EFFECT OF HEAT TREATMENT CONDITIONS ON ELECTRICAL RESISTIVITY OF 35KhGF MOLTEN STEEL

The authors have studied the effect of the grain structure, crystal structure and defects of 35KhGF steel samples on the character of temperature dependence of the melt specific electrical resistance at temperatures of 1450–1720  °C. Grain and crystalline structures changed as a result of heat treatment - normalization and tempering. The peculiarities of grain and crystalline structures, the defects were recognized according to the results of metallographic study. The metallographic study was carried out by diffraction of backscattered electrons-EBSD analysis. Scanning areas were chosen with the inclusion of defects in metal of technological origin, namely, microscopic discontinuities filled with gas or slag. The results of EBSD analysis are drawn as IPFpatterns; they show the texture state of the samples using the color assignment method. The microstructure of a 35KhGF steel sample after normalization at 910  °C has the smallest crystallites (of the order of 1  μm) and the largest extent of the grain boundaries. All samples have defects  – discontinuities of the order of 1 μm in size. Specific electrical resistance of molten 35KhGF steel samples was measured by the method of rotating magnetic field in heating mode and subsequent cooling. For samples preliminarily normalized at 910  °C, a discrepancy in the temperature dependences of resistivity and an irreversible decrease in the resistivity temperature coefficient were observed in cooling mode of the melt. The discrepancy between the temperature dependences of the electrical resistivity and the irreversible decrease in the temperature coefficient of the resistivity was analyzed on the basis of the microinhomogeneous structure concepts of metallic melts and the phenomenon of metallurgical heredity. According to the notion of the microheterogeneous structure of metallic melts, the melting of a multiphase steel ingot does not immediately produce a homogeneous solution of the alloying elements in the iron at the atomic level, and a chemically microinhomogeneous state is maintained in a certain temperature range. Looking at the branching of the temperature dependences of the electrical resistivity, the transition of the melt into the state of true solution occurs only near the temperature T*  =  1640  °C. The value of temperature T* according to the notion of the structural metallurgical heredity phenomenon depends on microstructure, phase composition and crystalline structure of the initial sample. The presence of discontinuities leads to appearance of an excess volume of melt during metal melting, which is partially retained during cooling and crystallization. In this case, the temperature coefficient of the resistivity in cooling mode is close to zero in absolute value, even at ingot cooling rates of the order of 10  °C/s the crystallization conditions change, in particular, the metal’s propensity to amorphization increases.

1. Ostrovskii O.A., Grigoryan V.A., Vishkarev A.F. Svoistva metallicheskikh rasplavov [Properties of metallic melts]. Moscow: Metallurgiya. 1988, 304 p. (In Russ.).

2. Fujita K., Ueda M., Ikeda M., Hayashi K. Monitoring of tempering behavior in Fe-C-Mn alloys by precise measurement of electrical resistivity (Conference Paper). THERMEC 2013; Las Vegas, NV; United States; 2-6 December 2013. 2014, vol. 922, pp. 173–176.

3. Popel P.S., Chikova O.A., Matveev V.M. Metastable colloidal states of liquid metallic solutions. High Temperature Materials and Processes. 1995, vol. 14, Issue 4, pp. 219–233.

4. Wang J., He S., Sun B., Guo Q., Nishio M. Grain refinement of Al–Si alloy (A356) by melt thermal treatment. Journal of Materials Processing Technology. 2003, vol. 141, Issue 1, pp. 29–34.

5. Calvo-Dahlborg M., Popel P.S., Kramer M.J., Besser M., Morris  J.R., Dahlborg U. Superheat-dependent microstructure of molten Al–Si alloys of different compositions studied by small angle neutron scattering. Journal of Alloys and Compounds. 2013, vol. 550, pp. 9–22.

6. Zu F.-Q. Temperature-induced liquid-liquid transition in metallic melts: a brief review on the new physical phenomenon. Metals. 2015, vol. 5, Issue 1, pp. 395–417.

7. Kolotukhin E. V., Popel’ P. S., Tsepelev V. S. Electrical resistivity of melts of cobalt-boron system and estimation of their microinhomogeneity scale. Rasplavy. 1988, vol. 2, no. 3, pp. 25–29. (In Russ.).

8. Kononenko V.I., Razhabov A.A., Ryabina A.B. Viscosity and specific electrical resistance of melts of Al-Li system. Rasplavy. 2011, no. 3, pp. 30–33. (In Russ.).

9. Li C., Du S., Zhao D., Zhou G., Geng H. Electrical resistivity feature of Cu–Sn–(Bi) alloy melts. Physics and Chemistry of Liquids. 2014, vol. 52, Issue 1, pp. 122–129.

10. PlevachukYu., Sklyarchuk V.,YakymovychA., Willers B., Eckert  S. Electronic properties and viscosity of liquid Pb–Sn alloys. Journal of Alloys and Compounds. 2005, vol. 394, Issue 1-2, pp.  63–68.

11. Wang M., Jia P., Li D., Geng H. Study on the microstructure and liquid–solid correlation of Al–Mg alloys. Physics and Chemistry of Liquids. 2016, vol. 54, no. 4, pp. 507–514.

12. Adams P.D., Leach J.S. Resistivity of Liquid Lead-Tin Alloys. Physical Review. 1967, vol. 156, Issue, pp. 178–183.

13. Zhuravlev S.N., Ostrovskii O.A., Grigoryan V.A. Measurement of the electrical conductivity of liquid metals by the eddy-current method. High Temperature. 1982, vol. 20, no. 4, pp. 551–555.

14. Regel’ A.R. Electrodeless method for measuring electrical conductivity and possibility of its application to the problems of physical and chemical analysis. Zhurnal neorganicheskoi khimii. 1956, vol.  1, no. 6, pp. 1271–1277. (In Russ.).

15. Regel’ A.R. Measurement of electrical conductivity of metals in rotating magnetic field. Zhurnal fizicheskoi khimii. 1948, vol. 18, no.  6, pp. 1511–1520. (In Russ.).

16. Regel’ A.R., Glazov V.M. Periodicheskii zakon i fizicheskie svoistva elektronnykh rasplavov [Periodic law and physical properties of electronic melts]. Moscow: Nauka, 1978, 308 p. (In Russ.).

17. Voronkov V.V., Ivanova I.I., Turovskii B.M. On application of rotating magnetic field method for measuring the electrical conductivity of melts. Magnitnaya gidrodinamika. 1973, no. 2, pp. 147–149. (In Russ.).

18. Ryabina A.B., Kononenko V.I., Razhabov A.A. Electrodeless method for measuring the electrical resistivity of metals in solid and liquid states and an installation for its implementation. Rasplavy. 2009, no. 1, pp. 34–42. (In Russ.).

19. Mokrovskii N.P., Regel’A.R. Electrical resistance of copper, nickel, cobalt, iron and manganese in solid and liquid states. Zhurnal tekhn. fiziki. 1953, vol. 23, no. 12, pp. 2121–2125. (In Russ.).

20. Zinov’ev V.E. Kineticheskie svoistva metallov pri vysokikh temperaturakh. Spravochnik [Kinetic properties of metals at high temperatures]. Moscow: Metallurgiya, 1984, 200 p. (In Russ.).

21. Tyagunov G.V. etc. Measurement of resistivity by the rotating magnetic field method. Zavodskaya laboratoriya. 2003, no. 2, vol. 69, pp. 36–38. (In Russ.).

22. Konashkov V.V., Povodator A.M., V’yukhin V.V., Tsepelev V.S. Sposob izmereniya elektricheskogo soprotivleniya metallicheskogo rasplava metodom vrashchayushchegosya magnitnogo polya [Method of measurement of metallic melt electrical resistance by rotating magnetic field]. Patent RF no. 2457473. Byulleten’ izobretenii. 2012, no. 21. (In Russ.).

23. Arsent’ev P.P., Yakovlev V.V., Krasheninnikov M.G., Pronin L.A., Filippov E.S. Fiziko-khimicheskie metody issledovaniya metallurgicheskikh protsessov [Physico-chemical methods of research of metallurgical processes]. Moscow: Metallurgiya, 1988, 511 p. (In Russ.).

24. Glazov V.M., Vobst M., Timoshenko V.I. Metody issledovaniya svoistv zhidkikh metallov i poluprovodnikov [Methods of research of properties of liquid metals and semiconductors]. Moscow: Metallurgiya, 1989, 384 p. (In Russ.).

25. Gol’dshtein M.I., Grachev S.V., Veksler Yu.G. Spetsial’nye stali [Special steel]. Moscow: MISIS, 1999, 408 p. (In Russ.).

26. Sorokin V.G. etc. Stali i splavy. Marochnik: Sprav. Izd. [Steel and alloys. Grade guide: Reference book]. Sorokin V.G., Gervas’ev  M.A. eds. Moscow: Intermet inzhiniring. 2001, 608 p. (In Russ.).

27. TyagunovA.G.,BaryshevE.E.,TsepelevB.C., KostinaT.K.,Baum  B.A., Savin O.V. Resistivity of liquid high-temperature strength alloys. Rasplavy. 1996, no. 6, pp. 23–28. (In Russ.).

28. Govorukhin L.V., Klimenkov E.A., Baum B.A. etc. Specific electrical resistivity of alloys of iron with chromium and oxygen at high temperatures. Ukr. fiz. zhurn. 1984, vol. 29, no. 2, pp. 291. (In Russ.).

29. Tyagunov A.G., Kostina T.K., Baryshev E.E., Tyagunov G.V. The effect of melts state on the structure of TsNK type superalloys. Vestnik YuUrGU. Seriya: Metallurgiya. 2013, no. 1, pp. 79–84. (In Russ.).

30. Kolotukhin E.V., Baum B.A., Tyagunov G.V. etc. Electric resistivity and density of liquid ferroalloys with boron. Izvestiya VUZov. Chernaya metallurgiya = Izvestiya. Ferrous Metallurgy. 1988, no.  6, p.  68. (In Russ.).

31. Ershov G.S., Kasatkin L.A., Gavrilin I.V. Electrical resistivity of liquid iron with different content of impurities. Izv. AN SSSR. Metally. 1976, no. 2, pp. 98–100. (In Russ.).

32. Zhuravlev S.N., Ostrovskii O.I., Grigoryan V.A. Electrical resistivity of iron melts with carbon, boron and phosphorus. Izvestiya VUZov. Chernaya metallurgiya = Izvestiya. Ferrous Metallurgy. 1982, no. 11, pp. 152–155. (In Russ.).

33. Lepinskikh B.M., Belousov A.A., Bakhvalov S.G. etc. Transportnye svoistva metallicheskikh i shlakovykh rasplavov: Sprav. izd. [Transport properties of metal and slag melts]. Vatolin N.A. ed. Moscow: Metallurgiya, 1995, 649 p. (In Russ.).

34. Gel’d P.V., Baum B.A., Klimenkov E.A. etc. Electrical resistivity of iron-carbon melts. DAN SSSR. 1980, vol. 254, no. 2, pp. 347–349. (In Russ.).

35. KudryavtsevaE.D., Dovgopol S.P.,RadovskiiI.Z. etc.Effect of composition on the electrical resistivity of liquid iron alloys with chromium. Zhurnal fizicheskoi khimii. 1980, vol. 54, no. 1, pp. 145–149. (In Russ.).

36. Kudryavtseva E.D., Singer V.V., Radovskii I.Z., Dovgopol S.P., Vorontsov B.S., Gel’d P.V. Electronic structure of liquid iron alloys with manganese, chromium, and vanadium. Soviet Physics Journal. 1983, vol. 26, no. 1, pp. 55–58.

37. Lepikhin S.V., Stepanova N.N. Investigation of the Ni3 Al-Fe alloys by resistivity measurements and differential thermal analysis. Russian Journal of Non-Ferrous Metals. 2013, vol. 54, Issue 6, pp.  475–479.

38. Gavrilin I.V. On the mechanism of formation of liquid cast iron alloys and their heredity. Liteinoe proizvodstvo. 1999, no. 2, pp.  10–12. (In Russ.).

39. Anikeev V.V., Zonnenberg N.N. Relation between heredity and quality of steel castings. Liteinoe proizvodstvo. 2010, no. 6, pp. 2–5. (In Russ.).

40. Nikitin V.I. Study of the application of charge structure heredity to improve the castings quality. Liteinoe proizvodstvo. 1985, no. 6, pp.  20–21. (In Russ.).