What Does Nickel Do in Welding Wire?

Nickel possesses excellent mechanical, physical, and chemical properties. Adding suitable elements can improve its oxidation resistance, corrosion resistance, high-temperature strength, and certain physical properties.

Cleanliness of the workpiece surface is a crucial requirement for successful welding of nickel-based corrosion-resistant alloys. Surface contaminants mainly consist of surface oxides and elements that cause embrittlement.

Elements that form low-melting-point eutectics with Ni, such as S, P, Pb, Sn, Zn, Bi, Sb, and As, are harmful elements. These harmful elements increase the tendency for hot cracking in nickel-based corrosion-resistant alloys.

These impurities must be completely removed before preheating or welding.

1. Workshop dirt and grease can be removed by steam degreasing or with acetone and other solutions.

2. Paints and other contaminants insoluble in degreasing agents can be cleaned with methylene chloride, alkaline cleaning agents, or special synthetic agents. Marking ink is generally cleaned with methanol.

3. Impurities pressed into the workpiece surface can be removed by grinding, shot blasting, or cleaning with a hydrochloric acid solution (10% by volume) followed by rinsing with clean water.

Welding nickel-based corrosion-resistant alloys using high heat input methods can have adverse effects. A certain degree of annealing and grain growth occurs in the heat-affected zone (HAZ).

High heat input can lead to excessive segregation, carbide precipitation, or other harmful metallurgical phenomena. This can cause hot cracking or reduce corrosion resistance.

The grain size of the base metal must also be considered when selecting welding methods and processes. Coarse-grained materials have more carbides and intermetallic compounds at the grain boundaries that promote liquefaction cracking, thus increasing the susceptibility to hot cracking.

1) Poor fluidity of liquid weld metal

The weld metal has poor fluidity and does not easily flow to both sides of the weld. Therefore, to obtain good weld formation, a weaving technique is sometimes used. However, this weaving is a small oscillation, with the oscillation distance not exceeding three times the diameter of the welding rod or wire. The groove angle of the joint is also larger.

2) Shallow weld penetration

This is also an inherent characteristic of nickel-based corrosion-resistant alloys. Similarly, increasing the welding current does not increase the penetration depth. As mentioned above, excessive current is detrimental to welding, causing cracks and porosity.

3) Preheating and post-weld heat treatment

Nickel-based corrosion-resistant alloys generally do not require preheating before welding. However, when the base metal temperature is below 15°C, the area within 250-300mm on both sides of the joint should be heated to 15-20°C to prevent moisture condensation. Post-weld heat treatment is generally not recommended.

1) Beveling should preferably be done using mechanical methods. If plasma cutting is used, the processed surface should be cleaned;

2) The beveling should be done with a large angle and small blunt edge, and should conform to the design and work instructions;

3) After beveling, a visual inspection should be performed. The bevel surface should be free of cracks, delamination, and other defects;

4) If the design requires non-destructive testing of the bevel surface, it should be carried out according to the design specifications. If there are no design specifications, for cast pipes, pipes and fittings used for highly hazardous media, and pipes or fittings with a design pressure equal to or greater than 10 MPa, the bevel should be subjected to penetrant testing. Any defects should be removed promptly.

Before assembly, oil stains, rust, etc., should be removed from the bevel and within 20mm on both sides until a metallic luster is exposed. The corresponding surface area should be cleaned with an organic solvent before welding; after the solvent evaporates, an anti-spatter coating should be applied within 100mm on both sides of the bevel.

1) During welding, use a welding method with low current, small oscillation, and low heat input;

2) When using TIG welding, the inside of the pipe should be purged with argon gas, with an argon purity of no less than 99.99%. During root pass welding, maintain a small hole with a diameter of 2mm-3mm at the leading edge of the weld pool, and the welding wire should be transferred to the weld pool in a droplet manner;

3) When performing manual arc welding for filling and capping, apply chalk powder to the base metal within a range of at least 100mm on both sides of the groove to prevent welding spatter from damaging the base metal;

4) Thoroughly clean the interlayers and surfaces using an angle grinder or stainless steel wire brush. Grinding and cutting must use white corundum grinding wheels, and must not be mixed with carbon steel;

5) Pipes and fittings should be placed on rubber or asbestos pads and should not be mixed with carbon steel;

6) If there is overlapping work during on-site installation, cover the potentially contaminated areas of the pipeline with asbestos cloth;

7) For pipes with large wall thickness, symmetrical welding should be used for filling to prevent welding deformation;

8) Socket welding must be completed in two passes;

9) After welding is completed, clean the weld surface promptly and perform a visual inspection of the weld. After meeting the quality standards, write the welder's code on the pipe 20mm-50mm away from the weld using a coating that does not contain zinc, sulfur, or other elements.

1) Due to the shallower penetration depth and poor fluidity of molten nickel-based corrosion-resistant alloys, welding parameters must be strictly controlled during the welding process. Nickel-based corrosion-resistant alloy electrodes generally use direct current, with the electrode connected to the positive terminal.

2) Each type and size of electrode has an optimal current range. The welding current for a specific joint should consider factors such as base metal thickness, welding position, joint type, and clamping rigidity.

3) Molten nickel-based corrosion-resistant alloys have poor fluidity. To prevent defects such as lack of fusion and porosity, it is generally required to appropriately oscillate the electrode during welding.

4) When breaking the arc, slightly lower the arc height and increase the welding speed to reduce the size of the weld pool. This can reduce crater cracking. When re-striking the arc at the welding joint, reverse arc striking technology should be used to facilitate the adjustment of the weld smoothness at the joint and help suppress the occurrence of porosity.