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AssigneeNippon Steel Corporation
InventorsShingo Yamasaki, Seiki Nishida, Toshiyuki Kajitani, Wataru Yamada, Yoshitaka Nishikawa, Nariyasu Muroga, Nobuyuki Komiya
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The present invention provides a high strength, high toughness steel wire rod useful for a PC steel wire, galvanized steel strands, spring use steel wire, cables for suspension bridges, etc. By hot rolling, then directly patenting or reaustenitizing, then patenting a high carbon steel wire rod of a specific chemical composition of the steel and chemical composition, size, and numerical density of inclusions, piano wire rod or high carbon steel wire rod having a structure of mainly pearlite, having an average value of the proeutectoid cementite area ratio of 5% or less in a center region of less than 20% of the wire rod diameter from the center of the wire rod, having a micromartensite size of the C section of 100 μm or less, having a tensile strength of the 170 kgf/mm2 class or more, and having a drawing ratio at break of 30% or more is obtained.
A high strength and high toughness carbon steel wire containing C in an amount of 0.95 wt % or less, characterized by further containing, Zr in an amount of 10 wt ppm or more and 500 wt ppm or less and by including in said wire rod inclusions having a size of 0.1 to 10 μm, having a mole fraction of Zr of 0.2 or more in the ZrO2 inclusions, and having a numerical density of 5,00 to 3000/mm2.
Dependencies are inferred from the claim text.