【国外标准】 Standard Specification for Steel Bars Subject to Restricted End-Quench Hardenability Requirements

This specification covers hot-worked alloy and carbon-boron steels designed to attain restricted depth of hardening in the end-quench test. These steel compositions are identified by the suffix letter “RH” added to the conventional grade number. The steel shall be made by one or more of the following primary processes: open-hearth, basic-oxygen, or electric furnace. The primary melting may incorporate separate degassing or ladle refining and may be followed by secondary melting using electroslag remelting or vacuum arc remelting. Where secondary melting is employed, the heat shall be defined as all the ingots remelted from a single primary heat. Immediately after hot working, the bars shall be allowed to cool when necessary to a temperature below the critical range under suitable conditions, to prevent injury by too rapid cooling. The steel shall have an austenitic grain size of five to eight. The grain structure shall be considered satisfactory when a minimum of 70% of the rated grains are within the specified size limits. Hardenability values specified are based on fine-grain steels and are not applicable to coarse-grain steel. All forged and rolled hardenability test specimens must be normalized prior to testing. Cast specimens need not be normalized.1.1 This specification covers hot-worked alloy and carbon-boron steels designed to attain restricted depth of hardening in the end-quench test. These steel compositions are identified by the suffix letter “RH” added to the conventional grade number.1.2 In general, steels with restricted hardenability (RH steels) will exhibit a hardness range not greater than 5 HRC at the initial position on the end-quench hardenability bar and not greater than 65 % of the hardness range for standard H-band steels (Specification A304) in the inflection region. Generally the restricted hardenability band follows the middle of the corresponding standard H-band. An example of the RH band compared with the H band is given for Grade 4140 in Fig. 1.FIG. 1 Comparison of H-Band and RH-Band for 4140 SteelA1.2.1 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.3 This specification is expressed in both inch-pound units and SI units. However, the material will be supplied to inch-pound units unless the purchase order specifies the “M” specification designation.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.