Surface part NRL-Extra-thick steel material excellent in physical properties for drop test and method for producing the same

摘要

By weight%, C: 0.04 to 0.1%, Mn: 1.2 to 2.0%, Ni: 0.2 to 0.9%, Nb: 0.005 to 0.04%, Ti: 0.005 to 0.03%, Cu: 0.1 to 0.4%, P: 100 ppm or less, S: 40 ppm or less, the balance is composed of Fe and inevitable impurities, and the position of t / 10 immediately below the surface (t is steel In the region up to the same thickness, the fine structure includes polygonal ferrite of 50% by area or more (including 100% by area) and bainite of 50% by area or less (including 0% by area). An ultra-thick high-strength steel material and a method for manufacturing the same are disclosed.