Excellent-strength and excellent-toughness steel and the method of manufacturing the same

Abstract

A steel with excellent-strength and excellent-toughness comprises, by weight percent, C: 0.02 to less than 0.15%; Si: not greater than 1%; Mn: 0.3 to 2.5%; P: not greater than 0.05%; S: less than 0.004%; sol. Al: 0.001 to 0.1%; Ti: not greater than 0.02%; N: not greater than 0.009%; wherein, the metal structure of the steel contains either or both of martensite and bainite, or the tempered structure thereof; an aspect ratio of prior austenite grains is not greater than 1.5, the average short diameter of the prior austenite grains is within a range of 60 to 700 μm; and the contents of Ti, N, S and the short diameter dr of the prior austenite grains satisfy the following expression (1) and (2): when Ti/N<3.4, Ti + 8.1 ⁢ S ≦ 0.315 d ⁢ ⁢ γ - 30 - 0.011 ( 1 ) when Ti/N≧3.4, 3.4 ⁢ N + 8.1 ⁢ S ≦ 0.315 d ⁢ ⁢ γ - 30 - 0.011 ( 2 ) The high-strength and excellent-toughness steel can be obtained with less alloy elements addition and produced with continuously high productivity.

Dependencies are inferred from the claim text.