Disclosed are a steel with controlled steel ratio and a manufacturing method therefor. The steel comprises the following components in percentage by mass: C: 0.245-0.365%, Si: 0.10-0.80%, Mn: 0.20-2.00%, P:≤0.015%, S:≤0.003%, Cr: 0.20-2.50%, Mo: 0.10-0.90%, Nb: 0-0.08%, Ni: 2.30-4.20%, Cu: 0-0.30%, V: 0.01-0.13%, B: 0-0.0020%, Al: 0.01-0.06%, Ti: 0-0.05%, Ca:≤0.004%, H:≤0.0002%, N:≤0.013%, O:≤0.0020%, and the balance of Fe and inevitable impurities, wherein the components satisfy (8.57*C+1.12*Ni)≥4.8% and 1.2%≤(1.08*Mn+2.13*Cr)≤5.6%. The steel has excellent low-temperature impact toughness and aging impact toughness at −20° C. and −40° C., a rationally controlled yield ratio, and ultra-high strength, ultra-high toughness, and ultra-high plasticity, which can be used in applications such as offshore platform mooring chains, mechanical structures, and automobiles that require high strength and toughness of the steel.

Disclosed are a steel with controlled steel ratio and a manufacturing method therefor. The steel comprises the following components in percentage by mass: C: 0.245-0.365%, Si: 0.10-0.80%, Mn: 0.20-2.00%, P:≤0.015%, S:≤0.003%, Cr: 0.20-2.50%, Mo: 0.10-0.90%, Nb: 0-0.08%, Ni: 2.30-4.20%, Cu: 0-0.30%, V: 0.01-0.13%, B: 0-0.0020%, Al: 0.01-0.06%, Ti: 0-0.05%, Ca:≤0.004%, H:≤0.0002%, N:≤0.013%, O:≤0.0020%, and the balance of Fe and inevitable impurities, wherein the components satisfy (8.57*C+1.12*Ni)≥4.8% and 1.2%≤(1.08*Mn+2.13*Cr)≤5.6%. The steel has excellent low-temperature impact toughness and aging impact toughness at −20° C. and −40° C., a rationally controlled yield ratio, and ultra-high strength, ultra-high toughness, and ultra-high plasticity, which can be used in applications such as offshore platform mooring chains, mechanical structures, and automobiles that require high strength and toughness of the steel.

A method of forming a coating of an Al—Zn—Si—Mg alloy on a steel strip to form an Al—Zn—Mg—Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al—Zn—Si—Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the p H of cooling water to be in a range of pH 5-9. Particular embodiments focus on Al—Zn—Si—Mg alloys that contain the following elements in % by weight: Zn: 2 to 19, Si: 0.01 to 2, Mg: 1 to 10, and Balance Al and unavoidable impurities.

A method of forming a coating of an Al—Zn—Si—Mg alloy on a steel strip to form an Al—Zn—Mg—Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al—Zn—Si—Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the p H of cooling water to be in a range of pH 5-9. Particular embodiments focus on Al—Zn—Si—Mg alloys that contain the following elements in % by weight: Zn: 2 to 19, Si: 0.01 to 2, Mg: 1 to 10, and Balance Al and unavoidable impurities.

A control device for a section of a hot rolling mill is supplied with respective primary data for a plurality of rolling materials and respective preliminary target values for the target variables of the respective rolling material. The respective primary data describes the respective rolling material before being supplied to the section of the hot rolling mill. The respective preliminary target values of the target variables describe a desired target state of the respective rolling material after passing through the section of the hot rolling mill. At least one of the target variables is a particular target variable, whereby the control device determines a respective final target value in such a way that it changes the respective preliminary target value by a respective offset. The respective offset is determined independently of the primary data and the other particular target variables and the normal target variables for the respective rolling material.

Disclosed is a steel for an alloy structure, the chemical elements of the steel being, in percentage by mass: 0.35-0.45% of C, 0.27-0.35% of Si, 0.6-0.8% of Mn, 0.015-0.05% of Al, 0.06-0.1% of V, 0.2-1.0% of Zr, 0.001-0.005% of Mg, 0.025% or less of P, 0.015% or less of S, 0.005% or less of N, 0.001% or less of 0, the balance being Fe and other inevitable impurities. In addition, also disclosed is a manufacturing method for the steel for an alloy structure, the method comprising steps of: (1) smelting, refining, and casting; (2) blooming and cogging; (3) secondary hot rolling to form a product; and (4) heat treatment including quenching and tempering. The steel for an alloy structure is designed by adding trace alloy elements, the steel for an alloy structure is further strengthened and toughened, and the manufacturing cost is low.

A metal-strip rapid cooling apparatus includes a cooling fluid ejection device including one set of nozzles or a plurality of sets of nozzles arranged in a horizontal direction, and configured to eject a cooling fluid onto the metal strip from both sides of the metal strip; cooling fluid removing rolls configured to remove a remaining fluid from the metal strip onto which the cooling fluid has been ejected; and movable masking plates on both sides of a metal strip pass line along which the metal strip passes, the movable masking plates each disposed between the metal strip pass line and the nozzles, and configured to move in the horizontal direction to adjust a cooling start position and control a distance from the cooling start position to the cooling fluid removing rolls, the cooling start position positioned such that the metal strip starts to be cooled with the cooling fluid.

The present invention is to provide a steel plate with physical properties superior to existing steel plates used in fields such as industrial machinery, especially excellent low-temperature impact toughness along with high strength and high hardness, and a method for manufacturing same.

A high-strength thin-gauge checkered steel plate/strip and a manufacturing method therefor, wherein residual elements such as Sn and Cu in steel scrap are fully utilized as alloy elements in the smelting of molten steel, and the steel has selectively added micro-alloy elements such as B; during the smelting process, the alkalinity of the slag, the types of inclusion in the steel and the melting point thereof, the content of free oxygen and the content of soluble aluminum (Als) in the molten steel are controlled; and twin-roll thin-strip continuous casting is performed to cast a cast strip (11); after exiting crystallization rollers (8a, 8b), the cast strip (11) directly enters a lower sealed chamber (10) containing a non-oxidizing atmosphere, and enters an online rolling machine (13) in a sealed manner so as to undergo hot rolling, then after rolling, the strip steel is cooled by means of air atomization. The resultant steel roll can be used directly as hot-rolled checkered plate/strip, or as a finished checkered plate/strip after being cut and finished, and is widely applicable to the fields of architecture, mechanical production, automobile, bridges, transportation, ship building, etc.

A water-soluble quenching fluid composition prepared by blending: water, at least one kind selected from a polyoxyalkylene glycol and a derivative thereof (A), and an alkylene glycol ether (B), the polyoxyalkylene glycol or a derivative thereof (A) having a mass average molecular weight of 10,000 or more and 100,000 or less, the alkylene glycol ether (B) having a solubility in 100 mL of water at 20° C. of 2.0 g/100 mL-H.sub.2O or less and a molecular weight per 1 mol of 1,000 g/mol or less.