Patent ID: 6890389

Claim:
A method of treating a machined workpiece of a sulfide-containing free-cutting alloy steel to remove granular sulfides of Mn, Cr and Mo from a surface thereof, comprising the steps of: soaking a machined workpiece of the sulfide-containing free-cutting alloy steel in an aqueous solvent consisting of water or water containing a member selected from the group consisting of an oxidizing agent, an acid, an alkaline agent and a salt, the aqueous solvent containing water having a dissolved oxygen content of no more than 3 ppm; and applying ultrasonic waves having a watt density of 1.0 to 2.0 W/cm 2 and a frequency of 40 kHz or superimposed ultrasonic waves of multi-frequencies of 25-300 kHz to the solvent containing the workpiece following the soaking step.