| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel material in which hydrogen is effectively trapped and precipitation strengthening is exerted by optimizing the form of precipitates in the steel material and hydrogen delayed fracture resistance is improved while securing high strength. SOLUTION: The high strength steel material with excellent delayed fracture resistance is composed of steel which has a composition containing, by mass, 0.005 to 0.2% C, 0.02 to 2.0% Si, 0.1 to 2.0% Mn and 0.001 to 0.2% N, further containing one or more precipitate-forming elements among Ti, V, Zr, Nb, Hf and Ta so that T value ranges from 0.01 to 1.0, and having the balance Fe with inevitable impurities. Moreover, a lamellar precipitate which consists of 1 to 2 atomic layers and is composed of the above precipitate-forming elements and either or both of C and N and in which a composition ratio between the total amount R of either or both of C and N and the total amount M of the above precipitate-forming elements, R/M, ranges from 0.7 to 0.9 is contained by 1×10<SP>4</SP>to 1×10<SP>7</SP>pieces/μm<SP>3</SP>in the steel. COPYRIGHT: (C)2007,JPO&INPIT
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