Studying the effect of heat treatment modes on corrosion resistance of welded joints

Welded joints with corrosion-resistant steels and heat-resistant alloys, which require different modes of heat treatment to achieve the level of mechanical properties specified in the design documentation, are used for the manufacture of parts and components of the turbo-pumping unit (TPU) and liquid rocket engine. Heat-resistant alloys are a large group of alloys on iron, nickel and cobalt bases with the addition of chromium and other alloying elements (C, V, Mo, Nb, W, Ti, Al, B, etc.), whose main feature is to maintain high strength at high and cryogenic temperatures. Heat-resistant alloys are used in the manufacture of many parts of gas turbines in rocketry and jet aircraft, stationary gas turbines, the pumping of oil and gas, hydrogenation of fuel in metallurgical furnaces and many other installations. For the doping of nickel chromium γ-solid solution, several elements are used, which differently influence the increase of heat resistance and processability. Along with the main reinforcing elements (Ti, Al), refractory elements (W, Mo, Nb) are introduced into the alloy, which increase the thermal stability of the solid solution. Heat resistant alloys are based on cobalt. Cobalt has a positive effect on the heat-resistant properties of alloys. The introduction of chromium in cobalt increases its heat resistance and hardness. In addition to chromium, alloys containing cobalt include additives of other alloying elements that improve their various properties at high temperatures. A characteristic feature of these alloys is that they have relatively low heat resistance characteristics at moderate temperatures, which, however, change a little with the temperature up to 900 ° C and therefore become quite high compared to the characteristics of other heat-resistant alloys. A significant drawback of these alloys is their high cost due to the costly cobalt. Nickel-based heat-resistant alloys typically have a complex chemical composition. It includes 12–13 components, carefully balanced to obtain the required properties. The content of impurities such as silicon (Si), phosphorus (P), sulfur (S), oxygen (O) and nitrogen (N) is also controlled. The content of elements such as selenium (Se), tellurium (Te), lead (Pb) and bismuth (Bi) should be negligible, which is provided by the selection of charge materials with low content of these elements, because it is not possible to get rid of them during melting. These alloys typically contain 10–12 % chromium (Cr), up to 8% aluminum (Al) and titanium (Ti), 5–10 % cobalt (Co), as well as small amounts of boron (B), zirconium (Zr) and carbon (C). Molybdenum (Mo), tungsten (W), niobium (Nb), tantalum (Ta) and hafnium (Hf) are sometimes added. Heat-resistant alloys are used for the production of many parts of gas turbines in rocketry and jet aircrafts, stationary gas turbines, for pumping oil and gas products, for hydrogenation of fuel in metallurgical furnaces and in many other installations. Nickel-based heat-resistant alloys are also cryogenic, i.e., they are capable of operating and retaining mechanical properties at very low temperatures (–100 °C to –269 °C). Such alloys are chromium-nickel alloys having an austenitic structure. Not only do they have good mechanical properties that do not change over a large temperature range (–200 °C to 900 °C), they can also work in corrosive environments. Nickel-based heat-resistant alloys typically have a complex chemical composition. It includes 12–13 components, carefully balanced to obtain the required properties. Welded and combined workpieces are made of separate components that are interconnected by various welding methods. Welded and combined blanks greatly simplify the creation of complex configuration designs. Improper workpiece design or incorrect welding technology can cause defects (grooves, porosity, internal stresses) that are difficult to correct by machining. Given that finding replacements with multiple materials, working them out in production, and investigating interconnectivity during thermal forces in a product can take considerable time and money, it would be best to replace one alloy. Unifying the material used would allow the structure to work as a whole, which would increase the manufacturability of the products. After examining the different replacement options, inconel 718 was selected for the study. Studies of welded specimens of inconel 718 alloy-stainless steel for resistance to the ICC have shown that it is not appropriate to use welded inconel 718 for the impeller, it is advisable to use material that would ensure uninterrupted operation in a corrosive environment at cryogenic temperatures. Based on the working conditions of the parts, it is most expedient to make it from heat-resistant chromium-nickel alloys, namely, from float inconel 718 which meets the necessary strength characteristics. The recommended soldering mode is heating up to 950 ± 10 oC, holding for 30 minutes from the moment of loading into the oven, cooling to 3000C with the oven, further in the air, since it has less influence on the corrosion resistance of steels in stainless steel joints. Quality control of inconel 718 alloy by GOST methods similar to that used for the control of X67MBHT type alloys showed the results similar to those obtained by the ASTM and AMS control methods.

Determination of thickness and quality of refractory linings in industrial furnaces using acousto ultrasonic echo

Refractory linings in metallurgical furnaces undergo deterioration and wearing with time. The deterioration is caused mainly by thermomechanical mechanisms leading to cracks, chemical degradation and loss of heat transfer capability. Any sudden failure of the lining is dangerous and could affect the structural integrity of the furnace, leading to production loss and costly refurbishment. Non-destructive testing (NDT) and monitoring of refractory lining would lead to better safety, longer use of the vessel, production optimization, controlled maintenance and increased production. Thickness measurements and monitoring of the refractory lining in operating furnaces is possible using Acousto Ultrasonic -Echo (AU-E) technique. This technique uses stress waves of both acoustic and ultrasonic ranges in order to determine thickness and integrity. This thesis presents the details of AU-E technique in addition to laboratory measurements to determine parameters leading to the in-situ measurements. Finally, three case studies are presented to substantiate the theoretical and laboratory measurements.

Determination of thickness and quality of refractory linings in industrial furnaces using acousto ultrasonic echo

Refractory linings in metallurgical furnaces undergo deterioration and wearing with time. The deterioration is caused mainly by thermomechanical mechanisms leading to cracks, chemical degradation and loss of heat transfer capability. Any sudden failure of the lining is dangerous and could affect the structural integrity of the furnace, leading to production loss and costly refurbishment. Non-destructive testing (NDT) and monitoring of refractory lining would lead to better safety, longer use of the vessel, production optimization, controlled maintenance and increased production. Thickness measurements and monitoring of the refractory lining in operating furnaces is possible using Acousto Ultrasonic -Echo (AU-E) technique. This technique uses stress waves of both acoustic and ultrasonic ranges in order to determine thickness and integrity. This thesis presents the details of AU-E technique in addition to laboratory measurements to determine parameters leading to the in-situ measurements. Finally, three case studies are presented to substantiate the theoretical and laboratory measurements.

Archaeological investigations of subsistence and household life of Ukrainian population of Luhansk region in XVII–XVIII centuries

This article examines in a complex way the peculiarities of organization of everyday and household life of the Ukrainian population of the Luhansk region in the XVII–XVIII centuries. The basis for the study of those or other aspects of this topic were materials of archaeological expeditions that were carried out in Luhansk region in the second half of the twentieth – early twenty-first century. It is noted that this topic is poorly covered in the works of Ukrainian academics. Among the few studies in this area, the works of N. N. Kaplun, O. V. Stadnik and A. I. Stadnik were the most valuable for the research. Also in the preparation of the article the author relied on the expert estimates of scientific collaborators of the Institute of Archaeology of the National Academy of Sciences of Ukraine S. A. Telizhenko, L. Chmiel, L. Mironenko. The aim of the article is to outline the way of life and economic life of the Ukrainian population during the active development of the Luhansk region – that is in the XVII–XVIII centuries. As a result of the conducted research, the authors reached the following conclusions. The presence of diverse archaeological artifacts: ceramic works, artisanal metallurgical furnaces, stone tombstones, the lower boundary of the dating of which falls on the XVII–XVIII centuries, In our view, indicates the existence of sufficiently developed material culture associated with the way of life and household utilities of Ukrainian settlers of the Cossack era in the Luhansk region. Today's assumption that the dynamic development of this region began only at the beginning of active development of the territory at the beginning of the XVIII century – the beginning of the XIX century. Russian Empire, it can be argued that even before its beginning, a significant part of the „Wild Field” did not yield in its development to other regions, both Ukraine and Russia, distant from the restless relations with the Nogai horde.

Kinematics of the Maneuver of the Multifunctional Machine for Metallurgical Furnaces

The article proposes a simulation model of a loading machine for metallurgical furnaces and builds a mathematical model that makes it possible to find optimal trajectories of motion and obtain laws of change in kinematic, dynamic and inertial characteristics for a full operation cycle. The description of the machine motion is made taking into account the nonholonomy of the imposed connections and provides for the possibility of considering arbitrary laws of motion along optimal trajectories. Compliance with optimal working conditions is also ensured by the choice of a special law of motion between the nodal points on the trajectory of movement, corresponding to the change in the direction of movement of the loading machine. Based on the research results, a design scheme and a simulation model with an analytical description of the mechanism operation, including kinematic graphs, are proposed. A simulation model of a loading machine for metallurgical furnaces and a description of its operation modes are made by methods of analytical mechanics.

Theory and Practice of Heat Transfer in Electric Arc Steelmaking and Flare Metallurgical Furnaces and Power Plants

The author describes the fundamental laws of physics, the laws of thermal radiation of ionized and non-ionized gas volumes. Based on open laws, a modern theory of heat transfer and methods for calculating heat transfer in electric arc and flare metallurgical furnaces, furnaces of steam boilers, and combustion chambers of gas turbine plants of power plants have been developed. The use of scientific discovery makes it possible to create innovative electric arc steel-smelting furnaces, flare heating furnaces, and combustion chambers in which the consumption of electricity and fuel is reduced, productivity and service life are increased, and the amount of harmful emissions into the environment is reduced.

Technological Processes of Receiving Metals in The Conditions of Moderate Temperatures

In article questions of physical and chemical transformations of starting materials at their heating in metallurgical furnaces are considered. It first of all moisture evaporation, dissociation of the difficult connections, oxidizing and recovery processes, formation of fusible eutectics. An attention to interaction of oxides and sulfides with formation of the new connections having smaller melting point than initial components. It is shown that these connections are the beginning of formation of melts and actually define thermodynamics and kinetics of all process. Transition of firm components of fusion mixture to flux has a great influence on technological indicators of smelting of metal. Considering it, the research on establishment was conducted began courses of these of reaction and a possibility of determination of this criterion without direct the made experiments

Best available technologies of wastes processing in mining and metallurgical industries

Mining and metallurgical industries are referred to high wastes productions. To decrease the damage to environment, progressive equipment and technologies are required. It was shown, that the modern approach to the environment protection should be based on implementation best available technologies (BAT). In the elaborated industry technical information BAT reference-book for the mining and metallurgical industries recommendation presented for utilization of main technological wastes of metallurgical production. A brief review of technologies presented, implementation of which allow providing practically complete processing of non-organic wastes, arising during raw materials mining and production of them ferrous metals. To choose the methods of construction and operation wastes utilization, one should be guided by recommendations, related to the thermal sterilization technologies for organic wastes as well as recommendations for utilization of organic wastes. It was noted, that the part of BAT reference book devoted to storing and disposal of production and consumption wastes is an evidence of high level of technologies used in Russia to realize the process. It was indicated, that in the BAT reference books the foreign experience of wastes utilization was not taken into account. Besides, a possibility to sterilize the wastes by thermal method in metallurgical furnaces was not also described. As a whole the application of the information presented in the BAT reference books, will allow to guide specialists of mining and metallurgical plants to choose best available technologies of handling with production wastes.