Definitions and Characteristics

Ultrapure ferritic stainless steel contains 11%~30% chromium, and the total amount of C and N is controlled below 150×10-⁶, which significantly improves the intergranular corrosion and low temperature brittleness of ferritic stainless steel. It has excellent resistance to chloride corrosion and oxidation resistance, and is suitable for automobile exhaust system, home appliances, chemical equipment and other fields.

smelting technology

The core of production is deep decarburization and denitrogenation, mainly using a three-step process (EAF + AOD/K-OBM/MRP decarburization + VOD-like vacuum refining). For example, the VOD PB method and SS VOD method can reduce [C+N] to below 37×10-⁶, enhancing high-temperature strength and corrosion resistance.1 Domestic companies such as Thai Steel have achieved a C+N concentration of less than 200 ppm through non-vacuum smelting technology, and plan to further enhance it by introducing VOD equipment.

Typical steel grades and applications

Automotive exhaust system: such as SUS436L, SUS444 (add Mo, Nb and other elements), high-temperature oxidation resistance and thermal fatigue performance is better than 430 series.

Low-cost alternative: due to fluctuations in nickel prices, ultra-pure ferrite (such as 409L) gradually replace the 300 series stainless steel, especially in the Korean market dominated.