Mechanical Testing Committee Revises Brinell, Rockwell Hardness Test Methods
ASTM International standards E 10, Test Method for Brinell Hardness of Metallic Materials, and E 18, Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials, have both recently undergone extensive revisions. Both standards are under the jurisdiction of Subcommittee E28.06 on Indentation Hardness Testing, which is part of ASTM International Committee E28 on Mechanical Testing.
Rockwell B hardness test data performed by several different laboratories illustrating the differences between measurement results when using tungsten carbide and steel ball indenters.
“The intention of these revisions was to improve the standards by specifying requirements for traceability, clarifying requirements and procedures, revising procedures to reflect current practice, and adding requirements and procedures to make them better test methods,” says Samuel Low, chair of Subcommittee E28.06. Low also says that it is important to note that there is no intention of removing from service any Rockwell or Brinell hardness testing machines that currently meet all of the requirements of ASTM E 10 or E 18.
The most important changes common to both standards are:
• New format;
• Additional information to clarify requirements;
• Accreditation requirements for test block and indenter standardizing agencies;
• Expanded requirements for verification of hardness machines in the field;
• New requirements for standardizing machines used to calibrate test blocks and indenters;
• Added traceability requirements;
• Increased reporting requirements, particularly for calibration agencies; and
•New precision and bias sections.
The most important changes specific to E 18 are:
• The tungsten carbide ball indenter is now the standard indenter to be used for the Rockwell ball scales. Steel indenter balls may be used only for testing thin sheet tin mill products specified in A 623, Specification for Tin Mill Products, General Requirements, and its metric companion standard, A 623M, using the HR15T and HR30T scales with a diamond spot anvil. The use of tungsten carbide balls will produce slightly different hardness results than steel balls. Subcommittee E28.06 believes that the advantage of reducing the common errors associated with the flattening of steel balls far outweighs the very small differences in hardness results obtained using the two types of balls in most Rockwell hardness testing circumstances.
• Revised shape tolerances and performance tolerances for diamond indenters.
• Revised testing cycle requirements. It is believed that all current tester designs are capable of meeting these requirements.
• New classifications of indenters.
The key changes specific to E 10 are:
• More information about the Brinell scales other than those that use a 10 mm ball;
• A revised table for calculating Brinell hardness numbers for all standard Brinell scales; and
• New classification of indentation measuring devices and revised tolerances for these devices.
Rockwell and Brinell hardness tests are used by companies that produce or purchase materials or parts in which the mechanical properties of the materials are important to their function. “This is particularly true for metallic materials and metal parts although some other materials, such as plastic, are tested using these methods,” says Low. These companies will need to follow the requirements of E 10 and E 18 to properly produce comparable test results. In addition, hardness calibration services that produce hardness test blocks, testing machines and indenters all need to use E 10 and E 18, according to Low.
Subcommittee E28.06 is interested in receiving feedback on the impact of the changes to E 10 and E 18 from any companies that use the standards.
Technical Information: Samuel Low, National Institute of Standards and Technology, Gaithersburg, Md.
ASTM Staff: Kevin Shanahan
November Committee Week