STEEL WITH LOW YIELD POINT SMALL IN STRAIN RATE DEPENDENCE OF YIELD POINT AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To provide steel with a low yield point, small in strain rate dependence of the yield point and used for an energy absorption device for a building at the time of an earthquake and its production method by reducing the amount of solid-solution C in ferrite as well as the amount of C relating to the formation of a hard second phase by adding proper amounts of Ti, Nb, and V in accordance with the amounts of C and N. ;SOLUTION: This steel, contains, by weight, ≤0.1% C, ≤0.4% Si, ≤1.5% Mn, ≤0.025% P, ≤0.015% S, ≤0.06% Al, 0.005-0.4% Ti, and ≤0.006% N, also contains one kind single or ≥2 kinds among Ti, Nb and V so that the amount of Excess C defined by Excess C=C-[(Ti+Nb/2+V)-3.4N]/4, satisfies -0.02%≤Excess C≤0.005% and contains the balance iron with inevitable impurities. The steel is hot-rolled at ≥750°C directly after casting or after reheating it to ≤1250°C and then, if necessary, tempering or normalizing treatment is performed.;COPYRIGHT: (C)2000,JPO