Effect of solutes on lüders strain in low-carbon sheet steels

Abstract

The effects of phosphorus, tin, and silicon on the magnitude of Lüders strain in low-carbon sheet steels have been studied. At equivalent grain sizes the Lüders strain was effectively reduced by the P or Sn additions. However, when various amounts of Sn were added to a steel containing 0.07 pct P, incremental effects of increasing Sn content could not be recognized; the combined effect of Sn and P on Lüders strain was nearly the same as the effect produced by a slightly higher P alone. Additions of Si to a 0.05 pct P-treated steel, even up to fairly high concentrations, produced very little effect on the Lüders strain. The magnitude of Lüders strain, as influenced by the grain size, is a linear function of d^-1/2, this relation being similar in form to the Hall-Petch relation for yield or flow stress and grain size. The effect of P or Sn on this relation is to decrease the slope of the straight-line plot. These observations have been analyzed on the basis of Lüders strain in relation to the band-front velocity and the contribution of the mobile dislocation density and velocity product (ρv) to the strain rate. Solutes that effectively increase the density of mobile dislocations generated from the grain-boundary sources should decrease the magnitude of Lüders strain.