Institute of Ferrous Metallurgy named after Z. I. Nekrasov (Dnepr, Ukraine):

V. A. Lutsenko, Dr. Eng., Leading Researcher, e-mail: lutsenkovlad2@gmail.com
T. N. Golubenko, Cand. Eng., Senior Researcher
O. V. Lutsenko, Cand. Eng., Researcher

It is necessary to obtain initial rolled product with a structure which has high ductility and low hardness for further mechanical processing of alloyed rolled metal products into the ready product. In this case the enterprises carry out a special softening heat treatment to increase the ductility of the metal. The treatment represents the annealing at subcritical temperatures (А1 — 25…40 °С) with long holding. During annealing the structural transformations are running and the formed structure has a granular morphology. To obtain spheroidizing in the steels with a mixed structure (contains at the same time pearlite, bainite or martensite) usually requires a lot of time and energy, because the structural transformations during heat treatment are running with different intensities in different phases. Established by study, that in the steels with a mixed structure during annealing the structural transformations begin from the thermodynamically less stable structures. So, to reduce the mode of the softening heat treatment (annealing) of the investigated steels it is rationally to change the cooling conditions after rolling and to provide the increased quantity of bainite and martensite. For medium-carbon steels alloyed by chromium, molybdenum and vanadium and also for low-carbon steel alloyed by manganese and silicon, an increase of the cooling rate after hot rolling by ~1.5 times allows to obtain more sensitive structure to annealing. So, the structure consists at least 80 % of the bainite, ~15 % of the ferrite and 5 % of the pearlite for chromium-molybdenum steel. The base of the structure contains bainite (~90 %), martensite (~5 %) and ferrite (up to 5 %) for chromium-molybdenum-vanadium steel. For low-carbon silicon-manganese steel an increase of the cooling rate leads to the formation of the structure which contains at least 35 % of the bainite-martensite, ~60 % of the ferrite and 5 % of the pearlite. The structural transformations proceed at the low temperatures and require a shorter duration of the holding in the obtained structures during further annealing. Receiving such structure after rolling, allows to speed up intermediate softening heat treatment, thereby reducing energy costs, and provides high ductility of steel before mechanical processing.

1. Mašek B., Jirková H., Ku+erová L. Rapid spheroidization and grain refinement caused by thermomechanical treatment for plain structural steel. Materials Science Forum. 2012. Vol. 706. pp. 2770–2775.
2. Karadeniz E. Influence of different initial microstructure on the process of spheroidization in cold forging. Materials and Design. 2008. Vol. 29, Iss. 1. pp. 251–256.
3. Harisha S. R., Sharma S. S., Kini U. A. Influence of spheroidizing heat treatment on mechanical properties of EN47 steel. Materials Science Forum. 2017. Vol. 880. pp. 136–139.
4. Xiaomin Y., Shanshan H., Yiwei Z., Lei Y. Effects of controlled cooling process on microstructure and mechanical properties of 12Cr1MoV boiler steel. Heat Treatment of Metals. 2015. Vol. 40, Iss. 6. pp. 116–119.
5. Bhadeshia H. K. D. H. Bainite in steels: theory and practice. 2019. CRC Press. 600 р.
6. Houdremont E. Handbuch der Sonderstahlkunde. Translation from German. Edited by Zaymovskiy A. S., Bernsteyn M. L., Meskina V. S. In 2 volumes, 2^nd edition. Moscow: Metallurgiya, 1966. 1274 p.
7. El R., Kruze М., Oklits R., Meren D., Raytman F. Controlled rolling of long products: current state. Chernye Metally. 2006. No. 10. pp. 60–65.

8. DIN EN 10083-1:2006. Steels for quenching and tempering. Part 1: General technical delivery conditions. Published: 01.10.2006.
9. DIN EN 10085:2001. Nitriding steels. Technical delivery conditions. Published: 01.07.2001.
10. DIN EN ISO14341:2008. Welding consumables. Wire electrodes and deposits for gas shielded metal arc welding of non alloy and fine grain steels. Classification. Published: 01.08.2008.
11. GOST 8233–56. Steel. Microstructure standard. Introduced: 01.07.1957.
12. GOST 1497–84 Metals. Methods for tension test. Introduced: 01.01.1986.
13. GOST 9450–76. Measurements microhardness by diamond instruments indentation. Introduced: 01.01.1977.
14. Lutsenko V. A., Anelkin N. I., Golubenko T. N., Shcherbakov V. I., Lutsenko O. V. Morphology modification of carbon chromium-molybdenum steel structure influenced by heat treatment. CIS Iron and Steel Review. 2012. Vol. 7. pp. 38–40.
15. Golovanenko S. А., Fonstein N. М. Two-phase low-alloy steels. Moscow: Metallurgiya, 1986. 207 p.
16. Meskin V. S. Fundamentals of steel alloying. 2^nd edition. Moscow: Metallurgiya, 1964. 685 p.
17. Abrams Premium Steel. Technical datasheets. Description 31CrMoV9, Premium 1.8519. Abrams Industries GmbH & Co.KG. Osnabruck, Germany [electronic resource] Available at: https://files.abrams-industries.com/steel/en_gb/1.8519.pdf (accessed: 23.03.2021).
18. Parusov V. V., Zhukova S. Yu., Evsyukov М. F., Sychkov А. B., Derevyanchenko I. V. et. al. Kinetics of phase transformations in a wire rod from continuously cast SV-08G2S electric steel during continuous cooling. Fundamentalnye i prikladnye problemy chernoy metallurgii. 2004. Iss. 9. pp. 193–199.
19. Kizhner М., Sychkov А. B., Sheksheev М. А.,Malashkin S.О., Kamalova G. Ya. Influence of metallurgical factors and heat treatment on formation of the welding wire rod structure. Vestnik Magnitogorskogo gosudarstvennogo tekhnicheskogo universiteta im. G. I. Nosova. 2016. No. 3. pp. 55–70.
20. Vdovin K. N., Feoktistov N. A., Gorlenko D. A., Nikitenko O. A. Investigation of microstructure of high-manganese steel, modified by ultra-dispersed powders, on the base of compounds of refractory metals. CIS Iron and Steel Review. 2017. Vol. 14. pp. 34–40.
21. Lutsenko V. А., Golubenko Т. N., Lutsenko О. V., Glazunova N. А. The grain size of austenite in chromium-molybdenum-bearing steels after austenitization at different temperatures. Chernye Metally. 2016. No. 12. pp. 17–20.
22. Korchunov A. G., Gun G. S., Shiryaev O. P., Pivovarova K. G. Study of structural transformation of hot-rolled carbon billets for highstrength ropes for responsible applications via the method of thermal analysis. CIS Iron and Steel Review. 2017. Vol. 13. pp. 39–42.
23. Lutsenko V. А., Parusov E. V., Golubenko Т. N., Lutsenko О. V. Energy effective mode of softening heat treatment of silicon-manganese steel. Chernye Metally. 2019. No. 11. pp. 31–35.