Nanoindentation measurement for TiN, Al{sub}2O{sub}3, Si{sub}O{sub}2 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 diamondindenter 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 2μm, because the AFM ultra--micro hardness tester has the imaging capability in ananometer 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, SiO{sub}2, Al{sub}2O{sub}3 and TiN inclusions, respectively, using two experimental equations betweennanoindentation 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.
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