Method for manufacturing black plated steel sheet, apparatus for manufacturing black plated steel sheet, and system for manufacturing black plated steel sheet

摘要

The purpose of the present invention is to provides a method for manufacturing a black plated steel sheet that is capable of more evenly blackening the area of the plated steel sheet to be blackened. The present invention relates to a method for manufacturing a black plated steel sheet by bringing a plated steel sheet with an Al- and Mg-containing hot-dip galvanized layer into contact with water vapor inside a sealed vessel. This method performs, in the following order: a first step for heating a plated steel sheet disposed inside a sealed vessel in the presence of a gas, the dew point of which is always less than the plated steel sheet temperature; a second step for evacuating the heated ambient gas inside the sealed vessel to make the pressure of the gas inside the sealed vessel to be 70 kPa or less; and a third step for introducing water vapor inside the sealed vessel in which the pressure of the gas therein has been reduced to 70 kPa or less to blacken the galvanized layer.