What is Inconel? What are the characteristics of Inconel?

Inconel is a nickel, iron, and cobalt-based alloy developed for applications where 2113 requires excellent mechanical and chemical properties at high temperatures. Inconel 718 is a 5261 precipitation hardening nickel-chromium alloy; the high nickel content of Inconel 600 makes the alloy have a very strong resistance to chloride stress cracking corrosion of 4102 and 1653, and can maintain its high corrosion resistance in the reduced state. And it also has strong corrosion resistance in alkaline solution; Inconel X-750 alloy is mainly nickel-based superalloy with γ, Ti, Nb)] phase aging strengthening, etc.

Inconel has a single-phase structure and has similar problems with austenitic stainless steel during welding, such as welding hot cracks, weld pores, and intergranular corrosion of welded joints.

(1) Sensitivity of welding hot cracks

Inconel welding sometimes produces macro cracks, micro cracks or both of the welds. Thermal cracking is caused by the mixing of sulfur, lead, phosphorus or low-melting-point metals to form intergranular thin films and cause severe embrittlement at high temperatures. Generally, it is caused by inclusions penetrating from the surface along the intergranular. In addition, the welding heat input is relatively large, which causes the welding joint to overheat and produce coarse grains. Some low-melting eutectic crystals are concentrated on the coarse columnar grain boundaries. They have low strength and high brittleness, and are easy to form hot cracks under the action of welding stress. When the arc is closed, the arc crater is not filled, the current decay time is short, the amount of deposited metal at the arc is small, and the pit appears, its strength is weak, and it is easy to produce micro-cracks at the arc under the action of phase transformation stress and restraint stress.

(2) The organization is easy to be coarse

Under the effect of heat during welding, the weld seam and base metal are prone to overheating, resulting in coarse crystal grains and lowering the mechanical properties and corrosion resistance of the joint.

(3) Liquid metal has poor fluidity, is not easy to wet and spread, and is prone to defects such as undercut and unfused

 Even if the welding current is increased, the fluidity of the liquid weld metal cannot be improved, but it will bring side effects. Excessive welding current will not only overheat the weld pool and increase the probability of thermal cracking, but also make the weld metal deoxidizer excessive Evaporation increases porosity.

(4) Sensitivity to stomata

Inconel, especially industrial pure nickel, etc., due to the small liquid phase spacing and poor fluidity, it is easy to produce pores when the welding is rapidly cooled. Oxygen, hydrogen, nitrogen, carbon dioxide, and carbon monoxide gas have great solubility in molten liquid Inconel, but their solubility in solid state is greatly reduced. When nickel-based alloy welding changes from high temperature to cold, the gas is in the deposited metal The solubility of pyruvate also decreases accordingly. The freed gas in the liquid nickel with poor fluidity cannot completely overflow before the solidification of the Inconel alloy welding seam to form pores.

(5) The depth of weld metal penetration

The penetration depth of some Inconel weld metals is only one-half of ordinary carbon steel.

(6) Corrosion in the welding zone

When the Ni-Mo alloy passes through the sensitization temperature zone (1200℃～1300℃ and 600℃～900℃), molybdenum-rich phases are precipitated along the grain boundaries, resulting in Mo depleted zones and intergranular corrosion.