This specification covers higher strength chromium-molybdenum-tungsten alloy steel forgings intended primarily for use in boilers and pressure vessels for elevated temperature service. Materials shall be manufactured by melting processes, except that the open hearth process shall not be used, and that the molten steel shall be vacuum degassed prior to or during teeming of the ingot. The alloy steels may then be given an intermediate heat treatment such as normalizing and tempering or a subcrititcal anneal prior to rough machining. Heat analysis shall be obtained from samples to ensure chemical composition requirements are met. The steel forgings shall also undergo tension and Charpy impact tests and shall conform to the following required mechanical properties: tensile strength, yield strength, elongation, reduction of area, lateral expansion, minimum average absorbed energy, and minimum single value. Nondestructive examination procedures, such as straight-beam and angle-beam ultrasonic examination, and magnetic particle examination, shall also be executed.

1.1 This specification covers chromium-molybdenum-tungsten alloy steel forgings intended primarily for use in boilers and pressure vessels for elevated temperature service.

1.1.1 Elevated temperatures are temperatures in the range where creep and stress rupture properties are important for the alloy steels in this specification.

1.2 Supplementary requirements are provided both in this specification and in the General Requirements Specification A 788/A 788M for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the purchase order or contract.

1.3 Unless the order specifies the applicable "M" specification designation, the forgings shall be supplied to the inch-pound units.

1.4 The values stated in either inch-pound or SI (metric) units are to be regarded separately as standard. Within the text and tables, the SI units are shown in brackets. 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 nonconformance with the specification.