Effect of Surface Finish on Microhardness Measurements PDF

Keywords

microhardness, steel, deformations

Abstract

Vickers microhardness indentations on steel cause deformations in only a small volume of the material. As a result, the values obtained greatly depend on the surface finish in the vicinity of the indentation. This study investigates the dependence of microhardness test results on the test loads and surface conditions of a BS 970 steel in three heat treatment conditions. Extensive measurements of the universally accepted roughness average were carried out on different grounds and polished metallographic surfaces. Profile graphs were recorded and microhardness measurements carried out under loads o 10, 20, 50 and 100 grams. At low loads, 10g, the measured hardness increased with the degree of polish (e.g. with the decreased in roughness average), whilst in hard steel, this effect persists up to 50g load. The shapes of indentations are affected by the directional characteristics of the grinding pattern.