Non-metallic inclusions (oxides, sulfides, silicates) are detrimental as they:
Act as stress raisers, initiating fatigue cracks or brittle fracture.
Reduce ductility and impact toughness, especially in the transverse direction.
Can harm machinability and surface finish.
Control is achieved through:
Secondary Steelmaking: Processes like Ladle Furnace (LF) and Vacuum Degassing (VD/VOD) are used to reduce oxygen and sulfur content, modify inclusion morphology, and clean the steel.
Inclusion Shape Control: Adding Calcium (Ca) treatment transforms hard, abrasive alumina (Al2O3) stringers into softer, globular calcium aluminates, improving machinability and reducing anisotropy.
Material standards often specify cleanliness requirements (e.g., according to ISO 4967 Method A for microscopic assessment) for critical applications.