An American National Standard
Standard Test Methods for
Rockwell Hardness and Rockwell Superﬁcial Hardness of Metallic Materials1,2
This standard is issued under the ﬁxed designation E 18; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parenthesesindicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense.
e1 NOTE—Table 15 was editorially revised in June 2004.
1. Scope* 1.1 These test methods cover the determination of the Rockwell hardness and the Rockwell superﬁcial hardness ofmetallic materials, including test methods for the veriﬁcation of machines for Rockwell hardness testing (Part B) and the calibration of standardized hardness test blocks (Part C). 1.2 Values stated in inch-pound units are to be regarded as the standard. SI units are provided for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use.It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (See Note 6.)
NOTE 1—The National Institute of Standards and Technology (NIST) maintains the national Rockwell hardness standards for the United States. In June 1998, NIST released new Rockwell C scale (HRC) test blocksas Standard Reference Materials (SRMs). The blocks were calibrated using NIST’s primary reference standardizing machine. The major beneﬁt of the NIST standards is that their HRC levels are in line with the other industrialized countries around the world. The NIST HRC levels establish the hardness of materials slightly harder than the historical standards used in the United States for the past 75years. The revision of E 18 requires that all performance veriﬁcations of Rockwell hardness indenters and hardness machines must be made using test blocks calibrated traceable to the Rockwell standards maintained by NIST. This can be accomplished through the use of commercial test blocks calibrated traceable to the NIST standards or by directly using the NIST SRMs. This requirement will apply onlyto the Rockwell scale(s) for which NIST supplies primary reference test blocks NOTE 2—In previous editions of this standard, ball indenters were required to be of hard steel. Beginning with this edition, tungsten-carbide balls are also allowed. This change is a ﬁrst step in a planned future transition to eliminate steel balls and allow only the use of tungsten carbide balls. The elimination ofsteel ball indenters is scheduled to occur
in about two years. The use of tungsten carbide balls will provide an improvement to the Rockwell hardness test because of the tendency of steel balls to ﬂatten with use, which results in an erroneously elevated hardness value. In addition, NIST is planning to standardize the HRB scale using tungsten-carbide balls. As a result of this change, this editionalso requires that when a ball indenter is used, the Rockwell hardness value must be reported with the scale designation followed by the letter “S” to indicate the use of a steel ball or the letter “W” to indicate the use of a tungsten carbide ball. The user is cautioned that Rockwell hardness tests comparing the use of steel and tungsten carbide balls have been shown to give different results.For example, depending on the material tested and its hardness level, Rockwell B scale tests using a tungsten carbide ball indenter have given results up to one Rockwell point lower than when a steel ball indenter is used.
1 These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and are the direct responsibility of Subcommittee E28.06 on Indentation Hardness...