PSI - Issue 43

Marie Ohanková et al. / Procedia Structural Integrity 43 (2023) 300–305

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Author name / StructuralIntegrity Procedia 00 (2022) 000 – 000

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Fig. 3. Fracture surface of (a) exposed sample; (b) non-exposed sample.

4. Conclusion The results showed that notch toughness, transition temperature, and time to creep rupture of non-exposed sample were significantly better than of exposed sample despite of all other mechanical properties, which were only slightly better or similar. However, fracture of creep, tensile and impact specimens of both samples were similar and always transgranular with the cleavage facets limited to grain size, if present. Only the appearance of ductile shear dimples in non-exposed samples was more elongated. Also metallographic investigations revealed very similar microstructure of both samples formed by mostly globularised bainitic and almost pure ferritic grains with a fine size. The only difference in the microstructure was the occupation of grain boundaries of exposed sample, which were strongly covered by particles of primary and secondary cementite instead of Cr-rich precipitates and nitrides as an expected result of in-service ageing. Although the strong occupation, grain boundaries of exposed sample are not weakened in contrary to its matrix. Therefore, the cause of embrittlement was determined not by rapid ageing, but by unsuitable initial heat treatment of the pipe material before its exposure. Acknowledgements The work presented was financial supported by the Technology Agency of the Czech Republic within the projects No. TK03020089 and project No. TN01000015/3, and by the Ministry of Trade of the Czech Republic within the project No. FV10645. A special thanks goes to Dr. Jaroslav Málek for TEM diffractions. References Cr-Mo-V Steel 15 128 (in Czech), Czech Technical Standards, 1986. Watanabe, J. et al., 1974. Temper Embrittlement of 2 1/4 Cr-1 Mo Pressure Vessel Steel, ASME 29th Petroleum Mech. Eng. Conf., Dallas, Sept. 15-18, 1974. Bruscato, R. M., 1987. Embrittlement Factors for Estimating Temper Embrittlement in 2.25Cr:1Mo, 3.5Ni-1.75Cr-0.5Mo-0.1V and 3.5Ni Steels, ASTM Conference, Miami, Florida. Gooch, D. J., Haigh, J. R., King, B. L., 1977. Relationship between Engineering and Metallurgical Factors in Creep Crack Growth. Metal Science 11, 545 – 550. Briant, C.L., Banerji, S.K., 1978. Intergranular failure in steel: the role of grain-boundary composition. International Metals Reviews, 23:1, 164 – 199. Zhao, Q. H., Jiang, B., Wang, J. M., 2016. Pearlite spheroidization mechanism and lifetime prediction of 12Cr1MoV steel used in power plant. In Proceedings of the 4th 2016 International Conference on Material Science and Engineering (ICMSE 2016), 195-201. Detemple, I., Kraut, R., Hüttenwerke, D. , 2011. Avoid temper embrittlement step by step. Hydrocarbon Engineering. 16, 75 – 78. Fürbacher, I., 2006 -. Lexicon of steels: material sheets with international equivalents (in Czech). Dashöfer (Ed.), Prague.