2021/8/7 21:53:19
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A 316 L modified - low Si, high Mo stainless steel for Urea plants The UREA 316L Modified grade has been specially developed for Urea plant applications. It is a 316L modified stainless steel with extra-low silicon content and substantial higher molybdenum contents. The low carbon content, combined with a well balanced chemistry (low silicon and nickel content close to 14%) makes the alloy fully austenitic, free of intermetallic phase precipitations. The ferrite level is kept under 0.5% in the solution annealing and water quenched conditions. The alloy is designed for improved corrosion resistance properties in Urea carbonate environments. The UREA 316L Modified grade is a fully austenitic stainless steel which ferrite content is guaranteed less than 0.5% after solution annealing heat treatment (1120°-1180°C (2048-2156°F) /water quenched). The carbon content is kept low while the steel making is optimized in order to improve the cleanliness properties of the steel. Hot forming Hot forming should be carried out in a temperature range of 1200-950°C (2732-1742°F) after the piece has been uniformly heat treated. Final full annealing tremperature is required to obtain the requested microstructure. It will be performed at 1120°-1180°C (2048-2156°F) followed by water quenching. Cold forming Due to its fully austenitic microstructure, the alloy can be cold formed without any problem. The higher molybdenum content and cold hardening behavior of the steel explains that it may require more powerful equipments than 304 stainless steel. Pickling The UREA 316L Modified grade must be used in the as pickled and passivated conditions. Pickling treatment may be performed with a Nitro-hydrofluoric acid bath (10-20 % HN03 - 1.5-5% HF) at room temperature (few hours) or 20 minutes approx. at 60°C (140°F).10-20% H2SO4 - 1.5-5% HF pickling bath may also be used. The UREA 316L Modified grade can be welded with most of the welding processes: TIG, Plasma, MIG welding, as well as SMAW, SAW or FCAW processes. The alloy is sensitive to hot cracking phenomenon due to its fully austenitic microstructure. Weld should be performed in order to obtain extra-low ferrite contents, no carbide or nitrides precipitations, low silicon contents as well as no intermetallic phase’s precipitations. Higher manganese content products should be considered. |
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