(1) influence the shape of section symmetry: after nitriding after inspection found, with key aspects of convex surface, due to the stress value is higher than that of no keyway position high, stress imbalance, resulting in distortion. Part section asymmetry, nitriding parts surface caused by the uneven distribution of stress is the main cause of nitriding distortion.
(2) before nitriding to eliminate the influence of stress treatment: eliminate the stress treatment, the size relation of parts after nitriding distortion of great. Because the parts have great processing in the mechanical machining stress, particularly in the keyway is most prominent.
(3) effect of nitriding furnace of hanging and placement: slender shaft parts if the vertical free suspension state, it is in the direction of gravity through the part itself center, is not also produce the additional stress.
(4) effect of nitriding process on distortion: nitriding temperature range of commonly used is 510~560 ℃, the nitriding temperature is low, heat preservation time should be extended to 60~72h. While improving the nitriding temperature, but the heat preservation time while compression, but the hardness is decreased, and the distortion increases. In the process under the guidance of a correct, furnace temperature uniformity should be less than ± 5 ℃. If the furnace temperature is not uniform, will lead to uneven decomposition rate of ammonia, resulting in various points within the furnace carburizing depth is not uniform, but can be formed in parts of additional thermal stress, because parts of the layer is not uniform, but also increases the unbalanced stress, this must increase the aberration after nitriding, the final grinding processing difficulties.