| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide steel having a tensile strength of 2.0 GPa or higher, and superior toughness and ductility, and a method for manufacturing the same. <P>SOLUTION: The steel includes, by mass, 0.33-0.40% C, 2.0-5.0% Ni, 0.01% or more and less than 0.5% Mn, 0.0001-0.01% B, 0.01-3% Al, 0.05% or less P, 0.03% or less S, 0.01% or less N, Ti in a range satisfying formula (1) below, and one or, two or more selected from a group of 0.5% or less Cr, 0.5% or less Si, 1% or less Cu, 1% or less V, 1% or less Nb, 1% or less Mo and 3% or less Co. The remainder has a chemical composition of Fe and impurities, and a steel structure formed of a martensite composed of former austenite grains with average sizes of 5 μm or more. Formula (1) is expressed by 3.42 N+0.001≤Ti≤3.42 N+0.5 (1), wherein N and Ti respectively show contents (mass%) of N and Ti in the chemical composition. <P>COPYRIGHT: (C)2012,JPO&INPIT |
