MOLD FOR HOT-FORMING Zn-PLATED STEEL SHEET

Abstract

A forming tool for use in a hot forming of a Zn-plated steel sheet is provided. At least a portion of the forming tool to be in contact with the Zn-plated steel sheet during the hot forming is covered with an amorphous-carbon coating film. The amorphous-carbon coating film satisfies the following conditions (1) to (4): (1) a film thickness is 0.5 μm or larger; (2) a surface has an arithmetic mean roughness Ra of 2.0 μm or less; (3) the surface has a root-mean-square slope RΔq of 0.50° or less; and (4) a hydrogen content is 30 atom % or less.

1 . A forming tool for a hot forming of a Zn-plated steel sheet, wherein at least a portion of the forming tool to be in contact with the Zn-plated steel sheet during the hot forming is covered with an amorphous-carbon coating film that satisfies the following conditions (1) to (4):
 (1) a film thickness is 0.5 μm or larger;   (2) a surface has an arithmetic mean roughness Ra of 2.0 μm or less;   (3) the surface has a root-mean-square slope RΔq of 0.50° or less; and   (4) a hydrogen content is 30 atom % or less.   
     
     
         2 . The forming tool according to  claim 1 , wherein the amorphous-carbon coating film has a negative skewness Rsk in the surface thereof. 
     
     
         3 . The forming tool according to  claim 1 , wherein the amorphous-carbon coating film comprises at least one metallic element of W and Si in a total amount of up to 20 atom % relative to all elements. 
     
     
         4 . The forming tool according to  claim 1 , wherein the amorphous-carbon coating film has a hydrogen content of 5 atom % or higher. 
     
     
         5 . The forming tool according to  claim 1 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         6 . The forming tool according to  claim 2 , wherein the amorphous-carbon coating film comprises at least one metallic element of W and Si in a total amount of up to 20 atom % relative to all elements. 
     
     
         7 . The forming tool according to  claim 2 , wherein the amorphous-carbon coating film has a hydrogen content of 5 atom % or higher. 
     
     
         8 . The forming tool according to  claim 3 , wherein the amorphous-carbon coating film has a hydrogen content of 5 atom % or higher. 
     
     
         9 . The forming tool according to  claim 6 , wherein the amorphous-carbon coating film has a hydrogen content of 5 atom % or higher. 
     
     
         10 . The forming tool according to  claim 2 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         11 . The forming tool according to  claim 3 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         12 . The forming tool according to  claim 4 , the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         13 . The forming tool according to  claim 6 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         14 . The forming tool according to  claim 7 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         15 . The forming tool according to  claim 8 , the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds. 
     
     
         16 . The forming tool according to  claim 9 , wherein the amorphous-carbon coating film comprises sp2 bonds equal to or larger than sp3 bonds.