Low alloy third generation advanced high strength steel and process for making
Prior third generation advanced high strength steels can produce ingots and hot bands that have a tendency to develop cracks. It has been found that an addition to third generation advanced high strength steels of one or more of molybdenum in an amount up to 0.50 wt % and nickel in an amount up to 1.5 wt %, eliminates the cracks in ingots, and improves the appearance of hot bands. More specifically the new exemplary alloys have shown to improve the toughness of ingots, as well as hot bands.
1 . A steel comprising 0.20 to 0.30 wt % carbon, 3.0 to 5.0 wt % manganese, 0.5 to 2.5 wt % silicon, 0.5 to 2.0 wt % aluminum, 0.25-0.5 wt % molybdenum, greater than 1.0% up to 1.5 wt % nickel; 0-0.050 wt % niobium, 0-1.0 wt % chromium, and the balance being iron and impurities associated with steelmaking, wherein the steel comprises 15-50% austenite by total area ratio, wherein a hot band comprised of the steel has a Charpy V-notch (“CVN”) impact testing energy above 20 J (14.75 ft-lbf) in a full size CVN specimen or 0.25 J/mm 2 (1427 in-lbf/in{circumflex over ( )}2) in a thinner hot band, as measured at room temperature.
2 . The steel of claim 1 further comprising 0.25 to 0.35 wt % molybdenum.
3 . The steel of claim 1 further comprising greater than 1.0% up to 1.2 wt % nickel.
4 . The steel of claim 2 further comprising greater than 1.0% up to 1.2 wt % nickel.
5 . The steel of claim 1 wherein Si+Al is 3 wt % or less.
6 . The steel of claim 1 further comprising 3.0 to 4.0 wt % manganese.
7 . The steel of claim 1 further comprising 1.0 to 2.0 wt % silicon.
8 . The steel of claim 1 further comprising 1.0 to 1.5 wt % aluminum.
9 . The steel of claim 1 further comprising 0 to 0.65 wt % chromium.
10 . The steel of claim 1 wherein an as-cast slab comprised of the steel exhibits substantially no edge cracking at room temperature.
11 . A process of making the steel of claim 1 wherein the steel is intercritical annealed at a temperature of 700 to 800° C.
12 . The process of claim 11 wherein the steel is intercritical annealed as a hot band.
13 . The process of claim 11 wherein the steel is intercritical annealed in a hot dip coating line.
14 . The process of claim 11 wherein the steel is intercritical annealed in a continuous annealing line.
15 . A steel comprising 0.20 to 0.30 wt % carbon, 3.0 to 5.0 wt % manganese, 0.5 to 2.5 wt % silicon, 0.5 to 2.0 wt % aluminum, 0.25-0.5 wt % molybdenum, 0.5-1.5 wt % nickel; 0-0.050 wt % niobium, 0-1.0 wt % chromium, and the balance being iron and impurities associated with steelmaking, wherein the steel comprises greater than 40% up to 50% austenite by total area ratio, wherein a hot band comprised of the steel has a Charpy V-notch (“CVN”) impact testing energy above 20 J (14.75 ft-lbf) in a full size CVN specimen or 0.25 J/mm 2 (1427 in-lbf/in{circumflex over ( )}2) in a thinner hot band, as measured at room temperature.
16 . The steel of claim 15 further comprising greater than 1.0% up to 1.5 wt % nickel.
17 . A process of making the steel of claim 15 wherein the steel is intercritical annealed at a temperature of 700 to 800° C.