Patent ID: 6264760
Filing Date: 2001-07-24
Classification: C21D,C22C

Abstract:
A steel plate having a tensile strength of at least about 930 MPa (135 ksi), an impact energy by Charpy V-notch test at -40.degree. C. (-40.degree. F.) of greater than about 120 J (88 ft-lb), a 50% vTrs of less than about -60.degree. C. (-76.degree. F.), and a microstructure comprising at least about 90 volume percent of a mixture of fine-grained lower bainite and fine-grained lath martensite, wherein at least about 2/3 of said mixture consists of fine-grained lower bainite transformed from unrecrystallized austenite having an average grain size of less than about 10 microns, and wherein said steel plate is produced from a reheated steel comprising iron and the following alloying elements in the weight percents indicated:about 0.05% to about 0.10% C,about 1.7% to about 2.1% Mn,less than about 0.015% P,less than about 0.003% S,about 0.2% to about 1.0% Ni,about 0.01% to about 0.10% Nb,0% to 0.8% Cu,about 0.005% to about 0.03% Ti, andabout 0.25% to about 0.6% Mo.