Heat treatment process for high-strength and high-toughness bainite steel rail welded joint for heavy haul railway

Abstract

The invention aims to provide a heat treatment process for a high-strength and high-toughness bainite steel rail welded joint for a heavy haul railway, which is characterized in that the joint is controlled within a bainite phase change interval as long as possible after the steel rail is normalized according to the structure transformation characteristic of the bainite steel rail by combining the process designed by changing each key temperature point in a steel rail CCT curve; a certain bainite structure proportion is guaranteed, and then low-carbon martensite structure transformation is conducted; and a tempering process is combined, so that the joint has a bainite and tempered martensite complex phase structure with excellent mechanical properties. After the joint heat treatment process is used, sufficient transformation of a metallographic structure of a welded joint can be guaranteed, residual stress of a welding seam and a heat affected zone is reduced, martensite segregation bands of part of the heat affected zone are relieved or eliminated, performance matching of the welding seam of the bainite steel rail and base metal can be effectively improved, and the welding quality of the bainite steel rail is improved. The comprehensive mechanical property and the contact fatigue property of the welding seam are improved, so that the service performance of the welding seam is effectively improved.

Description

technical field [0001] The invention relates to the technical field of rail welding, in particular to a heat treatment process for welded joints of high-strength and toughness bainitic rails for heavy-duty railways. Background technique [0002] As one of the important connection methods of rails, flash welding is widely used in the production of 500-meter-long rails. The welding performance of steel is mainly affected by the chemical composition of steel. The research and development of bainitic steel rails in my country are all alloys of "low carbon, high silicon, high manganese, and medium chromium" and "low carbon, medium silicon, high manganese, and medium chromium". system, the alloy content of the rail is significantly higher than that of the pearlitic rail. Due to the high alloy content, the weldability of bainitic rails is poor, mainly as follows: ①There are many defects in the welding overheating zone. Alloy composition segregation along austenite grain boundaries...

AI Technical Summary

Problems solved by technology

Due to the high alloy content of bainitic rails, the weldability is poor, mainly as follows: ① more defects in the welding overheating zone

In the superheated zone of flash welding, there is alloy composition segregation along the austenite grain boundary, resulting in uneven microstructure, increased joint brittleness, and possible liquefaction cracks

②Because welding is an unbalanced process of local heating, rapid heating and cooling, the welding residual stress inside the flash welding joint is high and unevenly distributed, especially large tensile stress will be generated on the surface of the weld, which is easy to occur when the weld is in service Surface cracks or even fractures

③ Due to the burning of the alloy during the welding process, the mechanical properties of the joints are significantly reduced, and the joints cannot reflect the characteristics of high strength and toughness of the bainite rail, and the properties of the base metal and the joints are poorly matched

The average hardness of the weld obtained by this process is 87% of the base metal of the rail, which does not meet the standard requirements of greater than or equal to 90%, and the physical fatigue of the joint is about 3 million times

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