Welding process specification for wear-resistant plates
Domestic wear-resistant plates: nm400, nm450, and nm500 wear-resistant steel plates have high wear resistance and good impact performance. They can be connected to other structures through welding, plug welding, bolt connection, and other methods. This article provides a detailed introduction to some welding processes:
1. Preheating before welding: Due to the large carbon equivalent, thickness, and tensile strength of the wear-resistant steel plate of the shovel plate, preheating can prevent cold cracks, reduce cooling speed, and reduce welding stress. Therefore, appropriate preheating should be carried out before welding. Based on the mechanical properties of NM360, the preheating temperature should be 120 ℃~150 ℃. In the near welding area, oxygen acetylene gas (or NAS gas) should be used for local preheating, and the preheating temperature should not be too high, Otherwise, it will increase the high-temperature residence time, slow down the cooling rate, and promote the occurrence of brittle cracks.
2. The positioning weld of low alloy high-strength steel is prone to cracking due to its small size, short length, and fast cooling rate, which belongs to the nature of cold cracking. When the wear-resistant steel plate of the shovel plate is fixedly fixed with the alloy cast steel of the shovel teeth, the fixedly fixed length is 40-60mm, and a small current is also used for fixedly fixing. Keep the entire structural component in a preheated state.
3. The welding between the wear-resistant steel plate of the shovel plate and the alloy cast steel of the shovel teeth adopts mixed gas shielded welding. Due to the stable arc and low splashing of the mixed gas shielded welding, it can achieve short circuit transfer with stable droplet transfer frequency, and can weld fine-grained structural steel. The mechanical properties of the weld seam are superior to pure Ar or CO2 gas shielded welding. Therefore, Ar+CO2 mixed gas shielded welding is adopted, with Ar accounting for 70%~80% and CO2 accounting for 20%~30%.
4. Selection of welding line energy: The wear-resistant steel plate is a low alloy steel, which is prone to low quenching and hardening structure in its heat affected zone, leading to cold cracking. In addition, the heat treatment state of the steel from hot rolling, normalizing to quenching and tempering reduces the welding line energy, which has a significant impact on the cold cracking resistance and mechanical properties of the weld metal. Therefore, from the perspective of reducing the tendency to harden and the generation of cold cracks, avoiding overheating of austenite during the welding process, and reducing the residence time in the high-temperature zone, it is considered that using a smaller linear energy can reduce the generation of welding defects.
5. Selection of welding speed: As the welding speed increases, the fusion ratio of the base metal will decrease. If the speed is too high, it will cause defects such as undercut, incomplete penetration, and porosity. If the speed is too slow, it will form defects such as large melt pool, overflow, and rough weld seam. Therefore, reasonable control of welding speed plays a decisive role in ensuring weld quality.
