Nickel and nickel alloys are highly heat-resistant and have good corrosion resistance so that they are used in a variety of techniques: chemical industry, electrical engineering ...
Nickel has a high melting temperature (1452 degrees Celsius). Specific gravity of nickel is 8.99g / cm³.
Characteristics of welding of nickel and nickel alloys
Weld of nickel and nickel alloys are often porous.
Cavitation in the weld is usually caused by H2 (the solubility of H2 in the alloy increases as the temperature decreases).
Welds usually appear crystalline cracks. The phenomenon of crystalline cracks during nickel and its alloys welding
process is due to the nickel and its alloy containing sulfur impurities. Nickel combined with sulfur makes sulfur compounds. The least sulfur-containing compound is Ni3S2, which produces nickel and Ni3S2 at low melting temperature(625 degrees Celsius). This leads to cracks in the welds
In order to reduce the harmful effects of sulfur, some elements are added to the weld such as:Mn, Mg. These elements combine with sulfur to form MnS, MgS at a higher flow temperature and this is also less harmful than Ni3S2. On the other hand, Mg and Mn combine with oxygen to form oxides like MnO, MgO which are insoluble in liquid metal and in slag.
Welding technology of nickel and nickel alloys:
Preparation of the workpiece:
Depending on the thickness of the workpiece, welders can use methods of welding: bevel groove weld, bevel weld or non-bevel weld
Bevel-groove welding used when the weld is less than 1.5mm thick. If it is less than 4mm thick, non-bevel welding should be applied
Bevel-weld for greater than 4mm thickness. The bevel can be either single-V weld or X-weld with a bevel angle (30 ÷ 45) degrees.
Use a welding rod with the same composition as the welding metal parts. The rod diameter is approximated by the formula:
dqh = S / 2 (mm)
S: Welding thickness (mm)
Flame welding and flame capacity
Select the welding flame
Flame to weld Nickel and Nickel alloy is normal flame or can use excess acetylene flame.
Flame power for 1mm welding thickness:
W = (140 ÷ 200) (liter / hour)
Welding used for welding is a mixture of coconut, boric acid and a small amount of calcium or chloride salts.