Institute of Metallurgy and Mechanical Engineering, JSC “SPA”Central Research Institute of Mechanical Engineering Technology”, Rosatom, Moscow, Russia

L. V. Palatkina, Cand. Eng., Associate Prof., Leading Researcher, Electric Melting Laboratory, e-mail: lv.palatkina@yandex.ru
A. P. Kulikov, Cand. Eng., Head of Electric Melting Laboratory, e-mail: APKulikov@cniitmash.com
I. A. Shchepkin, Leading Researcher, Electric Melting Laboratory, e-mail: IASchepkin@cniitmash.com

Volgograd State Technical University, Volgograd, Russia
V. O. Kharlamov, Cand. Eng., Associate Prof., Dept. of Welding Equipment and Technology, e-mail: harlamov_vo@mail.ru

Institute of Metallurgy and Mechanical Engineering, JSC “SPA”Central Research Institute of Mechanical Engineering Technology”, Rosatom, Moscow, Russia¹ ; National University of Science and Technology “MISIS“, Moscow, Russia²
A. S. Zharmukhambetov, Head of the Laboratory of Additive Technologies¹, Post-graduate Student², e-mail: alps98@mail.ru

It is shown that, all other things being equal, the smelting of foundry corrosion-resistant chromium-nickel steel of the martensitic class in an open induction furnace with deoxidation at the outlet of the melt with REM and zirconium provides low values of total contamination with non-metallic inclusions of melting at the level of 0.98×10-4 determined by the method “L2“ GOST 1778-2022. At the same time, the total content of rare earth (La, Ce, Nd) and surfactant elements (B, Zr, S) in the composition of non-metallic inclusions reaches 75 % (by weight), and the inclusions themselves exhibit an increased tendency to coalescence. The lines of the carbide phase with a length of 4.3 to 78.4 microns found during electron microscopic and metallographic studies located in the interbranch zones solidifying at the last stages of crystallization belong to primary and secondary niobium carbides, formed respectively when niobium is introduced into the melt and as a result of the eutectic reaction occurring at the final stage of solidification. Qualitative patterns of dendritic liquation of components for high-alloyed martensitic steels have not yet been found, however, for the compositions studied in the work, it was found that Sg, Ni, Si, Si, Mo and Mp during crystallization liquify directly and enrich the interbranch zones forming a solid solution with an increased content of carbide-forming elements. At the same time, at the stage of dendritic crystallization, due to the adsorption of active additive surfactants (S, Sn, B, Pb, Se, Sb, the total volume of which exceeded 0.09 % (wt.), an insurmountable barrier is formed to realize the composition-leveling diffusion redistribution of elements between the axes of dendritic branches and the interendritic space and, as a result, the observed even greater heterogeneity of the structure under any thermal influences. Metallographic studies of cast samples revealed abnormal «white» zones in their volume with an increased content of all alloying elements relative to the zone of regular crystallization. An intermetallic compound based on the Fe-Cr-Mo system (average composition % (wt.): 49.61 Fe, 27.33 Cr, 16.41 Mo, 2.59 Mn, 2.08 Si, 1.29 V, 0.69 Nb) with inclusions of ultrafine cubic primary niobium carbides was recorded in the volumes of the interbranches of the «white» zones crystallized at the last stages in volume. It is shown that niobium, unlike other elements, exhibits reverse liquation in the «white» zone, i. e., during crystallization it accumulates in dendrites, however, in the zone of regular crystallization, niobium liquates directly, enriching the interbranches.

1. Nießen F. Рhase transformations in supermartensitic stainless steels. Doctoral thesis. Technical university of Denmark department of mechanical engineering section of materials and surface engineering, 2018. 291 р.
2. Khimushin F. F. Stainless steels. 2^nd ed. Moscow : MISiS, 1999. 408 p.
3. Houdremont E. Handbuch der Sonderstahlkunde. Translated from Germany. Moscow : Metallurgizdat, 1959–1960. Vol. 1. 736 p.
4. Markova E. G. Improvement of heat treatment of precision parts based on regularities of structure formation of 09Kh16N4BL steel: inauguration of Dissertation … of Candidate of Engineering Sciences. Moscow, 2013. 23 p.
5. Scheuer C. J., Cardoso R. P., Brunatto S. F. An overview on plasma-assisted thermochemical treatments of martensitic stainless steels. Surface Topography: Metrology and Properties. 2023. Vol. 11, Iss. 1. 013001. DOI: 10.1088/2051-672X/acb372
6. Dalibón E. L., Dalke A., Biermann H., Brühl S. P. Short time nitriding and nitrocarburizing of martensitic stainless steel. Surface and Coatings Technology. 2024. Vol. 485. pp. 1–8. DOI: 10.1016/j.surfcoat.2024.130931
7. GOST 977–88. Steel castings. General specifications. Introduced: 01.01.1990.
8. GOST 1778–2022. Steel and alloy metal products. Metallographic methods for the determination of nonmetallic inclusions. Introduced: 01.06.2023.
9. Baron A. A., Palatkina L. V. Selection of the optimal criterion for assessing the strength of gray cast iron based on the parameters of the primary structure. Metally. 2021. No. 3. pp. 61–67.
10. M. Beckert, H. Klemm. Handbuch der metallographischen Atzverfahren. Translated from Germany. Moscow : Metallurgiya, 1979. 336 p.
11. Kostyleva L. V. Creation of new scientific principles of strengthening iron-carbon alloys based on the development of the theory of crystallization and microliquation: Dissertation … of Doctor of Engineering Sciences. Volgograd, 2002. 340 p.
12. Molyarov V. G., Belomytsev M. Yu., Molyarov A. V. Effect of heating temperature for quenching on structural and phase characteristics of heat-resistant steels with 12 % Cr. Metallovedenie i termicheskaya obrabotka metallov. 2024. No. 5. pp. 15–21.
13. Niessen F., Niels S. T., Hald J. Kinetics modeling of delta-ferrite formation and retainment during casting of supermartensitic stainless steel. Materials & Design. 2017. Vol. 118. pp. 1–19. DOI: 10.1016/j.matdes.2017.01.026
14. Bannykh O. A. et al. Phase diagrams of binary and multicomponent iron-based systems: refe rence book. Edited by O. A. Bannykh, M. E. Drits. Moscow: Metallurgiya, 1986. 439 p.
15. Bechtoldt C. J., Vacher H. C. Phase-diagram study of alloys in the iron-chromium-molybdenumnickel system. The Journal of Research of the National Institute of Standards and Technology. 1957. Vol. 58, Iss. 1. pp. 7–19.
16. Cao S., Zhao J.-Cheng. Application of dual-anneal diffusion multiples to the effective study of phase diagrams and phase transformations in the Fe-Cr-Ni system. Acta Mater. 2015. Vol. 88. pp. 196–206. DOI: 10.1016/j.actamat.2014.12.027
17. Okishev K. Yu. Mirzaev D. A. Special steels: tutorial. Chelyabinsk: Izdatelskiy tsentr YuUrGU, 2013. 36 p.
18. Palatkina L. V., Chubukov M. Yu., Matasova M. V., Kirilichev M. V. Features of the formation of niobium-rich carbide phases in the melt and their effect on the resistance of high-strength casing pipes to sulfide stress corrosion cracking. Chernye Metally. 2024. No. 5. pp. 36–42.
19. Cao S., Zhao J.-Ch. Determination of the Fe-Cr-Mo phase diagram at intermediate temperatures using dual-anneal diffusion multiples. Journal of Phase Equilibria and Diffusion. 2016. Vol. 37. pp. 25–38. DOI: 10.1007/s11669-015-0423-1
20. Zhukov A. A. Geometrical thermodynamics of iron alloys. Moscow : Metallurgiya, 1979. 232 p.
21. Silman G. I. Thermodynamics and thermokinetics of structure formation in cast iron and steels. Moscow : Mashinostroenie, 2007. 450 p.