PURPOSE:To extend considerably a service life by forming an effective hardened layer and a heat affected zone respectively in the surface layer in a specific range of the diameter of a large diameter hot-rolled steel rod consisting of low alloy steel and the remaining part up to the center and producing a titled rod. CONSTITUTION:A large diameter hot-rolled steel rod consisting of low alloy steel is successively passed through =2 induction heating coils and coolers provided apart from each other at a prescribed space along a feed passage while said rod is sent in the axial direction. The surface layer part from the surface of the steel rod to a prescribed depth is heated to a prescribed hardening temp. and the remaining part up to the center to the approximate temp. until the steel rod arrives at the first cooler after passing through the plural induction heating coils. The surface layer part is hardened and quickly cooled with the first cooler and is subjected to the cooling that accelerates the deprival of the return heat transmitted from the central direction to the surface direction of the steel rod with the succeeding cooler, whereby an effective hardened layer is formed in the surface layer to 10-25% thickness of the diameter of the steel rod and a heat affected zone is formed in the remaining part up to the center and a rod for a rod mill is thus produced.
展开▼
