METHOD AND APPARATUS FOR DIRECT HEAT TREATMENT OF MEDIUM- TO HIGH-CARBON STEEL RODS

摘要

A method and apparatus for the direct heat treatment of medium- to high-carbon steel rods which provides an increased tensile strength and drawability by subjecting hot-rolled steel rods to controlled cooling with a coolant. Expanded spiral coils of hot-rolled medium- to high-carbon steel rod having an austenitic structure and which is continuously transported in a generally horizontal direction is cooled by passing the spiral coils through a vessel containing a coolant of a gas bubble-water mixed fluid under a strong turbulent action. The coolant fluid contains a uniform dispersion of oxidizing gas bubbles and is maintained at a temperature of not higher than 95 DEG C. Preferably, the coolant is caused to flow in the same direction as the direction of movement of the coil in the vessel. The surface of the rod may be oxidized by allowing it to cool in air before it is immersed in the coolant fluid.