Effect of rare earth on microstructure and properties of niobiumizing layer on GCr15 steel for pin shaft

Abstract

The powder pack cementation was used for niobiumizing treatment of GCr15 pin steel, and the effects of different rare earth types and contents on microstructure and properties of niobiumizing layer were investigated. Optical microscope, x-ray diffractometer, scanning electron microscope, electrochemical workstation and ball-disk friction wear machine were used to observe the structure and evaluate the properties of the niobiumizing layer. And the kinetics and mechanism of niobiumizing layer with rare earths was explored. The results show that a dense and continuous niobiumizing layer formed under different rare earth types and contents condition. The layer is 3 μm-15 μm in average thickness, 1800 HV0.2-2500 HV0.2 in average microhardness and is composed of NbCx compound and α-Fe. Comprehensive comparison, La2O3 can significantly improve the wear and corrosion resistance of the niobiumizing layer. The self-corrosion potential of niobiumizing layer is −0.5759 V, the corrosion current density is 5.2365 × 10−7 A cm−2, and the average friction coefficient is 0.385 when La2O3 is added at 2%.