Properties and microstructure of 316 stainless steel

Wide variations in mechanical properties of type 316 stainless steel make it difficult to design components for use in critical situations. The variation is manifest in two forms; first there may be considerable cast-to-cast variation between steels within the 316 specification; second, individual casts show considerable variation in properties as a function of time and treatment. A particular variation which is of concern is the change of ductility. The strain at failure can cover a wide range, both in tensile tests and creep tests. There are corresponding changes in fracture mode which can be either intergranular/brittle or dimpled/ductile. In order to investigate these variations and, if possible, to establish their causes and to prevent brittle behaviour by optimising specifications, an extensive range of mechanical tests and microstructural characterisations have been carried out. In this paper some of this work is presented; in particular results on four steels together, where appropriate, with results from typical 316 are discussed. (author)