Steel wire rod having coating film that has excellent corrosion resistance and workability, and method for producing same

Abstract

The present invention provides a steel wire rod having a lubricating coating film, which can achieve both workabilities such as wire drawability, spike property and ball ironing property, and corrosion resistance such as long-term rust prevention property; and a method for producing the same. Disclosed are a steel wire rod having a coating film containing no phosphorus, wherein the coating film includes a lower layer coating film composed of oxide and/or hydroxide of zirconium and having a film thickness of 1.0 to 200 nm, and an upper layer coating film containing silicon and tungsten, in order from a steel wire rod side, a mass ratio of tungsten/silicon being in a range of 1.3 to 18; and a method for producing the above steel wire rod, which includes bringing an aqueous chemical conversion treatment solution, which has a pH in a range of 2.5 to 5.0 and contains a water-soluble zirconium compound dissolved therein, into contact with a surface of a steel wire rod to form a lower layer coating film.

1 . A steel wire rod comprising a coating film comprising no phosphorus, wherein
 the coating film comprises a lower layer coating film comprising an oxide and/or hydroxide of zirconium and having a film thickness of 1.0 to 200 nm, and an upper layer coating film comprising silicon and tungsten, in order from a steel wire rod side, wherein a mass ratio of tungsten/silicon is in a range of 1.3 to 18.   
     
     
         2 . The steel wire rod according to  claim 1 , wherein the silicon is derived from a water-soluble silicate, and the tungsten is derived from a water-soluble tungstate. 
     
     
         3 . The steel wire rod according to  claim 1 , wherein the silicon is derived from at least one selected from the group consisting of lithium silicate, sodium silicate and potassium silicate, and the tungsten is derived from at least one selected from the group consisting of lithium tungstate, sodium tungstate, potassium tungstate and ammonium tungstate. 
     
     
         4 . The steel wire rod according to  claim 1 , wherein the upper layer coating film further comprises a resin, and a mass ratio of resin/(silicon+tungsten) is in a range of 0.01 to 3.2. 
     
     
         5 . The steel wire rod according to  claim 4 , wherein the resin is at least one selected from the group consisting of a vinyl resin, an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, a cellulose derivative, a polymaleic acid and a polyester resin. 
     
     
         6 . The steel wire rod according to  claim 1 , wherein the upper layer coating film further comprises a lubricant, and a mass ratio of lubricant/(silicon+tungsten) is in a range of 0.01 to 3.2. 
     
     
         7 . The steel wire rod according to  claim 6 , wherein the lubricant is at least one selected from the group consisting of a wax, polytetrafluoroethylene, a fatty acid soap, a fatty acid metal soap, a fatty acid amide, molybdenum disulfide, tungsten disulfide, graphite and melamine cyanurate. 
     
     
         8 . The steel wire rod according to  claim 1 , wherein a mass of the coating film per unit area of the upper layer coating film is in a range from 1.0 to 20 g/m 2 . 
     
     
         9 . A method for producing the steel wire rod according to  claim 1 , which comprises bringing an aqueous chemical conversion treatment solution, which has a pH in a range of 2.5 to 5.0 and contains comprises a water-soluble zirconium compound dissolved therein, into contact with a surface of a steel wire rod to form a lower layer coating film.