering, then surface high speed steel layer was formed. The microstructure and properties of the surface were studied by optical microscopy, SEM, XRD, microhardness instrument and wear testing machine. The results show that a obvious co-cementation layer was formed on surface of the steel by pulse single power source. The thickness of the layer prepared at 1 000 ℃ for 8 h was 110 μm. The contents of W and Mo were 8.4% and 9.8%, respectively, and the surface tungsten equivalent was over 20%. The main phases of the layers were intermetallic compounds Fe7W6 and Fe3Mo. After carburizing and quenching, the forms of carbides were primary MC, M2C and M6C. The carbides were fine and distributed evenly. The wear resistance of the steel after tempered at 200 ℃ was improved by 1.7 times compared to that of the T10 steel after water quenched at 750 ℃ and tempered at 200 ℃. The anti-temper ability of the compound treated steel was similar to that of the high speed steel W6Mo5Cr4V2, whose hardness was 610 HV after tempered at 700 ℃.