DECAY OF SUPERCOOLED AUSTENITE OF LOW-CARBON PIPE STEEL WITH THE USE OF GLEEBLE 3500 COMPLEX

The promising direction in improving the strength properties of low-carbon steels is the use of controlled rolling providing formation of structures with prevalence of a bainite component. Analysis of the references has shown that now there are no detailed researches which allow to approve what morphological type of bainite provides the most optimal properties. In this regard in the present work the influence of cooling rate on the structure, properties, and structuralphase transformations of low-carbon complex-alloyed pipe steel containing 0.062 % C; 1.80 % Mn; 0.12 % Mo; 0.032 % Cr, 0.90 % Ni and other elements (Al, Cu, V, Nb, Ti) was studied. The dilatometric method was used to construct the CCT diagram of the decay of supercooled austenite of low-carbon complex-alloyed pipe steel. The qualitative and quantitative analysis of microstructure was carried out and hardness after various speeds of cooling was determined. There were identified the cooling rates providing bainite structures and increase in the strength properties of steel with specified composition. At a cooling rate since 0.05 to 6 °C/s, along with ferrite, a globular bainite is formed in the microstructure, consisting of bainitic α-phase and “islands” of martensite-austenite component ranging in size from 1 – 6 μm. At a cooling rate of 6 °C/s, conversion to reed bainite is observed, along with the borders of which the carbides and residual austenite are located. At cooling rates of more than 16 °C/s, bainite becomes bag-rack. With an increase in cooling rate from 50 to 150 °C/s, the average width of the bainite α-phase rails decreases from 2.22 to 1.32 μm.

1. Pyshmintsev I.Yu., Farber V.M. Strengthening pipe steel. Steel in Translation. 2005, vol. 35, no. 7, pp. 47–56.

2. Thompson S.W., Colvin D.J., Krauss G. Continuous cooling transformations and microstructure in low-carbon high-strength lowalloy plate steel. Met. Trans. 1990, vol. 21 A, no. 4, pp. 1493–1507.

3. Bramfitt B.L., Speer J.G. A perspective on the morphology of bainite. Met. Trans. 1990, vol. 21 A, no. 4, pp. 817–829.

4. Smirnov M.A., Pyshmintsev I.Yu., Boryakova A.N. Effect of cooling rate on the properties of low-carbon pipe steel. Vestnik YuUrGU. 2007, Issue 9, no. 21 (93), pp. 15–18. (In Russ.).

5. Efron L.I., Il’inskii V.I., Golovanov A.V., Morozov Yu.D. Production of cold-resistant tube steels by controlled high-temperature rolling. Steel in Translation. 2003, vol. 33, no. 6, pp. 60–65.

6. Krauss G., Thompson S.W. Ferritic microstructures in continuosly cooled low-and ultralow carbon steels. ISIJ International. 1995, vol. 35, no. 8, pp. 937–945.

7. Koptseva N.V., Chukin D.M., Efimova Yu.Yu., Nikitenko O.A., Ishimov A.S. Investigation of influence of cooling rate on the formation of wire rod structure from 80R steel for the production of highstrength reinforcement. Chernye metally. 2014, no. 2, pp. 23–31. (In Russ.).

8. Chukin M.V., Poletskov P.P., Koptseva N.V., Baryshnikov M.P., Efimova Yu.Yu., Nikitenko O.A., Ishimov A.S., Gushchina M.S., Berezhnaya G.A. tructural-phase transformations during continuous cooling of high-strength medium-carbon complex-alloyed lowblazed steels. Teoriya i tekhnologiya metallurgicheskogo proizvodstva. 2016, no. 1(18), pp. 57–62. (In Russ.).

9. Chukin M.V, Salganik V.M., Poletskov P.P., Denisov S.V., Kuznetsova A.S., Berezhnaya G.A., Gushchina M.S. Main types and applications of strategic high-strength sheet metal. Vestnik Magnitogorskogo gosudarstvennogo tekhnicheskogo universiteta im. G.I. Nosova. 2014, no. 4, pp. 41–44. (In Russ.).

10. Efron L. I. Formation of structures and mechanical properties of constructional steels during thermomechanical treatment in flow of the rolling mill. Stal’. 1995, no. 8, pp. 57–64. (In Russ.).

11. Bernshtein M.L., Zaimovskii V.A., Kaputkina L.M. Termomekhanicheskaya obrabotka stali [Thermomechanical treatment of steel]. Moscow: Metallurgiya, 1983, 480 p. (In Russ.).

12. Schastlivtsev V.M., Koptseva N.V., Artemova T.V. Electron microscopic investigation of the martensite structure in low-carbon iron alloys. Physics of Metals and Metallography. 1976, vol. 41, no. 6, pp. 109–118.

13. Sadovskii V.D., Fokina E.A., Schastlivtsev V.M. Ostatochnyi austenit v zakalennoi stali [Residual austenite in hardened steel]. Moscow: Nauka, 1986, 111 p. (In Russ.).

14. Rodionov D.P., Schastlivtsev V.M., Stepanova N.N., Smirnov L.V. Shape of the martensite crystals in packet (lath) martensite. Physics of Metals and Metallography. 1986, vol. 61, no. 1, pp. 109–114.

15. Smirnov M.A., Pyshmintsev I.Yu., Boryakova A.N. Classification of low-carbon pipe steel microstructures. Metallurgist. 2010, vol. 54, no. 7-8. pp. 444-454.

16. Efron L.I., Il’inskii V.I., Morozov I.D., Golovanov A.V. Tube steel of increased strength and low-temperature stability with predominantly bainite structure. Steel in Translation. 2003, vol. 33, no. 9, pp. 66–72.

17. Matrosov Yu.I. Razrabotka printsipov mikrolegirovaniya i rezhimov kontroliruemoi prokatki maloperlitnykh stalei dlya trub magistral’nykh gazoprovodov: avtoref. dis... doktora tekh. nauk. [Development of the principles of micro alloying and controlled rolling modes for low-perlite steels for main gas pipelines: Extended Abstract of Dr. Sci. Diss.]. Moscow: 1982, 42 p. (In Russ.).

18. Koptseva N.V., Chukin M.V., Nikitenko O.A. Use of the Thixomet pro software for quantitative analysis of the ultrafine-grain structure of low-and medium-carbon steels subjected to equal channel angular pressing. Metal Science and Heat Treatment. 2012, vol. 54, no. 7-8, pp. 387-392.

19. Bhadeshia H.K. Bainite in steels. 2nd ed. London: Ins. of Materials, 2001, 454 p.

20. Mirzaev D.A., Okishev K.Yu., Schastlivtsev V.M., Yakovleva I.L. Kinetics of the formation of bainite and packet martensite: I. Effect of the structure of packets. Physics of Metals and Metallography. 2000, vol. 90, no. 5, pp. 471–480.

21. Svishchenko V.V. Features of phase composition of intermediates in steel 24Kh2NАch. Polzunovskii Vestnik. 2005, no. 2, Part 2, pp. 95–97. (In Russ.).

22. ASM Handbook. Vol. 9: Metallography and Microstructures. ASM Int., 2004, 1184 p.