The effect of interstitial carbon on the initiation of plastic deformation of steels

Pop-in behavior in nanoindentation was studied as a mechanism for the initiation of plastic deformation in two kinds of steels with different interstitial carbon contents; interstitial free (IF) and ultra low carbon (ULC) steels. The critical load P(c) at which the pop-in occurs is higher in ULC than in IF, and the P(c) decreases with decreasing loading rate, indicating that the pop-in mechanism is based on a thermal activation process. The interstitial carbon is thought to yield higher friction stress against dislocation movement and have an influence on the critical stress for the activation of the dislocation source formed underneath the indenter. (C) 2011 Elsevier B.V. All rights reserved.