| The mileage of railway operation in China has exceeded 130,000 kilometers,and the total number of rails changed and replaced every year is about 6,000 kilometers.In order to improve the service life of the rail,a company in China has developed a Mn-Si 1380 MPa grade carbide-free bainitic rail.In order to promote the laying of such bainitic rails on the seamless line,the welding and welding processes were studied.Fixed flash welding is the main method of rail welding in China,accounting for about 80% of the number of rail joints in China’s railway seamless lines.Therefore,this paper uses the fixed flash welding method to study the process weldability and metallurgy of this kind of bainitic rail.Weldability and weldability.In the aspect of process weldability research,the drop hammer and mechanical properties are the main evaluation indexes.According to the physical properties of bainitic rails,the welding parameters are optimized successively based on the pearlite rail welding parameters,and the post-weld heat treatment temperature and cooling rate are studied.Welding process parameters and heat treatment process parameters suitable for the bainitic rail were developed for the first time.The innovative conclusions put forward are: for this kind of bainite rail,under the premise of controlling the total heat input,the larger preheating input + large forging amount can meet the falling weight requirement;control the current spike at the end of burning and control the welding line The width can effectively reduce the gray spots of the fracture.When the normalizing temperature of the joint is 930 ° C and the final cooling temperature of the spray is 430 ° C,the band structure can be significantly reduced,and the initial temperature of the heat preservation at 350 ° C can further improve the morphology of the band structure.In the aspect of metallurgical weldability research: for the phenomenon that the weld defects are more serious after joint austenitization,the conditions for element enrichment caused by reverse diffusion at a certain cooling rate and termination of enrichment are proposed for the first time,and tested by EPMA.The law proves.For the first time,the bainitic rail welding defects were classified,and the damage degree of the welding defects was evaluated by the cyclic stress test method.It was found that the occurrence of welding defects is very sensitive to the fluctuation of the steel base material composition and the rolling process.In the use of weldability research: the first study tested the mechanical properties of the bainitic rail welded joints under the four conditions of air cooling,air blowing,normalizing,normalizing + blowing,the conclusion is that the four processes The tensile strength under the condition is about 80% of the strength of the base metal;the hardness of the base material in the tempered zone of the welded joint is seriously reduced,and the hardness of the soft point is less than 70% of the base metal;the normalizing + blowing process can enhance the base material of the tempering zone.The hardness value is about 15%.It is found that the ultrasonic flaw detection rate of this kind of bainite rail welded joint is much higher than that of pearlite rail.The joint fatigue fracture phenomenon still occurs in the case of flawless detection without ultrasonic wave.The ability of ultrasonic flaw detection to detect the segregation structure needs further the study.In this paper,the welding properties of 1380 MPa grade bainitic rails are studied by means of fixed flash welding method,which reveals the characteristics of such rails in terms of weldability,metallurgical weldability and weldability.It is of positive significance to promote the popularization and use of 1380 MPa bainite rail and the research of welding and post-weld heat treatment.In this paper,the weldability of 1380 MPa grade bainite rail is studied by fixed flash welding method,which reveals the characteristics of weldability,metallurgical weldability and weldability of this kind of rail industry.It is of positive significance to promote the promotion and use of 1380 MPa bainitic rails and the research on welding and post-weld heat treatment. |
