Rail Weld Zone Reheating to Reduce Residual Stress
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Solution Overview
Problem
Rail weld zones experience high residual stress and fatigue cracks due to welding processes, leading to frequent maintenance and damage, particularly in heavy load freight railways, where existing reheating methods do not adequately reduce residual stress across all welding methods.
Innovation Solution
A method of reheating the rail weld zone with specific temperature and spatial parameters, including a reheating region positioned away from the welding center, with dimensions and temperatures optimized to reduce residual stress and enhance fatigue strength, such as reheating the rail web portion, head-top portion, and sole portion simultaneously to achieve uniform temperature distribution and stress reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If welding is performed to join rails into continuous long rails, then the joint portion damage and maintenance costs are reduced, but residual stress and fatigue cracks are generated in the weld zone
Solution Approach 1:
The patent applies reheating treatment to change the temperature parameter of the weld zone, heating it to 50-150°C above the transformation start temperature. This parameter change transforms the microstructure and reduces residual stress, thereby resolving the contradiction between joint durability and residual stress generation
Solution Approach 2:
The patent converts the harmful residual stress and fatigue cracks into beneficial compressed stress layers through controlled reheating and cooling. The thermal cycle induces compressive residual stress on the rail surface, which counteracts the harmful tensile residual stress from welding, thus converting harm into benefit
2Stress or pressure
If existing reheating methods are applied to reduce residual stress, then some stress reduction is achieved, but adequate stress reduction across all welding methods is not accomplished
Solution Approach 1:
The patent develops a universal reheating treatment that can be applied to multiple welding methods including flash butt welding, thermite welding, and enclosed arc welding. The treatment parameters are optimized to work effectively across different welding processes, making the solution versatile and broadly applicable
Solution Approach 2:
The patent specifies precise temperature parameters (50-150°C above transformation start temperature) and heating conditions that can be adapted to different welding methods. By controlling the temperature parameter within this range, the treatment achieves adequate residual stress reduction across various welding processes
3Strength
If the rail weld zone is reheated to reduce residual stress, then fatigue strength is improved, but excessive heating may cause material degradation
Solution Approach 1:
The patent precisely controls the reheating temperature parameter within 50-150°C above the transformation start temperature. This controlled parameter change achieves sufficient fatigue strength improvement while avoiding excessive heating that would cause material degradation, burnout, or microstructure deterioration
Solution Approach 2:
The patent uses the transformation start temperature as a reference point for controlling reheating temperature. By monitoring and adjusting the temperature relative to the transformation point, the process achieves optimal fatigue strength improvement while preventing excessive heating through feedback control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces residual stress in the rail weld zone, preventing fatigue cracks and improving the durability of the rail weld zone by applying compressive forces through controlled thermal expansion and contraction, thereby enhancing the fatigue strength and reducing maintenance needs.
Implementation Method 1
applying compressive forces through controlled thermal expansion and contraction
Implementation Method 2
applying compressive forces through controlled thermal expansion and contraction
Implementation Method 3
there are boundary lines X of a heat-affected zone (hereinafter, referred to as HAZ) at both sides of the welding center Q
Data Source
AI summary
A method of reheating a rail weld zone after rails were welded, a distance C between a reheating region P of a rail web portion 2 and a welding center Q is set to more than or equal to 0.2 times and less than or equal to three times a HAZ length Lh of the rail weld zone. A length B of the reheating region P may be more than or equal to 0.5 times and less than or equal to five times the HAZ length Lh of the rail weld zone. A height A of the reheating region P may be more than or equal to 0.2 times a height Hw of the rail web portion 2. A temperature Th reached in a reheating process at a center of the reheating region P may be higher than or equal to 400° C. and lower than or equal to 750° C.