The objective of the present invention is to provide a surface treatment composition capable of imparting excellent corrosive resistance, blackening resistance, alkali resistance, and an intrinsic surface color property on a ternary hot dip galvanized steel sheet. The present invention provides a surface treatment composition comprising, with respect to 100% by weight of the solid content of the composition: 70-90% by weight of a resin mixture including a high molecular weight polysilicon-modified polyurethane main resin, a low molecular weight polysilicon-modified polyurethane auxiliary resin, and an auxiliary epoxy resin; 0.5-10% by weight of a tarnish inhibitor; 0.5-10% by weight of an adhesion promoter; 0.5-10% by weight of an anticorrosive agent; 0.1-2% by weight of a coloring pigment; and 0.1-1% by weight of a pigment stabilizer.

A high strength galvanized steel sheet excellent in coating adhesiveness is made from a base material that is a high strength steel sheet containing Si, Mn, and Cr. A method includes performing an oxidation treatment on steel containing Si, Mn, and Cr in an oxidation furnace under the condition that a selected exit temperature T, reduction annealing and a galvanizing treatment, or optionally, further an alloying treatment under conditions that heating is performed at a temperature of 460 C. or higher and 600 C. or lower for an alloying treatment time of 10 seconds or more and 60 seconds or less.

A hot-dip coated steel substrate coated with a layer of Sn directly topped by a zinc or an aluminum based coating is provided, the steel substrate having the following chemical composition in weight percent: 0.10C0.4%, 1.2Mn6.0%, 0.3Si2.5%, Al<2.0%, and on a purely optional basis, one or more elements such as P<0.1%, Nb 0.5%, B 0.005%, Cr1.0%, Mo0.50%, Ni1.0%, Ti0.5%,
the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, the steel substrate further having between 0.0001 and 0.01% by weight of Sn in the region extending from the steel substrate surface up to 10 m.

A method by which a flat steel product containing 2-35 wt. % of Mn can be provided with a coating of Zn which adheres well by annealing at an annealing temperature T.sub.a of 600-1100 C. for an annealing time of 10-240 s under an annealing atmosphere which has a reducing effect on the FeO present on the flat steel product and an oxidizing effect on the Mn contained in the steel substrate thereby forming a layer of Mn mixed oxide which covers the flat steel product at least in sections and then cooling the flat steel product to a temperature for bath entry and conveying it through a bath of molten Zn saturated within iron at a temperature of 420-520 C., within a dip time of 0.1-10 s.

Disclosed is a method for producing a plated black heart malleable cast iron member including a black heart malleable cast iron member and a plating layer formed on a surface of the black heart malleable cast iron member, the method including the steps of: performing graphitization in a non-oxidizing and decarburizing atmosphere; performing a particle projection treatment on a surface of the black heart malleable cast iron member obtained after the graphitization such that silicon oxide remains on the surface; immersing the black heart malleable cast iron member obtained after the particle projection treatment in a flux for 3.0 minutes or more; and performing hot-dip plating on the black heart malleable cast iron member obtained after the immersion in the flux.

Provided are a coated steel product in which a coating layer has a predetermined chemical composition, and in a backscattered electron image of a ZnAlMg alloy layer, obtained by polishing a surface of the coating layer to 1/2 of a layer thickness, and observing the surface at a magnification of 100 with a scanning electron microscope, Zn/Al/MgZn.sub.2 ternary eutectics are present, and an average value of a cumulative circumferential length of the Zn/Al/MgZn.sub.2 ternary eutectics is from 100 to 300 mm/mm.sup.2 and a method of manufacturing the coated steel product.

A method for circulating an iron-based electroplating solution, a method for manufacturing an iron-based electroplating solution, and a method for manufacturing an alloyed hot-dip galvanized steel sheet, which can be used to obtain an iron-based electroplating solution that is stably capable of operating with high electrolytic efficiency without sludge contamination and is capable of being power-saved without requiring large-scale equipment. In the first method, an iron-based electroplating solution used in an electroplating cell for iron-based electroplating is circulated and adjusted. The iron-based electroplating solution used in the electroplating cell is caused to pass through at least a reduction tank, a vertical centrifugal solid-liquid separation device, and a final adjustment tank in this order, and then is put into the electroplating cell. In the reduction tank, an iron source for reduction according to a concentration of Fe.sup.3+ in the iron-based electroplating solution transferred to the reduction tank is put.

Provided is a method of manufacturing a clad steel sheet. The method includes: preparing a base material including C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities; preparing a cladding material including C: 0.1 to 0.45%, Mn: 0.1 to 3.0%, and a remainder of Fe and inevitable impurities; disposing the base material between two of the cladding material to obtain a laminate; welding an edge of the laminate; heating the welded laminate between 1050 and 1350 C.; finish-rolling the heated laminate between 750 and 1050 C. with a rolling reduction ratio of 30% or more in a first pass; coiling the hot-rolled steel sheet between 400 and 700 C.; pickling the coiled hot-rolled steel sheet, and applying a cold-reduction ratio of 35 to 90%; and annealing the cold-rolled steel sheet between 550 C. and A3+200 C. of the cladding material.

It is proposed a method to enable manufacturing of a steel sheet having a beautiful coated layer, when applying hot-dip galvanizing to a steel sheet containing oxidizable elements. The method comprises: an electroplating step of, in a gap between a steel sheet and an electrode plate, forming Fe-based plating on the surface of the steel sheet through electroplating, by supplying an Fe-based plating solution; an annealing step of subjecting the steel sheet to heat treatment; and a hot dip coating step of applying hot-dip galvanizing to the steel sheet, and, in the electroplating step, a plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side that is not facing the steel sheet of the electrode plate, to the flow rate of the plating solution supplied to the steel sheet, is less than 50%.

Provided is a hot pressed member for which an amount of hydrogen entering during the hot press process is small, that can release hydrogen that has entered in a short period of time, and that has excellent delayed fracture resistance. The hot pressed member includes: steel material; an AlFe intermetallic compound layer having a thickness of 10 m to 35 m, on at least one side of the steel material; and a diffusion layer at an interface between the AlFe intermetallic compound layer and the steel material. The AlFe intermetallic compound layer includes an Al-rich phase having an Al concentration of 40 mass % or more and an Fe-rich phase having an Al concentration of less than 40 mass %. Average length of the Fe-rich phase in a cross-section in a direction perpendicular to the thickness direction is 10 m or less.