Ultra-thick steel sheet with excellent strength and low-temperature impact toughness and manufacturing method thereof

Abstract

Disclosed are an ultra-thick steel sheet may have excellent strength and impact toughness, and a manufacturing method thereof. The ultra-thick steel sheet comprises, in percent by weight (wt %), 0.06 to 0.1% of C, 0.3 to 0.5% of Si, 1.35 to 1.65% of Mn, 0.015 to 0.04% of Al, 0.015 to 0.04% of Nb, 0.15 to 0.4% of Cr, 0.005 to 0.02% of Ti, 0.3 to 0.5% of Ni, 0.002 to 0.008% of N, 0.01% or less of P, 0.003% or less of S, and the remainder being Fe and inevitable impurities, and a microstructure, by area fraction, comprises 80% or more of polygonal ferrite with an average grain size of 40 μm or less and the remainder of pearlite with an average grain size of 20 μm or less.

Dependencies are inferred from the claim text.