Effect of super-rapid induction quenching on fatigue fracture behavior of spherical graphite cast iron FCD500

Recently, with the high performance and efficiency of machine, there have been required the multi-functions in various machine parts, such as the heat resistance, the abrasion resistance and the stress resistance as well as the strength. Rotary bending fatigue tests were carried out to investigate the fatigue characteristics of high performance ductile cast iron experienced by super-rapid induction treatment. The influence of super-rapid induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. By super-rapid induction treatment in FCD500, the circular martensite structure obtained differentially from conventional high frequency induction treatment was confirmed on the specimen surface. The fatigue crack initiation in the hardened surface layer was restricted by the circular martensite structure around the graphite nodule and compressive residual stress. Thus, it could be interpreted that the initiation stress would be increased by improved structure in the surface. The fatigue crack propagation in the hardened layer was retarded by the presence of the globular shape martensite around the graphite nodule and compressive residual stress and the crack propagation behavior has zigzag pattern in the hardened surface layer.