In industrial production, QU70 rails are prone to local wear, cracks and other damage due to long-term heavy loads and complex stresses. Welding repair technology has become a key means to extend its service life and reduce operating costs. Its systematic process and significant benefits are worth in-depth exploration.
Precise control of welding materials and process parameters
J857Cr welding rods are the core material for QU70 rail welding repair. Their high alloy steel characteristics are highly matched with the chemical composition of the rails, which can effectively ensure the performance consistency of the weld and the parent material. The chromium element in the welding rod enhances the wear resistance and corrosion resistance of the weld, providing reliable performance guarantee for the repaired rails. In the welding process, the preheating temperature is strictly controlled at 250-300℃. This temperature range is crucial: on the one hand, it can effectively dissipate the moisture on the surface of the rails and avoid the generation of hydrogen pores during welding; on the other hand, it can reduce the cooling rate of the weld joint, prevent the formation of hardened structures caused by rapid cooling, and reduce the risk of welding cracks.
The interlayer temperature is controlled at 150-200℃ to ensure that each layer of weld is welded at a suitable temperature for subsequent welding, maintaining the toughness and strength balance of the weld metal.
The key role of post-weld treatment process
Immediately after welding, 350℃×2h stress relief annealing is performed, which is a key step to eliminate welding residual stress. During the welding process, due to local high temperature and rapid cooling, large residual stress will be generated inside the rail, which will reduce the fatigue strength of the rail and increase the possibility of crack propagation. Through stress relief annealing, the metal structure of the welding part can be recrystallized, the internal stress can be released, the toughness of the material can be restored, and the comprehensive mechanical properties of the repaired part can be improved.
Post-repair processing and performance recovery
The repaired rail head is precisely processed by a profiling grinder, and the profile error is controlled to ≤0.3mm, ensuring that the shape of the repaired rail head is highly consistent with the standard rail head. This high-precision processing not only ensures good contact between the crane wheel and the rail, reduces vibration and noise during operation, but also avoids local stress concentration caused by profile deviation, further extending the service life of the rail.
The welding repair technology of QU70 rails achieves effective restoration of rail performance and significant cost reduction through scientific material selection, rigorous process control and precise subsequent processing, providing industrial enterprises with a cost-effective solution for track maintenance. It has important promotion and application value and broad development prospects.