Effect of combined loading on the microstructure and microhardness of austenitic steel

M.V. Karavaeva1, m.M. Abramova1, N.A. Enikeev1, G.I. Raab1, R.Z. Valiev1,2
1Ufa State Aviation Technical University, ul. K. Marxa 12, 450008, Ufa, Russia
2Saint Petersburg University, 7/9 Universitetskaya emb., 199034, St. Petersburg, Russia
Increasing the strength of low carbon austenitic steels, which are not hardened by quenching, is possible due to the formation of ultrafine-grained (UFG) structure during severe plastic deformation (SPD). However, the most notable hardening during SPD is observed at the initial stages of processing, after which the hardening rate decreases markedly. One of deformation parameters significantly affecting the structure is loading path. Using non-monotonic loading allows one to activate new glide systems resulting in an accelerated process of UFG structure formation and the resulting structures are characterized by high dislocation density and smaller grain sizes. In this work, non-monotonic loading by a combination of two methods, equal channel angular pressing (ECAP) and subsequent rolling with varying reduction rate, was used. It has been shown that the combination of SPD method (ECAP) and rolling leads to an additional increase in the microhardness of UFG austenitic steel. Additional hardening is associated with features of the microstructure formed under combined loading. The structure is characterized by a fine grain size and high density of dislocations compared with the structure after rolling or ECAP. It is shown that during deformation the microstructure changed from banded structure to a subrgrain-granular one. For the samples subjected to ECAP before rolling this process occurs at a less rolling strain. Furthermore, after the combined loading a noticeable volume fraction of twins in the microstructure was observed as compared to their rather small amount after ECAP. With a strain increase during rolling the rate of microhardness growth slows down.
Received: 30 October 2016   Revised: 18 February 2017   Accepted: 20 February 2017
Views: 66   Downloads: 34
R. Z. Valiev, Y. Estrin, Z. Horita, T. G. Langdon, M. J. Zehenbauer, Y. T. Zhu. Fundamentals of superior properties in bulk nano SPD materials. Mater. Res. Lett., 2016, Vol.4, No 1, pp.1 – 21.
F. Z. Utyashev, G. I. Raab. Deformation methods for obtaining and processing of ultrafine-grained and nanostructured materials. — Ufa: Guillem, Nick Bash. Encyc, 2013, 376 (in Russian) [Ф. З. Утяшев, Г. И. Рааб. Деформационные методы получения и обработки ультрамелкозернистых и наноструктурных материалов. Уфа: Гилем, НИК Башк. энцикл., 2013. — 376.].
M. M. Abramova, N. A. Enikeev, R. Z. Valiev, A. Etienne, B. Radiguet, Y. Ivanisenko, X. Sauvage. Grain boundary segregation induced strengthening of an ultrafine-grained austenitic stainless steel. Materials letters 136 (2014), pp. 349 – 352.
A. V. Ganeev, M. V. Karavaeva, X. Sauvage, E. Courtois-Manara, Y. Ivanisenko, R. Z. Valiev. On the nature of high-strength of carbon steel produced by severe plastic deformation. IOP Conf. Series Materials Science and Engineering 63 (2014), 012128. Doi:10.1088 / 1757-899X / 63 / 1 / 012128.
S. V. Dobatkin, O. V. Rybal’chenko, G. I. Raab. Structure formation, phase transformations and properties in Cr-Ni austenitic steel after equal-channel angular pressing and heating. Mater. Sci. Eng. A 2007, 463, pp. 41 – 45.
J. C. Pang, M. X. Yang, G. Yang, S. D. Wu, S. X. Li, Z. F. Zhang. Tensile and fatigue properties of ultrafine-grained low-carbon steel processed by equal channel angular pressing. Mater. Sci. Eng. A 2012, 553, pp. 157 – 163.
R. Z. Valiev, I. V. Alexandrov. Nanostructured materials produced by severe plastic deformation. M: Logos, 2000, 272 (in Russian) [Валиев Р. З., Александров И. В. Наноструктурные материалы, полученные интенсивной пластической деформацией. М: Логос, 2000. 272 с.].
Y. Iwahashi, Z. Horita, M. Nemoto, T. G. Langdon. The process of grain refinement in equal-channel angular pressing. Acta mater. Vol.46, 1998, No.9, pp.3317 – 3331.
G. Salischev, R. Zaripova, R. Galeev, O. Valiahmetov. Nanocrystalline structure formation during severe plastic deformation in metals and their deformation behavior. Nanostructured Materials, Vol.6, 1995, pp.913 – 916.
A. Belyakov, K. Tsuzaki, R. Kaibyshev. Nanostructure evolution in an austenitic stainless steel subjected to multiple forging at ambient temperature. Mat. Sci. Forum, Vols. 667 – 669 (2011), pp.553 – 558.
A. Polyakov, D. Gunderov, V. Sitdikov, R. Valiev, I. Sevenova, I. Sabirov. Physical Simulation of hot rolling of ultra-fine grained pure titanium. Metall. Trans. B, V.45B, December 2014, pp.2315 – 2326.
N. D. Stepanov, A. V. Kuznetsov, G. A. Salischev, G. I. Raab, R. Z. Valiev. Effect of cold rolling on microstructure and mechanical properties of copper subjected to ECAP with various number of passes. Mat. Sci. and Eng. A 554 (2012), pp. 105 – 115.
M. Yu. Murashkin, N. A. Enikeev, V. U. Kazykhanov, I. Sabirov, R. Z. Valiev. Physical simulation of cold rolling of ultra-fine grained Al 5083 alloy to study microstructure evolution. Rev. Adv. Mater. Sci. 35 (2013), pp.75 – 85.
S. Sabbaghianrad, T. G. Langdon. Microstructural saturation, hardness stability and superplasticity in ultrafine-grained metals processed by a combination of severe plastic deformation techniques. Letters of materials 5 (3), 2015, pp.335 – 340.
M. V. Karavaeva, M. M. Abramova, N. A. Enikeev, G. I. Raab and R. Z. Valiev. Superior strength of austenitic steel produced by combined processing, including equal-channel angular pressing and rolling. Metals, 2016, 6, 310.
N. А. Koneva. Nature of plastic deformation stage. Soros Educational Journal. 1998, № 10, pp. 99 – 105 (in Russian) [Н. А. Конева. Природа стадий пластической деформации. Соросовский образовательный журнал, 1998, № 10, сс. 99 – 105].
O. I. Bylja, R. A. Vasin, A. G. Ermachenko, M. V. Karavaeva, A. V. Muravlev, P. V. Chistjakov. The influence of simple and complex loading on structure changes in two-phase titanium alloy. Scripta Materialia Vol.36 (1997), № 8, pp.949 – 954.