Abstract: A continuous cast slab includes the following component: by mass %, C: 0.01˜0.3%, Si: 0.05˜0.5%, Mn: 0.4˜2%, P: 0.03% or less, S: 0.03 or less, Al: 0.005˜0.03%, Ni: 0.2˜2%, O: 0.006% or less, and N: 0.006% or less; wherein the balance is composed of Fe and inevitable impurities; wherein a structure in steel in a region within at least 2 mm from a broad surface is composed of ferrite and pearlite and a equivalent circular diameter of ferrite grains in the region is equal to or shorter than 30 ?m.

Abstract: A continuous cast slab includes the following component: by mass %, C: 0.01˜0.3%, Si: 0.05˜0.5%, Mn: 0.4˜2%, P: 0.03% or less, S: 0.03 or less, Al: 0.005˜0.03%, Ni: 0.2˜2%, O: 0.006% or less, and N: 0.006% or less; wherein the balance is composed of Fe and inevitable impurities; wherein a structure in steel in a region within at least 2 mm from a broad surface is composed of ferrite and pearlite and a equivalent circular diameter of ferrite grains in the region is equal to or shorter than 30 ?m.

Abstract: 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 ?m 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.

Abstract: 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 ?m 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.