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Heat treatment method for u71mnh rail welded joints

A heat treatment method and technology of welded joints, which are applied in the field of rail welding, can solve the problems of low hardness of welded joints, achieve the effects of improved performance status, normal microstructure, and good promotion and application prospects

Active Publication Date: 2020-06-09
PANZHIHUA IRON & STEEL RES INST OF PANGANG GROUP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0005] The invention aims to solve the problem that the hardness of the welded joint is low due to the generation of harmful tissues such as martensite due to the local cooling rate higher than the critical transformation temperature during the cooling process of the welded joint of the rail

Method used

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  • Heat treatment method for u71mnh rail welded joints
  • Heat treatment method for u71mnh rail welded joints
  • Heat treatment method for u71mnh rail welded joints

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0031] The welding seam area of ​​the 60kg / m U71MnH rail welded joint was heated to 935°C by intermediate frequency heating method, and then the heating was stopped, and the heating time was 141s. After the heating is stopped, when the temperature of the rail joint tread drops to 785°C, carry out jet cooling. The air jet is 30mm away from the rail joint surface, and the jet pressure is 0.1±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 431°C, the blast cooling was stopped, and then the rail joints were naturally cooled to room temperature. Referring to the requirements of the TB / T 1632.2-2014 standard, the HR-150A Rockwell hardness tester is used to test the Rockwell hardness of 5 mm below the tread of the rail head on the longitudinal section. In this embodiment, the ratio of the average hardness HJ of the post-weld heat treatment joint of 60kg / m U71MnH rail to the average hardness HP of the base metal is 0.95, and the ratio of the aver...

Embodiment 2

[0033] The welding seam area of ​​the 60kg / m U71MnH rail welded joint was heated to 915°C by intermediate frequency heating method, and the heating time was 135s. After stopping the heating, when the temperature of the rail joint tread drops to 810°C, carry out spray cooling. The distance between the air spray port and the rail joint surface is 30mm, and the spray air pressure is 0.1±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 405°C, the blast cooling was stopped, and then the rail joints were naturally cooled to room temperature. Referring to the requirements of the TB / T 1632.2-2014 standard, the HR-150A Rockwell hardness tester is used to test the Rockwell hardness of 5 mm below the tread of the rail head on the longitudinal section. In this embodiment, the ratio of the average hardness HJ of the post-weld heat treatment joint of 60kg / m U71MnH rail to the average hardness HP of the base metal is 0.93, and the ratio of the average ha...

Embodiment 3

[0035]The welding seam area of ​​the 60kg / m U71MnH rail welded joint was heated to 921°C by intermediate frequency heating method, and the heating time was 136s. After the heating is stopped, when the temperature of the rail joint tread drops to 800°C, spray air to cool it. The air spray port is 30mm away from the rail joint surface, and the spray air pressure is 0.1±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 432°C, the blast cooling was stopped, and then the rail joints were naturally cooled to room temperature. Referring to the requirements of the TB / T 1632.2-2014 standard, the HR-150A Rockwell hardness tester is used to test the Rockwell hardness of 5 mm below the tread of the rail head on the longitudinal section. In this embodiment, the ratio of the average hardness HJ of the post-weld heat treatment joint of 60kg / m U71MnH rail to the average hardness HP of the base metal is 0.91, and the ratio of the average hardness HJ1 of the...

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Abstract

The invention relates to a heat treatment method for a U71MnH steel rail welding joint, and belongs to the technical field of steel rail welding. The problem that harmful structures such as martensites are generated to influence the joint hardness due to the fact that the local cooling speed is higher than the critical transition temperature when an existing steel rail welding joint is cooled in the heat treatment process is solved. The heat treatment method for the U71MnH steel rail welding joint comprises the steps that a U71MnH steel rail welding joint welding seam area which is cooled to 300 DEG C or below after being welded is heated to 915-935 DEG C, then heating is stopped, air spraying cooling is adopted and stopped after the steel rail joint tread temperature is lowered to 405-432DEG C, and natural cooling is conducted till the room temperature is achieved. By adopting the method, it is guaranteed that the joint structure is normal while the hardness of the U71MnH steel railflash welding joint is effectively controlled.

Description

technical field [0001] The invention belongs to the technical field of rail welding, and in particular relates to a heat treatment method for U71MnH rail welding joints. Background technique [0002] Rail welding has the characteristics of high heating temperature, fast heating speed, short residence time at high temperature, uneven temperature distribution and continuous cooling under air-cooling conditions. In the joints, especially in the heat-affected zone, it is easy to have a coarse structure, and even easy to form martensite, shellfish, etc. At the same time, the joints after welding generate internal stress, and under the action of complex external stress, they are prone to fracture and become a weak link in line operation. In order to release the stress, refine the grain, change the microstructure of the joint, and improve the degraded performance state, it is necessary to perform post-weld heat treatment on the rail joint. [0003] Patent document CN108103299A dis...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C21D9/50C21D1/42C21D1/52
CPCC21D1/42C21D1/52C21D9/50Y02P10/25
Inventor 陆鑫李大东王若愚邓健
Owner PANZHIHUA IRON & STEEL RES INST OF PANGANG GROUP
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