Patent Number: 6,254,698

Title: Ultra-high strength ausaged steels with excellent cryogenic temperature toughness and method of making thereof

Abstract: An ultra-high strength, weldable, low alloy 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 (i) predominantly fine-grained lower bainite, fine-grained lath martensite, fine granular bainite (FGB), or mixtures thereof, and (ii) up to about 10 vol % retained austenite, 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; finish rolling the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ar.sub.3 transformation temperature; quenching the finish rolled plate to a suitable Quench Stop Temperature (QST); stopping the quenching; and either, for a period of time, holding the plate substantially isothermally at the QST or slow-cooling the plate before air cooling, or simply air cooling the plate to ambient temperature.

Inventors: Koo; Jayoung (Bridgewater, NJ), Bangaru; Narasimha-Rao V. (Annandale, NJ), Vaughn; Glen A. (Houston, TX), Ayer; Raghavan (Woodbridge, CT)

Assignee: ExxonMobile Upstream Research Company

International Classification: C22C 38/04 (20060101); C22C 38/08 (20060101); C22C 38/12 (20060101); C22C 38/16 (20060101); C22C 38/14 (20060101); C21D 1/19 (20060101); C21D 1/18 (20060101); C21D 8/02 (20060101); C21D 6/00 (20060101); C21D 1/20 (20060101); C21D 008/02 (); C21D 007/13 (); C22C 038/08 ()

Expiration Date: 07/03/2018