PSI - Issue 40

Oleg N. Komarov et al. / Procedia Structural Integrity 40 (2022) 231–238 Oleg N. Komarov at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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• form samples by filling the mold with iron-carbon alloys obtained as a result of aluminothermic remelting of thermites containing an aluminum-based reductant and scheelite concentrate; • study the impact of the reductant and scheelite concentrate content in thermites on the structure and mechanical properties (hardness, ultimate tensile strength, percentage elongation) of the experimental-alloy samples. 3. Methods and approaches It has been experimentally established that it is necessary to use iron-scale powder and PA-2 aluminum pow-der with a fraction of 0.2÷1.5 mm when formulating a thermite mixture (Komarov et al., 2020). The iron scale chemical composition is as follows: C = 0.150%; Mn = 1.188%; Si = 2.960%; S = 0.030%; P = 0.030%; Fe = 71.500%; Al = 0.697%; Ni = 0.188%; Cr =0.173%; Cu = 0.444%; O 2 = 22.639%. PA-2 has the following chemical composition: Al = 99%; Si = 0.4%; Cu = 0.02%; Fe = 0.35%. The reductant content in the basic thermite mixture has been determined in the course of preliminary studies (Komarov et al., 2018) and amounts to 20 – 25%. The lower range of the reductant content values provides for the required intensity of the exothermic reaction, while the upper one — for the permissible aluminum content in the metal phase. The first objective wa s accomplished through manufacture of “Cylinder” -type cast blanks, using the device shown in Fig. 1, a.

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b

Fig. 1. (a) Appearance and Section of the Blank (b) Intended for Obtaining Samples:1 - reactor crucible, 2 - rigid frame, 3 - casting mold.;.

Vertical unit comprising a fixed rigid frame with a reactor crucible pre-filled with thermite and heated to the temperature of 350 0 C, which is installed at the top of the frame. The said temperature was determined through a series of preliminary studies as a result of which the maximum weight yield of liquid phase was established (Popov et al., 2018). The temperatures before the start of the reaction and before casting the melt into the mold were recorded by means of an infrared pyrometer Kristall C-500.7. Once the reaction has started in the thermite by igniting a fuse placed on the surface of the thermite composition, the crucible is covered with a lid equipped with an outlet fitting for removal of the reaction product gases. In the course of the oxidation-reduction process, a liquid slag phase with an average density of ~4,000 kg/m 3 is formed in the upper part of the reactor crucible, while a metal phase is formed in the lower part thereof. Since the melting and boiling temperatures of tungsten oxides vary from 1,500 to 1,700°C and their density ranges between 7,440 and 12,110 kg/m 3 , the melt should be held in the reactor crucible for a certain period of time, so as to ensure effective separation of the metal and slag phases (Komarov et al., 2016). 10 seconds after the thermite has melted, the metal phase is cast into the mold located in the frame of the unit, just below the reactor crucible. Refractory properties of the material used for the reactor crucible, lid, and mold should allow for melting the ther mite at temperatures exceeding 2,050°C. For this purpose, EG15 electrode graphite was used, which is compliant with the requirements of the Russian standard TU 14-139-177- 2003 “Graphite Electrodes with the