There are many problems in the welding process of nickel-based alloys. There are two common problems. One problem is welding hot cracking. This is mainly because nickel-based corrosion-resistant alloys have high thermal cracking sensitivity, including crystallization cracks and liquefaction cracks. Secondly, the corrosion resistance will be reduced. Due to the increase of heat input, the deoxidizer in the weld metal will evaporate, which will seriously affect the gas slag protection and reduce the corrosion resistance.
Here is a brief analysis of how to prevent the occurrence of welding hot cracks, mainly by the following precautions:
Weldment cleaning: The debris on the weldment is easy to form harmful elements with Ni, resulting in an embrittlement field, which may increase the thermal cracks of the weldment, and also form fine slag or oxides during the welding process. Therefore, we must do a good job of cleaning up. The specific cleaning methods are as follows
①Greasy dirt and grease can be removed by steam degreasing or solvents such as acetone alcohol.
②Coatings and other sundries that are insoluble in degreasing agents can be cleaned with methyl chloride, alkali, special synthetic agents, etc.
③The ink traces can be cleaned with methanol.
④Surface oxides and impurities pressed into the surface of the weldment can be removed by grinding.
Groove production: According to the different welding methods, the form of the groove is slightly different. The common points are large grooves, small blunt edges, and large gaps. For butt welds smaller than 2.4mm, grooves are not required.
Preheating and dehumidification: There will be moisture and moisture on the surface of the weldment, and the weldment should be slightly preheated.
The choice of welding machine and welding rod: Generally, a stable DC power supply is used, and the connection method is DC reverse connection. Different types of nickel alloys should be welded with electrodes of the corresponding composition.
Welding parameters: The welding process of Harbin alloy, Inconel, Monel, and Incoloy alloys is similar to that of high-quality stainless steel, but the weld penetration is shallower and the fluidity of the liquid weld metal is worse. Therefore, the welding process must be strict with Control welding parameters and reduce heat input.
Welding position: Use a flat welding position as much as possible, and short arc welding must be used. When the welding position must be vertical welding or overhead welding and other welding positions, thin electrodes should be used for welding and small current welding should be used to reduce heat input and stay.
Welding process: During the welding process, the welding rod generally oscillates. The amplitude of the oscillating motion is generally not more than 3 times the diameter of the welding rod. When oscillating to the extreme positions on both sides, you should stop for a while to allow the viscous liquid weld metal to have sufficient time Carry out filling to prevent defects such as undercut, lack of fusion, and slag inclusion.
Arc extinguishing operation: When extinguishing the arc, the height of the arc should be slightly reduced and the welding speed should be appropriately increased to reduce the size of the molten pool, which can avoid arc crater cracks. When re-igniting the arc, the method of reverse ignition is generally used, which is beneficial to the smooth welding of the joints and the beautiful shape.
Hastelloy C-276，Inconel 600 and other non-precipitation hardening nickel alloys can be used for electrode arc welding, MIG welding, and submerged arc welding.These methods are not suitable for precipitation-hardenable nickel-based corrosion-resistant alloys such as Alloy 718, Incoloy 800H,methods such as tungsten gas shielded welding or plasma welding are usually used.
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