关键词: 超高强钢, 逆转变奥氏体, NiAl析出相, 强韧性

Abstract: Effect of tempering temperature (500, 550, and 600 ℃) on microstructure, nano-phase precipitation, and mechanical properties of an 1100 MPa grade low-carbon ultra-high strength steel produced by thermo-mechanical control process (TMCP)+tempering (T) process was systematically investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), tensile test and impact test. The results indicate that compared to the TMCP state, after tempering at 500 ℃, the yield strength and tensile strength increase to 1173 MPa and 1276 MPa, respectively, while the impact absorbed energy decreases to 107 J at －20 ℃ and 55 J at －84 ℃. With the increase of tempering temperature, the yield strength first increases and then decreases, the tensile strength gradually decreases, and the low-temperature toughness progressively improves. The microstructure of the TMCP state steel consists of lath martensite, which transformed into tempered martensite after tempering. Within the tempering temperature range of 500-600 ℃, fine NiAl nano-phases and reversed austenite form in the steel. The precipitation strengthening effect contributed by nano-phases and the toughening effect provided by the reversed austenite significantly influence the strength-toughness balance. Excellent strength-toughness combination is achieved after tempering at 600 ℃, exhibiting a yield strength of 1160 MPa, a tensile strength of 1212 MPa, an impact absorbed energy of 199 J at －20 ℃, and an impact absorbed energy of 194 J at －84 ℃.

Key words: ultra-high strength steel, reversed austenite, NiAl precipitates, strength-toughness