Influence of the Creep of Metals on the Service Life of Reactors for the Magnesium-Thermal Production of Titanium
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INFLUENCE OF THE CREEP OF METALS ON THE SERVICE LIFE OF REACTORS FOR THE MAGNESIUM-THERMAL PRODUCTION OF TITANIUM V. G. Mishchenko1 and N. A. Evseeva1,2 The influence of plastic deformation (creep) of corrosion-resistant 10Kh23N18, 04Kh18N10Т, and AISI 321 steels on the decrease in the thickness of the shell wall and the intensification of corrosion fracture processes is investigated. The comparative evaluation of the materials used in the retort production is performed. It is shown that the application of 10Kh23N18 steel with improved creep characteristics increases the service life of the retorts from 35 to 43 cycles. Keywords: reactor, corrosion-resistant steel, creep, plastic deformation, high-temperature corrosion, microstructure.
The solution of the problem of increasing the service life of retorts (reactors) used in the magnesiumthermal production of sponge titanium strongly depends on the materials used for their production [1]. At present, the mean duration of operation of the retorts with various levels of cyclic productivity (1000–4000 kg) constitutes about 35 cycles of continuous operation. Note that, in the domain close to the reaction zone, the material of retorts suffers the simultaneous action of several unfavorable factors responsible for the intense wear of the shell walls. The inner surface of the retorts is subjected to the successive action of the melts of magnesium chloride (MgCl 2 ) , metallic magnesium (Mg), and liquid or vaporous titanium tetrachloride (TiCl 4 ) . Moreover, the outer wall suffers the influence of the high temperature (1000–1200°С) of hot air in the reduction and separation ovens. Statement of the Problem and the Results of Investigations Numerous available scientific works devoted to the choice of materials gave no positive results [1–7]. Actually, they did not give any significant increase in the service life of high-performance reactors. Note that the authors of the cited works did not consider in detail the negative effect of deformation and the strain-induced fracture of the walls of devices caused by their thinning under the simultaneous action of the other abovementioned factors. The elongation of the devices with simultaneous thinning of the walls caused by plastic deformation do not lead to irreversible losses of the metal. Thus, the walls become thinner under the negative action of the high-temperature deformation of the walls of retorts caused by the joint loading of the mass of reducer (Mg) and the mass of the active part of the reactor itself and the corrosion of the inner and outer surfaces of the retorts with activation of corrosion processes due to the decrease in the cross section of the shell in the last cycles of operation. In turn, the plastic deformation of the reactors also activates the processes of corrosion of steels in the last cycles of operation of the devices. 1 2
Zapirizhzhya National University, Zapirizhzhya, Ukraine. Corresponding author; e-mail: [email protected].
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 48, No. 2, pp. 1
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