1.1This specification2 covers heat-treated carbon-manganese-silicon steel plates intended for fusion welded pressure vessels and structures.

1.2Plates furnished under this specification are available in the following three classes:

Class	Heat Treatment	Thickness	Yield Strength, min, ksi [MPa]	Tensile Strength, min, ksi [MPa]

1	Normalized	2¹/₂in. and under [65 mm and under]	50 [345]	70 [485]
		Over 2¹/₂in. [Over 65 mm]	45 [310]	65 [450]

2	Quenched and tempered	2¹/₂in. and under [65 mm and under]	60 [415]	80 [550]
		Over 2¹/₂to 4 in. [Over 65 to 100 mm]	55 [380]	75 [515]
		Over 4 in. [Over 100 mm]	46 [315]	70 [485]

3	Quenched and tempered	2¹/₂in. and under [65 mm and under]	55 [380]	80 [550]
		Over 2¹/₂to 4 in. [Over 65 to 100 mm]	50 [345]	75 [515]
		Over 4 in. [Over 100 mm]	40 [275]	70 [485]

1.3The maximum thickness of plates is limited only by the capacity of the material to meet the specified mechanical property requirements.

1.4The 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 is to be used independently of the other without combining values in any way.

1.5This 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.