PSI - Issue 13

Atsuhisa Kitade et al. / Procedia Structural Integrity 13 (2018) 1845–1854 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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at all at -40 ° C. Therefore, when analyzing with changing the value of G c at intervals of 1000 in increments, it was possible to express the desired temperature transition at G c of 52000 J/ 2 . Fig.19 shows the results of a full times precision analysis until the end of the fracture at an appropriate G c 52000 J/ 2 . From Fig.19, it was suggested that if the value of G c is properly determined, it is likely to express the correct temperature transition. However, at present, the correct temperature transition could not be expressed by analyzing using the same G c value under other rolling conditions. In the future, it is required to establish an analytical method that correctly shows the test results under all rolling conditions.

Fig.19 Calculated results at suitable dissipated energy

4. Conclusions

Authors aimed to elucidate the mechanism of brittle fracture occurrence in TMCP steel in order to explore further room for improvement. It is suggested that by measuring the crystal orientation near the brittle fracture trigger point, it is highly likely that fracture will occur from the MA present in the large crystal grain, and that the pile-up effect of dislocation works greatly. Also we succeeded in developing a prediction model of the DWTT test used for pipeline steel by using appropriate material composition formula. From now on, if we can formulate the fracture occurrence mechanism suggested in Chapter 2 and output critical stress from micro information, we can predict fracture characteristics by only inputting the micro information into DWTT prediction model developed in Chapter 3. References Kawabata, T., Inami, A. and Aihara, S., Numerical model of brittle crack propagation considering fracture surface energy on high tensile strength steel - Proposal of a numerical model of brittle crack propagation (report 1) -, Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol. 16 (2012) p. 77-87. Kawabata and Aihara, S., Effect of stress field around running crack tip on fracture surface energy during brittle crack propagation - Proposal of a numerical model of brittle crack propagation (report 2) -, J. Japan Soc. Naval Arch. Ocean Eng., 21 (2015), pp. 63-73. Kobayashi, Y., On recent natural gas · LNG situation, proceedings of symposium “Deepening of understanding of brittle crack propagation behavior of steels and new approach for high arrestability”, 2018.3. Meizoso,M. A. et al, Modeling cleavage fracture of bainitic steels, Acta Metallurgica et Materialia, 42, 2057.2068, 1994 Smith, E., The nucleation and growth of cleavage fracture in high carbon bainite, Materials Science and Engineering A, 158, 11-19, 1966 Tagawa, T. et al, Crystallographic Microstructure Analyses below Cleavage Triggers in Bainite Low Carbon Steels, Tetsu-to-Hagane, Vol.102, pp.295-303, 2016 EDAX Inc., OIM Analysis™ v7.3b, 201x. Asako, S., Master thesis, The University of Tokyo, 2017. ASTM E436 - 03(2014), Standard Test Method for Drop-Weight Tear Tests of Ferritic Steels