CC BY
21iSHS 2019
Moscow, Russia
COMBUSTION SYNTHESIS OF COMPOSITION ALLOYS
M. Kh. Ziatdinov
Tomsk State University, Tomsk, 634050 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10205
We are presenting research findings in the development of a specialized SHS technology for composite ferrous alloys for steel melting and blast furnace iron-making. To resolve the principle goal of creating metallurgical production lines we developed a new approach to practical implementation of the SHS method — a metallurgical SHS process. The metallurgical version of SHS is based on using different metallurgical alloys as the main raw stock; those include dust-type wastes of ferrite alloys production. In this case, the process of synthesis by combustion is implemented via exothermic exchange reactions. Here, composite materials form; they are based on inorganic compositions bound with iron and/or an alloy based on iron. It has been shown that depending on the aggregate state of source reagents, metallurgical SHS processes can be gasless, gas-absorbing or gas-yielding. Combustion modes for these processes largely differ. To arrange for metallurgical SHS process in weakly exothermic systems, we can use different versions of the thermal bonding principle. We have investigated self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome. It has been shown that the phase composition of the source alloy has strong impact on the consistent behaviors of the combustion flow and the combustion mechanism of ferrovanadium (if combustion is taking place in nitrogen atmosphere). In the course of nitriding o-(Fe-V), process activation takes place; the activation is related to the transformation of the intermetallide into a-solid solution when the phase transition temperature is reached (~ 1200°C). The composition structure of ferrovanadium nitride products is formed by the confluence of solid-liquid droplet-particles that consist of molten Fe and solid vanadium nitride. A 3-phase mechanism of ferrochrome interaction with nitrogen facilitates the achievement of a high degree of nitriding. We have shown that the combustion rates of ferrochrome (and chrome) during nitriding in coflow filtration mode increase as the nitrogen flow rate is increased. Here, the degree of ferrochrome nitriding during forced filtration (4.7-7.5% N) is much less than that during non-forced filtration (8.8-14.2% N).
It is shown that consistent patterns in the combustion of ferrosilicium in nitrogen are rather similar to those of metal silicon. As the concentration of silicon in initial ferrosilicium is increased, the intensity of its interaction with nitrogen increases as well, resulting in a significant growth of the combustion rate. The concentration of nitrogen in the combustion products here increases as well. In the entire investigated range of initial parameters (nitrogen pressure, powder fineness, burden mix), the main phase in the combustion products is P-Si3N4. No considerable amounts of a-Si3N4 have been observed. In practical applications, the use of FS75 and FS90 grade ferrosilicium is optimal for producing fire-resistant materials, while FS65 and FS75 (being the purest alloy grades) are optimal for obtaining alloying steel compositions. Introducing iron into the Ti-B (Tad = 3190 K) system significantly narrows down the concentration limits of combustion. (Fe-B) + Ti mixture with 16.9% B alloy burns in a narrow range of Ti:B concentrations close to 0.86. When a ferroboron-titanium mixture burns, an increase in the initial temperature significantly expands the synthesis concentration limits. In all the cases, an increase in the initial temperature leads to a significant increase in the combustion rate. Heating up to T0 > 300°C allows for involving mixtures with more coarse titanium powders (rav.Ti > 0.4 mm) into the SHS process. The synthesis is implemented in a
XV International Symposium on Self-Propagating High-Temperature Synthesis
wide range of B:Ti ratios. By burning such mixtures, we can obtain alloys with 6-14% B and 30-60% Ti. Specialized industrial equipment has been built: a series of SHS reactors with the operation volume of 0.06, 0.15, and 0.3 m3 for the serial production of manufacturing items based on hard-melting inorganic compositions (nitrides, borides, silicides, etc.) for metallurgical applications. Industrial SHS production of composite materials based on oxygenless compositions has been set up.
