Welding of Nickel and Nickel alloys
Welding Nickel alloys is fraught with significant difficulties, due to their particular physico-chemical qualities — a high propensity for the formation of pores with a sharp change of solubility of nitrogen, hydrogen and oxygen in the transition metal from solid to liquid. In arc welding of Nickel and high-purity argon as the main source is nitrogen, dissolved in large quantities in the liquid metal and almost not dissolved in solid Nickel.
To obtain welds without pore is important for the surface cleanliness of the electrode wire, welded edges, welding material and base metal (coatings, electrodes, fluxes, shielding gases) and the binding of hydrogen and deoxidation during the welding process of Nickel. This is solved by the introduction of strong deoxidizers in the weld pool (titanium, aluminum, etc.), as well as the use of coatings or fluxes, which are able to transfer hydrogen in the persistent volatile compounds HP or to bind the oxides of Nickel. For this reason, a welding procedure can provide reliable protection of the welding zone from ambient air, degassing of the weld pool and good deoxidation. Effective measure to prevent porosity is welding with short arc (1.5 mm), which significantly reduces the flow of gases from the atmosphere.
A high tendency of Nickel to the occurrence of crystallization cracks associated with the formation of the boundaries of large grains, which have a transcrystalline structure. To prevent the occurrence in the base metal and the weld cracks it is necessary to limit the content of harmful impurities and to introduce elements that bind the sulfur, the most refractory compounds: 0.1% MD and 5% MP.
In the development of welding technology the focus is on ensuring the required performance properties of the compounds. Technology can be very different even for the same alloy. In arc welding of Nickel alloys and Nickel do not have to get the seam of the same chemical composition as the base metal, because even if the match is exact not possible to avoid cracks, pores, etc. defects. To obtain the desired properties of the weld and prevent defects, you can resort to complex alloying.
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