Precipitation of Chromium Nitrides in the Super Duplex Stainless Steel 2507

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2015-03, Vol.46 (3), p.1062-1072
• Main Authors: Pettersson, Niklas, Pettersson, Rachel F. A., Wessman, Sten
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemical precipitation; Chemistry and Materials Science; Chromium compounds; Chromium nitride; Corrosion resistance; Duplex stainless steels; Ferrite; Materials Science; Materials Science and Engineering; Metallic Materials; Metallurgy; Nanotechnology; Nitrides; Pitting (corrosion); Precipitates; Precipitation; Stainless steel; Structural Materials; Surfaces and Interfaces; Teknisk materialvetenskap; Thin Films
• ISSN: 1073-5623; 1543-1940; 1543-1940
• DOI: 10.1007/s11661-014-2718-y

Precipitation of chromium nitrides during cooling from temperatures in the range 1373 K to 1523 K (1100 °C to 1250 °C) has been studied for the super duplex stainless steel 2507 (UNS S32750). Characterization with optical, scanning and transmission electron microscopy was combined to quantify the precipitation process. Primarily Cr 2 N nitrides were found to precipitate with a high density in the interior of ferrite grains. An increased cooling rate and/or an increased austenite spacing clearly promoted nitride formation, resulting in precipitation within a higher fraction of the ferrite grains, and lager nitride particles. Furthermore, formation of the meta-stable CrN was induced by higher cooling rates. The toughness seemed unaffected by nitrides. A slight decrease in pitting resistance was, however, noticed for quenched samples with large amounts of precipitates. The limited adverse effect on pitting resistance is attributed to the small size (~200 nm) of most nitrides. Slower cooling of duplex stainless steels to allow nitrogen partitioning is suggested in order to avoid large nitrides, and thereby produce a size distribution with a smaller detrimental effect on pitting resistance.