The effect of rapid cooling after ion-nitriding on fatigue behavior of low carbon steel(SM20C) was investigated under tension-tension loading for single edge notch specimens which were furnace cooled or water cooled after ion-nitriding. The initiation lives of the fatigue crack were measured and compared to each other for specimens that were non-nitrided, furnace cooled after nitriding, and water cooled after nitriding respectively.
It is found that in relatively low stress regime($ΔK/\surd\rho<70kg/mm^2$) the water cooled specimens were the largest, the furnace cooled specimens the second largest, the non-nitrided specimens the shortest in the fatigue crack initiation life. However, in high stress regime($ΔK/\surd\rho>70kg/mm^2$) the non-nitrided specimens show the longest initiation life and there appears no distinguishable difference in the initiation life between the water cooled and the furnace cooled specimens. The fatigue growth rate was larger for nitrided specimens (both the water cooled and funace cooled specimen) than for the non-nitrided specimens within the stress range used here.
