What are slag inclusions in welding?

Slag inclusions in welding refer specifically to nonmetallic solids that become trapped within the weld metal. During the welding process, flux or other materials are used to protect the weld pool from contamination and oxidation. These materials can produce a byproduct known as slag. If the slag is not properly removed before or during the welding process, it can become embedded in the molten metal and solidify with it, creating a defect known as a slag inclusion.

This defect can compromise the integrity and mechanical properties of the welded joint, potentially leading to weaknesses or failures under stress. Understanding the nature of slag inclusions is crucial for welders, as it informs proper technique and cleaning protocols to ensure the highest quality welds.

In contrast, the other options do not accurately define slag inclusions. Air bubbles would refer to gas pockets, crystalline structures suggest a solid formation different from nonmetallic inclusions, and fatigue cracks are specific types of fractures that occur under cyclic loading, unrelated to the composition of weld defects.