Vickers to Rockwell C

How Do You Convert Vickers to HRC?

To convert Vickers hardness (HV) to Rockwell C (HRC), you need to invert the HV-to-HRC relationship. The formula involves solving a quadratic equation: given HV = 0.171 x HRC² + 1.65 x HRC + 103, solving for HRC yields HRC = (-1.65 + sqrt(1.65² - 4 x 0.171 x (103 - HV))) / (2 x 0.171). In practice, most engineers use the ASTM E140 table to look up the HRC equivalent of a measured HV value. This conversion is needed when a Vickers hardness tester is used to verify parts that have been specified in HRC on engineering drawings. Vickers testing is common in laboratories and for microhardness profiling (measuring hardness gradients through case-hardened layers), while specifications and blueprints in the US almost always call out HRC. It is also common when metallography labs need to translate microhardness data into a production-friendly scale. This avoids confusion during release and inspection decisions. Quality control technicians must convert their Vickers readings to HRC to determine if a part passes or fails inspection.

How to Convert Vickers to Rockwell C

1. Start with your Vickers hardness (HV) measurement.
2. Apply the inverse formula: HRC = (-1.65 + sqrt(2.7225 + 0.684 x (HV - 103))) / 0.342.
3. For example, 500 HV: HRC = (-1.65 + sqrt(2.7225 + 0.684 x 397)) / 0.342 = (-1.65 + sqrt(274.2)) / 0.342 = (-1.65 + 16.56) / 0.342 = 43.6 HRC.
4. For critical work, use the ASTM E140 conversion table (ASTM E140 gives 500 HV = 49.1 HRC).
5. The formula is valid for HV values above roughly 200 (which corresponds to about 20 HRC).

Real-World Examples

History of Vickers and Rockwell C

The need to convert from HV to HRC arose as Vickers testing equipment became more sophisticated and widespread in the second half of the 20th century. Early metallurgical quality control relied almost exclusively on Rockwell testing due to its speed. However, advances in automated microhardness testers made Vickers testing practical for production environments. Automotive and aerospace manufacturers began requiring Vickers testing for case-depth profiles and thin-section analysis, creating a need for reliable HV-to-HRC conversions. The ASTM E140 standard was developed through extensive round-robin testing across multiple laboratories to establish empirically validated conversion tables. Updated periodically, it remains the gold standard for hardness scale conversions worldwide.

Common Mistakes to Avoid

• Converting HV below 200 to HRC. The Rockwell C scale is not valid below about 20 HRC (approximately 226 HV). For softer materials, convert to Rockwell B (HRB) or Brinell (HBW) instead.
• Using a single linear conversion factor. The HV-to-HRC relationship is nonlinear. At 300 HV, HRC is about 30; at 600 HV, HRC is about 55. A linear factor that works at one end fails at the other.
• Ignoring test load differences. Vickers hardness can be measured at different loads (HV 0.1, HV 0.3, HV 1, HV 5, HV 10, HV 30). ASTM E140 conversions assume a standard load. Microhardness readings (low load) may differ from macro-hardness readings on the same material.
• Applying the steel conversion table to stainless, nickel, titanium, or non-ferrous readings without checking the ASTM section. Different alloy groups can map to different HRC values at the same HV number.

Frequently Asked Questions