The Influence of Interstitial Solute Level on the Charpy Toughness Properties of a 40 % 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 teel. It is observed that carbon and nitrogen dramatically reduced the impact toughness properties while oxygen has only a small detrimental effect. 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 oughness data support he proposed theory that the toughness of ferritic stainless teels is controlled by the precipitation of carbides and nitrides on dislocations and not by the structure and morphology of precipitates. Finally, the brittle sigma phase was not identified in the present study and a detailed analysis revealed only the presence of chromium-rich carbides and nitrides and some iron-rich oxides.