Vacuum carburization of 12Cr2Ni4A low carbon alloy steel with lanthanum and cerium ion implantation

As bearing parts, 12Cr2Ni4A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12Cr2Ni4A. However, the traditional carburizing is limited by poor microstructure distribution and low rate of carburizing. The rare earth ion implantation is known to help improving the properties of tribology, corrosion resistance and oxidation resistance of metal. In this article, the RE implantation is employed to assist the carburizing. Lanthanum and cerium ion implantations are initially used to assist 12Cr2Ni4A low pressure vacuum carburization. The microstructure, content of retained austenite, hardness, thickness of layer and carbon diffusion were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Rockwell/Vickers hardness tester, respectively. It was shown that lanthanum and cerium implantations can improve structure of the vacuum carburizing layer, and enhance the uniformity of carbon element distribution on the carburized surface. Meanwhile the RE implantation plays a positive role in promoting the surface hardness and carburized rate. The lanthanum element has more significant effect on surface hardness and content of retained austenite than cerium element. The surface hardness of lanthanum element implanted layer was 62.9 HRC with 9.6% content of retained austenite, while the carburizing rate of cerium implanted layer increased by 12.4%.