Which expert can share some information on stainless steel zinc embrittlement?

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For forwarding, please note that galvanized pipes can be welded, but it is necessary to grind off 20–30 mm of the galvanizing layer from the welding area before welding; otherwise, bubbles, porosity, and weak welds may occur. It also makes the weld brittle and reduces its stiffness. Welding characteristics of galvanized steel: Galvanized steel is typically made by coating low-carbon steel with a layer of zinc, with the thickness of this zinc coating usually being around 20 um. The melting point of zinc is 419°C, and its boiling point is around 908°C. During welding, zinc melts into a liquid that floats on the surface of the molten pool or at the root of the weld. Zinc has a high solubility in iron; zinc liquid can penetrate along the grain boundaries and erode the weld metal, and the low-melting-point zinc causes \"liquid metal embrittlement\". At the same time, zinc and iron can form intermetallic brittle compounds; these brittle phases reduce the plasticity of the weld metal, leading to cracks under tensile stress. When welding fillet welds, penetration cracks are most likely to occur, especially in the fillet welds of T-joints. When welding galvanized steel, the zinc layer on the surface and edges of the groove undergoes oxidation, melting, and evaporation due to the heat from the arc, resulting in the release of white fumes and vapor; this can easily cause pores in the weld. ZnO formed as a result of oxidation has a high melting point, of around 1800°C or more; if the parameters used during welding are too low, this can lead to the formation of ZnO inclusions. Because Zn acts as a deoxidizer. Low-melting-point oxide inclusions of FeO-MnO or FeO-MnO-SiO2 are formed. Secondly, due to the evaporation of zinc, large amounts of white smoke are emitted, which can irritate and harm the human body; therefore, it is necessary to grind off the galvanized layer at the welded area. Welding process control: The pre-welding preparation for galvanized steel is the same as that for ordinary low-carbon steel; it is important to pay careful attention to the dimensions of the groove and the galvanized layer in its vicinity. To ensure full penetration, the groove dimensions should be appropriate, generally at 60–65°, with a certain gap left, usually between 1.5 and 2.5 mm. To reduce the penetration of zinc into the weld, the galvanized layer in the groove can be removed before welding. In actual supervision work, a process of concentrating groove preparation without leaving bevels was adopted for centralized control, along with a two-pass welding method, which reduced the likelihood of incomplete welding. The welding rod should be selected based on the base material of the galvanized pipe; generally, for low-carbon steel, J422 is commonly used due to its ease of use. Welding technique: When welding the first layer of a multi-layer weld, try to melt the zinc layer and cause it to vaporize and evaporate, thereby allowing it to escape from the weld – this can **reduce the amount of liquid zinc remaining in the weld**. When welding fillet welds, it is also necessary to melt the zinc layer in the first layer as much as possible and cause it to vaporize and evaporate, thereby allowing it to escape from the weld. To do this, move the end of the welding rod forward by about 5–7 mm first; once the zinc layer has melted, return it to its original position and continue welding forward. When performing transverse and vertical welding, if short-shrouded electrodes such as J427 are used, the tendency for undercutting is very low ； If the back-and-forth welding technique is used, defect-free welding quality can be achieved. Galvanized sheets can be welded using MIG arc welding, an innovative technique developed by the German company Cloos.