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 be heat treated. The steel specimens shall undergo heat analysis and product analysis and shall conform to the chemical requirements for carbon, manganese, phosphorus, sulfur, silicon, molybdenum, and nickel. Tension tests shall be performed wherein the steel specimens shall conform to the required values of tensile strength, yield strength, and elongation.