Nickel and nickel-based corrosion-resistant alloys are ideal metal structures for various harsh corrosive environments such as high temperature, high pressure, high concentration or mixed with impurities in chemical, petroleum, non-ferrous metal smelting, aerospace, nuclear energy and other industrial fields. Material. By adding corrosion-resistant metal elements such as Cr, Mo, Cu, and W to nickel, a nickel-based corrosion-resistant alloy with excellent corrosion resistance can be obtained.
Solid solution strengthened nickel-based corrosion-resistant alloys are very suitable for submerged arc welding, especially for thick plates. Compared with other welding methods, the welding dilution rate is higher, up to 30%~50%, and each weld is higher, up to 3~ 5mm, the arc burning is stable, the weld surface is smooth and there is no arc glare. Compared with low carbon steel and stainless steel, the welding of nickel-based corrosion-resistant alloys has similar problems that occur in austenitic stainless steel welding, such as the tendency of welding hot cracks, weld pores, and intergranular corrosion tendency of welded joints.
1. Welding wire and flux
In order to prevent the generation of hot cracks, a reasonable assembly sequence should be adopted in the process, and a smaller line energy should be selected, but the key issue is to select the appropriate welding material. It is the same wire used for MIG/MAG welding. For submerged arc welding of nickel-based corrosion-resistant alloys, in addition to the correct selection of welding wires, the flux that matches the alloy and base metal must also be correctly selected. Submerged arc fluxes for carbon steel and stainless steel are not suitable for nickel-based corrosion-resistant alloys. The commonly used fluxes are IncoFlux44, IncoFlux5 and IncoFlux6.
Among them, the No. 4 flux is the No. 3 flux that matches the Inconel 62, 82, and 625 welding wires. The flux is matched with Inconel 62 welding wire to weld Inconel 600 alloy. No. 5 flux is a special flux for submerged arc welding with Monel 60 and 67 wires. The flux with Monel 60 wire is suitable for submerged arc surfacing and butt welding of Monel 400 and 404, as well as submerged arc welding of butt joints of two alloys.
No. 6 flux is a submerged arc flux for nickel 61, Inconel 82, and 625 welding wires. This flux is suitable for submerged arc surfacing and nickel 200, 201 butt joints of the same or different materials. arc welding. Nickel-based corrosion-resistant alloy submerged arc flux has the property of absorbing moisture and should be stored in a dry container. Moisture-absorbing flux can be dried. The commonly used drying temperature is 580~880℃, and the drying time is 2h.
2. Connector form
The typical joint form of nickel-based corrosion-resistant alloys is consistent with that of MIG/MAG welding. The choice of joint form should minimize the amount of molten metal and reduce welding deformation and residual stress. Various V-shaped or V-shaped backing plate single-sided welding joints are suitable for welding plates with a thickness of less than 25mm. U-shaped groove and double U-shaped groove are suitable for plates above 20m or thicker. In the joint design, double V-shaped grooves should be used as much as possible to reduce welding molten metal, welding deformation or residual stress.
3. Process points
The cleaning of nickel-based corrosion-resistant alloy submerged arc welding butt weldments is an extremely important measure to prevent cracks, especially to prevent porosity, and must be strictly implemented. Dirt and grease can be degreased with steam or cleaned with acetone, paint can be cleaned with alkali and special detergent, and marking ink can be cleaned with methanol. When the temperature of the base metal is lower than 15°C, in order to prevent the moisture in the air from adsorbing on the surface of the base metal and causing pores, the groove should be heated to 15-20°C within a range of 250~300mm on both sides of the groove.
Rolled nickel-based alloys generally do not require pre-weld preheating, and post-weld heat treatment is not recommended, but sometimes to ensure that intergranular corrosion does not occur during use, post-weld heat treatment is required.
For reinforced alloys that have been bent, cold drawn or otherwise complicatedly formed, annealing heat treatment must be done after welding. For reinforced nickel-based alloys with complex structures, in order to effectively reduce welding stress, pre-weld preheating is beneficial, but preheating cannot replace post-weld heat treatment. The welding of cast nickel-based corrosion-resistant alloys needs to be preheated to 100~250 °C to reduce the tendency of weld cracks; it is also necessary to relieve stress after welding, such as hammering or annealing to relieve stress.
In the submerged arc welding process of nickel-based corrosion-resistant alloys, the coordination of base metal, welding wire, flux and welding process parameters is very important, which has a great impact on the processability, the chemical composition of the weld, and the performance of the joint.
