The use of plasma nitriding skills in crankshaft production (1)

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The use of plasma nitriding skills in crankshaft production (1)

Source: China Bearing Network Time: 2014-03-06
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In order to improve the fatigue strength of the crankshaft; many factories have chosen the plasma nitriding skills; in the meantime, this skill is used as the representative of Shandong Crankshaft General Factory, Dalian Diesel Engine Factory, Chunfeng Group Xiangyang Diesel Engine Company, etc. Only Shandong Crankshaft General Factory has LD. -150A type plasma nitriding equipment more than 20 sets; and Xiangyang Diesel Engine Co., Ltd. is famous for its LDMC-150A type, the largest, most powerful, and most loaded large pulse power plasma nitriding equipment in China. In the above-mentioned manufacturer's crank ion nitriding process experiment, let's talk about our understanding; for experts and colleagues to see.
First, the theoretical scale of crankshaft ion soft nitriding process parameters in terms of crankshaft plasma nitriding skills; most manufacturers have selected ion soft nitriding skills; the formulation of process parameters should generally follow the following criteria:
1. Selective scale nitriding temperature plasma nitriding is a chemical thermal treatment method that uses nitrogen glow discharge to introduce nitrogen into the metal surface to form FeN. In the iron-nitrogen phase diagram; 580 °C is the allotropic transformation point; Below 580 ° C it is arranged as alpha iron; above 580 ° C its arrangement is converted to gamma iron. Usually; the progress of the treatment temperature contributes to the composition of the nitride and to obtain a deeper layer (at the same time); this is because The diffusion coefficient is proportional to the exponential change of temperature. However, because the diffusion coefficient of nitrogen in γ-iron is only 1/4 of that of α-iron; when the treatment temperature is higher than 580°C; the increase of the permeable layer is slowed down; thus; Ion nitriding operating temperature scale is 520 ° C to 580 ° C.
2. The selection of soft nitriding temperature is about carbon steel or cast iron or low alloy steel; we often use ion soft nitriding (low temperature carbon, nitrogen osmosis) skills. Many theories indicate: hardness and permeability of nitrided layer There is an extreme relationship between time and concentration. Usually the ratio of ammonia to acetone is 10:1; the temperature is between 560 ° C and 580 ° C; the time is between 3 and 4 hours; the best hardness and permeability are obtained. In the ternary phase diagram of nitrogen and carbon; the isomorphic transformation point is slightly reduced; its isothermal section is reduced to 575 ° C. When the temperature is higher than 575 ° C; the temperature rises; the permeability and hardness decrease rapidly; At 600 ° C; the layer is completely gone. In order to have better carbon and nitrogen osmosis; the operating temperature of ion nitrocarburizing is usually 540 ° C to 580 ° C.
3. The influence of other factors on the process parameters The above is the process temperature control scale based on the phase diagram; in fact, it is subject to other factors. 1 is to ensure the induction of the function of the part; usually before the ion nitriding needs to be advanced Heat treatment; the upper limit temperature of ion nitriding should not exceed the pre-heat treatment temperature, 2 depending on the degree of deformation of the part; select the appropriate heating rate and should be properly homogenized in the pre-heat treatment. In summary: ion soft nitriding The temperature control scale should be above 540 °C; below the aging temperature; and according to the specific needs of the parts; select the appropriate heating rate.
Second, the crankshaft ion nitriding process is currently; the typical materials used for domestic production of crankshafts are ductile iron and 42CrMoTi.
Similar to the disposal of other nitrided parts; the ion nitriding process of the crankshaft is usually carried out by blowing, squeezing, squeezing and blowing for 4 periods; including the furnace; roughly taking 18 hours. Different manufacturers are in the ion nitrogen The process is slightly different.
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