Steel treatment method and electrical steel sheet

Abstract

An electrical steel sheet in which Al is appropriately diffused is manufactured at a relatively low cost. Disclosed is a steel treatment method including performing diffusion treatment in an oxidizing atmosphere on steel for an electrical steel sheet with an aluminum-containing layer formed on a surface of the steel. The steel preferably contains Si at more than 0.00 mass % and 7.00 mass % or less, and Al at more than 0.00 mass % and 2.00 mass % or less. The aluminum-containing layer is preferably in the form of a plating layer having a thickness of 2 μm or more and 30 μm or less. The composition of the plating layer includes Al, and may further contain another element such as Fe. The diffusion treatment is preferably performed under a treatment condition for obtaining a change gradient in which the Al concentration gradually decreases from the surface of the steel toward the inside.

1 . A steel treatment method comprising
 performing diffusion treatment in an oxidizing atmosphere on steel for an electrical steel sheet with an aluminum-containing layer formed on a surface of the steel.   
     
     
         2 . The steel treatment method according to  claim 1 , wherein
 the steel before the aluminum-containing layer is formed contains silicon (Si) in a range of more than 0.00 mass % and 7.00 mass % or less, aluminum (Al) in a range of more than 0.00 mass % and 2.00 mass % or less, and manganese (Mn) in a range of more than 0.00 mass % and 1.00 mass % or less.   
     
     
         3 . The steel treatment method according to  claim 2 , wherein
 the aluminum-containing layer is in a form of a plating layer having a thickness in a range of 2 μm or more and 30 μm or less, and   a composition of the plating layer includes aluminum (Al), or includes, in addition to aluminum (Al), one or more of iron (Fe), silicon (Si), and manganese (Mn).   
     
     
         4 . The steel treatment method according to  claim 2 , wherein
 the diffusion treatment is performed under a treatment condition for obtaining a change gradient in which an aluminum concentration gradually decreases from the surface of the steel toward a center of a thickness.   
     
     
         5 . The steel treatment method according to  claim 2 , wherein
 the diffusion treatment is performed at a temperature in a range of 900° C. or more and 1200° C. or less and for a period in a range of 0.1 minutes or more and 1920 minutes or less.   
     
     
         6 . The steel treatment method according to  claim 3 , wherein
 the diffusion treatment includes simultaneously forming an aluminum diffusion layer based on aluminum contained in the aluminum-containing layer, and an oxide layer based on the aluminum contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere.   
     
     
         7 . An electrical steel sheet comprising:
 an oxide layer forming an insulating coating on a surface of a base material, the oxide layer containing one or more of aluminum, iron, silicon, and manganese; and   an aluminum diffusion layer in which an aluminum concentration gradually decreases from the surface of the base material toward a center of a thickness of the base material.   
     
     
         8 . The electrical steel sheet according to  claim 7 , wherein
 the oxide layer has a thickness in a range of 1 μm or more and 25 μm or less, and contains the aluminum or the iron in a range of 20 mass % or more and 80 mass % or less.   
     
     
         9 . The electrical steel sheet according to  claim 8 , wherein
 assuming that an Al gradient is a change gradient of the aluminum concentration with respect to a change in a thickness direction in the aluminum diffusion layer, and an Al gradient-thickness ratio is a value obtained by dividing the Al gradient by the thickness of the base material, and   assuming that, when an infiltration amount of the aluminum in the aluminum diffusion layer is calculated based on a diffusion depth of the aluminum in the aluminum diffusion layer and concentrations of the aluminum on the surface of the base material and the center of the thickness of the base material, an Al infiltration amount-thickness ratio is a value obtained by dividing the infiltration amount by the thickness of the base material,   Al gradient-thickness ratio×(Al infiltration amount-thickness ratio) 1/2  is in a range of more than 0 and 0.000400 or less.   
     
     
         10 . The electrical steel sheet according to  claim 9 , wherein
 the Al infiltration amount-thickness ratio is in a range of more than 0 and 5.50 or less.   
     
     
         11 . The steel treatment method according to  claim 5 , wherein
 the diffusion treatment includes simultaneously forming an aluminum diffusion layer based on aluminum contained in the aluminum-containing layer, and an oxide layer based on the aluminum contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere.   
     
     
         12 . The steel treatment method according to  claim 4 , wherein
 the diffusion treatment includes simultaneously forming an aluminum diffusion layer based on aluminum contained in the aluminum-containing layer, and an oxide layer based on the aluminum contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere.   
     
     
         13 . The steel treatment method according to  claim 2 , wherein
 the diffusion treatment includes simultaneously forming an aluminum diffusion layer based on aluminum contained in the aluminum-containing layer, and an oxide layer based on the aluminum contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere.   
     
     
         14 . The steel treatment method according to  claim 1 , wherein
 the diffusion treatment includes simultaneously forming an aluminum diffusion layer based on aluminum contained in the aluminum-containing layer, and an oxide layer based on the aluminum contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere.   
     
     
         15 . The electrical steel sheet according to  claim 7 , wherein
 assuming that an Al gradient is a change gradient of the aluminum concentration with respect to a change in a thickness direction in the aluminum diffusion layer, and an Al gradient-thickness ratio is a value obtained by dividing the Al gradient by the thickness of the base material, and   assuming that, when an infiltration amount of the aluminum in the aluminum diffusion layer is calculated based on a diffusion depth of the aluminum in the aluminum diffusion layer and concentrations of the aluminum on the surface of the base material and the center of the thickness of the base material, an Al infiltration amount-thickness ratio is a value obtained by dividing the infiltration amount by the thickness of the base material,   Al gradient-thickness ratio×(Al infiltration amount-thickness ratio) 1/2  is in a range of more than 0 and 0.000400 or less.   
     
     
         16 . The electrical steel sheet according to  claim 15 , wherein
 the Al infiltration amount-thickness ratio is in a range of more than 0 and 5.50 or less.