ASTM E140 Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, and Superficial Hardness

Get Certified ASTM E140 for Reliable Hardness Scale Conversion 

Laboratories, manufacturers, and QC labs often need to compare Brinell, Vickers, Rockwell, Knoop, Scleroscope, or Leeb hardness data when manufacturing or quality control specifies different measurement scales. ASTM E140 conversion tables show that a laboratory applied the correct conversion for the specific metal type and condition being tested, rather than a generic conversion that may produce erroneous data. Accredited laboratory practice to verify compliance with the specification, cross-referencing test results with hardness data supplied by both the steel industry and the customer, and the quality documentation in the steel, brass, copper, white iron, and aluminum industries. Manufacturers use the certified ASTM E140 application to prevent applying a conversion table developed for one material or condition to a fundamentally different material or condition.

The scope of ASTM E140 includes: 

• Material type: Non-austenitic steels (carbon, alloy, and tool steels), cartridge brass, austenitic stainless steel, copper, alloyed white iron, and wrought aluminum products, with individual conversion tables for each. 
• Purpose: To provide a standard relationship between hardness scales, to convert values reported on one scale to another. 
• Properties measured: Hardness (Brinell, Vickers, Rockwell, Rockwell superficial, Knoop, Scleroscope, or Leeb scales). 
• Method: Reference the material/condition specific conversion table for the type of metal being evaluated.
• Result: An approximate equivalent hardness value on the desired scale, from the conversion table mentioned above.
• Test Limitations: Each conversion table is only applicable to the specific material and condition for which the table was developed; conversion of test data should be avoided whenever possible, and conversion is used mainly for the conversion of test specification limits. 
• Environmental conditions: These are the material condition (as forged, annealed, normalized, or quenched and tempered) and material homogeneity that may influence the validity of the application of a conversion table. 
• Applications: Specification compliance verification on all steels, brasses, cuprum, white iron, and aluminum products across all hardness ranges, cross-reference of supplier and customer hardness data, quality documentation, and historic data comparisons. 

What are the Uses of ASTM E140?

ASTM E140 conversion tables provide a way to correlate hardness reported on different scales for a specific metal type, between manufacturers and quality control laboratories. The purchasers and suppliers then refer to the tables to compare hardness data that is measured under various systems. This standard- 

• Provides Table 1 and Table 2 relating Brinell, Vickers, Rockwell, Rockwell superficial, Knoop, and Scleroscope hardness for non-austenitic steels in the Rockwell C and Rockwell B ranges.
• Provides Table 4 relating Brinell, Vickers, Rockwell, and Rockwell superficial hardness for cartridge brass.
• Provides Table 5 relating Brinell and Rockwell B hardness for austenitic stainless steel plate in the annealed condition.
• Provides Table 6 relating Rockwell hardness and Rockwell superficial hardness for austenitic stainless steel sheet.
• Provides Table 7 relating Brinell, Vickers, Rockwell, Rockwell superficial, and Knoop hardness for copper.
• Provides Table 8 relating Brinell, Rockwell, and Vickers hardness for alloyed white iron.
• Provides Table 9 relating Brinell, Vickers, Rockwell, and Rockwell superficial hardness for wrought aluminum products.

What Materials Can Be Tested Under ASTM E140? 

ASTM E140 applies to non-austenitic steels, such as carbon steels, alloy steels, and tool steels, in as-forged, annealed, normalized, and quenched-and-tempered conditions, as long as they are homogeneous; cartridge brass; austenitic stainless steel plate and sheet; copper; alloyed white iron; and wrought aluminum products. There are separate conversion tables for each of these groups of materials, because the hardness relationships within the scales vary depending on the elastic modulus, work hardening characteristics, and microstructures of a material. The analyst is cautioned to ensure that the material type and condition of the sample are appropriate for the sample for which the table was developed; otherwise, the results obtained may be misleading. 

Why is ASTM E140 Important? 

ASTM E140 contains conversion tables to help manufacturers and purchasers understand how to convert a hardness value to a different scale without redundant testing for each type of material properties. No universally applicable relationships exist between hardness scales, and relationships vary by material based on composition, condition, and microstructure. It is understood that hardness conversions of test results do not remove the uncertainty associated with the measurement, but rather add to the uncertainty, and the explicit call for hardness conversions to be applied only to values designated as such by agreement or mandate reflects that understanding. Manufacturers, quality control personnel, and others use this standard to help facilitate communication between parties operating different hardness testing instruments and to remember that no conversion is strictly accurate. 

Other referenced ASTM documents include ASTM E10, E18, E29, E92, E384, and E448.

ASTM E140 Process and Data Collection

The conversion process starts with identifying the sort of metal and condition of the specimen being assessed; ASTM E140 lists separate tables for non-austenitic steels, cartridge brass, austenitic stainless steel, copper, alloyed white iron, and wrought aluminum products. The conversion table used is selected according to the material and condition confirmed and the conversion table number, e.g., Table 1 for non-austenitic steels in the Rockwell C range, or Table 7 for copper. The operator finds the hardness value on the original test scale in the chosen table and reads the equivalent hardness on the desired test scale from that table. Technicians use the converted value, assuming that the interpretation of this standard is applicable; conversions are used near the specification limits agreed upon or mandated and, as far as possible, should not be used on actual test data. The table and material condition used to support the traceability of the converted value are recorded in the laboratories. 

Common Challenges and Troubleshooting

Common issues with ASTM E140 application are: a conversion table is used for the incorrect material or condition, the test data is converted instead of the specification limits, or certain steel conditions require a homogeneity requirement. These problems may lead to false converted hardness results. If a table is created for a type of material (e.g. steel) and used on a different type of material (e.g. aluminum), it does not account for the fact that hardness scale relationships are different for different materials, and can result in significantly incorrect values. The introduction of uncertainty by converting actual test data, as opposed to specifically limiting the conversion to specification limits agreed or mandated for this conversion, introduces extra uncertainty that this standard specifically recommends avoiding, where possible. If the conditions of the steel are not homogeneous prior to applying Table 1 or Table 2, then it is possible to use the tables incorrectly and have inappropriate conversions when using Table 1 or Table 2 for inhomogeneous or improperly heat-treated steel. Attention to material and condition identification, limiting the scope of conversion to specification limits, and verifying homogeneity requirements minimize these issues. Experienced technicians achieve reliable, appropriately qualified converted values by following this standard’s guidance and recommendations. 

• The laboratory provides the converted hardness number for the requested scale, as well as the original measured hardness number and scale.
• The laboratory records the specific conversion table used (Table 1, 2, 4, 5, 6, 7, 8, or 9) depending on the material type and condition.
• Results show the approximate equivalent hardness on the converted scale, which is an approximation and not a measured value.
• The laboratory records the material condition (as-forged, annealed, normalized, quenched and tempered, etc.) verified before conversion.
• Analysts apply conversions to specification limits where possible, in accordance with the recommendations of this standard.
• Analysts identify the material and condition carefully to ensure an appropriate and applicable conversion relationship.
• Analysts use converted hardness values to verify specification compliance and cross-reference supplier and customer hardness data.

• What Factors Should You Consider for ASTM E140 Testing?

• Expertise: Skilled technicians accurately determine the condition and type of materials, find the right conversion table, and apply the recommendation to prevent too many conversions for test data.
• Speed: Once the hardness value, material type, and condition have been established, applying a conversion table is a quick reference process.
• Cost: ASTM E140 conversion tables: This method saves costs, as it eliminates the necessity of redundant hardness testing on various scales of the same specimen. 
• Confidentiality: Matestlab maintains complete confidentiality of the testing process, and the results are kept confidential from the concerned stakeholders. 

Link to ASTM E140