Plasma nitriding technology application in the crankshaft production ( A)

In order to improve the crankshaft fatigue strength, many factories used plasma nitriding technology, which USES the technology to shandong crankshaft factory, dalian diesel engine factory, dongfeng chaoyang diesel engine company as the typical representative. Shandong crankshaft factory alone with LD - 150 - a type of plasma nitriding equipment more than 20 units, chaoyang diesel engine company adopted LDMC - 150 type a domestic most advanced, most powerful, furnace charging quantity of the most famous large pulse power plasma nitriding equipment. Only according to the below in the manufacturer of the crankshaft ion nitriding process test about our experience, the experts and our colleagues for reference. A soft, crankshaft ion nitriding process parameters theory scope in terms of crankshaft plasma nitriding technology, most manufacturers adopt ion of soft nitriding technology, its process parameters generally should be formulated in accordance with the following principles: 1. Nitriding temperature scope of the choice of plasma nitriding is the method of using vacuum glow discharge the nitrogen into the metal surface to form a chemical heat treatment method of FeN. In iron nitrogen phase diagram, 580 ℃ with different crystal transition point, below 580 ℃ its organization is alpha iron, higher than 580 ℃ the organization into a gamma iron. Usually, improve processing temperature contribute to the formation of nitride and have deep carbonitriding layer ( At the same time) Because of the diffusion coefficient is proportional to the temperature index. However, due to the diffusion coefficient of nitrogen in the gamma iron is only 1/4 of alpha iron, when processing temperature higher than 580 ℃, carbonitriding layer growth slows down instead, therefore, ion nitriding control temperature range of 520 ℃ to 580 ℃. 2. Soft nitriding temperature range of options for carbon steel or low alloy steel or cast iron, people often adopt ion of soft nitriding ( Low temperature carbon and nitrogen altogether permeability) Technology. Is a lot of practice show that the hardness of nitrided layer and layer permeability extremum relation with temperature, time and concentration. Usually in the ratio of ammonia to acetone as now, in a temperature of 560 ℃ to 580 ℃, the time between 3 to 4 hours, and get the best of hardness and permeability layer. In the iron carbon nitrogen ternary phase diagram, with different crystal transition point slightly lower, the isothermal section fell to about 575 ℃. When the temperature higher than 575 ℃, with the increase of temperature, permeability and hardness drops rapidly, higher than 600 ℃, carbonitriding layer almost entirely disappeared. In order to have better effect of carbon and nitrogen altogether permeability, soft ion nitriding control temperature of 540 ℃ to 580 ℃. 3. The influence of other factors on the technological parameters above is according to the phase diagram of process temperature control range, in fact, it is limited by other factors. (1) in order to ensure the comprehensive requirements, the performance of the parts before ion nitriding generally need to carry on the preliminary heat treatment, ion nitriding should not exceed the upper limit of temperature heat treatment temperature in advance; (2) according to the parts easy to deformation degree, select the appropriate speed and should be in advance make organization fully homogenization heat treatment. To sum up: ion of soft nitriding temperature control range should be above 540 ℃, under the aging temperature, and according to the specific requirements of the parts, choose the appropriate heating speed. Second, the crankshaft ion nitriding process at present, the domestic production of typical materials for nodular cast iron crankshaft and 42 crmoti. And processing is similar to other nitriding parts, crankshaft of ion nitriding process generally go through arc, heating, insulation, cooling and other four stages, including the furnace charging, roughly 18 hours. Different manufacturers on the ion nitriding process is slightly different.