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Studied this subject for the diesel engine plant camshaft, camshaft material is 20Cr. The camshaft production process, often due to the heat treatment carburizing and grinding on two processes should be controlled due to improper quality problems arising in the study of the design process and should be avoided, and early prevention.Requirements of the carburized layer was fine granular carbides evenly distributed, to improve the wear resistance of the diffusion layer is extremely beneficial, but the high concentration of carbon, carbides form a mesh, the diffusion layer will greatly decrease the mechanical properties. After the formation of carbide, the surface of the carburized layer is increased brittleness, toughness is reduced, reducing the service life of parts, the quenching and grinding, it is easy to form a network shape carbide distribution along the crack. Therefore, in the design process, we should be properly controlled carbon potential, to ensure the emergence of network carbide. Camshaft carburizing technical requirements is: (1) depth of the carburization layer: 1.4~1.9mm, (2) carbides reticular <five level.
In the selection of materials, the choice is 20Cr. 20Cr steel production in China is currently the largest one of several alloy structural steel, extensively used.
This design of content have: parameters of heat treatment process, which includes carburization temperature, holding time, carburization medium, carburization atmosphere and computer control, quality testing of the carburization and carburization equipment. Currently camshaft carburization generally carried out in the pit furnace, gas carburization process control is generally performed by the computer, technical personnel should pre-set the carbon potential, temperature and carburization depth. Then the microcomputer program will control the drop volume of kerosene and the holding time. Selection of furnace size of the workpiece should be considered to ensure that the furnace depth is greater than length of the part.
Through article’s designment. Finally, according to the impact of the infiltration depth and the level of the temperature, the selection of the carburization temperature is 930℃, according to carburization layer depth and carburization time,the selection of the insulation time is 6h. According to the advantages and disadvantages gas, solid and liquid carburization and the shape of parts, the choice is gas carburization, and use the drip gas carburization. Comparing all carburization media finally choose methanol and kerosene. In strong infiltration stage, the carbon potential is 1.15% C, the time is 2h; In diffusion the time is 3.5h, the carbon potential is 0.83%C. After carburization, we put the workpiece in the furnace and take out after slow cooling to 500 ℃.
Keywords: 20Cr；Camshaft；Carburization；The process design of heat treatment
目 录
1 绪论 1
1.1 凸轮轴简介 1
1.1.1 凸轮轴的概念 1
1.1.2 凸轮轴的构造 1
1.1.3 凸轮轴的功能 2
1.1.4 凸轮轴的性能要求 3
1.1.5 凸轮轴选材及其热处理工艺 3
1.2 20Cr钢 4
1.2.1 20Cr钢的成分 4
1.2.2 20Cr钢的特征 5
1.3 渗碳热处理 5
1.3.1 固体渗碳法 6
1.3.2 液体渗碳法 8
1.3.3 气体渗碳法 8
1.3.4 表面碳含量 9
1.3.5 渗碳层深度 10
1.3.6 碳化物网状 10
1.4 毕业设计的内容及意义 11
1.4.1 课题的任务内容 12
1.4.2 课题的研究意义 12
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