PURPOSE: To simply produce PC steel twisted wires having complete rustproofing characteristics for post-tensioning work without damaging the covering layer of the wire and also by improving the occurrence of plastic process strain in the conventional cold treatment.
CONSTITUTION: A PC steel twisted wire 10 subjected to a given bluing process is temporarily untwisted in order while being heated to a temperature at which no plastic process strain occurs by untwisting. Core wire 10b and side wire 10a are coated with melted synthetic resin paint at the heating temperature to form a synthetic resin inner melt covering layer 21, and the untwisted wire is then restored to twisted state. The PC twisted wire 10 so formed is covered with an outer covering cylinder 27 through a lubricant for unbonded rustproofing process of the wire 10.