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Rockwell A-Scale Hardness
Brale indenter, 60 kgf load
 
Symbol:  HRA 

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:

Scale Condition Application
A Brale indenter
60 kgf load
Thin, hard sheet materials, such as tungsten carbide.
B 1/16 in diamond ball
100 kgf load
Medium/low hard materials, such as annealed carbon steels.
C Brale indenter
150 kgf load
Materials harder than HRB 100.
D Brale indenter
100 kgf load
Case-hardened materials.
F 1/16 inch Brale indenter
60 kgf load
Soft materials, such as bearing metals.
N 1/16 inch Superficial Brale indenter
15, 30, or 45 kgf load
Unhardened materials, such as metals softer than hardened steel or hard alloys, or where shallow indentations are desired.
T 1/16 inch diamond ball
15, 30, or 45 kgf load
Unhardened materials, such as metals softer than hardened steel, or where shallow indentations are desired.
 

Convert   HRA       
(suggested range: 59 ~ 86)
  HRA   72   approximately*
Hardness
Symbol Amount Name Suggested
Range
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
HK  443   Knoop  97~920
HM  4   Mohs  1~10
HRB  >> Rockwell B-Scale  41~100
HRC  43   Rockwell C-Scale  19~69
HRD  58   Rockwell D-Scale  39~77
HRF  >> Rockwell F-Scale  88~100
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
HS  57   Shore Scleroscope  17~97
Approx. TS  1389 MPa   Tensile Strength (Approx.)  390~2450
HV  424   Vickers  20~1800

Legend
<< 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.

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