[Problem] To provide: a molten metal plating furnace that can increase plating quality and work efficiency; a system for producing and method for producing a metal plated product; and a metal plated steel tube obtained by means of the method for producing. [Solution] The system for producing has at least one plating implementation unit that performs molten metal plating of a plating processing subject, and at least one plating implementation unit has a plating bath and a heating device for heating the plating bath, wherein in the heating device, an array of fuel filling openings and an array of air filling openings are formed that are facing in a manner so as to discharge air and fuel to a combustion region in common along a combustion chamber, the effective opening cross-sectional size of at least the majority of the openings of at least one of the opening arrays can be adjusted by means of an adjustment mechanism for adjusting the extent of a medium filling opening array, and when the size of both opening arrays can be adjusted, individual adjustment of the arrays is possible.

Provided is a method for manufacturing a high-strength galvanized steel sheet. Heating in a first half of oxidizing treatment is performed at a temperature of 400 C. to 750 C. in an atmosphere having a particular O.sub.2 concentration and a particular H.sub.2O concentration, and heating in a second half of the oxidizing treatment is performed at a temperature of 600 C. to 850 C. in an atmosphere having a particular O.sub.2 concentration and a particular H.sub.2O concentration. Subsequently, heating in a heating zone for reduction annealing is performed to a temperature of 650 C. to 900 C. at a particular heating rate in an atmosphere having a particular H.sub.2 concentration and a particular H.sub.2O concentration with the balance being N.sub.2 and inevitable impurities, and soaking in a soaking zone for the reduction annealing is performed in an atmosphere having a particular H.sub.2 concentration and a particular H.sub.2O concentration with the balance being N.sub.2 and inevitable impurities.

The present invention relates to an ultra-high strength, hot-dip galvanized steel sheet having excellent surface quality and coating adherence and to a method for manufacturing thereof, the ultra-high strength, hot-dip galvanized steel sheet comprising: 0.1-0.3% by weight carbon (C); 0.1-2.0% by weight silicon (Si); 0.005-1.5% by weight aluminum (Al); 1.5-3.5% by weight manganese (Mn); 0.04% by weight or less phosphorus (P) (excluding 0% by weight); 0.015% by weight or less sulphur (S) (excluding 0% by weight); 0.02% by weight or less nitrogen (N) (excluding 0% by weight); the balance being Fe; and other inevitable impurities, and further comprising 0.01 wt.% to 0.07 wt.% of at least one kind of element selected from the group consisting of bismuth (Bi), tin (Sn) and antimony (Sb).

A steel product may include a metallic anticorrosion coating of an aluminum alloy. So that such a steel product possesses high media resistance, more particularly high acid resistance and corrosion resistance, the steel product may be immersed in a liquid-melt coating bath that includes an aluminum alloy. In addition to Aluminum and unavoidable impurities, the aluminum alloy may include at least one of 0.2-2% by weight Mn or 0.2-7% by weight Mg, 0.5-5% by weight Fe, and at least one of 0.05-0.4% by weight Ti or 0.05-0.4% by weight Zr. A method for producing such steel products may involve providing a steel product in a hot-rolled or cold-rolled state, activating a surface of the steel product to remove passive oxides, and coating the surface-activated steel product by immersion in a liquid-melt coating bath that comprises an aluminum alloy having the aforementioned composition.

A steel-strip production apparatus adapted to produce a hot-dip-plated steel strip and a cold-rolled steel strip includes a continuous annealing furnace, a snout connected to the continuous annealing furnace, a contact-type seal plate device and a noncontact-type seal roll device, a hot-dip-plating tank that is movable, and a roll configured to turn the path direction of the steel strip after passing through the snout, wherein a hot-dip-plated steel strip production unit configured to produce a hot-dip-plated steel strip by bringing the steel strip continuously annealed in the continuous annealing furnace into the hot-dip-plating tank; and a cold-rolled steel strip production unit configured to produce a cold-rolled steel strip by transferring the steel strip continuously annealed in the continuous annealing furnace without causing the steel strip to pass through the hot-dip-plating tank, are configured to be switchable with one another.

A method for producing a metallic coated steel sheet is provided. The method includes continuously annealing a steel sheet in a continuous annealing furnace and hot dip coating the steel sheet.

A method of forming a coating of an AlZnSiMg alloy on a steel strip to form an AlZnMgSi coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten AlZnSiMg 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 AlZnSiMg 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 plated steel material having a plating layer having an average chemical composition containing, in mass %, Zn: more than 50.00%, Al: more than 15.0% and less than 30.0%, Mg: more than 5.0% and less than 15.0%, and Si: 0.25% or more and less than 3.50%, and impurities, and wherein a total amount (?A) of at least one selected from the group consisting of Sn, Bi and In is less than 1.00%, a total amount (?B) of at least one selected from the group consisting of Ca, Y, La, Ce and Sr is 0.02% or more and less than 0.60%, 2.0?SMg/Si<20.0 (Formula 1), 3.0?Si/?B<24.0 (Formula 2), and 26.0?(Si/?B)?(Mg/Si)<375.0 (Formula 3) are satisfied, and in an X-ray diffraction pattern of the surface of the plating layer, a diffraction intensity ratio R1 defined by R1={I(16.18?)+I(32.69?)}/I(27.0?) (Formula 4) satisfies 2.5<R1 (Formula 5) is used.

A welded member includes: a first steel sheet including a base steel sheet and a zinc-based plating layer formed on a surface of the base steel sheet; and a second steel sheet spot-welded on the first steel sheet and facing the zinc-based plating layer of the first steel sheet, a spot-welded zone being formed between the first steel sheet and the second steel sheet. A surface layer of the base steel sheet has a decarburization ratio of 30% or more. The decarburization ratio is represented by equation: Decarburization ratio (%) of surface layer=(1?average carbon concentration in surface layer/bulk carbon concentration)*100 where the surface layer refers to a region of the base steel sheet from the surface thereof to a depth of 35 ?m. A shoulder portion of the spot-welded zone includes a B-type crack having a length of 100 ?m or less, and no C-type crack.

A method for manufacturing a hot-dip galvanized steel sheet having a high Si content and good plating adhesion. The method for manufacturing a hot-dip galvanized steel sheet includes the following: hot-rolling a steel raw material having a Si content of 1.0 mass % or more and coiling a steel sheet at 500? C. to 700? C.; subjecting a surface of the steel sheet after the coiling to an oxidation treatment at a heating temperature of a steel sheet temperature of 750? C. or lower, and subsequently subjecting the surface to a reduction treatment; and subjecting the steel sheet after the reduction treatment to a hot-dip galvanizing treatment to form a Zn-plated layer on a surface of the steel sheet.