Residual Stress Control and Rolling Cooling Process Optimization in Rails
How are residual stresses generated inside rails?
After high-temperature rolling, rails cool rapidly. The surface cools faster and shrinks more, while the core cools slower, creating constrained residual stresses. Uneven rolling deformation, excessive straightening, and mismatched heat treatment also increase residual stresses. Excessive stress causes deformation during storage, laying, and operation, even inducing internal cracks.
What are the main harms of residual stresses to rail performance?
Excessive tensile residual stress reduces fatigue strength. Under cyclic train loads, fatigue cracks easily initiate, shortening service life. Uneven stress causes slow bending, destroying track smoothness and stability. For welded rails, residual stress reduces joint stability and increases cracking risk.
Why is the cooling process critical for controlling rail residual stress?
The cooling process determines the temperature distribution. Too fast or uneven cooling creates a large temperature difference between surface and core, causing high residual stress. Controlling water flow, time, and method ensures uniform shrinkage, reducing temperature gradients and residual stresses at the source.
How to detect whether rail residual stress is qualified?
Common methods include drilling, layer stripping, X-ray diffraction, and ultrasonic testing. Drilling measures surface stress via deformation; X-ray diffraction tests surface stress nondestructively; ultrasound evaluates internal stress. In production, sampling inspection ensures stress meets standards.
What practical benefits do low-residual-stress rails bring to track operation?
They maintain straightness long, reducing maintenance. Higher fatigue resistance lowers breakage risk. Uniform stress reduces impact on fasteners and sleepers, extending track system life and improving operational safety and economy.