The Rockwell Hardness Test presses a steel or diamond hemisphere-conical penetrator against a test specimen and measures the resulting indentation depth as a gage of the specimen hardness. The harder the material, the higher the HR reading.
In the test, a minor load (10 kgf) is first applied, and the test dial (measuring the indention depth) is reset to zero. Then a major load (60, 100, or 150 kgf) is applied to create the full indention. The major load is reduced back to the minor load, and the indention depth measurement is taken.
The penetrator is usually 1/16 inch in diameter, although larger diameters (such as 1/8 inch) may be used for softer metals. Choosing the proper penetrator and the corresponding load requires experience. Some commonly used combinations are summarized below:
|HRA 72 approximately* =|
|HB (3000)||401||Brinell 10 mm Standard 3000 kgf||80~445|
|HB (500)||>>||Brinell 10 mm Standard 500 kgf||89~189|
|HB (Tungsten 3000)||401||Brinell 10 mm Tungsten 3000 kgf||80~620|
|HB (Indentation)||3.06 mm||Brinell Indentation||6~2|
|HR-15N||82||Rockwell Superficial 15N||69~94|
|HR-15T||>>||Rockwell Superficial 15T||77~93|
|HR-30N||62||Rockwell Superficial 30N||41~85|
|HR-30T||>>||Rockwell Superficial 30T||53~82|
|HR-45N||47||Rockwell Superficial 45N||19~76|
|HR-45T||>>||Rockwell Superficial 45T||28~71|
|Approx. TS||1389 MPa||Tensile Strength (Approx.)||390~2450|
|<<||The hardness value is below the acceptable range of the particular hardness scale.|
|>>||The hardness value is above the acceptable range of the particular hardness scale.|
|###||The hardness value is near the limit (within 15%) of the acceptable range of the particular hardness scale.|
The many hardness tests listed here measure hardness under different experimental conditions (e.g. indenters made in different sizes, shapes, and materials, and applied with different loads) and reduce their data using different formulae. As a result, there is NO direct analytic conversion between hardness measures. Instead, one must correlate test results across the multiple hardness tests.
This calculator is based on hardness data compiled from ASM Metals Reference Book 3rd ed, published by ASM International, and Machinery's Handbook 25th ed, published by Industrial Press. The calculator curve-fits multiple hardness data onto a common polynomial basis and then performs an analytic conversion. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits, and on the valid ranges spanned by the different hardness tests. Converted hardness values should be used for comparative purposes only.