Microporosity
Microporosity is fine, often network-like gas inclusions in the weld metal, resulting from the reduced solubility of gases during solidification. This porosity can impair the mechanical strength and toughness of the material.
Physicochemical mechanism of action
Microporosity forms when gases are dissolved in the molten pool and can no longer escape during cooling. These gases then form microscopic pores in the weld metal structure.
Metallurgical relevance & welding risks
Microporosity can reduce mechanical strength and toughness, since the pores act as weak spots. They can also cause material fatigue and shorten component life.
Workshop practice & action points
To minimize microporosity, make sure to degas thoroughly before welding. You can do this by using deoxidizers and increasing the melting pressure. Also, keep the weld well sealed to keep gases out. For steels with high gas content, pick the welding process carefully.