Abstract: An ultra-high strength, weldable, low alloy, triple phase steel with excellent cryogenic temperature toughness in the base plate and in the heat affected zone (HAZ) when welded, having a tensile strength greater than about 830 MPa (120 ksi) and a microstructure comprising a ferrite phase, a second phase of predominantly lath martensite and lower bainite, and a retained austenite phase, is prepared by heating a steel slab comprising iron and specified weight percentages of some or all of the additives carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum, and boron; reducing the slab to form plate in one or more passes in a temperature range in which austenite recrystallizes; further reducing the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ar.sub.3 transformation temperature; finish rolling the plate between the Ar.sub.3 transformation temperature and the Ar.sub.

Abstract: Welding methods are provided for use in joining ultra-high strength, low alloy steels to produce weldments having tensile strengths greater than about 900 MPa (130 ksi) with weld metals having fracture toughness suitable for cryogenic applications according to known principles of fracture mechanics.

Abstract: A container is provided for storing pressurized liquefied natural gas at a pressure of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature of about -123.degree. C. (-190.degree. F.) to about -62.degree. C. (-80.degree. F.). The container is constructed from an ultra-high strength, low alloy steel containing less than 9 wt % nickel and having a tensile strength greater than 830 MPa (120 ksi) and a DBTT lower than about -73.degree. C. (-100.degree. F.).

Abstract: An ultra-high strength, weldable, low alloy, dual phase steel with excellent cryogenic temperature toughness in the base plate and in the heat affected zone (HAZ) when welded, having a tensile strength greater than 830 MPa (120 ksi) and a microstructure comprising a ferrite phase and a second phase of predominantly lath martensite and lower bainite, is prepared by heating a steel slab comprising iron and specified weight percentages of some or all of the additives carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum, and boron; reducing the slab to form plate in one or more passes in a temperature range in which austenite recrystallizes; further reducing the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ar.sub.3 transformation temperature; finish rolling the plate between the Ar.sub.3 transformation temperature and the Ar.sub.

Abstract: Fuel storage and delivery systems are provided for storing pressurized liquefied natural gas (PLNG) fuel at a pressure of about 1035 kPa (150 psia) to about 7590 kPa (1100 psia) and at a temperature of about -123.degree. C. (-190.degree. F.) to about -62.degree. C. (-80.degree. F.) and delivering vaporized PLNG fuel on demand for combustion in an engine. The fuel storage and delivery systems have fuel storage containers that are constructed from ultra-high strength, low alloy steel containing less than 9 wt % nickel and having a tensile strength greater than 830 MPa (120 ksi) and a DBTT lower than about -73.degree. C. (-100.degree. F.). While not limited thereto, the present invention is especially useful for automobiles, buses, trucks and other vehicles with engines designed to operate through combustion of natural gas.