1.1 This specification covers one type of manganese-molybdenum and four types of manganese-molybdenum-nickel alloy steel plates for use in the quenched and tempered condition for the construction of welded pressure vessels. This specification covers manganese-molybdenum and manganese-molybdenum-nickel alloy steel plates for use in welded pressure vessels. The steel materials shall be killed and shall conform to the required values of fine austenitic grain and shall also b