In high purity Fe–Cr systems, the gamma loop extends as far as about 13.5% Cr, after which the structure is fully ferritic at all temperatures. Due to low alloying content, 3Cr12 lies in the dual phase region, and the structure would therefore consist of a mixture of untransformed delta ferrite, alpha ferrite which transformed from austenite on cooling and martensite, depending on the cooling rate [28] and that is why it is variously described as ‘‘ferritic” or ‘‘ferritic- martensitic” 12% Cr stainless steel.