Cold rolled, ductile, high strength steel strip and sheet and method therefor

Claim 1

A method of producing cold reduced low carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than about 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, and annealing at a temperature and for a time sufficient to recover ductility but not recrystallize whereby to obtain an elongation of greater than 10% with a yield strength of at least 90 ksi.

Claim 2

A method of producing cold reduced low carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than about 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, and annealing at a temperature and for a time sufficient to recover ductility but not recrystallize whereby to obtain an elongation of greater than 10% with a yield strength of at least 90 ksi.

Claim 7

A method of producing hot dipped metallic coated low carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed, low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon, oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, subjecting the cold reduced steel to wet chemical cleaning, heating in a hydrogen-inert gas atmosphere to a temperature about equal to that of the molten coating metal bath, said coating metal being chosen from the group consisting of aluminum, zinc, alloys of aluminum, alloys of zinc, and terne, passing said steel through said bath of molten coating metal, and solidifying said coating metal.

Claim 8

A method of producing hot dipped metallic coated low carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed, low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon, oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, subjecting the cold reduced steel to wet chemical cleaning, heating in a hydrogen-inert gas atmosphere to a temperature about equal to that of the molten coating metal bath, said coating metal being chosen from the group consisting of aluminum, zinc, alloys of aluminum, alloys of zinc, and terne, passing said steel through said bath of molten coating metal, and solidifying said coating metal.

Claim 9

A method of producing hot dip metallic coated carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon, oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, heating the cold reduced steel in strip form in a continuous furnace to a temperature sufficient to remove oil and related surface contaminants, heating in a hydrogen-inert gas atmosphere capable of reducing residual surface oxide wherein said strip is brought to a temperature and for a time sufficient to recover ductility but not recrystallize whereby to obtain an elongation of greater than 10% with a yield strength of at least 90 ksi, cooling said strip approximately to the temperature of the molten coating metal bath, said coating metal being chosen from the group consisting of aluminum, zinc, alloys of aluminum, alloys of zinc, and terne, passing said strip through said molten coating metal bath, and solidifying said coating metal.

Claim 10

A method of producing hot dip metallic coated carbon steel strip and sheet stock having a 0.2% offset yield strength of at least 90 ksi and an elongation in two inches of greater than 10% in the annealed condition, comprising the steps of providing a vacuum degassed, fully killed low carbon steel casting consisting essentially of, by weight percent, from 0.02% to about 0.10% carbon, about 0.1% to 0.9% manganese, 0.02% to about 0.18% columbium, residual phosphorus, sulfur, silicon, oxygen and nitrogen, about 0.01% to about 0.08% aluminum, and balance essentially iron except for incidental impurities, the columbium being substantially completely combined with carbon, hot rolling to intermediate gauge, coiling at a temperature not higher than 1300° F, removing hot mill scale, cold reducing to final gauge with a reduction in thickness of 40% to 70%, heating the cold reduced steel in strip form in a continuous furnace to a temperature sufficient to remove oil and related surface contaminants, heating in a hydrogen-inert gas atmosphere capable of reducing residual surface oxide wherein said strip is brought to a temperature and for a time sufficient to recover ductility but not recrystallize whereby to obtain an elongation of greater than 10% with a yield strength of at least 90 ksi, cooling said strip approximately to the temperature of the molten coating metal bath, said coating metal being chosen from the group consisting of aluminum, zinc, alloys of aluminum, alloys of zinc, and terne, passing said strip through said molten coating metal bath, and solidifying said coating metal.