Low Chromium Ferritic Stainless Steel 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
Low chromium ferritic stainless steel 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L) are two of the most commonly employed grades in the ferritic stainless steel family, due to their excellent combination of formability and corrosion resistance. Low chromium ferritic stainless steel is a type of non-hardenable stainless steel that features chromium between 10.5 and 20%. It contains no nickel and orders small amounts of molybdenum, and as a result can be magnetic and susceptible to intergranular corrosion.
AISI409 and AISI409L are both alloyed with iron and chromium, as well as trace amounts of manganese, phosphorus, sulfur, silicon and niobium. AISI409 contains typically 11.5wt% chromium with a balance of iron, and is the most commonly used grade of low chromium ferritic stainless steel. AISI409L low chromium ferritic stainless steel contains 0.03wt% carbon, is often referred to as a stabilized grade, and provides improved weldability and resistance to intergranular corrosion compared to AISI409.
Chromium in low chromium ferritic stainless steel is what provides its excellent corrosion resistance. Chromium forms a tightly adherent oxide film on the surface of the steel that is impervious to moisture and oxygen, creating a barrier that prevents further oxidation. Therefore, the higher the chromium content, the greater the corrosion resistance.
AISI409 and AISI409L exhibit good mechanical strength and formability. Thanks to their magical nature, they hold up well to moderately high temperatures and extreme conditions, including thermal cycling, making them suitable for automotive and process equipment applications, where low-cost heat exchangers must resist crevice and stress corrosion as well as oxidation and sulfuric acid attack. In addition, they offer comparatively good oxidation resistance in stressful environments and have good creep strength, making them preferred in fabrications used at high temperatures, such as automotive exhaust systems and other industrial plants.
Since the carbon content in AISI409L is very low, weldability is much better than with AISI409. The low carbon content makes it less susceptible to sensitization during welding, which can occur when carbon combines with chromium to form chromium carbides in the heat-affected zone of a weld. This restricts the chromium from forming its oxide film, leaving the ferrite matrix of the material vulnerable to corrosion.
Low chromium ferritic stainless steel AISI409 and AISI409L are cost effective, reliable and perform well in a majority of common environments, making them highly sought after in the industry.
