Question 1

Which hardness scales are supported?

Accepted Answer

Vickers (HV), Rockwell C (HRC), Rockwell B (HRB), Brinell 3000 kgf ball (HBW), and approximate tensile strength (MPa and ksi). The Mohs scale is shown in a separate reference table for minerals.

Question 2

Why do some outputs show '-'?

Accepted Answer

The ASTM E140 table does not define all scale combinations for all ranges. For example, Rockwell C is only defined for HV values above ~200 (hard steels), and Rockwell B is only defined for softer ranges (HV ~108–200). When a scale is not defined for the input range, the tool shows '-' rather than an inaccurate extrapolated value.

Question 3

Are the conversions accurate for all metals?

Accepted Answer

The lookup table is based on ASTM E140-12b, which is defined for non-austenitic steel (carbon and alloy steels). For other materials - aluminium, copper, titanium, cast iron - the conversions are approximate at best. Hardness conversion between scales is empirical and material-dependent.

Question 4

What is the difference between HBW and HB?

Accepted Answer

HBW (Brinell Hardness with tungsten carbide ball) replaced the older HB designation (which used a steel ball). ASTM requires HBW for all Brinell tests above HB 100. HBW and HB values are numerically very close but not identical. This tool uses the HBW scale with a 3000 kgf load.

Question 5

What is tensile strength and how is it estimated from hardness?

Accepted Answer

Tensile strength (UTS) is the maximum stress a material can withstand before breaking. For steels, there is an empirical relationship between Brinell hardness and UTS: UTS (MPa) ≈ 3.45 × HBW. This is an approximation and varies by steel grade and heat treatment. The value shown is interpolated from the ASTM E140 table.

Question 6

Can I convert Mohs hardness to HV?

Accepted Answer

Mohs hardness and Vickers hardness are measured by fundamentally different methods (scratch resistance vs. indentation), so a precise mathematical conversion does not exist. The Mohs–Vickers table shows approximate equivalent ranges from the literature. For minerals above Mohs 6, the Vickers values climb sharply and the ranges are very wide.

Material	HV	HRC	HBW
Soft aluminium	15–35	-	15–35
Annealed copper	40–60	-	40–60
Mild steel	100–140	-	100–135
Stainless steel	150–220	-	145–210
Normalised steel	200–250	~5	190–240
Through-hardened steel	350–500	35–50	340–480
Case-hardened steel	600–750	55–62	-
High-speed steel	800–900	60–66	-

Hardness Scale Converter

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