Effect Of Quenching And Tempering Heat Treatment And Phosphorus Content On Mechanical Properties At Room Temperature And Service Safety At Low Temperature Of EA4T Axle Steel

As an important transmission component,the high-speed motor axle requires its material to have good toughness and fit,and has certain ability to withstand impact loads.Its performance is crucial for the driving safety of high-speed motor trains.The European standard EA4T steel is important for high-speed motor axles.Steel grade is a high-speed train axle steel designed with the characteristics of quenching and tempering and alloying.China's north-south span is extremely large,which makes the temperature difference during the driving process very large.When the southern part of the train travels to northern China,the temperature tends to drop below 0?.The high-speed moving axle is an important transmission component in the moving car.The overall force of the moving car is very complicated.In addition to the low temperature environment in the cold region,the axle needs to be guaranteed in addition to the high-strength and high-toughness performance in normal operation.Mechanical properties at low temperatures.At the same time,with the further development of China's railways,and with the implementation of the National Strategy of the Belt and Road,China's high-speed rail has begun to go abroad and push the world.Among the countries along the Belt and Road,there are many high-latitude alpine regions such as Russia.This puts great demands on the low-temperature service safety performance of high-speed axles.In this paper,the effects of different quenching and tempering heat treatment processes on the microstructure and mechanical properties of EA4T steel were investigated.The thermodynamic simulation shows that the composition of the precipitated phase changes in the EA4T steel during high temperature tempering.In the high temperature range,the carbide precipitation phase of EA4T steel is mainly M₇C₃,M₂₃C₆ and cementite.The content of M₇C₃in EA4T steel decreases gradually around 580?.while the content of M₂₃C₆ increased and cementite began to appear,and finally M₇C₃ completely disappeared at 667?.The effect of quenching and tempering process on the microstructure of EA4T steel was investigated.As the quenching temperature increases,the original austenite grains of the EA4T steel gradually grow.After the quenching and tempering heat treatment,the microstructure of the EA4T steel is tempered sorbite,and through a reasonable heat treatment process,the microstructure is obtained by laminating the ferrite with the nano-precipitate dispersed around the ferrite.Ideally tempered Soxite structure.With the increase of tempering temperature,the tensile strength of EA4T steel decreases gradually,and the toughness gradually increases.The tempering temperature has good comprehensive mechanical properties at 550-600?,and the tempering temperature should be no less than 1h.The nucleation and growth of the precipitated phase in the tempering heat treatment and the decomposition of martensite to ferrite are the main reasons for the change of mechanical properties of the material after high temperature tempering.By adding the phosphorus content,it was found that temper embrittlement occurred when EA4T steel was tempered near 550?.The quenching and tempering heat treatment process of 850? water quenching+600? tempering was finally determined.The temper embrittlement was eliminated,and the EA4T axle steel structure with excellent tensile mechanical strength and low temperature toughness was obtained with a tensile strength of 985MPa,a normal temperature impact absorption of 109J,and an impact absorption of 42J at -20?.