| 摘要 |
<p>PURPOSE:To obtain the title wire rod for a high-strength spiral hoop capable of being easily bent at a prescribed high yield strength by heating the wire rod surface to a sufficiently high temp. in an extremely short time, and then quenching the surface to make the hardness of the center part high and that of the surface layer part low. CONSTITUTION:A wire rod is continuously heat-treated, and highly strengthened. In this case, the wire rod surface is heated by a high-frequency induction heating means to a sufficiently high temp. in an extremely short time as compared with the conventional case to impart the prescribed yield strength to the surface, and finally heated. As the final heating, the tempering after hardening, especially the temper heating after direct hardening of the hot-rolled wire rod, is preferably carried out. After the succeeding quenching, the hardness of the surface layer part of the obtained wire rod is controlled to lower than the hardness necessary for maintaining the prescribed yield strength, and the hardness of the center part is controlled to higher than the necessary hardness. By this method, a high-strength spiral hoop with the mean yield strength over the entire cross section of the wire rod kept at >=130kgf/mm<2> is obtained.</p> |
