What can cause porosity, or tiny bubbles, to form in welds on mild steel?

The formation of porosity in welds, particularly on mild steel, is influenced significantly by the presence of gas pockets, such as carbon dioxide (CO2). When CO2 is introduced into the arc welding process, it can mix with the molten weld pool, leading to the entrapment of gas bubbles as the weld solidifies. These bubbles can create voids or imperfections, which compromise the integrity and strength of the weld.

In this context, high temperatures are a necessary aspect of the welding process and are not directly responsible for the formation of porosity. Similarly, low pressure does not generate conditions conducive to porosity; rather, it typically relates to gas diffusion and shielding effectiveness. Excessive speed could affect weld penetration and bead shape but does not primarily lead to the introduction of gas pockets into the weld, which is the root cause of porosity. Understanding the role of gas in the welding environment is crucial for preventing defects such as porosity and ensuring high-quality welds.