Rockwell Hardness
HRA, HRB, HRC measure indentation depth. HRC for hardened steel; HRB for softer metals. Convert to BHN, Vickers, tensile strength.
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HRC 60+ for cutting tools HRB for non-ferrous, soft steel HRA for thin case hardening 1 in. ball for HRB; diamond for HRA/HRC
Ready to run the numbers?
Why: Different scales for different materials. HRC 20-70 for tool steel; HRB for brass, aluminum. ASTM E18 standard.
How: HRC to BHN: BHN โ 100 + 5รHRC. HRB to BHN: BHN โ 2รHRB (HRB<60). Tensile ฯ โ 3.45รBHN MPa.
Run the calculator when you are ready.
โ๏ธ Hardened Tool Steel
Tool steel H13: HRC 60
๐ฅ Stainless Steel 304
Annealed stainless: HRB 70
โ๏ธ Aluminum 6061-T6
Aircraft aluminum: HRB 60
๐ Tungsten Carbide
Ultra-hard material: HRA 88
๐ HRC to BHN Conversion
Convert HRC 45 to BHN
Enter Values
Calculation Mode
Hardness Scale Conversion
Material
For educational and informational purposes only. Verify with a qualified professional.
๐ฌ Physics Facts
HRC uses 120ยฐ diamond cone, 150 kg
โ ASTM E18
HRB uses 1/16 in. ball, 100 kg
โ ASTM
HRA for thin/tough materials
โ NIST
ฯ โ 3.45รBHN MPa for steel
โ ASM
What is Rockwell Hardness?
The Rockwell hardness test is one of the most widely used methods for measuring material hardness. Developed by Hugh and Stanley Rockwell in 1919, it measures the depth of penetration of an indenter under a specific load. The Rockwell test is fast, reliable, and provides direct hardness readings without requiring optical measurements.
Test Method
A minor load is applied first, then a major load. The depth difference is measured and converted to a hardness number.
Multiple Scales
Different scales (HRA, HRB, HRC) use different indenters and loads for different material hardness ranges.
Applications
Used for quality control, material selection, heat treatment verification, and design specifications.
Rockwell Hardness Scales
Rockwell A (HRA)
Diamond cone (120ยฐ)
60 kgf (588 N)
HRA 20-88
Very hard materials, thin materials, carbides
Tungsten carbide, Hardened steel, Thin sheets
Rockwell B (HRB)
1/16" steel ball
100 kgf (980 N)
HRB 0-100
Softer materials, non-ferrous metals
Brass, Aluminum, Copper, Soft steel
Rockwell C (HRC)
Diamond cone (120ยฐ)
150 kgf (1471 N)
HRC 20-70
Hardened steel, tool steel
Hardened steel, Tool steel, Heat-treated alloys
Scale Selection Guide
When to Use HRA (Rockwell A)
- Very hard materials (HRA 60-88)
- Thin materials or thin sections
- Tungsten carbide and similar carbides
- Hardened steel when HRC is too high
- Materials that would exceed HRC 70
When to Use HRB (Rockwell B)
- Softer materials (HRB 0-100)
- Non-ferrous metals (aluminum, brass, copper)
- Annealed or soft steel
- Materials too soft for HRC scale
- When HRC would be below 20
When to Use HRC (Rockwell C)
- Hardened steel (HRC 20-70)
- Tool steel and heat-treated alloys
- Most common scale for hardened materials
- Materials with hardness between HRB and HRA ranges
- General purpose hardness testing for steel
Conversion Formulas and Accuracy
Hardness conversions are approximate and depend on material type, composition, and heat treatment. Different formulas exist, and results may vary:
HRC to BHN:
BHN โ 100 + (HRC ร 5)
Most accurate for carbon and low-alloy steels
HRB to BHN:
BHN โ HRB ร 2 (for HRB < 60)
Less accurate, varies significantly with material
HRA to BHN:
BHN โ 10^((HRA - 20) / 30) ร 100
Logarithmic relationship for very hard materials
Note: Conversions are approximate. For critical applications, test directly on the desired scale rather than converting.
Hardness and Material Properties
Tensile Strength
For steel: ฯ โ 3.45 ร BHN (MPa). Higher hardness generally correlates with higher strength.
Wear Resistance
Harder materials resist wear better. HRC 55+ provides excellent wear resistance.
Machinability
Softer materials (HRB range) are easier to machine. Hard materials (HRC 50+) require specialized tools.
Toughness
Very high hardness (HRC 60+) may reduce toughness. Balance hardness with toughness requirements.
Factors Affecting Hardness
Heat Treatment
Quenching and tempering dramatically change hardness. Hardening increases HRC, tempering reduces it.
Material Composition
Carbon content, alloying elements, and microstructure all influence hardness.
Cold Working
Plastic deformation increases dislocation density, resulting in higher hardness.
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