| The frog is a kind of plane crossing equipment which makes the train to change lines.Because of its special location in the railway structure,it is often the most vulnerable to damage.With the progress of the times,the load and speed of the train are also constantly improved,and the alternating stress and contact stress of the frog in the course of service are also increasing,while the traditional high manganese steel frog is easy to produce fatigue cracks,peeling off blocks and other damages.the safety of the train is not guaranteed,and the cost of maintenance is getting higher and higher,and the average service life is about 70 million ~ 80 million t.The traditional high manganese steel frog has been unable to meet the requirements of China’s railway development;In order to obtain the frog with higher performance and avoid the failure caused by the above reasons,a new generation of bainite steel frogs has been developed at home and abroad.Many research results show that when the bainite structure is in a certain form,it can obtain excellent combination of strength and toughness,and its wear resistance and contact fatigue resistance are much higher than those of pearlite under the same conditions.Therefore,the new generation of bainite steel frog is currently the main research hotspot,and many countries at home and abroad have achieved good results.The experimental material of this paper is a new type of bainitic steel for heavy-load railway frog,which is researched and designed by Xihua University.Firstly,the effect of different heat treatment processes on the microstructure and properties of bainitic steel was studied,and the optimum process parameters were determined.The results show that carbon-free bainite can be obtained in both forging state and normalized under air cooling condition.The TEM results show that there is a thin-film retained austenite between the adjacent bainitic ferrite lath.Compared with the forged sample,the comprehensive mechanical properties of the material after normalizing are better: the sample after normalizing + tempering at 300 ℃ has the best comprehensive mechanical properties,the tensile strength is as high as 1380 MPa,the yield strength is 1253 MPa,the elongation and reduction of area were 20% and 52% respectively,the room temperature impact strength is as high as 63.33 J,and the strength and toughness combination is obviously higher than that of ordinary and quenched pearlitic rail steel,The results of low temperature impact test show that the material meets the requirements of application in low temperature environment.The material has strong anti-tempering stability,and obvious recrystallization occurs only around 600 ℃.In addition,in the process of observing the microstructure,it is found that there are a small amount of inclusions in the matrix,and the energy spectrum analysis shows that the inclusions mainly exist in the form of(Mn,Fe)S.Secondly,the normal temperature compression test is carried out in this paper,and the rule of deformation and hardening is obtained according to the changes of microstructure and hardness.The results show that when the bainitic steel is subjected to enough applied stress,obvious plastic deformation will occur,and the strength and hardness of the material will increase with the increase of deformation.Based on the analysis of the changing rules of stress-strain curve and work hardening rate curve,the process of work hardening of test steel can be divided into three sections.The first interval is the part where the strain is less than 0.08.In this interval,the test steel undergoes an elastic deformation stage;the second interval is the part of strain between 0.08 and 0.34.In this interval,the mechanism of work hardening is mainly dislocation strengthening,and the stress-strain relationship is linear;the third interval is the part of strain > 0.34,in which the curve of work hardening rate is slightly higher than that of the second interval.Because the test steel is low-carbon steel and has excellent plasticity,as the deformation continues to increase,The work hardening effect is strengthened.Finally,This paper simulates the service environment of the coastal area and tests the corrosion resistance of the material.In order to avoid the damage caused by corrosion,it is very important for the material to have good salt resistance because some railway sections are in high salt zone.The research shows that: after being placed on the same concentration of dilute hydrochloric acid solution for a period of time,compared with the bainitic steel on the heavy-load railway forg made by my brother in the past,the steel used in this experiment has better salt resistance,and the addition of Cu element significantly improves the material’s corrosion resistance. |
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