Mechanism and prediction of screw dislocation strengthening by interstitials in advanced high-strength steels: Application to Fe–C and Fe–N alloys

Abstract

Screw dislocations control the yield strength of low-alloyed body-centered-cubic (e.g. steels). Interstitials such as C and N play a key role in the strengthening mechanisms, yet a mechanistic theory that enables the prediction of strength of alloys over a broad range of compositions and interstitial contents is not available. Here, we provide such a theory and apply it to screw dislocations with C and N in iron, from dilute to larger concentrations. The theory, which accounts for interstitial solute segregation by Cottrell atmospheres, is validated with respect to atomistic simulations and used to predict the yield strength of a broad range of alloys, including fully ferritic, martensitic and precipitation-strengthened microstructures. By using a recent model developed by the authors to predict the dislocation density of martensite as a function of the interstitials content, we find a new scaling of the yield strength with the dislocation density, which matches experiments and differs from the commonly used Taylor equation. The demonstrated predictive power of the theory paves the way for theory-guided alloy design, based on reduced and hence more sustainable testing.