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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Diameter from 75 to 555 mm and Nipples Thereto. Te chnical Specifications”. Prior to the experiment, the refractory elements of the unit are coated with a parting paint which contains marshallit (20%), liquid glass (5%), water (74%), and boric acid (1%); the paint is applied at the temperature of 150°C. Th e volume of the thermite placed into the reactor crucible allows for obtaining a cylindrical blank with the diameter of 0.03 m and height of 0.15 m. Upon cooling down, the blanks are cut. It has been experimentally established that the high temperature inherent in the exothermic processes and the excess of scheelite concentrate in thermites lead to the formation of pores in the cast product structure due to the significant content of residual aluminum in the melt. The latter induces an increase in the rate of oxygen intake from the environment. Blanks having no visually identifiable defects internal gas pores or shrinkage cavities were used for de-termination of the chemical composition, structure, and mechanical properties (Fig. 1, b). Chemical analysis of the metal used for the experimental blanks was performed in accordance with the Russian standard GOST 18895- 97 “Steel. Method of Photoelectric Spectral Analysis”, by means of a TASMAN Q4 170 optical-emission spectrometer manufactured by BRUKER (USA). AXIO VERT A1 light microscope was used for determining the microstructure of the metal. The Brinell hardness number for the iron-carbon alloys obtained was determined with the use of a Metolab 703 universal hardness tester. The ultimate tensile strength and percentage elongation values for the experimental samples obtained by mechanical cutting from the blanks were determined in accordance with GOST 1497-84 “Interstate Standard. Metals. Methods of Tension Test”, with the use of an AG -X plus SHIMADZU universal testing machine with the constant grip displacement rate of 0.05 mm/s. Fractographic examination of the failure zones of the samples was carried out by means of a ZEISS EVO LS10 focused-beam scanning microscope. 4. Description of the experiment The original component ratio and temperature conditions of the melt formation largely determine the structure, as well as mechanical properties and performance characteristics of the finished cast product. In order to obtain the required product structure in the conditions of the aluminothermic process used for obtaining the melt and associated with high temperatures, it is necessary to ensure precise selection of the components to be reacted. There is a lack of practical information about the mutual influence of the reductant and scheelite concentrate present in the thermite in case of aluminothermic manufacture of blanks from iron-carbon alloys on the properties of the latter, which necessitates experimental simulation of such processes. Optical emission spectroscopy has shown that as the content of the reductant in the thermite mixtures in-creases from 20% to 25%, the content of C and Al also increases, that of Si decreases, and the Mn content remains the same in the experimental alloys. The Mn and Si content in the final alloys decreases with the increase in the scheelite content in the thermites. Increase in the scheelite content in the thermites predictably results in the increased W content in the alloys. In general, increased W content in the alloys leads to the decrease in the Al, Si, Mn content and minor de-crease in the C content therein. The content ranges of the basic elements in the metal of the samples obtained from the thermites containing 23% of the reductant and 0 – 20% of scheelite concentrate are as follows [%]: С = 0.8…0.26; Mn = 0.47…0.13; Si = 0.49…0.3; Al = 1.53…0.16; W = 0.086…19.703. Fig. 2 shows the structures representative of the experimental alloy samples with no visually identifiable internal gas pores. The images o f the structures shown in Fig. 2 were obtained at 1,000× magnification using an AXIO VERT optical microscope equipped with a camera and software that allows one to determine the real area of the images. Thus, the area of the images shown in Fig. 2 is 5 * 10-3 mm 2 . For the samples of experimental alloys, a cast structure is inherent, characterized by inhomogeneity of the composition, dendritic and zonal segregation. The study of the influence exerted by the reductant and scheelite concentrate content in a thermite on the experimental metal hardness has shown that the latter tends to increase with the increase of the number of tungsten containing phases in the alloy. In case of the samples obtained from the thermites with the reductant content of 21 and 25%, the maximum hardness value of 359HB is reached when using thermites with the scheelite concentrate content of 10%. The samples obtained from the thermites with the reductant content of 23% feature the most stable hardness values which range from 333 to 311HB. The maximum hardness of the samples obtained from compositions with the reductant content of 22% is reached at the scheelite concentrate content of 15% and equals 342HB.