高強度鋼中の介在物のAFM超微小硬さ試験(<小特集>材料のミクロ・メゾ評価)

抄録

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.