Research On Heat Treatment And Tribological Properties Of Bainitic Crossing

With the rapid development of the railway industry,new requirements have been put forward for railway wheel and rail materials.Under the high-speed and heavy-load development of the railway,the large-axis-loaded,high-density and large-capacity transport conditions constitute extremely harsh operating conditions for the turnout equipment.For this reason,steel used for crossing must develop toward high hardness,high toughness,and high wear resistance.However,at present,the domestic steel used for crossing is mainly based on high-manganese steel.Due to the influence of factors such as impact toughness and wear resistance instability,compared with the developed countries in Europe and the United States,bainite steel crossing has a smaller application range in China.How to improve the impact toughness and frictional wear performance of the bainite steel crossing has become a problem to be solved by railway material workers.To study the heat treatment process and friction-wear properties of the bainite steel crossing,this paper aims to find a suitable technical route and method to improve the impact toughness and friction-wear performance of bainite steel crossing.JMat Pro was used to analyze the phase diagram,hardenability curves,TTT curves and CCT curves of the bainite steel crossing,and a suitable range of process parameters for heat treatment process was obtained.Aiming at the hardness and impact toughness problems of the bainite steel crossing,the dehydrogenation process and the tempering heat treatment process were studied.The relationship between impact toughness,hardness and microstructure and heat treatment process parameters was obtained.The friction-wear properties of bainite steel crossingand wheel steel were studied,and the related frictional wear mechanism was studied.The research shows that the smelting of 30MnSiCrMoNi steel is treated by refining and degassing,and the forging process is good.Its metallographic structures are mainly bainite and 10%～20%tempered martensite.After forging,heat treatment and dehydrogenation process can reduce the hydrogen content in 30Mn Si Cr Mo Ni steel and improve its impact toughness.When the normalizing temperature is 930°C and the tempering temperature is 350°C,the 30Mn Si Cr Mo Ni steel has the best matching of hardness and toughness.In the test of friction-wear,the friction pair composed of bainite steel has a friction coefficient smaller than that of the pearlite friction pair.Therefore,the amount of wear is relatively small.The experiments show that the number of cycles,contact stress and the matrix of friction pairs will affect the wear mechanism,the main wear in dry friction is mainly adhesive wear,oxidation wear and abrasive wear.The wear of the lower specimen of the pearlite structure is mainly the adhesive wear,and the wear of the lower specimen of the pearlite-pearlite friction pair is significantly larger than that of the bainite-pearlite friction pair.Moreover,as the number of cycles and the contact stress increase,oxide adhesion may occur,which results in the wear of the lower specimen of the bainite-pearlitefriction pair is negative and the wear of the lower specimen in bainite structure is mainly oxidized wear under the conditions that the contact stress is 75 kgf and the number of cycles is 2×10~4.