Abstract: 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.

Abstract: The present invention is a welded high-strength steel structure having a TS of not less than 900 MPa and excellent low-temperature toughness and a method of manufacturing the steel structure. The base steel is formed of a mixed structure of martensite and lower bainite and has a TS of not less than 900 MPa, and the weld metal is steel which has the following elements based on % by weight: C: 0.01% to 0.15%; Si: 0.02% to 0.6%; Mn: 0.6% to 3%; Al: 0.004% to 0.08%; Ti: 0.003% to 0.03%; O (oxygen): not greater than 0.06%; B: 0.0002% to 0.00%; and as optional components, Cu, Ni, Cr, Mo, V, and Nb and which satisfies the following two equations: 0.25 ≦ Pcm ≦ 0.32 and 0.6 ≦ Al/O (oxygen) ≦ 1.4.

Abstract: High-tensile-strength steel having excellent arrestability and a TS of not less than 900 MPa, as well as a method of manufacturing the same. The steel of the invention has the following composition (% by weight): C: 0.02% to 0.1%; Si: not greater than 0.6%; Mn: 0.2% to 2.5%; Ni: greater than 1.2% but not greater than 2.5%; Nb: 0.01% to 0.1%; Ti: 0.005% to 0.03%; N: 0.001% to 0.006%; Al: not greater than 0.1%; and optional elements. Ceq of the B-free steel is 0.53-0.7%, and Ceq of the B-bearing steel is 0.4-0.58%. The microstructure of the steel may be a mixed structure of martensite (M) and lower bainite (LB) occupying at least 90 vol. % in the microstructure, LB occupying at least 2 vol. % in the mixed structure, and the aspect ratio of prior austenite grains is not less than 3.

Abstract: High-tensile-strength steel having excellent arrestability and a TS of not less than 900 MPa, as well as a method of manufacturing the same. The steel of the invention has the following composition (% by weight): C: 0.02% to 0.1%; Si: not greater than 0.6%; Mn: 0.2% to 2.5%; Ni: greater than 1.2% but not greater than 2.5%; Nb: 0.01% to 0.1%; Ti: 0.005% to 0.03%; N: 0.001% to 0.006%; Al: not greater than 0.1%; and optional elements. Ceq of the B-free steel is 0.53-0.7%, and Ceq of the B-bearing steel is 0.4-0.58%. The microstructure of the steel may be a mixed structure of martensite (M) and lower bainite (LB) occupying at least 90 vol. % in the microstructure, LB occupying at least 2 vol. % in the mixed structure, and the aspect ratio of prior austenite grains is not less than 3.