| abstract |
By subjecting a threaded joint for OCTG (oil country tubular goods) to surface conditioning with an aqueous solution of potassium tetraborate or sodium tetraborate prior to manganese phosphate chemical conversion treatment, a manganese phosphate chemical conversion coating having coarse crystal grains with an average crystal grain diameter of 10-110 micrometers is formed on the surface of the steel member which may be any steel including a high Cr steel. This manganese phosphate chemical conversion coating can hold a large amount of a liquid lubricant, and it is effective at preventing the occurrence of galling at the time of makeup of a threaded joint for OCTG. |