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

As bearing parts, 12 Cr2 Ni4 A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12 Cr2 Ni4 A. 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 12 Cr2 Ni4 A 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%.

Computer Modeling and Validations of Steel Gear Heat Treatment Processes Using Commercial Software DANTE

The heat treatment process of a gear made of AISI 9310 carburized steel is modeled using the commercial heat treatment simulation software DANTE.Both carburization and quenching processes affect the residual stress distribution and distortion of heat-treated parts,which are important to service quality and fatigue life.DANTE/VCARB is used to design the boost/diffuse schedule of a vacuum carburization process.Oil quenching is modeled following the vacuum carburization process.Thermal gradient and phase transformation are two main sources of distortion and residual stresses in quenched parts.The relation of the carbon distribution,thermal gradient,and phase transformations during quenching is studied through the gear modeling example.Because of geometry,the residual stress distribution after quenching is non-uniform along the gear surface.In general,the root fillet has higher residual compression than either the root or tooth face locations after traditional oil quenching of carburized gears.The predicted residual stresses from the oil quenching model are imported into a single tooth fatigue bending model.The gear stresses under bending load indicate the possible cracking locations during the bending fatigue test.The importance of heat treatment residual stresses during gear design is pointed out,and it is commonly ignored in the gear design and manufacturing industry.