Evaluation of the matrix strength of Fe-0.4 wt% C tempered martensite using nanoindentation techniques

摘要

Nanoindentation techniques were applied to evaluate the matrix strength of the as-quenched and the tempered martensite of an Fe-0.4 wt% C binary alloy. The matrix strength was compared with the micro Vickers hardness H-v. The nanohardness H-n of the matrix decreases with increasing tempering temperature, which is similar to the temper softening observed in the micro Vickers hardness. The ratio H-n/H-v, which corresponds to the contribution of the matrix strength to the macroscopic strength, increases markedly when the specimen is tempered at 450degreesC. This is due to a reduction in the grain size effect caused by the grain growth of the blocks that are analogous to the effective grain. The pop-in behaviour that appears in the specimens tempered at or above 550degreesC is due to the reduction in the dislocation density caused by recrystallization. [References: 17]