1998 Volume 84 Issue 8 Pages 566-572
Phosphorus (P), which is widely used as solid solution hardening element in ultra-low carbon interstitial free (IF) steel, often exhibits unpreferable increment of yield strength. In this study, the influence of phosphorus on yielding characteristics in IF steel by focusing the segregation behavior of P to grain boundary. Higher P addition shows normally higher yield elongation compared to its lower addition, leading to relatively high yield strength when the steel is subjected to conventional recrystallization annealing. On the other hand, when additional heat treatment at 700°C is employed, the yield strength of the high P added steel can be significantly reduced. This corresponds to the reduction of the k-value of the Hall-Petch equation. This phenomena is well related to the segregation characteristics of P at grain boundary. Segregated P may induce to a sort of structural change of the grain boundary of steel, resulting in lowering the yield strength. The equilibrium estimation of the segregated P content by considering the grain diameter can lead to considerably good agreement with the experimental data obtained in this study.
