Research On Metro Transmission Case Material And Manufacturing Process For Ultra-low Temperature Environment

In recent years,rail transportation equipment has been greatly developed in China,including high-cold regions such as Harbin and Urumqi.Lots of research about rail transportation equipment applied in the environment of-20? and-40? has been carried out,however,there are few studies on rail transportation equipment used for lower temperatures.Therefore,it is especially important to study and develop the rail transportation equipment(the subway transmission box)used in extremely cold environment(-60?),especially for the high-cold regions.The content of this thesis is divided into three parts,including theoretical analysis,process determination and optimization,trial production of subway transmission boxes.To obtain a better casting process by the combination of theoretical analysis and experiments,and then trial-produce the subway transmission box suitable for extreme cold environment(-60?).In the first part,the theoretical analysis is conducted to determine the approximate range of chemical composition,the selection and ratio of raw and auxiliary materials,the optimization of smelting and pre-treatment process,the heat treatment process etc.,which provides theoretical basis for the following experiments.In the second part,experimental study is carried out based on the results obtained in the first part.The spheroidal graphite cast iron containing 0.8% Ni or not is heat treated,the microstructure and mechanical properties of the sample were tested and the fracture morphology is analyzed.The results show that better performance of spheroidal graphite cast iron can be obtained when 0.8% Ni is added and the annealing rate is 70?/h.In the third part,the subway transmission box is trial-produced by selecting suitable chemical composition and heat treatment process based on the experimental results of the second part.The microstructure properties,mechanical properties and the quality properties of the trial-produced subway transmission box are tested,it is found that the qualified rate of the product is over 86%.In this thesis,the heat treatment process of the subway transmission box material for ultra-low temperature environment is studied.The heat treatment process that ductileiron with 0.8% Ni and annealing rate of 70?/h is determined,and the subway transmission box for the extremely cold environment(-60?)is successfully produced,which has great significance for the development of rail transportation such as high-speed rail and subway in high-cold regions.