1989 Speller Award Lecture: New Stainless Steels for Seawater Service^☆ Available to Purchase

A review is presented of the research and development effort that has been aimed at providing new stainless steels for use in seawater and seawater-cooled systems. Three new categories of highly corrosion-resistant stainless steels are described, namely the superaustenitics (i.e., austenitic nitrogen-containing 6% molybdenum grades), the titanium-stabilized superferritics, and the superduplexes (i.e., duplex grades containing molybdenum and nitrogen). The key microstructural and alloy composition effects that improve resistance to localized corrosion (which is the main mode of failure of stainless steels in seawater) are discussed. The joint effect of molybdenum and nitrogen is found to be exceptionally beneficial for the localized corrosion resistance of the austenitic and duplex grades, whereas inclusions and second phases are generally detrimental for all grades. Problems encountered with thick sections, such as sigma and chi phase precipitation in the superaustenitics and high ductile-to-brittle transition temperatures in the superferritics are identified and areas for further research are noted.