Heat Treatment Process Research Of 18CrNi8 Nozzle

On the basis of investigation of the nozzle's working principle and its functions, the technology of heat treatment for the nozzle was studied in this paper according to the technical requirements, the characteristic of its shape and at the same time in this study we take the reference of other experiences and make full use of the newest technology of heat treatment.In order to fulfill the technical requirements and use the present machine and technology we now have, we made a deep study of the carburizing ,quenching ,deep freezing and tempering process for the nozzles.It is really a big problem for the carburizing because the length and diameter ratio is very big , further more the diameter of the ball is very small and also with several smaller holes in it. So we took 4 schemes, namely: (1)gas carburizing (2)carbon-nitrogen carburizing (3)outside gas carburizing and inside solid carburizing (4)low pressure vacuum carburizing. After comparing the results we found that the gas carburizing and carbon-nitrogen carburizing can't fulfill the requirement of case depth. The process of outside gas carburizing and inside solid carburizing can meet the requirement, but the process is too complicated and the working condition is too bad. The last scheme of low pressure vacuum carburizing can meet all the above requirement, so low pressure vacuum carburizing is the best process ,detailed parameters are : carburizing temperature is 930℃,convention heating.C2H2 inletted with pulse, its flow rate is 1500～4500l/h,both carburizing and diffusion have 5 stage, total time for carburizing is 14Min and for diffusion is 69Min.We also took 3 schemes for the process of quench for comparison, namely (1)oil quenching in multi-function furnace, (2)oil quenching in vacuum furnace (3) high pressure N2 quenching in vacuum furnace. At last we found that the high pressure N2 quenching in vacuum is the best through testing the hardness, distortion and microstructure, especially distortion is the lowest. Detailed parameters are: temperature is 840℃,holding time is 70min, cooling medium is 10bar N2.After finishing testing the two main processes, we also made several experiments on the deep freezing and tempering process. Finally we got the whole heat treatment processes for the nozzles. The heat treatment quality of nozzles was checked by the reliability experiment and also confirmed by the customers .The thesis has finished all the experiments and got the best process for nozzles'heat treatment, the process not only took the newest technology but also greatly increased the quality of nozzles.