If the content of moisture and other hydrogen-containing substances in the shielding gas is controlled within a certain range according to relevant standards, CO2 gas shielded arc welding and argon-rich gas mixture (80% Ar+20% CO2) are used to protect the weld metal. Generally do not produce a lot of hydrogen holes. This is because the CO2 gas will undergo a decomposition reaction (CO2=CO+O) at a high temperature of the arc. The decomposed atomic oxygen has a strong oxidizing property, and reacts with the gas phase to form an OH that is insoluble in the liquid metal, thereby effectively Prevents the formation of hydrogen gas holes in the weld. The use of pure CO2 gas protection will produce CO pores. When the carbon dioxide gas shielded arc welding is performed, the following reaction occurs: Fe+CO2=FeO+COFeO+C=Fe+CO This reaction is performed inside the molten bath. Since the solubility of the metal to carbon monoxide is very low, the generated carbon monoxide comes out of the bath. If the pool metal is completely crystallized, there is still a portion of the carbon monoxide that is not exhausted, and pores are formed in the weld. And then there is the decomposition reaction of CO2 gas at a high temperature arc of 3500°C: 2CO2=2CO+O2O2=2O This reaction is endothermic, so the cooling effect of carbon dioxide gas flow is more significant, so that the metal in the bath cooling is particularly fast, plus the weld seam Because the molding is narrow and deep, the gas discharge conditions are deteriorated, so that air holes are generated.