Overflatebehandlet stålmateriale, en fremgangsmåte for fremstilling derav,og en kjemisk omformings-behandlingsv¶ske

摘要

A chemical conversion treatment liquid which can stably form a phosphate-type chemical conversion film on a steel material for a joint portion of an oil well steel pipe containing 0.5 - 13% Cr is developed. Using a chemical conversion treatment liquid to which a prescribed amount of potassium is added, a chemical conversion film containing a prescribed amount of potassium compounds and having a prescribed thickness can be formed on the threaded surface of a joint portion of an oil well steel pipe.