THE INFLUENCE OF INTERSTITIAL SOLUTE LEVEL ON THE CHARPY TOUGHNESS PROPERTIES OF A 40-PERCENT CR-FE STAINLESS-STEEL

The present report describes a study aimed at assessing the influence of interstitial solute concentrations, in the form of carbon, nitrogen and oxygen, on the mechanical properties of a 40% Cr-Fe stainless ste el. It is observed that carbon and nitrogen dramatically reduced the i mpact toughness properties while oxygen has only a small detrimental e ffect. Above a certain level of carbon and nitrogen the toughness was insensitive to the amount of interstitial solute. This was ascribed to the saturation of dislocation precipitation sites. The present toughn ess data support the proposed theory that the toughness of ferritic st ainless steels is controlled by the precipitation of carbides and nitr ides on dislocations and not by the structure and morphology of precip itates. Finally, the brittle sigma phase was not identified in the pre sent study and a detailed analysis revealed only the presence of chrom ium-rich carbides and nitrides and some iron-rich oxides.