Why is ferroniobium added to stainless steel?

Ferroniobium is added to stainless steel primarily to introduce niobium, which serves several critical metallurgical functions. Because pure elements can be difficult to incorporate into molten metal, ferroalloys like ferroniobium are used as efficient sources to achieve a specific chemical composition.12

The addition of niobium provides the following benefits:

• Stabilization and Corrosion Resistance: Niobium prevents the formation of chromium carbide, which would otherwise cause intergranular corrosion and embrittlement in the material. In ferritic stainless steels, it is specifically used to stabilize interstitial impurities like carbon and oxygen.1
• Dispersion Hardening: Niobium forms carbide precipitates that create a beneficial dispersion hardening effect within the steel matrix.1
• Grain Refinement: By forming small carbide or nitride crystals, niobium acts as a grain refiner. A smaller grain size improves the toughness and strength of the steel.13
• Improved Performance: In martensitic stainless steel, these refinements contribute to better creep resistance and overall toughness.1