Inclusions are non-metallic contaminants that become trapped or held within a metal during solidification or processing. These contaminants, in the form of oxides, sulfides, or silicates, can severely detriment the mechanical properties, surface finish, and therefore, quality of the metal.
Key Features:
- Non-metallic impurities: Common inclusions can include aluminum oxide, manganese sulfide, and silica, all of which are derived generally from flux, slag, or reactions formed during melting.
- Affect mechanical properties: Inclusions can act as stress raisers and can decrease toughness, ductility, fatigue strength, and weldability.
- Classified as endogenous or exogenous:
- Endogenous: Inclusions formed from reactions within the metal.
- Exogenous: Inclusions that enter the melt from external sources such as furnace linings or slag.
Most, if not all, industries that use a significant quantity of metal have a serious quality problem with inclusions (automotive, aerospace, and tool manufacturers, for example), and this is exceptionally problematic for the durability and integrity of their structural properties. Highly refined embedded inclusions are very evident; however, people would prefer no inclusions. With modern and advanced refining methods (i.e., vacuum degassing, ladle metallurgy, and filtration), we minimize their content in steel and other alloys. Clean metals with fewer embedded inclusions have significantly better fatigue resistance, polished or shiny surfaces, and improved reliability. Therefore, it is imperative to monitor and control inclusions as part of producing defect-free and high-quality metallic components.
