ULTRA-HIGH-STRENGTH STEEL BAR AND METHOD FOR MANUFACTURING SAME

摘要

The present invention relates to an ultra-high-strength steel bar and to a method for manufacturing same, wherein the steel bar comprises: C: 0.05 to 0.45 wt %, Si: 0.10 to 0.35 wt %, Mn: 0.1 to 0.85 wt %, Cr: 0.6 to 1.20 wt %, Mo: 0.05 to 0.35 wt %, with the remainder being Fe and other impurities. The method for manufacturing the steel bar involves twice performing a process of reheating and rough-milling billets for the steel bar comprising the above-described alloy composition so as to reduce the prior-austenite grain size, and performing intermediate roll-milling and finishing roll-milling to manufacture steel bars and cooling the steel bars with water to a temperature of 400 to 600°C through a Tempcore process such that a fine ferrite structure is formed at a center layer. The method of the present invention involves forming a martensite structure, serving as a hardening layer, at a surface layer, by means of the alloy design, heat treatment, rolling ratio control, Tempcore process, etc., and enables the center layer to have a fine ferrite structure, thereby producing an ultra-high-strength steel bar which has a yield strength of 800MPa or higher, a tensile strength of 900 MPa or higher, and an elongation percentage of 10% or higher, and which satisfies 180° bending test. The steel bar of the present invention can be combined with high-strength concrete to be effectively used as a main bar or a shear-reinforcing bar in a building structure.