Microscopic and Mesoscopic Evaluations of Materials. AFM Ultra-Micro Hardness Test for Inclusions in High Strength Steels.

Abstract

Nanoindentation measurement for TiN, Al2O3, SiO2 and MnS inclusions in SCM440, SUP12 and SWOSC-V steels was carried out, using an AFM ultra-micro hardness tester and a special lever which has a three-sided pyramidal diamond indenter with the edge angle of 60°. Results obtained are as follows. (1) A force-penetration curve was obtained on the inclusion with the diameter smaller than 2 μm, because the AFM ultra-micro hardness tester has the imaging capability in a nanometer scale. (2) Vickers hardness values were estimated from force-penetration curves as 100, 400∼450, 900∼2 500 and 1 000∼4 000 for MnS, SiO2, Al2O3 and TiN inclusions, respectively, using two experimental equations between nanoindentation measurement and micro-Vickers measurement. (3) The hardness measurement for the base metal showed that the Vickers hardness from the nanoindentation measurement was lower than that from the micro-Vickers measurement. This was because the effect of grain boundaries and precipitates on the hardness was stronger in the micro-Vickers measurement.