Evaluation of crack resistance of 38KhN3MFA-Sh structural steel by fracture properties and elastic wave velocities

The results of the study on the effects of tempering temperature on 38KhN3MFA-Sh steel static strength and crack resistance are given. The fractured surface texture has been studied after various heat treatment modes using electron-fractography analysis. Relationships between the fracture properties and the critical stress intensity factor have been established. The effect of tempering temperature on the velocities of ultrasonic bulk waves has been investigated. A linear relationship has been found between the velocity of elastic waves and the critical stress intensity factor of 38KhN3MFA-Sh steel. The dependence discovered allows us to estimate the changes in crack resistance of steel using a non-destructive test method with variations in tempering temperature. The method of electron fractography has been used to analyze specimen fractures having a crack in structural high-quality 38KhN3MFA-Sh steel. Investigations of the fractured surface texture subjected to various heat treatment modes have shown that the microrelief is represented by flattened cone-shape pits. An increase in tempering temperature is accompanied by an increase in the diameter of flattened cone pits on the fractured surface. A quadratic dependence has been established between the crack resistance parameter and the diameter of the pits. It is shown that the contribution of ferrite matrix structural condition to crack resistance value is much more significant than the contribution of isolated carbides. The velocities of elastic waves in steel have been measured; their values increase with the growth of tempering temperature. The characteristics of strength and crack resistance of structural steel exposed to hightemperature tempering have been predicted based on the values of transverse wave velocities. Deviation of the predicted values of crack resistance K1С and ultimate strength σb from the experimental values does not exceed 5.4% and 12.6%, respectively.

1. Vladimirov, V.I., Fizicheskaya priroda razrusheniya metallov [Physical nature of destruction of metals], Moscow: Metallurguiya, 1984, p. 264.

2. Gross D., Seelig T. Fracture Mechanics: Springer-Verlag Berlin Heidelberg, 2011, p. 74.

3. Muravyev, V.V., Zuev, L.B., Komarov, K.L., Skorost zvuka i struktura stalej [Acoustic speed and structure of staly], Novosibirsk: Nauka, 1996, p. 43.

4. Raj, B., Moorthy, V., Jayaku mar, T., Rao, K.B.S., Assessment of microstructures and mechanical behaviour of metallic materials through non-destructive characterization, International Materials Reviews, 2003, V. 48, No 5, pp. 273–325.

5. Droney, B.E., Klinman, R., Ultrasonic techniques for determining the mechanical properties of steel, AIP Conference Proceedings, 1982, No 84, p. 210. URL: https://doi.org/10.1063/1.33537

6. Pavlov, A.M., P avlov, A.V., Zhilkashinova A.M., Satbaeva Z.A. Studies of the relationship of the speed of ultrasound with the mechanical properties of cast steel, Technical Sciences - from theory to practice. 2016, V. 56, No 8, pp. 60–68.

7. Botaki, A.A., Ulyanov, V.L., Sharko, A.B.,Ultrazvukovoj kontrol prochnostnykh svoistv konstruktsionnykh materialov [Ultrasonic examination of strength properties of structural materials], Moscow:Mashinostroenie, 1983, p. 11.

8. Gouldstein, J., Nyubury, D., Echlin, P., Joy, D., Fiori, Ch., Lifshin, E.,Rastrovaya elektronnaya mikroskopiya i rentgenovsky mikroanaliz [Raster electronic microscopy and x-ray microanalysis], Moscow: Mir, 1984, Book 1, p. 134.

9. Krishtal, M.M., Yasnikov, I.S., Polunin, V.I., Skaniruyushchaya elektronnaya mikroskopiya i rentgenovsky mikroanaliz v primerakh prakticheskogo primeneniya [The scanning electronic microscopy and the X-ray microanalysis in examples of practical application], Krishtal, M.M. (Ed.), Moscow: Teknosphera, 2009, p. 34.

10. Izotov V.I., Kireeva E.Yu. Investigation of the peculiarities of brittle fracture of carbon steel in various structural states using scanning electron microscopy of the etched surface of kinks, Physics of Metals and Metal Science, 2011, V. 112, No 3, pp. 320–327.

11. Prakticheskaya rastrovaya elektronnaya mikroskopiya [Practical raster electronic microscopy], Gouldstein, J., Yakovits. H. (Eds.), Moscow: Mir, 1978.

12. Gulyaev, A.P., Gulyaev, A.A., Metallovedenie [Metal science], Moscow: Alliance, 2011.

13. Kurdyu mov, G.V., Yavleniya zakalki i otpuska stali [Steel hardening and tempering], Moscow: Metalurgizdat, 1960, p. 53.

14. Shaimanov, G.S., Simonov, M.Yu., Simonov, Yu.N., Osobennosti poverkhnosti razrusheniya stali 09G2S posle kholodnoy radialnoy kovki [Features of the destruction surface of steel 09G2S after cold radial forging], Vestnik PNIPU. Mashinostroenie, materialovedenie, 2016, V.18, No 3, pp. 119–134.

15. Georgiev, M.N., Lipchin, N.N., Simonov, Yu.N., Svyaz struktury metalla s fraktograficheskimi osobennostyami poverkhnosti ustalostnykh izlomov [Connection of the metal structure with the fractographic features of the surface of fatigue fractures], The Physics of Metals and Metallography, 1987, V. 63, No 3, pp. 622–624.

16. Grigorenko, V.B., Morozova, L.V., Orlov, M.R. Investigation of the causes of the appearance of areas with different fracture morphology in forged billets made of steel 38KHN3MFA, Proceedings of VIAM, 2014, No 8, p. 11.

17. Botvina, L.R. Destruction. Kinetics, mechanisms, general patterns, Moscow: Science, 2008, p. 25.

18. Georgiev, M.N., Dogadushkin, V.Yu., Mezhova, N.Ya., Minaev, V.N., Strok, L.P.,O mekhanizme rasprostraneniya ustalostnoy treshchiny v metallicheskikh materialakh [The mechanism of distribution of a fatigue crack in metal materials], Physical and chemical mechanics of materials, 1982, V. 18, No 4, pp. 35–42.

19. Belousov, M.V., Cherepin, V.T., Vasilyev, M.A., Prevrashcheniya pri otpuske stali [On transformations under steel tempering], Moscow: Metallurguiya, 1973, p. 32.

20. Souissi, M., Numakura, H., Elastic properties of Fe−C and Fe−N martensites, ISIJ International, 2015, V. 55, No 7, pp. 1512–1521.

21. Vorobyov, R.A., Evstifeeva, V.V., Litovchenko, V.N., Mishakin, V.V., Dubinsky, V.N., Primenenie ultrazvukovoy diagnostiki dlya otsenki treshchinostoykosti stali 38KhN3MFA [Application of ultrasonic diagnostics for assessment of crack resistance of steel 38HN3MFA], Zavodskaya laboratoriya. Diagnostika materialov, 2018, V. 84, No 2, pp. 64–69.

22. Novikov, I.I.,Teoriya termicheskoy obrabotki metallov [Theory of heat treatment of metals], Moscow: Metallurguiya, 1978, p. 305.