@article{oai:soar-ir.repo.nii.ac.jp:00018001,
 author = {Kobayashi,  Junya and Ina,  Daiki and Futamura,  Asahiko and Sugimoto,  Koh-ichi},
 issue = {4},
 journal = {ISIJ INTERNATIONAL},
 month = {Jun},
 note = {The fracture toughness of an advanced ultrahigh-strength 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb (in mass%) transformation-induced plasticity (TRIP)-aided steel with a bainitic ferrite and/or martensite structure matrix was investigated for applications in automobiles, construction machines, and pressure vessels. After the steel was austenitized and isothermally transformed via heat treatment at temperatures between 200 degrees C and 350 degrees C below the martensite-finish temperature, it exhibited a good combination of tensile strength (1.4 GPa) and total elongation (15%). In addition, the steel achieved a much higher plane-strain fracture toughness (K-IC = 129-154 MPa m(1/2)) than conventional structural steel such as SCM420 steel (K-IC = 57-63 MPa m(1/2)). Surprisingly, the fracture toughness was nearly the same as that of a maraging steel. Our results indicate that the high fracture toughness was associated with (1) a softened wide lath-martensite matrix with a low carbide content and carbon concentration and (2) effective plastic relaxation of localized stress concentration by the strain-induced transformation of fine metastable retained austenite in the narrow lath-martensite and retained austenite mixture, which suppresses void formation and cleavage crack initiation at the pre-crack tip., Article, ISIJ INTERNATIONAL. 54(4):955-962 (2014)},
 pages = {955--962},
 title = {Fracture Toughness of an Advanced Ultrahigh-strength TRIP-aided Steel},
 volume = {54},
 year = {2014}
}