| 摘要 |
PROBLEM TO BE SOLVED: To provide high strength superfine ferritic steel having increased uniform elongation and high strength and high toughness without requiring special additive elements and having an excellent balance of strength-ductility and to provide its production method. SOLUTION: Low alloy steel having a composition containing, by weight, 0.02 to 0.20% C, 0.01 to 1.0% Si, 0.2 to 2.0% Mn, <=0.050% P, <=0.010% S, 0.001 to 0.10% Al, <=0.060% Nb and <=0.020% Ti, and the balance Fe with inevitable impurities is subjected to warn intensive working in a ferritic temperature region to induce recovery or recrystallization into superfine ferritic steel essentially consisting of a superfine ferritic grain structure with an average grain size of <2μm, and this superfine ferritic steel is subjected to warm intensive working and is immediately or, after cooling to <350 deg.C, subjected to annealing treatment of performing heating to the temperature range of 350 deg.C to (Ac1-40) deg.C and slowly cooling or isothermally holding the same within the above temperature range to produce high strength superfine ferritic steel.
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