Surface pore
Open pores are gas pores that extend to the surface of the weld and are open there. They are directly visible and can promote corrosion.
Physical-Chemical Mechanism of Action
Open pores form due to incomplete degassing during the welding process. Gas (often oxygen or nitrogen) forms in the molten pool and gets trapped. As the pool cools, it can no longer dissolve the gas, leading to pores. If these pores reach the surface, they stay open.
Metallurgical Relevance & Welding Risks
Open pores can promote corrosion because they act as anchor points for hydrogen reactions. They can also cause mechanical cracking and weaken the weld. Additionally, they can lead to water entrapment, which further damages the material.
Shop Practice & Action Items
To avoid open pores, careful gas removal during welding is essential. This can be achieved by using deoxidizers and controlling the shielding gas atmosphere. Adequate cooling and avoiding too-fast cooling rates also help prevent pore formation.