1.1 本规范涵盖通过淬火和自回火工艺（QST）生产的50[345]、60[415]、65[450]、70[485]和80[550]级高强度低合金结构钢型材。这些形状用于桥梁、建筑物和其他结构的铆接、螺栓连接或焊接施工。 1.2 QST工艺由在线热处理和冷却速度控制组成，这些控制可以使成品的机械性能与使用热处理工艺获得的机械性能相当，热处理工艺需要在轧制后重新加热。 QST过程的描述见 附录X1 . 1.3 由于QST工艺的固有特性，不得形成50[345]、60[415]、65[450]和70[485]级形状，也不得在超过1100°F[595°C]的温度下进行焊后热处理，也不得形成80[550]级形状，也不得在超过1000°F[540°C]的温度下进行焊后热处理。 1.4 在焊接钢材时，先决条件是采用适合钢材等级和预期用途或服务的焊接工艺。 见规范附录X3 A6/A6M 有关焊接性的信息。 1.5 以英寸-磅单位或国际单位表示的数值应单独视为标准值。在文本中，国际单位显示在括号中。每个系统中规定的值不是精确的等价物；因此，每个系统必须相互独立使用。合并两个系统的值可能会导致不符合本规范。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。

1.1 This specification covers high-strength low-alloy structural steel shapes in Grades 50 [345], 60 [415], 65 [450], 70 [485], and 80 [550], produced by the quenching and self-tempering process (QST). The shapes are intended for riveted, bolted or welded construction of bridges, buildings and other structures. 1.2 The QST process consists of in line heat treatment and cooling rate controls which result in mechanical properties in the finished condition that are equivalent to those attained using heat treating processes which entail reheating after rolling. A description of the QST process is given in Appendix X1 . 1.3 Due to the inherent characteristics of the QST process, Grade 50 [345], 60 [415], 65 [450], and 70 [485] shapes shall not be formed nor post weld heat treated at temperatures exceeding 1100°F [595°C] and Grade 80 [550] shapes shall not be formed nor post weld heat treated at temperatures exceeding 1000°F [540°C]. 1.4 When the steel is to be welded, it is presupposed that a welding procedure suitable for the grade of steel and intended use or service will be utilized. See Appendix X3 of Specification A6/A6M for information on weldability. 1.5 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with this specification. 1.6 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.