Production method of building structures for low yield ratio refractory steel

摘要

PURPOSE: To obtain the steel improved in weldability by applying the precipitation strengthening of the carbides of Mo, V, Nb, and Ti in a steel with a specific composition, performing reheating treatment in the (α+γ) two-phase region, and specifying the structure before reheating treatment. ;CONSTITUTION: A slab of a steel having a composition containing, by weight, 0.02-0.15% C, ≤0.40% Si, 0.80-2.00% Mn, ≤0.020% P, ≤0.015% S, and one or more kinds among 0.15-0.80% Mo, 0.005-0.30% V, 0.005-0.10% Nb, and 0.005-0.250% Ti is used. This slab is heated up to ≥1000°C, by which Mo, V, Nb, and Ti are sufficiently allowed to enter into solid solution. Subsequently, hot rolling is finished at ≥900°C to form the structure into a fine matrix structure containing bainite or martensite. After air cooling or accelerated cooling, the resulting steel plate is treated by the two phase region reheating hardening method consisting of reheating up to the two phase region temp. between the Ac₁ point and the Ac, point. By this method, the steel plate where low yield ratio at ordinary temp. is maintained and which has the necessity high strength at high temp. can be obtained, and the necessary of fireproofing coating at the time of building application can be reduced or removed.;COPYRIGHT: (C)1993,JPO&Japio