Abstract: In controlling the cooling of a hot-rolled steel sheet after hot rolling, a target value of a transformation rate required for obtaining mechanical properties ultimately expected from the hot-rolled steel plate is previously determined, a rate of gamma to alpha transformed fraction of the hot-rolled steel sheet in a section in which the cooling is controlled is detected by transformed fraction detectors, and an elapsed time from the start of cooling is measured to determine the transformation rate of the steel sheet in a cooling stage, the conditions of cooling being controlled so that the transformation rate can coincide with the target value.

Abstract: The invention concerns cooling apparatus for strip metal of the kind comprising a series of spaced cooling rolls around which the strip metal is passed such that it follows a serpentine path and is cooled by contact with the rolls, and elongate gas jet devices disposed widthwise of the strip opposite the outer surface parts of respective cooling rolls in contact with the strip.

Abstract: A cold rolled dual-phase structure steel sheet having an excellent deep drawability is disclosed, which consists of ferrite phase and low temperature transformation product phase and comprises 0.001-0.008 wt % of C, not more than 1.0 wt % of Si, 0.05-1.8 wt % of Mn, not more than 0.15 wt % of P, 0.01-0.10 wt % of Al, 0.002-0.050 wt % of Nb and 0.0005-0.0050 wt % of B provided that the value of Nb (%)+10B (%) is in a range of 0.010-0.080%, and, if necessary, 0.05-1.00 wt % of Cr and the balance being substantially Fe with inevitable impurities. This steel sheet is manufactured by hot and cold rolling a steel slab with the above chemical composition and continuously annealing the resulting steel sheet in such a manner than the steel sheet is heated and soaked at a temperature from .alpha..fwdarw..gamma. transformation point to 1,000.degree. C. and then cooled at an average cooling rate of not less than 0.5.degree. C./sec but less than 20.degree. C.

Abstract: Based on the investigation as to the correlative relationship between the composition of a steel material, particularly the content of carbon and a soaking temperature for the hot rolling, the improvements of the stretch formability, deep-drawability and aging resistance of the cold rolled steel sheet and the peculiar behaviors of the effective additive ingredients under the above correlative relationship, a cold rolled steel sheet having excellent press-formability is obtained by soaking at 800.degree.-1,100.degree. C., a steel slab consisting of not more than 1.2% by weight of Si, 0.05-1.00% by weight of Mn, not more than 0.150% by weight of P, at least one of elements selected from the group consisting of Nb, Cr, Ti, Al, B and W in a total amount of 0.002-0.150% by weight in an extremely low range of not more than 0.005% by weight of C, followed by ordinary hot rolling, cold rolling and recrystallization annealing.

Abstract: The present invention provides high tensile strength cold rolled steel sheets having excellent formability, which consist of 0.002-0.015% of C, not more than 1.2% of Si, 0.04-0.8% of Mn, 0.03-0.10% of P, 0.02-0.10% and not less than N%.times.4 of Al, C%.times.3-{C%.times.8+0.020%} of Nb and the remainder being substantially Fe, as the high tensile strength steel sheets which reduce the weight of automobiles and the like. The steel sheet is produced by hot rolling a steel slab having the above described composition to obtain a hot rolled coil, in the hot rolling the total reduction rate being at least 90%, the rolling speed in the finishing rolling being at least 40 m/min and the coiling-up temperature being at least 600.degree. C.; cold rolling the above described hot rolled coil in a conventional process to obtain a cold rolled steel strip having a final gauge; subjecting the above described cold rolled steel strip to a continuous annealing at a temperature of 700.degree.-900.degree. C.

Abstract: A method of cooling band or hoop steels with hollow cooling rolls through which a cooling medium flows to absorb the heat of the steel strips trained about and in contact with the hollow cooling rolls, thereby cooling the steel strips. According to the invention this method is carried out so as to fulfil the following equation (1) with the cooling roll having a diameter D>600 mm when a thickness h of the steel strip is within 0.2.ltoreq.h<0.6 mm,.DELTA.T.sub.S <0.65.multidot..sigma..sub.T.sup.1.5 .multidot..theta..multidot.h.sup.-0.75 (1)and so as to fulfil the following equation (2) with the cooling roll having a diameter D>1,000 mm when a thickness h of the steel strip is within 0.6 mm.ltoreq.h,.DELTA.T.sub.S <1.05.multidot..sigma..sub.T.sup.1.5 .multidot..theta..multidot.h.sup.-0.83 (2)where .DELTA.T.sub.S is temperature fall .degree.C. per one cooling roll, .sigma..sub.T is tensile stress in a lengthwise direction of the steel strip and .theta. is winding angle about the cooling roll.

Abstract: The present invention provides high tensile strength cold rolled steel sheets having excellent formability, which consist of 0.002-0.015% of C, not more than 1.2% of Si, 0.04-0.8% of Mn, 0.03-10% of P, 0.02-0.10% and not less than N%.times.4 of Al, C%.times.3-{C%.times.8+0.020%} of Nb and the remainder being substantially Fe, as the high tensile strength steel sheets which reduce the weight of automobiles and the like. The steel sheet is produced by hot rolling a steel slab having the above described composition to obtain a hot rolled coil, in the hot rolling the total reduction rate being at least 90%, the rolling speed in the finishing rolling being at least 40 m/min and the coiling-up temperature being at least 600.degree. C.; cold rolling the above described hot rolled coil in a conventional process to obtain a cold rolled steel strip having a final gauge; subjecting the above described cold rolled steel strip to a continuous annealing at a temperature of 700.degree.-900.degree. C.

Abstract: Non-ageing cold rolled steel sheets having a very excellent formability are produced by hot rolling a steel consisting of not more than 0.008% of C, not more than 0.20% of Si, 0.04-0.30% of Mn, not more than 0.03% of P, 0.01-0.10% of Al, a content of Al being more than N%.times.4, not more than 0.02% of S, not more than 0.01% of N, 0.01-0.07% of Nb, a content of Nb being C%.times.3-{C%.times.8+0.02}%, and the remainder being substantially Fe, at a total reduction of not less than 90%, a rolling speed of not less than 40 m/min in the finishing rolling and a finishing temperature of not lower than 830.degree. C., coiling the hot rolled strip at a temperature of 600.degree.-800.degree. C., cold rolling the coiled strip following a conventional manner to obtain a cold rolled strip having final gauge and then continuous annealing or hot-dip galvanizing the cold rolled strip within a temperature range of 700.degree.-900.degree. C. for 10 seconds-5 minutes.

Abstract: A method of producing substantially non-ageing cold rolled steel sheets having a remarkably excellent deep drawing property, wherein an extra low-carbon steel is melted together with niobium in an amount of less than the necessary amount for fixing completely carbon contained in the extra low-carbon steel to prepare a molten steel, the molten steel is made into an ingot and then the ingot is slabbed, or the molten steel is continuously cast to produce a slab, the slab is subjected to a hot rolling and a cold rolling to produce a cold rolled sheet according to an ordinary method, and the cold rolled sheet is subjected to a box annealing.