Use of impact bending curve parameters for fracture behavior assessment of pipe steels in the ductile-to-brittle transition region

The use of modern pendulum impact testers capable of recording specimen deformation curve during loading has made it possible to consider the impact bending test not only as a standard type of technological acceptance test for assessing metal quality in accordance with regulatory requirements. Recording curves in force-displacement coordinates provide an additional opportunity to obtain a more objective assessment of metal fracture resistance, and also generally expands the understanding of the fracture mechanism, especially in the transition temperature range. In this regard, it is of interest to analyze dynamic impact bending curves to obtain information about the nature of fracture, in particular about the quantitative ratio of ductile and brittle components in the fracture surface. In this study, using the example of steel grades 06GFBA, 26KhMFA and 35KhGMA, developed as a material for oil and gas pipes, it is experimentally shown that using force values at characteristic points on a pre- smoothed dynamic impact loading curve allows for a high-accuracy determination of the shear fracture appearance (SFA) by the evaluation method without visual analysis of the fracture surfaces of the failed specimens. Research has shown that the brittle component in the fracture occurs at the moment a sharp drop appears on the curve while the magnitude of the specimen deflection characterizes its resistance to the initiation and growth of a brittle crack during fracture. Temperature dependency of characteristic force and displacement values is determined. The pronounced dependence of the parameters of the impact bending curve on the test temperature can serve as a qualitative indicator for identifying incorrectly determined characteristic point values. Ductile-to-brittle transition curve is plotted by fitting calculated SFA values and ductile-to-brittle transition temperature is obtained. A comparison of ductile-to-brittle transition curves constructed from proposed and experimental (fractographic measurement) SFA data showed similar values of the ductile-to-brittle transition temperature. This confirms the possibility of using the proposed method for rapid and qualitative assessment with satisfactory approximation, especially when dealing with a large number of specimens, and also as an additional control method during acceptance tests.

1. Pavlov V. A. Physical principles of the cold deformation of BCC metals. — Moscow: Nauka, 1978. — 208 p. [in Russian].

2. Chernov V. M., Kardashev B. K., Moroz K. A. Cold brittleness and fracture of metals with various crystal lattices: dislocation mechanisms / Techn. Phys. 2016. Vol. 61. P. 1015 – 1022. DOI: 10.1134/s1063784216070070

3. Kazantsev A. G., Markochev V. M., Sugirbekov B. A. Statistical simulation in determination of the critical temperature of metal brittleness of the VVER-1000 reactor shell from data of bending impact test / Industr. Lab. Mater. Diagn. 2017. Vol. 83. No. 3. P. 47 – 54 [in Russian].

4. Toth L., Rossmanith H. P., Siewert T. A. Historical background and development of the Charpy test / Eur. Struct. Integrity Soc. Elsevier. 2002. Vol. 30. P. 3 – 19. DOI: 10.1016/s1566-1369(02)80002-4

5. Manahan M. P., Siewert T. A. The history of instrumented impact testing / Siewert T. A., Manahan M. P., McCowan C. N. (eds.). Pendulum impact machines: procedures and specimens. — West Conshohocken, PA: ASTM International, 2006. P. 3 – 12. DOI: 10.1520/stp37597s

6. Voloshenko-Klimovitsky Yu. Ya. Dynamic yield strength. — Moscow: Nauka, 1965. — 180 p. [in Russian].

7. Shtremel M. A. Informativeness of measurements of impact toughness / Metal Sci. Heat Treatment. 2008. Vol. 50. P. 544 – 557. DOI: 10.1007/s11041-009-9099-7

8. Makhutov N. A., Morozov E. M., Matvienko Yu. G. Formation and development of tests on the impact strength in the USSR and Russia / Industr. Lab. Mater. Diagn. 2001. Vol. 67. No. 7. P. 42 – 49 [in Russian].

9. Canonico D. A., Stelzman W. J., Berggren R. G., et al. Use of instrumented charpy tests to determine onset of upper-shelf energy. ORNL-5086. — Oak Ridge, TN: Oak Ridge National Laboratory, 1975. — 18 p.

10. Smirnov M. A., Pyshmintsev I. Yu., Boryakova A. N. Classification of low-carbon pipe steel microstructures / Metallurgist. 2010. Vol. 54. No. 7. P. 444 – 454.

11. Moura C. M., Miqueri F., Vilela J. J., et al. Evaluation of the ductile-to-brittle transition temperature in the ABNT 1016 steel using instrumented Charpy impact testing / 19th International congress of mechanical engineering. — Brasília, RJ: ABCM, 2007. — 10 p.

12. Kobayashi T., Niinomi M., Koide Y., et al. Instrumented impact testing of ceramics / Trans. Jap. Inst. Metals. 1986. Vol. 27. No. 10. P. 775 – 783.

13. Huang T., Yang G., Tang G. A fast two-dimensional median filtering algorithm / IEEE Trans. Acoust. Speech Signal Proc. 1979. Vol. 27. No. 1. P. 13 – 18.

14. Savitzky A., Golay M. J. E. Smoothing and differentiation of data by simplified least squares procedures / Anal. Chem. 1964. Vol. 36. No. 8. P. 1627 – 1639.

15. Sreenivasan P. R. Instrumented impact testing — accuracy, reliability and predictability of data / Trans. Ind. Inst. Metals. 1996. Vol. 49. No. 5. P. 677 – 696.

16. Botvina L. R. Principles of fractodiagnostics. — Moscow: Tekhnosfera, 2022. — 394 p. [in Russian].

17. Sreenivasan P. R., Shastry C. G., Mathew M. D., et al. Dynamic fracture toughness and Charpy transition properties of a service-exposed 2.25 Cr-1 Mo reheater header pipe / J. Eng. Mater. Technol. 2003. Vol. 125. No. 2. P. 227 – 233. DOI: 10.1115/1.1543969

18. Gulyaev A. P. Impact toughness and cold brittleness of structural steel. — Moscow: Mashinostroenie, 1969. — 69 p. [in Russian].

19. Kantor M. M., Bozhenov V. A. Scattering of values of impact toughness of low-alloy steel in the ductile-brittle transition temperature region / Inorg. Mater. Appl. Res. 2014. Vol. 5. No. 4. P. 293 – 302. DOI: 10.1134/s207511331404025x

20. Kantor M. M., Sudin V. V., Bozhenov V. A., et al. Microstructure and impact toughness of acicular ferrite in low alloy steel weld joints from results of multiple impact bending tests / Inorg. Mater. 2023. Vol. 59. No. 4. P. 451 – 467. DOI: 10.31857/s0002337x23040024

21. Chegurov M. K., Sorokina S. A. Fundamentals of fractographic analysis of fractures of structural alloy samples: textbook. — Nizhny Novgorod: NGTU im. R. E. Alekseeva, 2018. — 79 p. [in Russian].

22. Erdelen-Peppler M., Hillenbrand H.-G., Calvo S., et al. Investigation of the applicability of the projected capacity for the retention of high-strength distribution for the destruction of the pipeline at low temperatures / Izv. Vuzov. Cher. Met. 2012. No. 3. P. 3 – 12 [in Russian]. DOI: 10.17073/0368-0797-2012-3-3-12

23. Duan Q. Q., Qu R. T., Zhang P., et al. Intrinsic impact toughness of relatively high strength alloys / Acta Mater. 2018. Vol. 142. P. 226 – 235. DOI: 10.1016/j.actamat.2017.09.064

24. Böhme W. Experience with instrumented Charpy tests obtained by a DVM round-robin and further development / van Walle E. (ed.). Evaluating material properties by dynamic testing (ESIS 20). — London: Mechanical Engineering Publications, 1996. P. 1 – 23.

25. Windle P. L., Crowder M., Moskovic R. A statistical model for the analysis and prediction of the effect of neutron irradiation on Charpy impact energy curves / Nucl. Eng. Design. 1996. Vol. 165. Nos. 1 – 2. P. 43 – 56. DOI: 10.1016/0029-5493(96)01198-3