In the welding and installation of wear plates for mining machinery, the core issues are crack initiation and ensuring structural strength, requiring a comprehensive approach encompassing material selection, process control, and environmental management. Wear plates are typically made of high-carbon, high-chromium alloy steel or low-alloy, high-strength steel, which have poor weldability and are prone to cracking due to thermal stress, microstructural transformation, or hydrogen-induced embrittlement. Therefore, it is necessary to ensure weld quality through measures such as optimizing welding materials, controlling preheating and interpass temperature, selecting welding methods, and post-weld treatment.
The choice of welding materials directly affects crack susceptibility. When welding wear plates, low-hydrogen electrodes or flux-cored wires with compositions matching the base metal should be prioritized, such as low-hydrogen potassium electrodes or metal powder-cored wires. These materials have low hydrogen content, reducing the risk of hydrogen-induced cracking. Simultaneously, the strength grade of the welding material must match that of the base metal to avoid stress concentration due to strength differences. For example, when welding high-hardness wear plates, using welding materials with excessively low strength may lead to preferential failure of the weld metal under stress; conversely, excessively high strength may result in brittle fracture due to insufficient toughness. Preheating and interpass temperature control are crucial for preventing cold cracking. Before welding wear plates, the workpiece must be preheated, either overall or locally. The preheating temperature is typically determined based on the plate thickness and material properties, generally not lower than 150℃. Preheating reduces the cooling rate in the welding area, decreasing martensite formation and thus reducing cracking tendency. During welding, the interpass temperature must be maintained above the preheating temperature to avoid thermal stress concentration due to sudden temperature drops. For example, in multi-layer, multi-pass welding, if the interpass temperature is too low, the welded layers will experience shrinkage stress due to rapid cooling. This stress, combined with the thermal expansion stress of subsequent weld layers, can easily lead to lamellar tearing or transverse cracks.
The choice of welding method must be considered in conjunction with the thickness and structural characteristics of the wear plates. For thin wear plates, gas shielded welding (such as MAG or MIG welding) can be used, as its heat input is controllable and welding deformation is minimal. For thick plates or complex structures, submerged arc welding is more suitable due to its high efficiency and deep penetration characteristics. Regardless of the method used, welding heat input must be controlled to avoid overheating that leads to grain coarsening or softening of overheated areas. For example, when welding high-carbon steel wear plates, excessive heat input can lead to carbon migration in the weld metal, forming high-carbon martensite and significantly reducing toughness; while insufficient heat input may cause cracks due to incomplete fusion or penetration.
Groove design and assembly precision are crucial to weld quality. When welding wear plates, a U-shaped or double U-shaped groove should be preferred to reduce the proportion of base metal fused into the weld, lowering the carbon content and thus reducing the risk of cracking. Simultaneously, the groove machining must ensure dimensional accuracy to avoid insufficient weld metal filling due to excessive gaps or stress concentration due to excessive misalignment. During assembly, the fit between the wear plates and the base material must be strictly checked to ensure no gaps or misalignments, preventing cracks caused by uneven local stress during welding.
Post-weld treatment is a crucial step in consolidating weld quality. After welding, wear plates should be immediately subjected to post-heat treatment, such as heating to 200-300℃ with an oxy-acetylene flame and holding at that temperature to promote hydrogen escape and reduce the risk of delayed cracking. For thick plates or high-stress structures, post-weld hydrogen removal treatment or stress-relieving annealing is necessary to eliminate residual welding stress and improve the microstructure stability of the weld metal. Furthermore, the weld surface needs to be ground or machined to remove defects such as undercut and porosity, preventing crack propagation caused by stress concentration.
Environmental factors have a significant impact on welding quality. When welding wear plates, avoid operating in low-temperature, humid, or windy environments to prevent rapid cooling of the weldment due to low ambient temperatures or hydrogen-induced cracking due to high humidity. For example, during winter or rainy season construction, the weldment should be preheated and a windproof shelter should be erected to ensure that the temperature and humidity of the welding area meet process requirements. Simultaneously, the surface of the weldment must be thoroughly cleaned before welding to remove oil, rust, or moisture to prevent hydrogen sources from entering the weld.
The welding and installation of wear plates for mining machinery requires comprehensive measures, including material matching, process optimization, and environmental control, to prevent cracking and ensure structural strength. From the selection of welding materials to post-weld treatment, every step must strictly follow the process specifications to ensure that the welded joint has sufficient strength, toughness and crack resistance, so as to meet the long-term operation requirements of mining machinery under harsh working conditions.
