Welding to choose the right welding material. The chemical composition of the wire has an important effect on the corrosion resistance of the weld. The electrode should have a chemical composition similar to that of the base metal. This allows the weld metal to have a similar chemical composition to the base metal and is generally considered to be the best Corrosion resistance.
Stainless steel welding characteristics
As the resistance coefficient of stainless steel is much larger than the low-carbon steel, welding and welding of the base metal are more likely to be heated lead to melting, will melt around the base overheating, making the welding zone deformation and grain coarsening.
Stainless steel linear expansion coefficient, and the thermal conductivity of small, easy to transfer heat, and welding depth of penetration, welding heat will cause the expansion of the structure, there are relatively large cooling shrinkage and tensile stress, easy to cause thermal cracking.
After the welding of stainless steel, it is easy to cause intergranular corrosion in the heat affected zone. Because in the heat affected zone, at the sensitization temperature (450 ℃ -850 ℃) interval, the substrate is partially poor chromium, it is difficult to passivation, resulting in corrosion resistance was significantly reduced, so will be the first corrosion, stainless steel grain boundary corrosion width. At this point the corrosion of stainless steel parts of the plasticity and strength has been seriously missing, there will be cracks in the cold bend, brittle fracture, corrosion of metal parts floor landing sound.
Precautions against welding of stainless steel
Control welding current
The current magnitude of the welding stainless steel is smaller than the low carbon steel, the current capacity is about 80% of the low carbon steel.
Speed up the welding speed
Welding speed to be faster, thus reducing the width of the heat affected zone, shortening the weld in the sensible temperature range of residence time, so that the weld in a stable state, and refine the weld structure.
Reasonable selection of welding materials
Select the appropriate welding material and shielding gas. As the chemical composition of the wire will significantly affect the corrosion resistance of the weld, so the chemical composition of the electrode should be similar with the base metal, which will help the weld show the best corrosion resistance.
Welding before and after cleaning
The surface of the material must be cleaned before welding and the weld residue removed after welding.
Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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