Solid State Phenomena Vol. 212

Abstract: The paper analyses methods, the influence of use of charges of steel scrap of different qualities in the EAF on the index of liquid steel output from a melt using statistical analysing methods. The used research methodology consists of analytical simulation of variations in mass of liquid steel obtained from melts differing in steel scrap content in the metallic charge and of statistical analyses of industrial results acquired from the corresponding process documentation (so called melt cards). The obtained research results can be utilized in each steelmaking facility, which employs the Electric Steelmaking process, in order to “design” the metallic charge compositions, having in view the quality and economic aspects. The results presented in this paper are directed to the steelmakers employing the Electric Steelmaking process and constitute the authors original study.

Abstract: The iron and steel industry is one of the largest sources of waste materials, primarily in the form of steelmaking dusts, sludge and slag. Those wastes are a serious threat to the environment. Main precondition for the protection of natural resources in the environment is to recover raw material and energy from waste. The use of waste as raw materials does not involve the storage and creates the possibility of closure of the existing landfill. The article presented utilization of same metallurgical waste containing 4-20 wt. % zinc in non-metallurgical industry. Performed chemical analyzes of pollutants contained in waste tested (dusts, sludge and slag) and in manufactured products (cement bricks, ceramic construction materials, colored glass products and slag for road construction). Aqueous extracts analysis results were compared with the maximum values for the sewage entering into water and soil. The performed research proves that proposed technologies (production of cement clinker, construction bricks, hollow glass, decorated glass) do not pose threat to environment. Harmful impurities are eluted from the products – clinker, constructions bricks and slag after the recovery of zinc recovery. Proposed technologies substitution of primary raw materials recyclable materials can reduce environmental degradation.

Abstract: We examine the mechanical and physical properties of Sanicro 25 steel that are relevant to the performance requirements of supercritical boilers (e.g., resistance to high-temperature corrosion). Sanicro 25 is mainly used in the construction of power plant components. Materials research has demonstrated the stability of properties at elevated temperatures (700 to 750°C) during long-term use. We conducted tests of corrosion resistance for Sanicro 25 steel, and confirmed its resistance to oxidation in steam and exhaust gas heat .

Abstract: We propose in this publication the introduction of new, additional definition describing the multiple orifice ceramic filters used in research works on the liquid steel filtrations, calling this the filter slenderness ratio. In order to confirm the theoretical assumptions we have performed a series of the laboratory scale experiments (for the filter slenderness ratio S_F - 1.67 to S_F - 8.36). The influence of the filter slenderness on the filtration process efficiency has been determined through variations in quantities and surface shares of the non-metallic phase in the filtrated steel in relation to the non-filtered steel. We present also the results of researches on the separating surfaces between the liquid steel and the ceramic filter material, which in form of photos and scanning microscope microanalyses are put together in the publication.

Abstract: The paper presents investigations concerning causes of non-metallic inclusions forming in castings made of nickel-base superalloys. The most common reason of inclusions forming is erosion and thermal decomposition of crucibles and molds by the action of liquid alloy. In case of superalloys containing reactive elements (Hf), many reactions at the alloy-crucible and alloy-mold interfaces take place.

Abstract: The paper presents the results of ATD thermal analysis of feed ingots (master heat) and castings made from IN-713C, MAR-247 and MAR-509 superalloys. Metallurgical quality assessment was made based on the analysis of dT/dt curve in rage from T_eut to T_sol. Furthermore, impurities (oxides of Al, Zr, Hf, Cr etc.) have been identified inside the shrinkage cavities of feed ingots and castings. Significant similarities has been observed between impurities found in ingots, ATD test samples and finished castings. It has been demonstrated that ATD analysis of samples taken from different parts of feed ingot can be effective method of metallurgical quality assessment for these ingots.

Abstract: In the paper an effect of alloy modification, the mold material and the heat dissipation on the structure of hypereutectic silumin AlSi17 are presented. The investigated alloy was cast into: a ceramic (ATD), graphite and copper molds. In order to verify the conditions of heat dissipation through the mold, were used an additional cooling agents, such as water and liquid nitrogen. From the obtained ingots were prepared samples, which were stereological analyzed in the Metilo program.

Abstract: The influence of prolonged ageing on the kinetics of the precipitation process of the secondary phases in an A-286 type Fe-Ni superalloy has been studied. The samples were subjected to a solution heat treatment at 980°C for 2 h and water quenched, and then aged at temperatures of 715, 750 and 780°C at holding times from 0.5 to 500 h. Structural investigations were conducted using X-ray diffraction methods. The values of the austenite lattice constant were estimated with the use of the cos²θ extrapolation function, and by the Toraya (WPPF) and Rietveld methods. It was found that the largest decrease in the austenite lattice constant took place during the initial period of ageing at all investigated temperatures, which corresponds to the spinodal decomposition of supersaturated austenite and formation of the γ'-Ni₃(Al,Ti) intermetallic phase. Good agreement between the values of the austenite lattice constant determined using the extrapolation function and the Rietveld method was found.

Abstract: mpact of heat treatment on durability has been evaluated in this study in conditions of high-temperature creep of castings made from nickel superalloy MAR-247 post production rejects. Castings made in the processes of modification and filtration when pouring into moulds were subject to solubilization (1185°C/2 h) with subsequent ageing (870°C/20 h). It has been found on the basis of performed tests that in conditions of high-temperature creep at temperature 980°C with stress σ = 150 MPa the resistance of specimens of coarse-grain structure was significantly higher when compared to fine-grain material. The conditions of initiation and propagation of cracks in these specimens were analysed with consideration of morphological properties of material macro-, micro-and substructure. Moreover, it has been proven that creep resistance of heat treated MAR-247 superalloy significantly improves when compared to its condition after the process of modification only. Macrostructural changes in the MAR-247 superalloy that determine the increase of superalloy creep resistance after solubilization and ageing, as observed in the tests, were also examined.

Abstract: The article describes the process of crystallization of an AlSi17Cu5 (the A3XX.X series according to ASTM standard) alloy which has been modified with 0.05 wt. % P (CuP10 master alloy) and overheated to a temperature of 920°C. It has been shown that, so-called, "time-temperature treatment" (TTT) of alloy in the liquid state, which consists in overheating the alloy to a temperature above T_liq (about 250-300°C), holding at this temperature and rapid cooling, alters the morphology of primary silicon crystals. By the ATD method of thermal analysis, the characteristic temperature of crystallization (T_liq., T_Emin., T_Emax., T_E(Cu), T_E(Fe), T_sol.) were determined, and exothermic effects of the modifier and high-degree overheating on the crystallization course of the investigated alloy were examined. A new mechanism of proeutectic crystallization of the a(Al, Me=Cu, Fe) dendrites was proposed. The course of this process is dynamic enough to promote, due to local undercooling, the evolution of heat, which in the ATD curve appears as a well visible additional exothermic effect designated as T_X. It is due to the presence in the liquid alloy of microregions with varied content of dissolved silicon.