ASTM E140-Hardness Conversion Tables

Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, and Tensile Strength

Purpose:

ASTM E140 provides standardized conversion tables that relate different hardness scales (like Rockwell, Brinell, Vickers) and in some cases, tensile strength for a variety of metallic materials.

This is especially useful when:

A material’s hardness was tested using a different method than the customer requires.

You're comparing hardness values from different testing standards.

Only one type of test equipment is available, but another result is needed.

1.Conversion Scales Covered

ASTM E140 includes conversion between the following hardness tests:

2.Example: Rockwell C to Brinell Conversion (for Steel)

Note: These are approximate values, subject to material type and structure.

3.Important Notes on Use

Conversion is approximate – especially between different methods. It's not a substitute for direct testing.

Valid only within specified ranges of each table.

Material-dependent – Different conversion tables apply to different materials (e.g., carbon steel, stainless, titanium).

Accuracy is best when near center of test range for each method.

4.Example Applications

Converting a Brinell hardness from a mill certificate to Rockwell C for a customer

Verifying expected tensile strength from hardness on forged bar stock

Comparing lab results when different test methods were used

5.Reporting & Best Practices

When using ASTM E140 conversions:

State the original test method and value (e.g., 235 HBW)

State the converted method and indicate it's estimated (e.g., ~23 HRC)

Reference ASTM E140 as the source of conversion