Residual gas inclusion in weld metal
Residual gas entrapment causes pores in the weld metal that impair its strength and toughness. Gases like nitrogen, hydrogen, or carbon monoxide dissolve in the molten weld pool and cause porosity during solidification.
Physicochemical mechanism of action
Residual gas entrapment occurs when gases such as nitrogen (N2), hydrogen (H2), or carbon monoxide (CO) are dissolved in the molten weld metal and penetrate into the crystalline structure of the metal as gas during cooling. This leads to porosity, since the gas does not fully outgas.
Metallurgical relevance & risks in welding
Porosity in the weld metal can lead to various problems: it lowers the strength and toughness of the material, increases stress concentration, and makes the material susceptible to cracking. In extreme cases, this can lead to hot cracks or damage to the component structure.
Workshop practice & instructions
To minimize residual gas entrapment, the following measures should be taken:
• Use clean welding materials and consumables.
• Make sure the weld metal is dry before welding.
• Keep the weld bead as short as possible and cool it quickly if possible.
• Use a degassing device if necessary to remove gases from the melt.