Monel Alloy 400 welding notes and welding examples

Monel is a nickel-copper Alloy that comes in two grades, Monel 400 and K-500, which generally refer to Alloy 400. Alloy 400, with its excellent resistance to neutral and basic salts, has long been standard in salt-making systems. It is one of the few materials that can come into contact with fluorine, hydrofluoric acid, and hydrogen fluoride, or their compounds. The material has high resistance to alkaline media. Compared with copper-nickel alloy, it behaves better in seawater and has higher cavitation resistance. Alloy 400 works with highly diluted inorganic acids such as sulfuric and hydrochloric acid, provided they are not ventilated. Since the alloy does not contain chromium, the corrosion rate is significantly increased under oxidation conditions. Although Alloy 400 is resistant to stress corrosion cracking, stress cracking is demonstrated in the presence of mercury or moist, aerated HF vapors. Under these conditions, stress relief annealing is necessary. The microstructure of Monel alloy is single austenite, and its welding characteristics are similar to that of austenitic stainless steel. Monel and other nickel-based corrosion resistant alloys have the following welding characteristics: The following problems should be paid attention to when welding Monel alloy: 1. Selection of welding methods The MONEL400 alloy can be welded in the same way as chrome-nickel austenitic stainless steel 316L. Tungsten gas arc welding has been widely used in 400 alloy welding. The corresponding ENICU-7 electrode can be used for manual arc welding or the corresponding ERNICU-7 electrode can be used for argon arc welding. Nickel-copper Monel alloy and pure nickel are welded with strong porosity sensitivity and large weld grain, so titanium is generally added to the electrode and wire as a deoxidizer and modifier to obtain a satisfactory weld. 2. Key points of welding process For Monel alloy manual welding and automatic welding, direct current welding is generally used. The welder is usually equipped with high frequency current to ensure arc initiation and current attenuation device, so as to gradually reduce the size of the flame when the arc is broken. During welding, the arc should be avoided to stir the molten pool; The heating wire end shall be in the protective gas to avoid oxidation and pollution of the hot end; The welding wire should enter the molten pool at the front end of the molten pool to avoid contact with the tungsten pole. The shielding gas flow rate is approximately 4L/min for thin plates and increases to 14L/min for thick plates. It is important to note that too large a gas flow may increase turbulence and even produce premature weld cooling. For complete penetration of one side welding, a copper liner with a concave groove should be used on the back, and at the same time pass to protect the gas. In order to enhance the protective effect of the welding area, a trailing cover can be added to the rear side of the nozzle to assist the transmission of protective gas. Example of argon arc welding of Monel alloy The φ520mm cylinder of a company is made of two Monel alloy plates with a thickness of 16mm. The processing sequence is: plate butt welding, processing round front pressure head, round, welding cylinder longitudinal seam. Monel alloy welding using tungsten argon arc welding process, cerium tungsten electrode, diameter of 4mm, the end ground into a cone. The diameter of welding wire was selected as 3mm, and the composition (mass fraction) was 0.2%~0.4% Al, 1.5%~3.0% Ti and 1.2-1.8% Mn. The welding power supply is direct current connection. Beveling size as shown in figure. Before welding, clean the 40mm area on both sides of the groove with grinding wheel, sand the welding wire, cut each wire into about 1m length, and scrub the welding area and the surface of the welding wire with acetone. Welding process requirements The welding current of the first layer is 90~100A, the reverse side is added with pure copper plate (with R groove) and argon protection, argon flow: 12L/min welding gun protection; The plate is protected by argon 8L/ min. When welding, the welding wire is pressed to the gap, requiring penetration. The welding current of the second layer is 120~130A; The current of the third layer is 130~140A: The current of the fourth and subsequent layers is 180~200A, and the flow rate of the welding gun protection gas is 12L/min. When welding 1~3 layers, the workpiece is placed in the flat welding position; After welding the fourth layer, pad the end of the longitudinal seam of the workpiece up 20°~30° for uphill welding, so as to cause the backward flow of molten liquid metal. The welding sequence is shown in the figure. For each welding layer, the surface of the weld is carefully polished with an angular polishing machine to remove surface oxides and inclusions, and the next layer of weld is welded when the temperature is cooled to 80~100℃. The surface of each layer of weld passage must be concave. During the welding process, the welding gun cannot stay for too long at a certain point. When changing the welding wire and extinguishing the arc in the middle, the manual switch of the welding gun should be closed, but the protective gas should continue to be provided. All mechanical properties after welding meet the technical requirements, σb≥40kgf/mm2, α≥120°, ak≥12kgf.m/mm2.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods