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.

Disclosed are a high strength thin specification high corrosion resistance steel and a manufacturing method therefor. The chemical ingredients of the steel in percentages by weight are as follows: 0.02-0.06% of C, 0.1-0.5% of Si, 0.4-1.7% of Mn, ≤0.02% of P, 4.0-6.0% of Cr, 1.0-3.0% of Ni, ≤0.007% of S, 0.004-0.010% of N, <0.001% of Als, 0.001-0.006% of B, 0.007-0.020% of total oxygen [O].sub.T, and the balance is Fe and inevitable impurities, and same simultaneously satisfy: comprising one or both elements of 0.01-0.08% of Nb or 0.01-0.08% of V; and Mn/S≥250. In the invention, micro-alloy elements such as Nb/V and a B element are selectively added to steel, the basicity of slag, the type and melting point of the inclusion in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als during the smelting process are controlled, and a strip is then cast by means of twin-roll thin strip continuous casting, and enters an online rolling mill for hot rolling in closed conditions, and after rolling, the strip steel is cooled by air atomization cooling.

Disclosed are a high strength thin specification high corrosion resistance steel and a manufacturing method therefor. The chemical ingredients of the steel in percentages by weight are as follows: 0.02-0.06% of C, 0.1-0.5% of Si, 0.4-1.7% of Mn, ≤0.02% of P, 4.0-6.0% of Cr, 1.0-3.0% of Ni, ≤0.007% of S, 0.004-0.010% of N, <0.001% of Als, 0.001-0.006% of B, 0.007-0.020% of total oxygen [O].sub.T, and the balance is Fe and inevitable impurities, and same simultaneously satisfy: comprising one or both elements of 0.01-0.08% of Nb or 0.01-0.08% of V; and Mn/S≥250. In the invention, micro-alloy elements such as Nb/V and a B element are selectively added to steel, the basicity of slag, the type and melting point of the inclusion in steel, the content of free oxygen in molten steel and the content of acid-soluble aluminum Als during the smelting process are controlled, and a strip is then cast by means of twin-roll thin strip continuous casting, and enters an online rolling mill for hot rolling in closed conditions, and after rolling, the strip steel is cooled by air atomization cooling.

A valve spring which has an excellent fatigue limit is provided. A chemical composition of the valve spring according to the present embodiment contains, in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less. S: 0.020% or less: Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, Ca: 0.0001 to 0.0050%, and N: 0.0100% or less, with the balance being Fe and impurities. In the valve spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm.sup.3, and a numerical proportion of Ca sulfides with respect to a total number of oxide-based inclusions and sulfide-based inclusions is 0.20% or less.

The present invention discloses a wire rod for an ultrahigh-strength steel cord and a manufacturing method thereof. The manufacturing method includes: smelting molten steel where inclusions in sizes ≥5 μm are at a number density ≤0.5/mm.sup.2 and sizes of inclusions are ≤30 μm; casting the molten steel into an ingot blank with a center carbon segregation value of 0.92-1.08; cogging the ingot blank into an intermediate blank with a center carbon segregation value of 0.95-1.05; rolling the intermediate blank into a wire rod; and performing temperature control cooling on the wire rod to obtain a wire rod with high purity, high homogeneity and tensile strength ≤1,150 MPa. The wire rod may be used for an ultrahigh-strength steel cord with single tensile strength ≥3,600 MPa.

The present invention discloses a wire rod for an ultrahigh-strength steel cord and a manufacturing method thereof. The manufacturing method includes: smelting molten steel where inclusions in sizes ≥5 μm are at a number density ≤0.5/mm.sup.2 and sizes of inclusions are ≤30 μm; casting the molten steel into an ingot blank with a center carbon segregation value of 0.92-1.08; cogging the ingot blank into an intermediate blank with a center carbon segregation value of 0.95-1.05; rolling the intermediate blank into a wire rod; and performing temperature control cooling on the wire rod to obtain a wire rod with high purity, high homogeneity and tensile strength ≤1,150 MPa. The wire rod may be used for an ultrahigh-strength steel cord with single tensile strength ≥3,600 MPa.

A hot-rolled steel plate/strip for sulfuric acid dew point corrosion resistance and manufacturing method therefor. In said method, elements such as Sn and Cu remaining in steel scrap are fully utilized to smelt molten steel, and micro-alloy elements such as Cr, Ti, and Sb are selectively added; in a smelting process, basicity of slag, types and melting points of inclusions in steel, and a free oxygen content and an acid-soluble aluminum (Als) content in molten steel are controlled, a cast strip (11) is casted by means of twin-roll strip continuous casting, the cast strip (11) exits from crystallization rolls (8a, 8b) and directly enters a lower closed chamer (10) having a non-oxidizing atmosphere, then enters, in a closed condition, an on-line rolling mill (13) for hot rolling, after rolling, strip steel is cooled by means of gas atomization cooling, and finally the strip steel is wound up. The steel can be widely applied to the fields of products, such as tobacco baking apparatuses, air preheater heat exchange elements in industries such as petroleum, chemical industry, electric power, and metallurgy, delivery pipe, flue, and stack manufacturing structural parts, and boiler preheater and economizer equipment, of which the use environments have requirements for sulfuric acid dew point corrosion resistance performance.

A hot-rolled steel plate/strip for sulfuric acid dew point corrosion resistance and manufacturing method therefor. In said method, elements such as Sn and Cu remaining in steel scrap are fully utilized to smelt molten steel, and micro-alloy elements such as Cr, Ti, and Sb are selectively added; in a smelting process, basicity of slag, types and melting points of inclusions in steel, and a free oxygen content and an acid-soluble aluminum (Als) content in molten steel are controlled, a cast strip (11) is casted by means of twin-roll strip continuous casting, the cast strip (11) exits from crystallization rolls (8a, 8b) and directly enters a lower closed chamer (10) having a non-oxidizing atmosphere, then enters, in a closed condition, an on-line rolling mill (13) for hot rolling, after rolling, strip steel is cooled by means of gas atomization cooling, and finally the strip steel is wound up. The steel can be widely applied to the fields of products, such as tobacco baking apparatuses, air preheater heat exchange elements in industries such as petroleum, chemical industry, electric power, and metallurgy, delivery pipe, flue, and stack manufacturing structural parts, and boiler preheater and economizer equipment, of which the use environments have requirements for sulfuric acid dew point corrosion resistance performance.

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.