A Study On The Production Process And Performance Of Forged Train Hook And Tail Frame Steel

The train hook and tail frame is a key part of the train coupler buffer device,since it plays an important role in vehicle traction,connection and buffer.Also,the train hook and tail frame undertakes the transmission of the longitudinal force between the vehicles,so it needs to bear great tensile stress.Moreover,the railway wagons work in the open air environment all the year,and should bear the winter environment even at temperature of-20℃ to-40℃in China northern region.Therefore,the steel for train hook and tail frame should have features such as higher strength,higher resistance to fatigue,high resistance to low temperature.Compared with the traditional casting process,the hook and tail frame made by the forging process have the advantages of ideal microstructure,better toughness and higher fatigue strength.Thus,it become a trend to use forging technology to process hot rolled round steel into train hook and tail frame.Based on the Lai gang industrial practice and customer requirement,this thesis mainly concerns the production technology of hot rolled round steel 25MnCrNiMoA for the train hook and tail frame.The emphasis is laid on the study and analysis of production technology,especially chemical composition optimization design,cleanliness control during smelting and continuous casting,quality control of continuous casting billets,hot rolling process control and performance test of round steel.The commercial production of this steel is finally realized and the customer requirement is met.The contents and main conclusions are summarized as follows.(1)Base on the evaluation of the production technology in Laigang,φ500 mm continuous casting round billet can be produced by EAF smelting+LF refining+VD vacuum treatment+continuous casting process,and 25MnCrNiMoA train hook and tail frame steel of φ140 mm to φ160 mm specification can be feasibly manufactured by semi-continuous hot rolling process.The parameters such as Alkalinity of refining slag,superheat,drawing speed,electromagnetic stirring parameters,heating system,rolling temperature and finishing rolling temperature are reasonably formulated to meet the production requirements of this steel.(2)The 25MnCrNiMoA steel produced by this process is homogeneous in composition,clean in steel,finer in grain and excellent in hardenability,which satisfies the basic technical requirements for train hook and tail frame steel.(3)The impact Charpy test of this steel at various temperatures was carried out to determine the ductile-brittle transition temperature as-50℃ at quenched and tempered state.This can meet the requirement of domestic train hook tail frame steel for working at-20℃ to-40℃.(4)According to the processing technology proposed in this thesis,the train hook and tail frame steel can be produced in Laigang and meet the requirement.During 2014-2017,the total production and sales of this steel have been more than 30 thousand tons and the value of sales is nearly 150 million RMB Yuan,net profit is nearly 10 million RMB Yuan.There is a significant economic benefits and positive response from the customers.