Gas pore
Gas inclusion is the entrapment of gases in the weld metal during cooling. These gases can be dissolved when heated and become trapped as pores during cooling, which reduces the cross-section and impairs mechanical properties.
Physical-chemical mechanism
Gases such as oxygen or nitrogen can be dissolved in the weld during heating. During cooling, these gases condense again and form pores. These processes are especially likely at high temperatures and long cooling times.
Metallurgical relevance & risks in welding
Gas inclusion reduces the cross-section of the weld, which impairs mechanical properties like strength and toughness. Pores can also act as starting points for cracks and can increase the service life of components. Additionally, gas pressure can affect the weld, leading to deformation or even collapse.
Workshop practice & instructions
To minimize gas inclusion, the cooling pass should be controlled and fast. This can be achieved by using cooling water or special cooling gases. The weld should not be cooled too slowly to prevent pore growth. Recommended cooling times are between 10 and 30 seconds depending on the steel type and welding process.