HIGH-TENSILE-STRENGTH STEEL AND METHOD OF MANUFACTURING THE SAME

摘要

A high-tensile-strength steel having excellent toughness throughout its thickness, excellent properties at welded joints, and a tensile strength (TS) of at least about 900 MPa (130 ksi), and a method for making such steel, are provided. Steels according to this invention preferably have the following composition based on % by weight: carbon (C): 0.02 % to 0.1 %; silicon (Si): not greater than 0.6 %; manganese (Mn): 0.2 % to 2.5 %; nickel (Ni): 0.2 % to 1.2 %; niobium (Nb): 0.01 % to 0.1 %; titanium (Ti): 0.005 % to 0.03 %; aluminum (Al): not greater than 0.1 %; nitrogen (N): 0.001 % to 0.006 %; copper (Cu): 0 % to 0.6 %; chromium (Cr): 0 % to 0.8 %; molybdenum (Mo): 0 % to 0.6 %; vanadium (V): 0 % to 0.1 %; boron (B): 0 % to 0.0025 %; and calcium (Ca): 0 % to 0.006 %. The value of Vs as defined by Vs = C + (Mn/5) + 5P (Ni/10) - (Mo/15) + (Cu/10) is 0.15 to 0.42. P and S among impurities are contained in an amount of not greater than 0.015 % and not greater than 0.003 %, respectively. The carbide size in the steel is not greater than 5 microns in the longitudinal direction.