Plasma nitriding is a common thermochemical surface treatment for porous PM steels to increase the hardness, the wear resistance, and the fatigue strength at the knee point. That thermochemical surface treatment is of interest for thin-walled PM structures which are sensitive against warpage. The local formation of the compound layer on the surface prevents an embrittlement of the metallic matrix. Therefore, the effect of the density is much smaller than during the classical gas nitriding in ammonia. Chromium-rich PM steels are good candidates for a successful plasma nitriding surface treatment due to their content of nitride-forming elements. For that study sinter-hardened and tempered AS 4300 + 0.6 % C was plasma nitrided to improve the bending fatigue strength at the knee point. Obtained bending fatigue experiments on notched bending bars with different densities have shown a strong improvement. The derived values are discussed and compared with recommendations from the FKM-guideline.
Fatigue of PM Steels