Patent ID: 6228183
Filing Date: 2001-05-08
Classification: C21D,C22C

Abstract:
A low alloy, boron-containing steel having a tensile strength of at least about 900 MPa (130 ksi), a toughness as measured by Charpy V-notch impact test at -40.degree. C. (-40.degree. F.) of at least about 120 joules (90 ft-lbs), and a microstructure comprising (i) about 50 vol % to less than 90 vol % fine-grained lower bainite, fine-grained lath martensite, or mixtures thereof, transformed from substantially unrecrystallized austenite grains, (ii) less than 20 vol % ferrite, and (iii) the remainder upper bainite, and wherein said steel comprises iron and the following additives in the weight percents indicated:about 0.03% to about 0.10% C,about 1.6% to about 2.1% Mn,about 0.01% to about 0.10% Nb,about 0.01% to about 0.10% V,about 0.2% to about 0.5% Mo,about 0.005% to about 0.03% Ti, andabout 0.0005% to about 0.0020% B,and is further characterized by:0.3.ltoreq.Ceq.ltoreq.about 0.7, andPcm.ltoreq.about 0.35,wherein ""Ceq"" is defined as ""(wt % C+wt % Mn/6+(wt % Cr+wt % Mo+wt % V)/5+(wt % Cu+wt % Ni)/15)"" and ""Pcm"" is defined as ""(wt % C+wt % Si/30+(wt % Mn+wt % Cu+wt % Cr)/20+wt % Ni/60+wt % Mo/15+wt % V/10+5(wt % B))"".