Patent ID: 6364967
Filing Date: 2002-04-02
Classification: C21D,C22C

Abstract:
A high-strength, high-toughness rolled steel shape having mechanical properties of a tensile strength of not less than 590 MPa, a yield strength or 0.2% proof strength of not less than 440 MPa and a Charpy impact absorption energy at 0Â° C. of not less than 47 J, characterized in comprising, in percentage by weight,C: 0.02-0-06%, Si: 0.05-0.25%, Mn: 1.2-2.0%, Cu: 0.3-1.2%, Ni: 0.1-2.0%, Ti: 0.005-0.025%, Nb: 0.01-0.10%, V: 0.04-0.10%, N: 0.004-0.009%, and O: 0.002-0.004%, the balance being Fe and unavoidable impurities, having a chemical composition wherein, among the impurities, B is limited to not more than 0.0003% and the A1 content is limited to not more than 0.005% and having a microstructure wherein area ratio of bainite is not greater than 40% and the remainder is ferrite, pearlite and high-carbon island martensite, the area ratio of the high-carbon island martensite being not greater than 5%.