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The 95<sup>th</sup> anniversary of the Chair for Plastic Metal Working of the Ural Federal University
ArticleName Effect of process isothermy on a stress-strain state during rolling of bars from titanium alloy
DOI 10.17580/tsm.2018.09.11
ArticleAuthor Loginov Yu. N., Postylyakov A. Yu., Inatovich Yu. V.

Ural Federal University Named After the First President of Russia B. N. Eltsin, Ekaterinburg, Russia

Yu. N. Loginov, Professor of the Chair for Plastic Metal Working, e-mail:
A. Yu. Postylyakov, Associate Professor of the Chair for Plastic Metal Working
Yu. V. Inatovich, Associate Professor of the Chair for Plastic Metal Working


A simulation of the titanium alloy bar rolling process using the Shape Rollingspecial module of the DEFORM finite element analysis system in the isothermal and non-isothermal settings has been performed. The first option assumes a constant temperature of the billet, the second — the calculation of the stress-strain state taking into account the change of the temperature field. The distribution of temperatures of the billet to be rolled is given for the stationary stage of the process. The billet`s temperaturefield is a heterogeneous predominantly related to its surface layers which are continuously cooled for the entire time of the contact with the rolls. The regions of deformation heating at the interface of contact and free surfaces were revealed. Moreover, heated zones exist near to cooled zones resulting in large gradients of deformation. The distribution of the deformation degree and deformation rate in the plane of the billet exit from rolls is shown. The general feature of the deformation field is the presence of a less deformed central area of the billet, where the deformation degree is about 0.26–0.35, and peripheral local regions, where the deformation degree is 0.44–0.53, that is, 50–70% higher. Non-isothermal setting brings about the larger values of the deformation rate in comparison with isothermal one. The graphs of changes in the intensity of stresses along the metal particles motion are given.The features of formation of a round section explain the form of graphsfrom the billet with an oval section. The practical significance of the work performed is concluded in the identification of the closely localized heated and cooled zones of the metal at the deformation site that can result in formation of cracks. Increasing the reduction ratio in the rolling process can bring about overheating in the indicated areas with transfer of the metal from a two-phase state into a single-phase one and with the subsequent manifestation of a grain-inhomogeneity effect. Calculations showed that the hot rolling of a nickel alloy according to a round-oval-system with the reduction rate of 1.2 is accompanied by formation of closely located cooled zones due to thermal transfer to rolls and the heated zones because of deformation heating. It was found that the increase in the deformation heating temperature is only 16 оС, and a forecast was made about the possibility to increase it significantly at reduction rate growth. At the preset reduction rate, dependence of the general pattern of reduction rate and stress state characteristics distribution on the process isothermy degree is very low. However, the pattern of the deformation rage distribution shows a significant difference in the interfaces of cooled and deformation heated zones that can result in formation of cracks.

This work was carried out with the partitial financial support of the governmental order No. 211 of the Russian Federation, contract No. 02.A03.21.0006.

keywords Section rolling, titanium alloys, deformation, deformation rates, temperature gradients, isothermal process, non-isothermal process, finite element method

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