DOI: 10.18503/1995-2732-2025-23-2-97-110
Abstract
Problem Statement (Relevance). In the practice of production of reinforcing rolled products, both hot-rolled and thermally strengthened according to the scheme of interrupted or intermittent (thermal cycling technology) quenching with self-tempering using the heat of pre-roll heating in the flow of section mills, a number of features of the formation of the microstructure and variability over time of the mechanical properties of the reinforcement are observed. Objective. Establishment of patterns of changes in the properties of reinforcing bars over time. Development of methods for reliable certification of rolled metal products. Methods used. Research methods used were retesting the properties of rolled products at certain intervals, as well as determining the microstructure of rolled products. Newness. The newless lies in the establishment of patterns of changes in the mechanical properties of reinforcing bars over time, predicting the achievement of the level of characteristics over time depending on the production scheme - the production of reinforcement in a hot-rolled state and with heat strengthening. Results. The physical reasons for the variability of mechanical properties over time include: hydrogen reversible embrittlement of carbon and low-alloyed steels with manganese and silicon; hydrogen aging, especially of reinforcement produced in the hot-rolled state, which consists in reducing the yield strength values in such metal (in some cases below standard values) and the ratio of the yield strength to the temporary tensile strength. This is facilitated by high temperatures at the end of rolling, which cause the formation of large austenitic and then actual grains. Hydrogen aging is that within 2-3 weeks from the date of the initial test, the values of the yield strength and the ratio of the yield strength to the temporary tensile strength are significantly reduced by 55-60 MPa and to 0.55-0.50, respectively, and is due to the fact that in the process of diffusion release of hydrogen from micropores and “traps”, including structural ones, due to the partial removal of internal stresses, dislocations are released and plasticity increases locally. Subsequently, over time (up to 1 year), the yield strength values asymptotically approach the initial values and are higher. Practical Relevance. If you do not take into account the behavior of mechanical properties over time, then you can incorrectly certify metal products when assigning them to a specific consumer order. In the hot-rolled stat dynamic and collective recrystallization, abnormal structure formatione, abnormal structure formation of the reinforcement is also possible - selective replacement of pearlite with upper and lower bainite with embrittlement of the metal. A technology is proposed that eliminates this phenomenon, consisting of accelerated cooling of the rolled product with refinement of the austenite and, accordingly, the actual grain of the rolled product.
Keywords
hot-rolled and thermally strengthened reinforcing bars, mechanical properties, variability of properties over time, hydrogen embrittlement and aging, dynamic and collective recrystallization, abnormal structure formation
For citation
Sychkov A.B., Zavalitshin A.N., Atangulova G.Ya., Malashkin S.O., Shecsheev M.A., Kasimov D.T. Features of Structure Formation and Temporary Changes of Mechanical Properties of Hot-Rolled Reinforcing Bars Made of Steel 25G2S. Vestnik Magnitogorskogo Gosudarstvennogo Tekhnicheskogo Universiteta im. G.I. Nosova [Vestnik of Nosov Magnitogorsk State Technical University]. 2025, vol. 23, no. 2, pp. 97-110. https://doi.org/10.18503/1995-2732-2025-23-2-97-110
1. State standard GOST 5781-82. Hot-rolled steel for reinforcement of ferroconcrete structures. Specifications. Status for 2023 - replaced by GOST 34028-2016.
2. State standard GOST 10884-94. Thermomechanically hardened steel bars for reinforced concrete constructions. Specifications. Status for 2023 - replaced by GOST 34028-2016.
3. State standard GOST 34028-2016. Reinforcing rolled products for reinforced concrete constructions. Specifications.
4. Levchenko L.N., Natapov A.S., Mashkin L.F. et al. Proizvodstvo armaturnoy stali [Production of reinforcing steel]. Moscow: Metallurgy, 1984, 136 p. (In Russ.)
5. Sychkov A.B. Improvement of technology for the production of reinforcing bars in coils. Stal [Steel], 1995;(2):37-39. (In Russ.)
6. Khudik Yu.T., Rybalka E.M., Bolshakov V.I., Kekukh A.V. Armaturniy prokat dlya zhelezobetonnyh konstruktsiy i izdeliy. Spravochnoe posobie [Reinforcing bars for reinforced concrete structures and products. Reference book]. Krivoy Rog: Mira, 2000, 115 p. (In Russ.)
7. Sychkov A.B., Zhigarev M.A., Perchatkin A.V. Tekhnologicheskie osobennosti proizvodstva armaturnogo prokata shirokogo naznacheniya. Monografiya [Technological features of the production of wide-purpose reinforcing bars. Monograph]. Magnitogorsk: State Educational Institution of Higher Professional Education MSTU, 2006, 499 p. (In Russ.)
8. Ershov Yu.L., Shakurov A.G., Parshin V.M., Kolesnikov A.G., Shishov A.Yu. Hydrogen era in domestic metallurgy. Report 1. Stal [Steel], 2021;(11):50-56. (In Russ.)
9. rshov Yu.L., Shakurov A.G., Parshin V.M., Kolesnikov A.G., Shishov A.Yu. Hydrogen era in domestic metallurgy. Report 2. Stal [Steel], 2021;(12):48-57. (In Russ.)
10. State standard GOST 5639-82. Steels and alloys. Methods for detection and detеrmination of grain size.
11. State standard GOST 10243-75. Steel. Methods of tests and estimation of macrostructure.
12. State standard GOST 5640-2020. Steel. Metallographic method for determination of microstructure of flat rolled product.
13. Sychkov A.B., Oleynik A.A., Zhigarev M.A. On the variability of the mechanical properties of rolled products over time. Trudy pyatogo kongressa prokatchikov, Cherepovec, oktyabr 2003g. [Proceedings of the fifth congress of distributors, Cherepovets, October 2003]. Moscow: JSC Chermetinformatsiya, 2004, pp. 264-269. (In Russ.)
14. Parusov V.V., Belitchenko A.K., Bogdanov N.A., Sychkov A.B., Nesterenko A.M., Parusov O.V. Termomekhanicheskaya obrabotka prokata iz nepreryvno-litoн zagotovki malogo secheniya [Thermo-mechanical processing of rolled products from continuously cast blanks of small cross-section]. Zaporizhzhia: ZNU, 2000, 142 p.
15. Zaika V.I., Kashchenko Yu.A., Brekharya G.P. Vodorod v promyshlennyh stalyah [Hydrogen in industrial steels]. Zaporizhzhia: ZNU, 1998, 192 p.
16. Naumenko V.V., Muntin L.V., Baranova O.A., Smetanin K.S. Resistance to hydrogen cracking of rolled structural steel after heat treatment. Stal [Steel], 2021;(3):44-50. (In Russ.)
17. Kurbsky S.V., Velikotsky R.E., Dolzhikov V.V. Development of ideas about the mechanism of hydrogen fragility based on the theory of molecular pressure of hydrogen. Byul. CHernaya metallurgiya [Bull. Ferrous metallurgy], 2023;79(6):476-48. (In Russ.)
18. Popov A.A., Popova A.E. Izotermicheskie i termokineticheskie diagrammy raspada pereohlazhdennogo austenita. Spravochnik termista [Isothermal and thermokinetic diagrams of the decomposition of supercooled austenite. Heat treater's handbook]. Moscow, Sverdlovsk: State Scientific and Technical Publishing House of Mechanical Engineering Literature, 1961, 431 p. (In Russ.)
19. Sychkov A.B., Nesterenko A.M., Zavalishchin A.N., Shubin I.G., Moller A.B., Kulakov B.A. Formation of microstructure and mechanical properties of reinforcing bars in coils made of two- and multiphase steel. Vestnik Magnitogorskogo gosudarstvennogo tekhnicheskogo universiteta im. G.I. Nosova [Vestnik of Nosov Magnitogorsk State Technical University], 2023;21(4):70-80. (In Russ.)
20. Madatyan S.A. Massovye vidy armaturnoy stali s kompozitnoy strukturoy dlya zhelezobetonnyh konstruktsiy [Mass types of reinforcing steel with a composite structure for reinforced concrete structures]. V knige: Chernaya metallurgiya Rossii i stran SNG v XXI veke [In the book: Ferrous metallurgy of Russia and the CIS countries in the 21st century]. Moscow: Metallurgy, 1994, .vol. 4, pp. 73-75. (In Russ.)
21. Kanaev A.T., Bogomolov A.V. Formation of a gradient-layered structure during deformation-thermal treatment of reinforcing steel. Stal [Steel], 2020;(7):67-72. (In Russ.)
22. Blinova E.N., Libman M.A., Petrovsky V.N., Pimenov E.V. Principles of creating materials with a spatial distribution of macroscopic regions with different physical and mechanical properties. Stal [Steel], 2021;(11):46-50. (In Russ.)
23. Sychkov A.B. Tulupov O.N., Zavalishchin A.N., Baranov N.A. Structure formation and development of mechanical and technological properties of reinforcing bars during in-line heat treatment. Chernye metally [Ferrous Metals]. 2024;3(1107):47-55.