Brinell to Rockwell C

How Do You Convert Brinell to Rockwell C?

Converting Brinell hardness (HBW) to Rockwell C (HRC) requires going through an intermediate step, since neither scale converts directly to the other via a simple formula. The most reliable method is using the ASTM E140 conversion table, which provides empirically determined equivalences. As an approximation, you can convert HBW to Vickers (HV is roughly 1.05 times HBW for values under 350, rising above that), then HV to HRC. Common reference points from ASTM E140: 200 HBW = about 15 HRC (borderline — HRC is not recommended below 20), 300 HBW = about 32 HRC, 400 HBW = about 43 HRC, 500 HBW = about 51 HRC. The Brinell test uses a 10mm tungsten carbide ball under a 3,000 kgf load (for steel), making it ideal for castings, forgings, and raw materials with coarse grain structures. Rockwell C is better for finished, hardened parts. Foundries and forges test incoming material hardness in Brinell, while heat treatment shops report final hardness in Rockwell C, creating a constant need for HBW-to-HRC conversion in the manufacturing chain.

How to Convert Brinell to Rockwell C

1. Start with your Brinell hardness (HBW) measurement.
2. Refer to ASTM E140 for the direct conversion, or approximate using the two-step method: convert HBW to HV, then HV to HRC.
3. For values under 350 HBW, HV is approximately HBW x 1.05.
4. Then apply the HV-to-HRC inverse formula or table.
5. Key ASTM E140 reference points: 250 HBW = 24 HRC, 300 HBW = 32 HRC, 350 HBW = 37 HRC, 400 HBW = 43 HRC, 450 HBW = 47 HRC, 500 HBW = 51 HRC.

Real-World Examples

History of Brinell and Rockwell C

The Brinell test was invented in 1900 by Swedish engineer Johan August Brinell. It was the first widely standardized hardness test and used a hardened steel ball (later tungsten carbide, designated HBW) to create an indentation whose diameter was measured. The Brinell test became the standard for testing raw materials — castings, forgings, and bar stock — because the large indentation averages out microstructural variations. The Rockwell test (1914) was faster and became the standard for finished parts. The gap between incoming material tested in Brinell and finished parts tested in Rockwell C created an enduring need for conversion tables. ASTM E140 bridges this gap with experimentally validated equivalences that manufacturing has relied on for over 70 years.

Common Mistakes to Avoid

• Assuming HBW equals HRC. These are completely different scales with different numerical ranges. 300 HBW does not equal 300 HRC (which would be physically impossible — HRC only goes to about 70).
• Using the Brinell test above its valid range. The standard Brinell test (10mm ball, 3000 kgf) is generally reliable up to about 450-500 HBW. Above this, the tungsten carbide ball begins to deform, giving falsely low readings. For very hard materials, use Rockwell C or Vickers.
• Forgetting to specify the Brinell test conditions. HBW (tungsten carbide ball) and HBS (steel ball, obsolete) give different results on the same material. Modern standards require HBW. Old data reported as HBS may not convert accurately.
• Using a cast-iron or non-ferrous Brinell reading with a steel HRC conversion table. ASTM E140 separates materials because the same HBW number can correspond to different Rockwell behavior across alloys.

Frequently Asked Questions