OBRABOTKAMETALLOV Vol. 26 No. 1 2024 150 MATERIAL SCIENCE Relationship between microstructure and impact toughness of weld metals in pipe high-strength low-alloy steels (research review) Yulia Karlina 1, a, *, Roman Kononenko 2, b, Vladimir Ivancivsky 3, c, Maksim Popov 2, d, Fedor Derjugin 2, e, Vladislav Byankin 2, f 1 National Research Moscow State University of Civil Engineering, 26 Yaroslavskoe Shosse, Moscow, 129337, Russian Federation 2 Irkutsk National Research Technical University, 83 Lermontova str., Irkutsk, 664074, Russian Federation 3 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation a https://orcid.org/0000-0001-6519-561X, jul.karlina@gmail.com; b https://orcid.org/0009-0001-5900-065X, istu_politeh@mail.ru; c https://orcid.org/0000-0001-9244-225X, ivancivskij@corp.nstu.ru; d https://orcid.org/0000-0003-2387-9620, popovma.kvantum@gmail.com; e https://orcid.org/0009-0004-4677-3970, deryugin040301@yandex.ru; f https://orcid.org/0009-0007-0488-2724, borck3420@gmail.com Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 1 pp. 129–154 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.1-129-154 ART I CLE I NFO Article history: Received: 19 September 2023 Revised: 21 October 2023 Accepted: 16 January 2024 Available online: 15 March 2024 Keywords: Steel Ferrite Perlite Beinite Martensite Impact toughness Fracture Hybrid laser welding Standards Acknowledgements Research was partially conducted at core facility “Structure, mechanical and physical properties of materials”. ABSTRACT Introduction. The modern pipeline industry requires the development of materials of high strength and toughness for the production of steels for oil and gas pipelines. Changes in steel production and rolling technologies have become a challenge for developers of welding materials and joining technologies. This problem is more critical for strength levels above 830 MPa, where there are no special rules for the approval of welding consumables. Research methods. The failure of stainless steel pipeline welds is becoming a serious problem in the pipeline industry. Multiphase microstructures containing acicular ferrite or an acicular ferrite-dominated phase exhibit good complex properties in HSLA steels. This paper focuses on the results obtained using modern methods of scanning electron microscopy for microstructural analysis, backscattered electrons (BSE) for electron channel contrast imaging (ECCI) and orientation microscopy based on electron backscatter diff raction (ORM), as well as characteristic X-rays for compositional analysis using X-beam spectroscopy (XEDS) and secondary electrons (SE) to observe surface morphology. Results and discussion. This paper analyzes the characteristics of the microstructure of the weld and its relationship with impact toughness. It is shown that predicting impact toughness based on the microstructural characteristics of steel weld metals is complicated due to the large number of parameters involved. This requires an optimal microstructure of the steel. Satisfactory microstructure depends on several factors, such as chemical composition, hot work processing, and accelerated cooling. Alloying elements have a complex eff ect on the properties of steel, and alloying additives commonly added to the steel composition include Mn, Mo, Ti, Nb and V. From a metallurgical point of view, the choice of alloying elements and the metallurgical process can greatly infl uence the resulting microstructure. A longer cooling time tend to improve the toughness and reduce the mechanical strength of weld deposits on high-strength steels. Welding thermal cycles cause signifi cant changes in the mechanical properties of the base material. The analysis showed that impact toughness strongly depends on the microstructure of the multi-pass weld of the material under study, which contains several sources of heterogeneity, such as interdendritic segregation, and the eff ective grain size can also be a signifi cant factor explaining large deviations in local impact toughness values. Acicular ferrite nucleated in intragranular inclusions has been shown to produce a fi ne-grained interlocking arrangement of ferrite plates providing high tensile strength and excellent toughness, and is therefore a desirable microstructural constituent in C-Mn steel weld metals. At the same time, discussion regarding the relationship between acicular ferrite and toughness is very complex and still open at present. Relating impact toughness to acicular ferrite, taking into account the top bead, is not a reliable procedure, even for single-pass deposit welding. Impact strength depends on several factors, and the strong eff ect of acicular ferrite is generally recognized due to its fi ne-grained interlocking structure, which prevents the propagation of brittle cracks by cleavage. The large-angle boundaries and high dislocation density of acicular ferrite provide high strength and toughness. However, for the same amount of acicular ferrite, diff erent viscosity values may be observed depending on the content of microalloying elements in the steel. An analysis of the results of various studies showed that other factors also aff ect the impact strength. For example, microphases present along the Charpy-V notch are critical for the toughness of weld metals. The combination of OM, SEM and EBSD techniques provides an interesting method for metallographic investigation of the refi ned metal microstructure of stainless steel pipeline welds. Conclusion. This review reports the most representative study regarding the microstructural factor in the weld of pipe steels. It includes a summary of the most important process variables, material properties, regulatory guidelines, and microstructure characteristics and mechanical properties of the joints. This review is intended to benefi t readers from a variety of backgrounds, from non-welding or materials scientists to various industrial application specialists and researchers. For citation: Karlina Y.I., Kononenko R.V., Ivancivsky V.V., Popov M.A., Derjugin F.F., Byankin V.E. Relationship between microstructure and impact toughness of weld metals in pipe high-strength low-alloy steels (research review). Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 1, pp. 129–154. DOI: 10.17212/1994-6309-2024-26.1-129-154. (In Russian). ______ * Corresponding author Karlina Yulia I., Ph.D. (Engineering), Research Associate National Research Moscow State Construction University, Yaroslavskoe shosse, 26, 129337, Moscow, Russian Federation Tel.: +7 914 879-85-05, e-mail: jul.karlina@gmail.com
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