The railway transport is one of the main types of communications in the world. Analysis of service conditions of the most critical elements of the railway transport rolling stock （mils, wheels and tyres） shows that ...The railway transport is one of the main types of communications in the world. Analysis of service conditions of the most critical elements of the railway transport rolling stock （mils, wheels and tyres） shows that one of the main factors determining their reliability and service life is the structural-phase state of steel, which is formed in the process of its producing. Complication of service conditions leads to the more severe requirements, specified by the consumers, where the high level of strength and hardness should be combined with high values of ductility and toughness. Realization of these requirements is possible only at the integrated approach to the improvement of technology of their production on the basis of profound knowledge in kinetics of austenite decay processes of structure formation and its contribution to the mechanical properties. With the formation of mainly bainite-martensite structures in the HAZ （heat-affected zone） metal of welded joints of these steels and saturation of this region with diffusive hydrogen their susceptibility to the cold cracking is increased. In this connection this work presents the results of investigations of effect of the WTC （welding thermal cycles） on the nature of structural transformations, hardness, static strength and resistance to the formation of cold cracks in HAZ metal of high-strength carbon rail steel M76. For this purpose, the structure and kinetics of transformation of an overcooled austenite was studied using the advanced methods of physical materials science by the modeling of phase transformations in the Gleeble 3800 unit. It was found that the cause of reduction in mechanical properties of welded joints of steel M76 is the formation of regions with a completely martensite structure in the amount of up to 5%. Results of investigations will be applied for the optimizing the technology and conditions of FBW of the advanced rail steels. 10 Ref., 4 Tables, 11 Figures.展开更多
Microstructural analysis and fatigue crack propagation behavior of three types of rail steels, was performed. These are premium pearlitic, austenitic manganese （AM） and bainitic rail steels. Rectangular un-notched a...Microstructural analysis and fatigue crack propagation behavior of three types of rail steels, was performed. These are premium pearlitic, austenitic manganese （AM） and bainitic rail steels. Rectangular un-notched and notched test specimens were machined from railheads of each material using electrical discharge machining （EDM） and used for the mechanical properties and fatigue evaluation respectively. Bainitic steel has the highest yield strength, ultimate strength, and strain to failure as compared to both pearlitic and austenitic manganese steels. Fatigue studies showed that the crack speed for the bainitic steel is lower than that for the pearlitie and the AM steels over the entire range of the energy release rate. The bainitic steel exhibits a higher rate of crack deceleration in the second stage, as indicated by the lower slope of the fatigue crack propagation kinetics curve in comparison with the pearlitic and manganese rail steels. This attests to the superior fatigue damage tolerance of the bainitic rail steel in comparison to pearlitic and austenitic manganese rail steels. Microstructural analysis of the three rail steels revealed that bainitic steel has a more intricate structure than AM and pearlitic steels. AM steel shows very few signs of being work hardened or toughened, which usually increases the mechanical properties of the material. As the number of alloying elements increase, the microstructure of the steel becomes more complex, resulting in the increase of mechanical properties and fatigue fracture resistance of bainitic rail steel.展开更多
The contributions of different strengthening mechanisms to yield strength of bainite/martensite multiphase rail steel with different finish cooling temperatures in the controlled cooling process were quantitatively in...The contributions of different strengthening mechanisms to yield strength of bainite/martensite multiphase rail steel with different finish cooling temperatures in the controlled cooling process were quantitatively investigated.Dislocation density and substructure size of the rail steel were measured by scanning electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the dislocation density increases with the decrease in block width in rail steel.Based on the correlation among dislocation density,block width and yield strength,a physical model was proposed to predict the yield strength of rail steel.The variation of block width and dislocation density in different positions of rail head microstructure was integrated with temperature field simulation.Dislocation density and block width reveal significant correlations with the finish cooling temperature.展开更多
文摘The railway transport is one of the main types of communications in the world. Analysis of service conditions of the most critical elements of the railway transport rolling stock （mils, wheels and tyres） shows that one of the main factors determining their reliability and service life is the structural-phase state of steel, which is formed in the process of its producing. Complication of service conditions leads to the more severe requirements, specified by the consumers, where the high level of strength and hardness should be combined with high values of ductility and toughness. Realization of these requirements is possible only at the integrated approach to the improvement of technology of their production on the basis of profound knowledge in kinetics of austenite decay processes of structure formation and its contribution to the mechanical properties. With the formation of mainly bainite-martensite structures in the HAZ （heat-affected zone） metal of welded joints of these steels and saturation of this region with diffusive hydrogen their susceptibility to the cold cracking is increased. In this connection this work presents the results of investigations of effect of the WTC （welding thermal cycles） on the nature of structural transformations, hardness, static strength and resistance to the formation of cold cracks in HAZ metal of high-strength carbon rail steel M76. For this purpose, the structure and kinetics of transformation of an overcooled austenite was studied using the advanced methods of physical materials science by the modeling of phase transformations in the Gleeble 3800 unit. It was found that the cause of reduction in mechanical properties of welded joints of steel M76 is the formation of regions with a completely martensite structure in the amount of up to 5%. Results of investigations will be applied for the optimizing the technology and conditions of FBW of the advanced rail steels. 10 Ref., 4 Tables, 11 Figures.
文摘Microstructural analysis and fatigue crack propagation behavior of three types of rail steels, was performed. These are premium pearlitic, austenitic manganese （AM） and bainitic rail steels. Rectangular un-notched and notched test specimens were machined from railheads of each material using electrical discharge machining （EDM） and used for the mechanical properties and fatigue evaluation respectively. Bainitic steel has the highest yield strength, ultimate strength, and strain to failure as compared to both pearlitic and austenitic manganese steels. Fatigue studies showed that the crack speed for the bainitic steel is lower than that for the pearlitie and the AM steels over the entire range of the energy release rate. The bainitic steel exhibits a higher rate of crack deceleration in the second stage, as indicated by the lower slope of the fatigue crack propagation kinetics curve in comparison with the pearlitic and manganese rail steels. This attests to the superior fatigue damage tolerance of the bainitic rail steel in comparison to pearlitic and austenitic manganese rail steels. Microstructural analysis of the three rail steels revealed that bainitic steel has a more intricate structure than AM and pearlitic steels. AM steel shows very few signs of being work hardened or toughened, which usually increases the mechanical properties of the material. As the number of alloying elements increase, the microstructure of the steel becomes more complex, resulting in the increase of mechanical properties and fatigue fracture resistance of bainitic rail steel.
基金The research is supported by the National Key Research and Development Program of China(2017YFB0304504)Fund of Key Laboratory of Advanced Materials of Ministry of Education(No.XJCL201908)National Key Basic Research Program of China(2015CB654804).
文摘The contributions of different strengthening mechanisms to yield strength of bainite/martensite multiphase rail steel with different finish cooling temperatures in the controlled cooling process were quantitatively investigated.Dislocation density and substructure size of the rail steel were measured by scanning electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the dislocation density increases with the decrease in block width in rail steel.Based on the correlation among dislocation density,block width and yield strength,a physical model was proposed to predict the yield strength of rail steel.The variation of block width and dislocation density in different positions of rail head microstructure was integrated with temperature field simulation.Dislocation density and block width reveal significant correlations with the finish cooling temperature.
