Abstract
Alloy UNS N08031 is combining the advantages of high-chromium alloyed materials, i.e. a high resistance to corrosive attack by oxidizing media, with a molybdenum content of more than 6 %. The nickel content is comparatively low. This way it was possible to create the highly corrosion resistant material UNS N08031 in using only small amounts of expensive alloying elements.
Alloy UNS N08031 exhibits good resistance to pitting and crevice corrosion in neutral and acid aqueous solutions, which makes it advantageous to the known 6 % Mo stainless steels, and even several nickel alloys. Therefore, it lends itself to applications as e.g. flue gas desulfurization, concentrating of diluted sulfuric acid, pulp & paper, phosphoric acid, acetic acid, salt brines and hot seawater as a promising material for a multitude of applications. Alloy UNS N08031 is readily weldable without risk of intercrystalline corrosion.
The successful and widespread use of alloy UNS N08031 resulted in the need to make it easier to handle since the original alloy is requiring a solution annealing treatment at about 1180 °C followed by fast cooling which is not so easy to perform in every place of manufacturing. This requirement was met by a recent adaptation of alloy composition resulting in an alloy UNS N08031 Plus. The alloy UNS N08031 Plus can be solution annealed at lower temperatures between 1140 and 1160 °C, which is much more convenient in manufacturing. The alloy modification facilitates manufacturing of large components as much as in roll bond cladding as in shaping and heat-treating of large dished vessel heads.
The aim of this paper is to present the main properties and applications of both alloys and the advantage of alloy UNS N08031 Plus, which is the possibility of being roll bond cladded.
