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Post weld heat treatment method for flash welding joints of U71MnH rails

A technology for post-weld heat treatment and welded joints is applied in the field of rail welding, which can solve the problems of low hardness of welded joints, and achieve the effects of improving performance status, good promotion and application prospects, and normal structure and morphology.

Active Publication Date: 2018-12-18
CHENGDU ADVANCED METAL MATERIALS IND TECH RES INST CO LTD +1
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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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  • Post weld heat treatment method for flash welding joints of U71MnH rails
  • Post weld heat treatment method for flash welding joints of U71MnH rails
  • Post weld heat treatment method for flash welding joints of U71MnH rails

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 940°C by intermediate frequency heating method, and the heating time was 145s. After the heating is stopped, when the temperature of the rail joint tread drops to 810°C, carry out air spray cooling. The air spray port is 30mm away from the rail joint surface, and the spray air pressure is 0.15±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 435°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 0.98, and the ratio of the average hardness H...

Embodiment 2

[0033] The welding seam area of ​​the 60kg / m U71MnH rail welded joint was heated to 919°C by intermediate frequency heating, and the heating time was 138s. After the heating is stopped, when the temperature of the rail joint tread drops to 785°C, carry out air spray cooling. The air spray port is 30mm away from the rail joint surface, and the spray air pressure is 0.15±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 410°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 average hardness HJ1 of t...

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, carry out jet cooling. The air jet is 30mm away from the rail joint surface, and the jet pressure is 0.15±0.05MPa. When the joint tread temperature drops to the final cooling temperature of At 435°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 soft spot...

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Abstract

The invention relates to a post weld heat treatment (PWHT) method for flash welding joints of U71MnH rails, and belongs to the technical field of rail welding. The invention provides the PWHT method for the flash welding joints of the U71MnH rails in order to solve the problem that when existing rail welding joints are cooled during heat treatment, the hardness of the joints is affected by martensite and other harmful structures which are formed because local cooling rate is higher than critical transition temperature. The PWHT method comprises the steps of heating U71MnH rail welding joint welding seam areas, which are cooled to be below 300 DEG C after welding, to 919-940 DEG C and then stopping heating, performing air jet cooling, stopping air jet cooling after the temperature of treadsurfaces of the joints of the rails drops to 410-435 DEG C, and performing natural cooling to room temperature. While effectively controlling the hardness of the welding joints of the U71MnH rails, the PWHT method ensures the normality of the structures of the joints.

Description

technical field [0001] The invention belongs to the technical field of rail welding, and in particular relates to a post-weld heat treatment method for U71MnH rail flash 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 ...

Claims

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Application Information

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Patent Type & Authority Applications(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 CHENGDU ADVANCED METAL MATERIALS IND TECH RES INST CO LTD
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