Volgograd State Technical University (Volgograd, Russia):

N. A. Zyuban, Dr. Eng., Prof., Head of Chair of Materials Technology
D. V. Rutskii, Cand. Eng., Ass. Prof., Chair of Materials Technology
E-mail (common): tecmat@vstu.ru

Production of turbine set rotors from one-piece forgings is an important sector of modern power engineering industry. As a rule, ferritic steel of grade 38ХН3МФА (38KhNMFA) is used to manufacture rotors. A vacuum-cast large forging ingot serves as a part blank for the turbine set rotor; as a result, a comparatively high metallurgical quality of metal is ensured. The paper considers in detail blowing an inert gas through a hollow stopper to evaluate the eff ect of inert gas degassing on the quality of solid forgings manufactured from steel 38ХН3МФА (38KhNMFA). The findings prove that a more vigorous degassing during vacuum casting results in the size reduction of non-metallic inclusions which do not exceed 20 μm. An overall arrangement of non-metallic impurities over the length and cross-section of the forgings produced from a conventional and experimental ingots is identical and coincides with the classical arrangement of inclusions in the ingot. The greater portion of inclusions is located in the forging center line area. The size reduction of non-metallic inclusions due to argon blowing of molten metal stream has a favorable effect on the mechanical properties of the forgings produced power engineering needs. Despite a negligible decrease in strength, ductile properties of experimental forgings increase by 10 to 20 % (particularly in case of impact strength). In addition, ductile-to-brittle transition temperature also falls; it impedes microcrack development and prevents micro-cracks from transforming into macro-cracks thus contributing to product reliability.

1. Tsukanov V. V. Modern steels and technologies in power plant industry : monograph. Saint Petersburg : ANO LA : «Professional», 2014. 464 p.
2. Zhulev S. I., Zyuban N. A., Rutskiy D. V. Steel ingots: quality problems and new technologies: monograph. Volgograd : VolgGTU, 2016. 176 p.
3. Rutskiy D. V., Zhulev S. I., Titov K. E. Liquation in large forged products. Problemy chernoy metallurgii i materialovedeniya. 2008. No. 2. pp. 21–27.
4. Romashkin A. N., Malginov A. N., Tolstykh D. S. et al. Influence of ingot geometry on its axial looseness volume. Elektrometallurgiya. 2013. No. 7. pp. 36–39.

5. Rutskiy D. V., Zyuban N. A. Development of defect zones and cast metal structure in elongared two-piece Cr-Ni-Mo steel ingots. CIS Iron and Steel Review. 2015. Vol. 10. pp. 14–18.
6. Efi mov V. A., Eldarkhanov A. S. Modern technologies of casting and crystallization of alloys. Moscow : Mashinostroenie, 2004. 359 p.
7. Ubukata T., Suzuki T., Ueda S., Shibata T. Dehydrogenation in Large Ingot Casting Process. Proceedings ICS 2008: The 4^th International Congress on the Science and Technology of Steelmaking. pp. 227–230.
8. Zyuban N. A. Creation of technology of production of large forged ingots with improved properties based on the control of parameters of ingot and processes of steel casting in vacuum : thesis of inauguration of Dissertation … of Doctor of Engineering Sciences. Volgograd : RPK «Politekhnik», 2005.
9. GOST 1778-70. Steel. Metallographic methods for the determination of nonmetallic inclusions. Moscow, 1970. 32 p.
10. Yavoyskiy V. I., Bliznyukov S. A., Vishkarev A. F. et al. Inclusions and gases in steels. Moscow : Metallurgiya, 1973. 272 p.
11. Korotkova E. E., Altzitser M. Ya., Maksimov M. A. Influence of thermal treatment on resistance to fragile destruction of steel 17GS, refined with synthetic slag. Trudy VZPI «Ob aktualnykh problemakh sovremennoy metallurgii». 1976. Iss. 98. pp. 62–71.
12. Georgiev M. N. Viscosity of low-carbon steels. Moscow : Metallurgiya, 1973. 224 p.
13. Smirnova A. V., Barantseva Z. V., Gromova G. P. Application of transparent and raster electronic microscopy in metallurgy. Moscow : MDNTP, 1976. pp. 94–96.
14. Kryussar Sh., Plato Zh., Tamkhonkar R. et al. Comparison of viscous and fatigue destruction. Atomic mechanism of destruction. Moscow : Metallurgizdat, 1963. pp. 535–574.
15. Ezhov A. A., Petrova G. L. Defects in metals. Reference book, atlas. Moscow : Russkiy universitet, 2002. 360 p.
16. Grigorenko V. B., Morozova L. V., Orlov M. R. Research of the reasons of emergence of sites with different morphology of a break in shod preparations from steel 38HN3MFA. Trudy VIAM. 2014. No. 8. pp. 11–14.
17. Mintz B. The Infl uence to the Problem of Composition of Transverse on the Hot Cracking. ISIJ Iternational. 1999. Vol. 39, No. 9. pp. 833–855.
18. Krewerth D., Lippmann T., Weidner A., Biermann H. Influence of non-metallic inclusions on fatigue life in the very high cycle fatigue regime. International Journal of Fatigue. 2016. March, Vol. 84. pp. 40–52.
19. Passoja D. E., Hill D. C. Metallurgical Transaction. 1974. Vol. 5, No. 8. pp. 1851–1854.
20. Ivanov V. P., Mordukhovich A. M., Finel V. M. Risk level of non-metallic inclusions in steel. Problems of metal destruction. Moscow : MDNTP, 1975. pp. 172–181.