Low Chromium Iron Ferritic Stainless Steel 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L)
Ferritic stainless steels are defined as having a ferrite crystal structure in the as-quenched condition and having a chromium content usually exceeding 10.5%. These steels are generally low cost, non-hardenable and resistant to corrosion in a wide range of environments. Alloying elements, in particular molybdenum, provide increased corrosion resistance in acid and chlorides environments, such as those found in the automotive and chemical industries. Low chromium (Cr) iron ferritic stainless steels, 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L), are widely utilized due to their low price and great life cycle performance when compared to austenitic grades.
0Cr11Ti (AISI409) is a low chromium ferritic stainless steel containing 0.08%~0.2% Cr, lower than 0.5% Ni and usually containing trace amounts of Mg, Ti, Nb and other elements. AISI-409 provides excellent combination of oxidation resistance, thermal fatigue, chloride stress corrosion and atmospheric heat resistance. This makes 0Cr11Ti (AISI409) ideal for exhaust system and other applications, such as catalytic converters, mufflers, heat exchangers, surface treatments, etc.
The microstructure of 0Cr11Ti (AISI409) is composed of ferrite and small amounts of austenite and carbides. Good weldability can be achieved by taking the proper welding techniques. The heat affected area of AISI-409 may exhibit evidence of sensitization (golden brown colour) on the surface after welding. This may be reduced by introducing Ni in the welding filler to reduce sensitization and re-establish the passive film. While 0Cr11Ti (AISI409) is not recommended for aqueous chloride media, it performs very well in a variety of other aggressive environments.
00Cr11Ti (AISI409L) is a low-chromium ( Cr content of 0.03%-0.035%) ferritic stainless steel. This alloy is similar to 0Cr11Ti (AISI409) and it only has a minor difference in their chemical composition; Mn and P level is slightly different in the two grades. 00Cr11Ti (AISI409L) has no Ni or Mo alloy, which are not required due to the low-chromium content, but an increased amount of Mg has been added to maintain its rust protection capabilities.
00Cr11Ti (AISI409L) has good ductility and formability, but similar to other ferritic alloys, it behaves differently than austenitic stainless steels. 00Cr11Ti (AISI409L) work-hardens quickly, so heating and/or annealing may be required to restore the ductility when forming. The welding of00Cr11Ti (AISI409L) can be done by conventional arc welding and may need additional attention in order to ensure good joint strength and good corrosion resistance.
The properties of 00Cr11Ti (AISI409L) are very similar to 0Cr11Ti (AISI409), but a major difference is the fact that this material has a greater resistance to corrosion, making it more suitable for applications that require higher levels of durability, such as industrial applications exposed to corrosive environments. While 0Cr11Ti (AISI409) performs well in most applications, 00Cr11Ti (AISI409L) is a good choice for applications exposed to high temperatures, making it popular in commercial kitchens, since it has greater resistance to corrosion and pitting when compared to other ferritic alloys.
In conclusion, the low chromium (Cr) iron ferritic stainless steels, 0Cr11Ti (AISI409) and 00Cr11Ti (AISI409L), offer a wide range of advantages. 0Cr11Ti (AISI409) is a low cost non-hardenable stainless steel with good oxidation resistance, thermal fatigue and corrosion resistance, while 00Cr11Ti (AISI409L) offers improved environmental corrosion resistance and is ideal for applications exposed to high temperature environments. Both of these low chromium (Cr) iron ferritic stainless steels provide a cost-effective and easy to use option for many applications.
