Railway development is closely related to people’s life and national development. With the sixth speed increase of railway, railway freight cars are facing the full implementation of speed increase, heavy load and mixed operation of passengers and freight. The speed of railway freight cars has been increased from 70-80km / h to 120km / h, the train formation has been increased from 3500-3700t to 5000-5500t, and 10000-20000 t trains have been operated on some special lines. The above data have no precedent even in the railways of developed countries. Therefore, it can be said that China’s high-speed railway technology is gradually moving towards the cutting-edge ranks of the world.
The new situation of “high speed and heavy load” will inevitably put forward higher quality requirements for steel castings of railway freight cars, and the important steel castings of railway freight cars are basically produced by casting, so it is necessary to make a new leap in casting quality. The working conditions of the running part and bearing part of railway freight cars are very bad, and they are often subjected to complex stress effects such as impact, bending, shear and tension. Once they are broken due to defects, they will be destroyed and killed, resulting in huge economic losses. Therefore, there are high requirements for their casting quality. The main steel castings of railway freight cars include: coupler and its buffer device, bolster, side frame, etc. This paper mainly studies the steel castings of coupler body and coupler tongue.
Coupler steel castings are mainly used to realize the coupling between locomotives and vehicles or between vehicles, and transmit traction force and impact force. In the process of train operation, the coupler steel castings not only bear the random and alternating traction, compression and impact, but also bear the bending moment. Therefore, the service conditions are very bad, and the ultimate faults such as crack, deformation, wear and poor three state action are easy to occur. The figure shows the actual service condition of coupler steel castings.
Compared with cast iron, cast steel has poor casting performance, low fluidity, easy to form cold barrier and oxidation, large gettering, easy to form inclusions and pores, large volume shrinkage and linear shrinkage, easy to form shrinkage cavity, shrinkage porosity, hot crack and cold crack, high melting point and easy to stick to sand. Therefore, the production process of railway steel castings must be scientifically selected and strictly controlled.