Effect of Mn Contents on Fatigue Properties of Plasma-Nitrided Fe-C-Mn Steels

Rotating bending fatigue tests were conducted for a series of plasma-nitrided Fe-C-Mn steels in order to investigate the effect of manganese contents. 5 types of steels were prepared, i.e., 0.0Mn, 0.5Mn, 1.0Mn, 2.0Mn and 4.0Mn. Microstructures of the steels were ferrite-pearlite except 4.0Mn whose microstructure was martensite. 2.0Mn and 4.0Mn of the nitrided specimens had a hardened layer of 0.5 to 1 mm in depth, while the no hardening was observed in 0.0Mn, 0.5Mn and 1.0Mn of the nitrided specimens. In case of 0.0Mn, 0.5Mn and 1.0Mn, the nitrided specimen showed surface fracture and increase of fatigue strength was very small. The 2.0Mn nitrided specimen showed surface fracture and fatigue strength were largely improved by plasma-nitriding. On the other hand, in case of 4.0Mn, the nitrided specimen showed internal fracture beneath the hardened layer and the fatigue strength were lower than that of the 2.0Mn nitrided specimen.