Non-metallic inclusions are tiny bits of non-metallic materials, such as oxides, sulfides, or silicates, that become trapped inside a metal matrix during processing. They can impact the metal's strength, toughness, and its ability to perform adequately.

Key Features:

• Types of Inclusions: The three most common types of inclusions are oxide inclusion (which form as a result of oxygen reacting with the molten metal), sulfide inclusion (which form when sulfur is present), and silicate inclusion (which form from the presence of slag or impurities). Each type can impact the metal property differently.
• Sources of Formation: Inclusions typically occur during melting, casting, or refining due to contaminants, chemical reaction, or lack of control over the processing parameters.
• Effect on Properties: Non-metallic inclusions are an issue as they can degrade ductility, fatigue strength, and surface finish quality. That said, non-metallic inclusions there can also help achieve improved machinability in some steels when applied in a controlled format.

The importance of non-metallic inclusion stems from the negative effect they have on the quality of the metal and reliability. Industries such as aerospace, automotive, and construction require controlled parameters for non-metallic inclusions in order to have the most consistent performance of the material. The existence of non-metallic inclusions can be reduced or minimized metallurgically through processes such as refining the steel, filtering or vacuum treatment. Once processed, various inspection techniques such as microscopy and ultrasonic testing may be employed to inspect and classify any detectable non-metallic inclusion, thus assisting the manufacture in quality control and improving product life.