Nickel-based alloy has good properties of resistance to active gas, wear and acid medium corrosion, high strength, good plasticity, cold and hot deformation, processing and welding, and is a very important corrosion-resistant metal material.
In surfacing applications, carbon steel or stainless steel can be surfacing with a layer of nickel-based metal as the medium layer, so that it has the advantages of the two metals. This type of welding material is completely different from ordinary alloying elements. In welding, different welding methods should be adopted for welding.
Due to the different physical properties of metals in surfacing welding, the nickel-based alloy welding pool is very viscous and the melting depth is shallow. Increasing the welding current cannot significantly improve the fluidity of the metal and increase the melting depth.
Unlike the concave weld bead usually formed by stainless steel, the weld bead surface of nickel-based alloy is obviously convex.In order to prevent crystal cracking, especially the first layer of crystal cracking at the welding root, it can be eliminated by filling more weld metal with a small current.
When argon arc welding is used, the welding material should not be directly immersed in the molten pool. The welding material should be placed in front of the tungsten electrode and fed while melting. The end of the welding material is always under argon protection.
Nickel-based welding consumables have poor fluidity and the current should not be too large. The welding speed is slow, and the welding should be carefully controlled.
When welding, whether it is interlayer welding or cover welding, pay attention to argon protection during welding to prevent the welding part from being oxidized.
The cold hardening tendency of different materials is different. For example, the cold hardening tendency of nickel-based alloys is 1~2 times higher than that of stainless steel, so welding is prone to bending if the control is not paid attention to.
The strength of the two dissimilar steels in surfacing welding is different. Pay attention to the root stress cracking after welding.
Nickel-based alloy weld metals do not wet and spread as readily as steel weld metals. Even if the welding current is increased, the fluidity of the weld metal cannot be improved, but it has a harmful effect. If the welding current exceeds the recommended range, it not only overheats the molten pool, increases the sensitivity to hot cracks, and reduces corrosion resistance due to coarse grains, but also evaporates the deoxidizer in the weld metal, resulting in pores.
During electrode arc welding, excessive welding current also overheats the electrode and causes the coating to fall off, losing its protective effect. Due to the poor fluidity of the weld metal, it is not easy to flow to both sides of the weld. To obtain good weld formation, a weaving process is sometimes used. But this swing is a small swing, and the swing distance does not exceed 3 times the diameter of the welding wire or electrode. Sometimes stick arc welding is found to be defective even with the wobble process.
Defects mainly include undercut and unmelted edges. In order to eliminate these defects, when the welding is swinging to the extreme position of each side, it is necessary to pause for a while to allow enough time for the molten weld metal to fully fuse with the base metal, and Fill in the undercut. Another important technological measure to be adopted in electrode arc welding is that the welding arc should be as short as possible.
During the welding process, the inherent characteristics of the nickel-based alloy electrode determine that the molten iron penetration is relatively shallow, and this problem cannot be solved simply by adjusting the welding parameters.
According to trial and error, the method to overcome the shallow penetration is to modify the traditional groove form, and the angle of the groove position is more suitable between 40 degrees and 65 degrees.
The welding of nickel-based materials has stricter requirements on the surface of the weld than carbon steel and stainless steel. When welding nickel-based materials, it must be welded into a convex bead. Most cases of cracking in welds of nickel-based materials are due to uneven forces caused by the concave weld bead.
The interlayer temperature during the welding process of nickel-based surfacing materials should not be too high, generally below 100°C. Welding of nickel-based alloy materials generally does not require preheating and post-heat treatment.