A steel part includes a steel sheet substrate and a coating on at least one surface of the steel sheet substrate. The coating includes between 0.2 and 0.7% by weight of Al, with a remainder of the metal coating being Zn and inevitable impurities. The steel sheet substrate and the coating have at least one deformation. An outer surface of the coating has a waviness Wa.sub.0.8 of less than or equal to 0.43 m.

A method of producing a galvannealed steel sheet includes: annealing a steel strip by conveying the steel strip through a heating zone including a direct fired furnace, a soaking zone, and a cooling zone in this order in an annealing furnace; hot-dip galvanizing the steel strip discharged from the cooling zone; and heat-alloying a galvanized coating formed on the steel strip. Mixed gas of humidified gas and dry gas is supplied into the soaking zone from at least one gas supply port located in a region of lower of the soaking zone in a height direction so that a dew point measured in a region of upper of the soaking zone in the height direction and a dew point measured in a region of lower of the soaking zone in the height direction are both 20 C. or more and 0 C. or less.

The present invention provides a method for manufacturing a metal sheet. In this method, at least one of the following equations is satisfied: $\begin{array}{cc}\frac{Z}{d}+18\ln \left(\frac{Z}{d}\right)<8\ln \left(\frac{P}{V}\right)-27.52& \left(A\right)\\ f{O}_2<\frac{2.304.Math.{10}^{-3}}{{(27.52+\frac{Z}{d}+8\ln (}^{}}\end{array}$

The present invention provides a method for manufacturing more beautiful black coated steel sheets by uniformly blackening the coating layer. Specifically, the present invention provides a method for manufacturing black coated steel sheets, which brings ZnAlMg alloy coated steel sheets (1) into contact with steam in a closed container (10), wherein said closed container (10) can maintain a predefined internal pressure through variable control of the amount of steam flowing into said closed container (10) and/or the amount of steam flowing out of said closed container (10), and in said closed container (10) that can maintain said predefined pressure, said ZnAlMg alloy coated steel sheets (1) have contact with the steam introduced into said closed container (10).

Cooling section for a steel strip continuous annealing or galvanizing line arranged to handle a metal strip (1), said section comprising at least one area (2) for dry cooling set up to project gas on said steel strip and at least one wet cooling area (5) set up to project a liquid or a mixture of gas and liquid on said steel strip.

A facility for dip-coating a metal strip in continuous motion includes: a liquid coating metal bath from which the strip exits in a vertical strand; a bottom roller, a decambering roller, and, optionally, a stabilizing roller, all immersed in the liquid-metal bath; drying blades at an exit of the bath, for injecting compressed gas in order to remove excess coating that has not yet solidified so as to create a drying wave having a downward return stream of liquid metal; and a dissipating hydrodynamic-stabilization device placed between the drying blades and a last immersed roller, the dissipating hydrodynamic-stabilization device including a plurality of hydrodynamic pads for applying a load to at least one side of the metal strip and mounted so as to pivot around hinges so as to self-align the pads, the plurality of hydrodynamic pads extending transversely across a width of the strip.

When a portion for measuring the plating adhesion amount reaches an upstream side position, plating adhesion amount estimation values are calculated by using a plating adhesion amount estimation expression at positions away from a position that faces the distance sensors, that is, the upstream side position, by strip-width direction distances, of the surfaces of the steel strip. When the portion for measuring the plating adhesion amount reaches a downstream side position, the strip-width direction distances of the plating adhesion amount meters are matched to the strip-width direction distances, and the plating adhesion amount actual measurement values are obtained. The plating adhesion amount estimation expression is corrected on the basis of the differences between the plating adhesion amount estimation values and the plating adhesion amount actual measurement values. Accordingly, the control accuracy of the plating adhesion amount is improved.

The present invention provides a cooling device for a hot-dip plating device provided on an upper side of a plating thickness control device in a conveyance route of a hot-dip plated steel sheet that is conveyed from a plating bath in a vertically upward direction. The cooling device includes: a main cooling device that vertically sprays a main cooling gas to the hot-dip plated steel sheet; and a preliminary cooling device that is provided in a preliminary cooling section between the main cooling device and the plating thickness control device in the conveyance route, and sprays a preliminary cooling gas to a plurality of gas collision positions which are set along the preliminary cooling section.

Disclosed are a system and method for controlling a thickness of a hot-dip galvanized coating on a strip material with a continuously varying thickness. The system of the present disclosure is capable to provide a zinc coating with a uniform thickness on a coiled starting material with a continuously varying thickness, and the method of the present disclosure provides a simplified process to achieve such objective.

A dross removal device including: a dross robot that is configured to collect a bath surface dross present on a bath surface of a coating bath; a dross sensor that is configured to measure an intensity of infrared light from the bath surface of the coating bath; a dross sensor control device that is configured to specify a position of the bath surface dross according to a temporal change amount in the intensity of the infrared light; and a dross robot control device that is configured to cause the dross robot to collect the bath surface dross at the position specified by the dross sensor control device.