Which hardness test is most suitable for measuring the hardness of an individual carbide particle (~50 μm diameter) in a steel matrix?
ABrinell (HB) — large ball averages the microstructure well
BRockwell C (HRC) — fast and direct reading
CVickers microhardness (HV) at low load — indent fits within the particle
DRockwell B (HRB) — designed for softer materials
A 50 μm carbide particle requires an indent smaller than the particle itself. Brinell and Rockwell indents are hundreds of micrometers to millimeters in diameter — far too large. Vickers microhardness at loads below 1 kgf produces indents in the 10–50 μm range, allowing measurement within a single phase or microstructural feature.
Question 2 Short Answer
A steel component has a Brinell hardness of 200 HB. Estimate its approximate ultimate tensile strength.
Think about your answer, then reveal below.
Model answer: UTS ≈ 3.45 × 200 = 690 MPa. This correlation is reliable for carbon and low-alloy steels.
The empirical relationship UTS (MPa) = 3.45 × HB applies well to carbon and alloy steels because their strengthening mechanism (martensite, pearlite) produces consistent hardness-strength ratios. For a steel with HB = 200, the estimate is 690 MPa. This should not be used for stainless steels, aluminum alloys, or other materials where the correlation breaks down.