NRL-DWT EXTREMELY THICK STEEL HAVING EXCELLENT SURFACE PART NAVAL RESEARCH LABORATORY-DROP WEIGHT TEST PROPERTY

摘要

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.04 to 0.1% of C, 0.05 to 0.5% of Si, 0.01 to 0.05% of Al, 1.6 to 2.2% of Mn, 0.5 to 1.2% of Ni, 0.005 to 0.050% 0.03%, Cu: 0.2 to 0.6%, P: not more than 100 ppm, S: not more than 40 ppm, the remainder Fe and unavoidable impurities, and in a region up to the surface direct t / 10 position (t is the thickness of the steel) The microstructure is composed of bainite of 90% by area or more (including 100% area%), grain grains having grain boundaries of 15 degrees or more measured by EBSD, grain size of not more than 10 μm (excluding 0 μm) / RTI