Ultra-high strength triple phase steels with excellent cryogenic

Details Ultra-high strength triple phase steels with excellent cryogenic Ultra-high strength triple phase steels with excellent cryogenic

1998-12-19

2000-12-12

Yee, Deborah

Metal treatment

Stock

Ferrous

148654, 148648, C22C 3808, C21D 802

Patent

active

061593125

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.1 transformation temperature; quenching the finish rolled plate to a suitable Quench Stop Temperature (QST); and stopping the quenching.

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Reference cited by the Taiwan Patent Office in counterpart to parent application, reference title--"Structure Controlling and Toughening of Steel Material", Monthly Journal of Mechanics, vol. 18, No. 3 (1992) pp. 227-235; English language translation of captions of the drawings; English language translation of the paragraph marked A on p. 228.

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