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 Pc at which the pop-in occurs is higher in ULC than in IF, and the Pc 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.

► ULC needs higher stress to initiate plastic deformation than IF does.
► The critical stress for pop-in in ULC decreases with decreasing indentation rate.
► In-solution carbon in ULC affects on the initiation of plastic deformation.
► A model for understanding the effect of carbon on the pop-in behavior is proposed.