| 摘要 |
PROBLEM TO BE SOLVED: To reduce nitric acid content and to effectively and sufficiently clean the surface of an iron-based metal wire rod by immersing the iron-based metal wire rod into an acid pickling solution comprising a sulfuric acid-nitric acid system which contains sulfuric acid and nitric acid in specified amounts and is kept at a specified elevated temp. SOLUTION: The surface of iron-based metal wire rod (high carbon chromium bearing wire rod or the like) is subjected to acid treatment by immersing it into an acid pickling solution comprising a sulfuric acid-nitric acid system which contains 5-30 wt.%, preferably 7-15 wt.% sulfuric acid and 1-6 wt.%, preferably 2-5 wt.% nitric acid and which is heated to 50-70 deg.C, preferably 55-65 deg.C. By this treatment, it is possible to make the center line average surface roughness Ra 0.8-6μm, if desired, 2-6μm, and ten-point average surface roughness Rz can be made 9-40μm, if desired, 15-30μm. When the iron-based metal wire rod is subjected to wire drawing processing or the like, the lowering of the life of a drawing die is suppressed by controlling the surface roughness of the finished surface without making the surface extremely smooth.
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