| 摘要 |
PURPOSE: A niobium-added high strength low alloy steel having superior ductility at high temperature is provided to prevent formation of corner cracks by improving ductility at high temperature in the niobium-added high strength low alloy steel. CONSTITUTION: The niobium-added high strength low alloy steel having superior ductility at high temperature comprises 0.05 to 0.1 wt.% of carbon, 0.05 to 0.5 wt.% of manganese, 0.10 to 0.5 wt.% of silicon, 0.005 to 0.1 wt.% of niobium, 0.001 to 0.0055 wt.% of boron and a balance of iron and other inevitable impurities, wherein iron boron carbide (Fe23(B,C)6) precipitate having a size of 2 to 6 μm exists on grain boundary and in the grain of the alloy steel, wherein ferrite exists on grain boundary and in grain of the micro-structure of the low alloy steel, and ferrite in grain of the low alloy steel is 10 vol.% or more, and wherein the alloy steel has a yield strength of 50 ksi or more and a cross-section reduction ratio of 0.85 or more in the temperature range of 700 to 850 deg.C.
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