高速重载机车用50crva弹簧钢淬火等温工艺探索-probe into isothermal quenching process of 50crva spring steel for high-speed and heavy-duty locomotives.docx

Investigation on quenching-isothermal 50CrVA spring steel for high speed and heavy load locomotiveAbstractThe spring of high speed and heavy load on locomotive is one of the key components of train. At present, its traditional heat treatment is quenching and tempering after austenite by inducing, which obtains the /search/en/troostitetroostite. Unfortunately, the toughness and fatigue is poor in use, which obliges to improve the property.A new train of thought was given by a new heat treatment advanced by J.G.Speer in 2003, namely quenching and partitioning, using remained austenite to improve the toughness.This research topic combined with the national science support plan to explore the quenching and isothermal process by using the 50CrVA spring steel. Quenching under the Ms in lower temperature salt bath and then put it in salt bath isothermal immediately at nearby Ms based on the TTT curve of 50CrVA. The best process was determined by adjusting the temperature and time of isothermal, measuring the hardness, observing the microstructure and surface of fracture and SEM analyze. The outstanding mechanical properties of experimental steel obtained by new process:1). The breaking strength arrives at 1760MPa and the yield strength arrives at 1510MPa;2). The reduction of area and elongation arrives at 49% and 15% independently;3). The shape impact arrives at 32.5J and K1c arrives at 44 MN·m-3/2;4). The tension-compression fatigue strength arrives at 675MPa under R=-1;The results indicates that the obtained microstructure of 50CrVA steel after quenching and isothermal is matensite, austenite and film retained austenite after treating. The matensite with lower dislocation density obtained during quenching. The low bainite was fined by matensite divide original austenite grains. The second matensite was delimited by adopting low temperature tempering which secures the remained austenite for the contribution on toughness and ductile.Analyzing indicated the quenching and i