Hot-dip al-plated steel sheet production method, and hot-dip al-plated steel sheet

Abstract

Provided is a method for producing a hot-dip Al-based metal-plated steel sheet including a plated layer having a surface on which fine spangle are stably formed. A method for producing a hot-dip Al-based metal-plated steel sheet, includes a composition adjusting step of adding a B-containing master alloy so as to adjust a composition of an Al-based hot-dip plating bath (3) containing aluminum as a main component, the composition being adjusted so that the Al-based hot-dip plating bath has a B concentration of not less than 0.005 mass % and a K concentration of more than 0 mass % and less than 0.0005 mass %, the K concentration being reduced in the Al-based hot-dip plating bath by supplying gas into the Al-based hot-dip plating bath so as to remove a suspended matter on a surface of the Al-based hot-dip plating bath.

1 . A method for producing a hot-dip Al-based metal-plated steel sheet, comprising:
 a composition adjusting step of adding a B-containing master alloy so as to adjust a composition of an Al-based hot-dip plating bath containing aluminum as a main component, the composition being adjusted so that the Al-based hot-dip plating bath has a B concentration of not less than 0.005 mass % and a K concentration of more than 0 mass % and less than 0.0005 mass %; and   a plating step of dipping a substrate steel sheet in the Al-based hot-dip plating bath, which has the composition thus adjusted, so as to cause the substrate steel sheet to pass through the Al-based hot-dip plating bath,   in the composition adjusting step, the K concentration being reduced in the Al-based hot-dip plating bath by supplying gas into the Al-based hot-dip plating bath so as to remove a suspended matter on a surface of the Al-based hot-dip plating bath.   
     
     
         2 . The method as set forth in  claim 1 , wherein in the composition adjusting step, the gas is supplied into the Al-based hot-dip plating bath by blowing the gas into the Al-based hot-dip plating bath. 
     
     
         3 . The method as set forth in  claim 1 , wherein in the composition adjusting step, the gas is supplied into the Al-based hot-dip plating bath by using a stirring mechanism to stir the Al-based hot-dip plating bath on or near the surface of the Al-based hot-dip plating bath. 
     
     
         4 . The method as set forth in  claim 3 , wherein the stirring mechanism is a stirring machine including a stirring blade. 
     
     
         5 . The method as set forth in  claim 3 , wherein
 the stirring mechanism is a drive roll including a rotation part that is rotatable on an axis by external power, and   the gas is supplied into the Al-based hot-dip plating bath by dipping a part of the rotation part in the Al-based hot-dip plating bath so as to rotate the rotation part.   
     
     
         6 . A hot-dip Al-based metal-plated steel sheet produced by a method recited in  claim 1 , comprising:
 a substrate steel sheet; and   a hot-dip Al-based metal-plated layer provided on a surface of the substrate steel sheet and having an average B concentration of not less than 0.005 mass % and an average K concentration of more than 0 mass % and less than 0.0005 mass %.   
     
     
         7 . The hot-dip Al-based metal-plated steel sheet as set forth in  claim 6 , wherein the hot-dip Al-based metal-plated layer has a surface on which not less than 100 spangle crystal nuclei are present per square centimeter surface area of the hot-dip Al-based metal-plated layer.