PROBLEM TO BE SOLVED: To obtain excellent brittle fracture resistance even in high speed deformation caused by a big earthquake or the like in a steel by prescribing the contents of S and 0 therein. ;SOLUTION: By strictly limiting the contents of S and 0 as follows for increasing the plastic deformability in the stress concentrated part, heating value in the case of high speed deformation is made large, and excellent brittle fracture resistance can be obtd, namely, the content of S is regulated to, by weight, ≤0.005% and that of 0 to ≤0.003%. It is considered that such effects of S and 0 are due to the situation that oxide and sulfide inclusions present in the steel cause the generation of microvoids to remarkably deteriorate the plastic deformability in the stress concentrated part. Furthermore, by incorporating 0.05 to 0.20% C, 0.05 to 0.50% Si, 0.5 to 1.8% Mn and 0.001 to 0.06% Al therein, mechanical properties required for construction and civil engineering can be obtd.;COPYRIGHT: (C)1998,JPO
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