DWTT HOT ROLLED STEEL PLATE HAVING EXELLENT STRENGTH AND HIGH DWTT TOUGHNESS AT LOW TEMPERATURE AND METHOD FOR MANUFACTURING THE SAME

摘要

Preferred aspects of the present invention are by weight, C: 0.04-0.06%, Si: 0.05-0.5%, Mn: 1.4-1.7%, P: 0.01% or less (excluding 0%), S: 0.001% or less (0% Al: 0.02-0.05%, Nb: 0.04-0.07%, V: 0.02-0.05%, Ti: 0.005-0.015%, N: 0.002-0.006%, Ni: 0.1-0.3%, Cr: 0.1-0.3 %, Mo: 0.05 ~ 0.15%, Ca: 0.0005 ~ 0.003%, balance Fe and other unavoidable impurities, and the microstructure contains less than 2 area% of pearlite in the needle-like ferrite and bainite composites and the average effective grain size. The present invention provides a thick hot rolled steel sheet excellent in strength and DWTT cryogenic toughness of less than 10 μm in size and a method of manufacturing the same.