A Nanoindentation Study on the Correlation between Strength and Microstructures in Advanced High Cr Steel

Abstract

Nanoindentation experiments were performed on an advanced high Cr steel having extremely fine and complex martensitic microstructures, in order to analyze the strengthening mechanism of the steel and its change with aging. At a low load level (such as 0.5 ~ 1 mN), it was possible to evaluate the matrix strength (assumed by calculating plastic zone size) alone without the contribution of high angle boundary effects. Comparing the sizes of microstructures with the predicted size of indentation plastic zone leads to suggest that the most effective microstructural unit on strengthening mechanism in this steel is indeed block rather than lath and prior austenite grain. Also, the relative values of nanohardness and macrohardness of aged samples are discussed in terms of providing a way to explain a possible mechanism for aging-induced softening phenomena in this steel.