OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 the range of 0.02–0.05 wt. %. The improvement in toughness with increasing titanium content is due to the greater amount of acicular ferrite, as other factors do not interfere. Adding Mo in an amount of 0.881 wt. % in the weld metal provides optimal toughness at −45 °C due to a microstructure consisting of 77 % acicular ferrite and 20 % granular bainite. 4. It is necessary to take into account the overall chemical composition of the welding wire, which signifi cantly aff ects the formation of acicular ferrite (AF). It is shown that the best mechanical properties in welds of Cr70 steels corresponded to two compositions of electrode wires, i.e. 1.92 wt. % Mn with 0.02 wt. % Ti and 1.40 wt. % Mn with 0.08 wt. % Ti. A further increase in the Ti or Mn content contributed to the nucleation of bainite at the grain boundaries, rather than intra-granular nucleation of acicular ferrite. Therefore, a satisfactory combination of strength and toughness depends on the control of the composition of the weld metal. 5. An important factor determining the microstructure of the weld is the cooling rate, which is usually defi ned as the time required for cooling from 800 to 500 °C (Δt8/5) [34–36]. As shown in numerous works by various authors, the cooling rate depends on the heat input during welding. Therefore, it makes sense in further work to study the evolution of the microstructure of the weld metal at various heat inputs. 6. It is shown that the manufacture or repair of steel pipelines with a relatively large section thickness, as a rule, requires multi-pass welding. Numerous works extensively studied the brittleness of the heat-aff ected zone (HAZ) caused by thermal cycles from successive thermal welding cycles. Similarly, weld metals are subjected to thermal cycling from subsequent welding passes. The eff ect of uneven reheating causes a nonuniform microstructure of the welds. In this regard, in the course of further research, it is very important to understand the infl uence of thermal cycles of welding on the microstructure of the weld metal during multipass welding performed by various methods. References 1. Karlina Yu.I., Kononenko R.V., Ivancivsky V.V., Popov M.A., Deriugin F.F., Byankin V.E. Obzor sovremennykh trebovanii k svarke trubnykh vysokoprochnykh nizkolegirovannykh stalei [Review of modern requirements for welding of pipe high-strength low-alloy steels]. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2023, vol. 25, no. 4, pp. 36–60. DOI: 10.17212/1994-6309-2023-25.4-36-60. 2. Efron L.I. Metallovedenie v «bol’shoi» metallurgii. Trubnye stali [Metallurgy in “big” metallurgy. Pipe steels]. Moscow, Metallurgizdat Publ., 2012. 696 p. ISBN 978-5-902194-63-7. 3. Matrosov Yu.I., Litvinenko S.A., Golovanenko S.A. Stal’ dlya magistral’nykh truboprovodov [Steel for main pipelines]. Moscow, Metallurgiya Publ., 1989. 288 p. 4. Jorge J.C.F., Monteiro J.L.D., Gomes A.J.C., Bott I.S., Souza L.F.G., Mendes M.C., Araújo L.S. Infl uence of welding procedure and PWHT on HSLA steel weld metals. Journal of Materials Research and Technology, 2019, vol. 8 (1), pp. 561–571. DOI: 10.1016/j.jmrt.2018.05.007. 5. API Spec 5CT. Obsadnye i nasosno-kompressornye truby. Tekhnicheskie usloviya [API Spec 5CT. Casing and tubing. Specifi cations]. 9th ed. American Petroleum Institute Publ., 2011. 287 p. 6. ISO 11960. Petroleum and natural gas industries – Steel pipes for use as casing or tubing for wells. 4th ed. International Organization for Standardization, 2011. 269 p. 7. DSTU ISO 11960:2020. Petroleum and natural gas industries – Steel pipes for use as casing and tubing for wells. Geneva, Switzerland, IOS, 2020. 8. GOST R 53366–2009. Truby stal’nye, primenyaemye v kachestve obsadnykh ili nasosno-kompressornykh trub dlya skvazhin v neftyanoi i gazovoi promyshlennosti. Obshchie tekhnicheskie usloviya [State Standard R 53366– 2009. Steel pipes for use as casing or tubing for wells in petroleum and natural gas industries. General specifi cations]. Moscow, Standardinform Publ., 2010. 190 p. 9. STO Gazprom 2-4.1-158–2007. Tekhnicheskie trebovaniya k obsadnym trubam dlya mestorozhdenii OAO «Gazprom» [Standard organization STO Gazprom 2-4.1-158–2007. Technical requirements for casing pipes for Gazprom fi elds]. Moscow, Gazprom Publ., 2007. 23 p. 10. STO Gazprom 2-4.1-228–2008. Tekhnicheskie trebovaniya k nasosno-kompressornym trubam dlya mestorozhdenii OAO «Gazprom» [Standard organization STO Gazprom 2-4.1-228–2008. Technical requirements for tubing for OAO Gazprom fi elds]. Moscow, Gazprom Publ., 2008. 32 p.
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