Duplex stainless steels - a review after DSS '07 held in Grado

Duplex stainless have always been an exiting area of interest for researchers, stainless steel producers, fabricators and end users. They present very diversified technical challenges and simultaneously attractive in-service properties at excellent cost/properties ratios, particularly in critical markets including oil and gas, chemical industry, pulp and paper industry, water systems, desalination plants, pollution control equipments, chemical tankers, etc. This explains why although they still remain a marginal production in the stainless steel business (less than 1%) dedicated international conferences have been organised since about 25 years. The purpose of this paper is to present a review of the 100 scientific contributions presented during the latest international duplex stainless steel conference witch took place in Grado, Italy, on 18-20 June 2007. The main topics concerned microstructure and mechanical properties, weldability, corrosion resistance and in-service properties. The "standard" duplex stainless steels, i.e. the 2304, 2205, and the family of 2507 (Cu,W,...) grades were confirmed as very valuable grades with outstanding performances proven in more than 20 years successful in-service applications. New grades including the so-called lean duplex dedicated to volume oriented markets (possible replacement of 304/316 grades) and some "niche" grades dedicated to very specific markets were presented. It was pointed out that the duplex grades start to be well established products particularly suitable for corrosion resistance applications. They show a two-digit yearly growth thanks to the production of new grades and production ranges (coils and bars) targeting the replacement of the more costly 300 series including 304 but also rusty carbon steel in e.g. structural application.