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Welder’s Handbook
Inclusions
Inclusions refer to solid materials that become trapped within the weld metal. Tungsten, oxides, slag, and flux are among the typical foreign substances that can become entrapped in the molten weld pool and form inclusions.
Slag
Inclusions
Slag inclusions are nonmetallic materials that get trapped in the weld material. Slag is nonmetallic product resulting from chemical reactions of flux and nonmetallic impurities. Slag inclusions can occur between passes or at the groove face. Slag inclusions often occur during certain welding methods like SMAW, FCAW and SAW. Slag inclusions are lighter than the surrounded metal and usually rise to the surface of molten metal, unless they become entrapped in the weld metal. Multiple-pass welds are more likely to have slag inclusions than single-pass welds because slag from the previous pass if not completely removed will become entrapped in the subsequent pass.
Tungsten
Oxide
When droplets of tungsten get entrapped within the weld metal this is called Tungsten Inclusion.
When surface oxides get entrapped in the weld metal this is called Oxide Inclusion.
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