2012 Volume 53 Issue 5 Pages 907-912
The effect of pre-existing dislocations and interstitial carbon on the initiation of plastic deformation in interstitial free (IF) steel and ultra low carbon (ULC) steel were investigated by the nanoindentation technique. The critical load, Pc, of the pop-in phenomenon, which corresponds to plasticity initiation, appeared clearly on the loading curve. The Pc in high dislocation density materials was smaller than that in low dislocation density materials with no difference between IF and ULC while the Pc in low dislocation density materials was remarkably higher in ULC than in IF. These results indicate that the interstitial carbon in the matrix does not affect the pop-in phenomenon when there are pre-existing dislocations or dislocation sources, and we discuss the reason for their occurrence occurs in high dislocation density materials.