Evaluation of grain boundary effect on strength of Fe-C low alloy martensitic steels by nanoindentation technique

Abstract

The grain boundary effect on the strength was evaluated through nanoindentation technique for Fe-0.4C-Cr-Mo steels that were produced by the ausform-tempered (AF) and conventional quench-tempered (QT) processes. A semiquantitative Hall-Petch plot was made to determine the locking parameter k for the two alloys using nanohardness, micro-Vickers hardness, and grain size. The k value for the QT sample is significantly larger than that for the AF sample and is attributed to the film-like carbides on the grain boundaries of the QT sample. The lower k value of the AF sample is one of the factors for the improved delayed fracture property in the AF compared to that of the QT sample. ©2005 The Japan Institute of Metals.