Welding Metallurgy of Austenitic Stainless Steels

Abstract

Stainless steels can generally be defined as steels with at least 11–12% chromium and carbon contents which are normally below 0.15%. With increasing demands on corrosion resistance, however, the chromium contents must be increased to above 16%. In ferritic stainless steels, the structure can be rather brittle which means poor weldability. Austenitic stainless steels show marked advantages here, particularly with regard to toughness properties and weldability. In stainless steels, the austenitic structure is generally produced by alloying with nickel. Nitrogen, a strong austenitizing element, has also gained increasing importance in recent years. One of the most important properties of austenitic stainless steels is their corrosion behaviour. The latter also determines their chemical composition. Beginning with the classical austenitic 18/8 chromium-nickel steel (AISI 302), Fig. 107 shows in a simplified but illustrative manner the effect that the basic elements and alloying additions have on the corrosion properties of the alloy, based on the representation of Sedriks [390]. For most types of corrosion an increase in the chromium content of the alloy above 18% will produce an improvement in corrosion resistance. A reduction in the carbon content to 0.030% max. or the stabilization of carbon by alloying with titanium or niobium will increase the alloys resistance against intergranular corrosion. Additions of molybdenum mainly improve the resistance to pitting and crevice corrosion.