| 摘要 |
Provided is a TRIP-aided dual-phase martensitic steel which is excellent in terms of strength-elongation balance and Charpy impact value and has dual-phase martensite composed of a soft lath martensitic structure and a hard lath martensitic structure as a matrix phase, regardless of forging temperature or forging reduction ratio, by controlling heat treatment conditions. The dual-phase martensitic steel contains 0.1-0.7%C, 0.5-2.5%Si, 0.5-3.0%Mn, 0.5-2.0%Cr, 0.5% or less (including 0%) of Mo, 0.04-2.5%Al, and the balance Fe with incidental impurities; has its metallographic structure in which a matrix phase is composed of a soft lath martensitic structure and a hard lath martensitic structure; and obtained by heating its raw steel material to a ³-range, rapidly cooling the heated material to a temperature slightly above a martensite transformation starting temperature (Ms), and then performing an isothermal transformation process the cooled material in the temperature range from Mf to [(Mf)-100°C]. |
