| 简介 |
PROBLEM TO BE SOLVED : To provide a high tensile strength steel for a building structure having tensile strength in a class of ≥780 Mpa with little deterioration in yield stress in the case of being subjected to heat such as a fire, and to provide a method of inexpensively producing the steel.
SOLUTION : The high tensile strength for a building structure comprises, by mass, 0.02 to 0.2% C, 0.01 to 0.5% Si, 0.4 to 2.5% Mn, 0.1 to 1% Cr, 0.1 to 1% Mo, 0.0003 to 0.005% B, 0.001 to 0.02% Nb and 0.001 to 0.1% Al, and the balance Fe with impurities in which the content of P is ≤0.05%, wherein the content of S is ≤0.008% and the content of N is ≤0.01%, also, the value expressed by the following formula (a) is ≤110, and the ratio of martensite is ≥80% : the formula (a) is 100-886×Nb(%)-12×Mo(%)+2.44×(RFe/C(%)); wherein the atomic symbol in the formula is the content (mass%) of the element, and RFe is the content (mass%) of Fe present as precipitates measured by an extraction residue method. The steel may contain one or more kinds selected from Cu, Ni, V, Ti, Ca, Mg, rare earth metals and Zr as well. In the production method, specified slag heating temperature, quenching conditions and heat recuperating conditions are applied.
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