Abstract: The present invention relates to a high strength cold rolled steel sheet consisting of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol.Al, 0.01% or less of N, 0.2% or less of Ti, by mass %, and the balance of Fe and inevitable impurities. In this steel sheet, 1?([Ti]/48)/([C]/12+[N]/14) is satisfied, in which [M] represents the content of the element M. Since having the superior deep drawability and the TS of 340 to 590 MPa, the high strength cold rolled steel sheet of the present invention is preferably used for automobiles parts difficult to be press formed, such as a side outer panel and a door inner panel.

Abstract: The invention relates to a high strength hot-dip galvanized steel sheet consisting essentially of 0.03 to 0.25% C, 0.7% or less Si, 1.4 to 3.5% Mn, 0.05% or less P, 0.01% or less S, 0.05 to 1% Cr, 0.005 to 0.1% Nb, by mass, and balance of Fe, and being made of a composite structure of ferrite and secondary phase, and having an average grain size of the composite structure of 10 ?m or smaller. Since the high strength hot-dip galvanized steel sheet of the present invention hardly induces softening at HAZ during welding, it is applicable to structural members of automobiles for “Tailor Welded Blanks” (TWB).

Abstract: The invention provides a high strength cold rolled steel sheet comprising ferrite phases and second phases, in which the mean grain size of the ferrite phases is 20 &mgr;m or less, the volume fraction of the second phase is 0.1% or more to less than 10%, the absolute value |&Dgr;r| of in-plane anisotropy of r value is less than 0.15, and the thickness is 0.4 mm or more. The high strength cold rolled steel sheet of the present invention has a tensile strength of 370 to 590 MPa, and has excellent stretchability, dent resistance, surface precision, secondary working embrittlement, anti-aging, and surface appearance, therefore it is suitable for outer panels of automobile.

Abstract: The present invention relates to a high strength steel sheet consisting essentially of 0.04 to 0.1% C, 0.5% or less Si, 0.5 to 2% Mn, 0.05% or less P, 0.005% or less O, 0.005% or less S, by weight, having 10 &mgr;m or less of average ferritic grain size, and 20 mm/mm2 or less of generation frequency A, which generation frequency A is defined as the total length of a banded secondary phase structure observed per 1 mm2 of steel sheet cross section along the rolling direction thereof. The steel sheet is manufactured by, for example, a method comprising the steps of: hot-rolling a continuously cast slab having the composition described above at temperatures of Ar3 transformation point or above directly or after reheating thereof; and cooling the hot-rolled steel sheet within 2 seconds down to the temperatures of from 600 to 750° C. at cooling speeds of from 100 to 2,000° C./sec, followed by coiling the cooled steel sheet at temperatures of from 450 to 650° C.

Abstract: A method of producing cold rolled and annealed dual phase high strength steel sheets, and sheets produced by the method, including hot dip galvanized and galvannealed steel sheets having a tensile strength of at least about 750 MPa and a superior balance of strength and ductility using conventional thermomechanical processing parameters robust to the processing conditions. The synergistic effect on hardenability of Cr and V, within a controlled range, facilitates production using robust processing conditions, enabling production of a high strength product having a very low yield ratio.

Abstract: A high strength cold rolled steel sheet consists essentially of 0.0040 to 0.01% C, not more than 0.05% Si, 0.1 to 1.0% Mn, 0.01 to 0.05% P, not more than 0.02% S, 0.01 to 0.1% sol.Al, not more than 0.004% N, 0.01 to 0.14% Nb, by weight, and a balance of substantially Fe and inevitable impurities, and having an n value of not less than 0.21 calculated from two points (1% and 10%) of nominal strain determined by the uniaxial tensile test, and a method for manufacturing the cold rolled steel sheet. The high strength cold rolled steel sheet has excellent combined formability, resistance to embrittlement during secondary operation, formability at welded portions, and anti-burring performance, and has a desirable surface appearance and uniformity of material in a coil, and thus can be desirably used for automobile exterior panels.

Abstract: A high strength cold rolled steel sheet consists essentially of 0.0040 to 0.01% C, 0.05% or less Si, 0.1 to 1.0% Mn, 0.01 to 0.05% P, 0.02% or less S, 0.01 to 0.1% sol.Al, 0.004% or less N, 0.01 to 0.14% Nb, optionally 0.05% or less Ti, optionally 0.

Abstract: The invention relates to a high strength hot-dip galvanized steel sheet consisting essentially of 0.03 to 0.25% C, 0.7% or less Si, 1.4 to 3.5% Mn, 0.05% or less P, 0.01% or less S, 0.05 to 1% Cr, 0.005 to 0.1% Nb, by mass, and balance of Fe, and being made of a composite structure of ferrite and secondary phase, and having an average grain size of the composite structure of 10 &mgr;m or smaller. Since the high strength hot-dip galvanized steel sheet of the present invention hardly induces softening at HAZ during welding, it is applicable to structural members of automobiles for “Tailor Welded Blanks” (TWB).

Abstract: The present invention relates to a very low C—Nb cold rolled steel sheet giving 340 to 440 MPa of tensile strength. For example, the cold rolled steel sheet consists essentially of 0.0040 to 0.01% C, not more than 0.05% Si, 0.1 to 1.0% Mn, 0.01 to 0.05% P, not more than 0.02% S, 0.01 to 0.1% sol.Al, not more than 0.004% N, 0.01 to 0.14% Nb, by weight, and balance of substantially Fe and inevitable impurities, and has not less than 0.21 of n value calculated from two points (1% and 10%) of nominal strain determined by the uniaxial tensile test, and relates to a method for manufacturing the cold rolled steel sheet. The present invention provides a high strength cold rolled steel sheet for automobile exterior panels having excellent combined formability, resistance to embrittlement during secondary operation, formability at welded portions, anti-burring performance, good surface appearance, and uniformity of material in a coil.

Abstract: The present invention relates to a very low C-Nb cold rolled steel sheet giving 340 to 440 MPa of tensile strength. For example, the cold rolled steel sheet consists essentially of 0.0040 to 0.01% C, not more than 0.05% Si, 0.1 to 1.0% Mn, 0.01 to 0.05% P, not more than 0.02% S, 0.01 to 0.1% sol.Al, not more than 0.004% N, 0.01 to 0.14% Nb, by weight, and balance of substantially Fe and inevitable impurities, and has not less than 0.21 of n value calculated from two points (1% and 10%) of nominal strain determined by the uniaxial tensile test, and relates to a method for manufacturing the cold rolled steel sheet. The present invention provides a high strength cold rolled steel sheet for automobile exterior panels having excellent combined formability, resistance to embrittlement during secondary operation, formability at welded portions, anti-burring performance, good surface appearance, and uniformity of material in a coil.

Abstract: A hot-dip galvanized steel sheet is produced by rough rolling a steel, finish rolling the rough rolled steel at a temperature of Ar3 point or more, coiling the finish rolled steel at a temperature of 700° C. or less, and hot-dip galvanizing the coiled steel at a pre-plating heating temperature of Ac1 to Ac3. A continuous hot-dip galvanizing operation is performed by soaking a pickled strip at a temperature of 750 to 850° C., cooling the soaked strip to a temperature range of 600° C. or less at a cooling rate of 1 to 50° C. per second, hot-dip galvanizing the cooled strip, and cooling the galvanized strip so that the residence time at 400 to 600° C. is within 200 seconds. The steel sheet has a structure consisting essentially of ferrite and martensite.

Abstract: A hot-dip galvanized steel sheet is produced by rough rolling a steel, finish rolling the rough rolled steel at a temperature of Ar3 point or more, coiling the finish rolled steel at a temperature of 700° C. or less, and hot-dip galvanizing the coiled steel at a pre-plating heating temperature of Ac1 to Ac3. A continuous hot-dip galvanizing operation is performed by soaking a pickled strip at a temperature of 750 to 850° C., cooling the soaked strip to a temperature range of 600° C. or less at a cooling rate of 1 to 50° C. per second, hot-dip galvanizing the cooled strip, and cooling the galvanized strip so that the residence time at 400 to 600° C. is within 200 seconds. The steel sheet has a structure consisting essentially of ferrite and martensite.

Abstract: The present invention relates to a high strength steel sheet consisting essentially of 0.04 to 0.1% C, 0.5% or less Si, 0.5 to 2% Mn, 0.05% or less P, 0.005% or less 0, 0.005% or less S, by weight, having 10 &mgr;m or less of average ferritic grain size, and 20 mm/mm2 or less of generation frequency A, which generation frequency A is defined as the total length of a banded secondary phase structure observed per 1 mm2 of steel sheet cross section along the rolling direction thereof. The steel sheet is manufactured by, for example, a method comprising the steps of: hot-rolling a continuously cast slab having the composition described above at temperatures of Ar3 transformation point or above directly or after reheating thereof; and cooling the hot-rolled steel sheet within 2 seconds down to the temperatures of from 600 to 750° C. at cooling speeds of from 100 to 2,000° C. /sec, followed by coiling the cooled steel sheet at temperatures of from 450 to 650° C.

Abstract: A cold-rolled steel sheet or a zinc or zinc alloy layer coated steel sheet containing 0.0010 to 0.01 wt % of C and having a steel composition containing one or two kinds of 0.005 to 0.08 wt % of Nb and 0.01 to 0.07 wt % of Ti in the ranges given by {(12/93)Nb+(12/48)Ti*} .gtoreq.0.0005, 0.ltoreq.C-{(12/93)Nb+(12/48)Ti*}.ltoreq.0.0015, and Ti*=Ti-{(48/32)S+(48/14)N } , in which a bake hardenability BH f the steel sheet at 170.degree. C..times.20 min after 2% tensile prestrain is 10 to 35 MPa and the BH (MPa) and a yield strength YP (MPa) of the steel sheet satisfy the ranges given by BH.gtoreq.exp(-0.115.multidot.YP+23.0) and 0.67.multidot.BH+160.ltoreq.YP.ltoreq.-0.8.multidot.BH+280.

Abstract: A method for manufacturing an ultra-high-strength cold-rolled steel sheet having desirable delayed fracture resistance, which comprises: preparing a material consisting essentially of 0.1 to 0.25 wt. % carbon, up to 1 wt. % silicon, 1 to 2.5 wt. % manganese, up to 0.020 wt. % phosphorus, up to 0.005 wt. % sulfur, 0.01 to 0.05 wt. % soluble aluminum, 0.0010 to 0.0050 wt. % nitrogen, optionally at least one of Nb, Ti or V, optionally at least one of Cu, Ni, B, Cr or Mo, the balance being iron and incidental impurities; subjecting the material to a hot rolling, a pickling and a cold rolling to prepare a cold-rolled steel sheet; and subjecting the cold-rolled steel sheet to a continuous heat treatment which comprises: subjecting the cold-rolled steel sheet to a soaking treatment at a temperature of Ac.sub.3 to 900.degree. C. for 30 seconds to 15 minutes, quenching the cold-rolled steel sheet at a quenching rate of at least 400.degree. C./second from a temperature of at least a lower limit temperature (T.sub.