HIGH STRENGTH PC STEEL BAR HAVING HIGH TEMPERATURE RELAXATION PROPERTY AND PRODUCTION METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a PC (prestressed concrete) steel bar which has excellent high temperature relaxation properties, and to provide a production method therefor.;SOLUTION: The high strength PC steel bar has a tempered martensite single phase structure in which fine precipitates with a particle diameter of 10 nm are dispersedly precipitated. The PC steel bar comprises, by mass, ≤0.7% C, ≤3.5% Si, 0.2 to 3% Mn, 0.03 to 0.20% Ti and 0.05 to 0.6% Mo, further one or more kinds of metals selected from ≤0.08% Nb, ≤0.15% V and ≤1.5% W, and the balance Fe with inevitable impurities, wherein 0.5≤(C/12)/{(Ti/48)+(Mo/96)+(Nb/93)+(V/51)+(W/192)}≤9.5 is satisfied. The steel having the above composition is heated at ≥1,100°C, and is thereafter rolled at a finish rolling temperature of ≥800°C. Cooling is subsequently performed at 550 to 700°C at 0.5°C/sec to form bar steel. The bar steel is formed into a PC steel bar. The PC steel bar is thereafter quenched, and is subsequently held at 550 to 700°C for ≥10 min.;COPYRIGHT: (C)2004,JPO