Volume 35, Issue 1 -

The effect of aging heat treatment on the microstructure and mechanical properties of 10Cr20Ni25Mo1.5NbN austenitic steel was investigated in this article. The microstructure was characterized by scanning electron microscopy, energy dispersive spectrometry and transmission electron microscopy. Results show that the microstructure of 10Cr20Ni25Mo1.5NbN austenitic is composed of austenite. This steel was strengthened by precipitates of secondary phases that were mainly M23C6 carbides and NbCrN nitrides. As aging treatment time increased, the tensile strength first rose (0–3,000 h) and then fell (3,000–5,000 h) due to the decrease of high density of dislocations. The impact absorbed energy decreased sharply, causing the sulfides to precipitate at the grain boundary. Therefore, the content of sulfur should be strictly controlled in the steelmaking process.

Present investigation is an attempt to study the weldability characteristics of sintered hot-forged plates of AISI 4135 steel produced through powder metallurgy (P/M) route using matching filler materials of ER80S B2. Compacts of homogeneously blended elemental powders corresponding to the above steel were prepared on a universal testing machine (UTM) by taking pre-weighed powder blend with a suitable die, punch and bottom insert assembly. Indigenously developed ceramic coating was applied on the entire surface of the compacts in order to protect them from oxidation during sintering. Sintered preforms were hot forged to flat, approximately rectangular plates, welded by pulsed current gas tungsten arc welding (PCGTAW) processes with aforementioned filler materials. Microstructural, tensile and hardness evaluations revealed that PCGTAW process with low heat input could produce weldments of good quality with almost nil defects. It was established that PCGTAW joints possess improved tensile properties compared to the base metal and it was mainly attributed to lower heat input, resulting in finer fusion zone grains and higher fusion zone hardness. Thus, the present investigation opens a new and demanding field in research.

The interpretation of marker experiments in studying the formation mechanism and defect structure of higher oxides during oxidation of lower oxides, showing rather high deviations from stoichiometry, has been discussed. It has been shown that correct results can be obtained only if the concentration of point defects in the substrate is taken into account. Theoretical considerations presented in this paper have been illustrated by the experimental results obtained during sulphidation of highly disordered Co 1- y S to form CoS 2 , as well as Ni 1- y S to form NiS 2 .

The semi-solid deformation behavior of Ti-7Cu titanium alloy in the temperature range of 1,223 K to 1,473 K and strain rate range of 0.005 to 5 s −1 have been investigated by hot compressive testing. The results show that the maximum and stability stresses decrease with decreasing strain rate and increasing temperature. A yielding occurred to the alloy at a higher strain rate under all experimental temperatures. The flow behaviors were described by a constitutive equation based on the Arrhenius equations and the deformation activate energies is also calculated. By comparing with microstructure of the solid deformation, the liquid in semi-solid deformation can overcome the restriction of the movement of solid particle, which reduced the dislocation pile-up during deformation and caused low deformation resistant stress.

Thermodynamic properties of ternary Al-Ni-Pd system, such as ex G AlNPd , µ Al(AlNiPd), µ Ni(AlNiPd) and µ Pd(AlNiPd) at 1,373 K, were predicted on the basis of thermodynamic properties of binary systems included in the investigated ternary system. The idea of predicting ex G AlNiPd values was regarded as calculation of values of the ex G function inside a certain area (a Gibbs triangle) unless all boundary conditions, that is values of ex G on all legs of the triangle are known ( ex G AlNi , ex G AlPd , ex G NiPd ). This approach is contrary to finding a function value outside a certain area, if the function value inside this area is known. ex G and L Al,Ni,Pd ternary interaction parameters in the Muggianu extension of the Redlich–Kister formalism were calculated numerically using the Excel program and Solver. The accepted values of the third component x x differed from 0.01 to 0.1 mole fraction. Values of L AlNiPd parameters in the Redlich–Kister formula are different for different x x values, but values of thermodynamic functions: ex G AlNiPd , µ Al(AlNiPd) , µ Ni(AlNiPd) and µ Pd(AlNiPd) do not differ significantly for different x x values . The choice of x x value does not influence the accuracy of calculations.

Top slag melting experiment was conducted in a silicon molybdenum furnace with tire cord steel billet. The influence of top slag composition on the plasticity of CaO–Al 2 O 3 –SiO 2 –MgO inclusion and inclusion plasticization conditions was calculated by thermodynamic software FactSage. Use the thermodynamic calculation to guide the laboratory experiments to study slag compositions influence inclusions composition. Then industrial experiments were conducted based on the theoretical calculation and results of laboratory experiments. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to determine the morphology and composition of inclusions in steel. All studies show that in the CaO–Al 2 O 3 –SiO 2 –10% MgO diagram, when CaO = 8–48%, SiO 2 = 35–75%, Al 2 O 3 = 0–32%, inclusions are in the plastic area. When basicity of top slag is certain, Al 2 O 3 content in inclusions increases with the increase of Al 2 O 3 content in the slag, and the distribution of inclusions becomes scattered with the increase of Al 2 O 3 content in slag. Inclusion plasticization can be achieved when the binary basicities of top slag are 0.6, 0.8–1.2, 1.4 and corresponding w(Al 2 O 3 ) s are 2–15%, 2–10%, <2%. According to industrial experimental results, when top slag basicity decreases from 1.5 to 0.67–0.9 and Al 2 O 3 content decreases below 10 wt%, the inclusion falls into plastic area. It is feasible in practice to control the CaO–Al 2 O 3 –SiO 2 –MgO inclusions plastic through adjusting Al 2 O 3 content in slag.

The hot deformation behaviors of a solution-treated Ni-based superalloy are investigated by hot compression tests over wide ranges of strain rate and forming temperature. Based on the experimental data, the effects of forming temperature and strain rate on the hot deformation behaviors are discussed in detail. Considering the effects of strain on material constants, comprehensive constitutive models are developed to describe the relationships between the flow stress, strain rate and forming temperature for the studied superalloy. The three-dimensional processing map is constructed to optimize the hot working parameters. Meanwhile, the microstructures are analyzed to correlate with the processing map. It is found that the flow stress is sensitive to the forming temperature, strain rate and deformation degree. With the increase of forming temperature or the decrease of strain rate, the flow stress significantly decreases. The predicted flow stresses agree well with experimentally measured results, which confirm that the developed constitutive model can accurately estimate the flow stress of the studied superalloy. The three-dimensional processing map shows that the optimum deformation windows for hot working are the domains with 980–1,040°C or 0.001–0.1 s−1$${{\rm{s}}^{- {\rm{1}}}}$$ when the strain is 0.6. Also, it is found that the dynamically recrystallized grain size increases with the increase of forming temperature or the decrease of strain rate.

Since the beginning of the extensive applications in numerous high temperature processes such as iron- and steel-making, coke-making etc. partly in the place of coke, the investigation into the reaction mechanism of waste plastics has become increasingly necessary. In this paper a fundamental study on the behavior of a typical component of waste plastics, high density polyethylene (HDPE), in a mixture with coke at a 1:1 ratio in mass base was conducted during the reaction with iron oxide in steel-making slag at 1823 K and was compared with coke and graphite. The reaction mechanism of carbonaceous materials was analyzed based on the contents of CO and CO 2 in the off-gas monitored by an infrared (IR) gas analyzer. It is clear from the results that the reaction of HDPE and coke mixture with steel-making slag approached equilibrium of the Boudouard reaction more quickly and closely than coke or graphite.

The tuyere small sleeve in blast furnace works under poor conditions. The abnormal damage of it will severely affect the performance of the blast furnace, thus it should be replaced during the damping down period. So it is of great significance that we study and reduce the burnout of tuyere small sleeve. Melting loss is one case of its burnout. This paper studied the reasons of tuyere small sleeve’s melting loss, through computational simulation and microscopic analysis of the melting section. The research shows that the temperature of coppery tuyere small sleeve is well distributed when there is no limescale in the lumen, and the temperature increases with the thickness of limescale. In addition, the interruption of circulating water does great harm to the tuyere small sleeve. The melting loss of tuyere small sleeve is caused by iron-slag erosion, with the occurrence of the melt metallurgical bonding and diffusion metallurgical combination.

Fracture toughness is an important parameter to study fracture characteristic of rock under external loads. Based on splitting tensile test on flattened Brazilian disc specimen of rock after high temperature, load–displacement curves of rock sample in the fracture process are obtained and three mechanical parameters of rock including fracture toughness, splitting tensile strength and elastic modulus are calculated according to the experiment. Then, the change rules of fracture toughness, splitting tensile strength and elastic modulus with temperature are discussed, and the relations between splitting tensile strength, elastic modulus and fracture toughness are established. Experimental results show that there exist two inflection points in load–displacement curves. The fracture toughness, splitting tensile strength and elastic modulus reduce gradually with increasing temperature, among which, the mechanical parameters of granite decrease approximately linearly while that of marble decrease approximately as exponential function. There is a close connection between splitting tensile strength, elastic modulus and fracture toughness, nearly a good linear relationship. Since the test method of splitting tensile strength is relatively simple and that of fracture toughness is complex, the fracture toughness can be roughly estimated by splitting tensile strength.

The gasification of a sub-bituminous coal using CO 2 –O 2 gas mixtures was studied in a plasma-augmented fluidized bed gasifier. Firstly, the coal was chemically characterized and the gasification process was examined using Thermogravimetric and Differential Thermal Analysis (TGA/DTA) in CO 2 , O 2 and at a CO 2 to O 2 ratio of 3 to 1. Secondly, the equilibrium gas compositions were obtained using the Gibbs free energy minimization method (HSC Chemistry®7). Thirdly, gasification tests were performed in a plasma-augmented fluidized bed and the off-gas temperatures and compositions were determined. Finally, for comparison purposes, control tests were conducted using a conventional fluidized bed coal gasifier and these results were compared to those achieved in the plasma-augmented fluidized bed gasifier. The effects of bed temperature and CO 2 to O 2 ratio were studied. For both gasifiers, at a given bed temperature, the off-gas compositions were in general agreement with the equilibrium values. Also, for both gasifiers, an experimental CO 2 to O 2 ratio of about 3 to 1 resulted in the highest syngas grade (%CO + %H 2 ). Both higher off-gas temperatures and syngas grades could be achieved in the plasma-augmented gasifier, in comparison to the conventional gasifier. These differences were attributed to the higher bed temperatures in the plasma-augmented fluidized bed gasifier.

The research samples used in this study were based on the Inconel 625 alloy; the examined samples were coated with aluminide films deposited in a low-activity chemical vapor deposition (CVD) process. The samples’ microstructure was investigated with optical and electron microscopy and energy dispersive X-ray spectroscopy analysis. Hardness measurements were performed using Vickers and Berkovich test methods. The adhesion of the aluminide coating was determined by fractography. It was shown that the fracture mechanism was different for the respective zones of the aluminide coating and the substrate material. The outer zone of the aluminide coating is characterized by an intercrystalline fracture, with a small contribution of transcrystalline fracture within individual grains (large crystallites in the bottom of the zone, composed of smaller crystallites, also show an intercrystalline fracture). The substrate material exhibited a ductile intercrystalline fracture. Based on this investigation, an increase of the microhardness of the material occurring at loads below 0.2 N was observed. When determining microhardness of aluminide coating it is necessary to take into account the optimal choice of the indentation tip.

This paper proposes an analytical approach to optimize the thickness of refractories for achieving maximum microwave power transmission in microwave heating based on the analysis of power transmission coefficient (PTC). The microwave PTCs of alumina (Al 2 O 3 ) ceramics over the temperature range of 22–1,379°C at 2,450 MHz, mullite ceramics in the temperature range of 27–1,027°C at 2.45 GHz and 400–1,300°C at 915 MHz are studied. The results show that there are several transmission peaks in the PTC patterns. The transmission peak amplitude depends sensitively on the thickness of the refractory and the peak shifting towards a smaller thickness as the temperature of the refractory increases. We also show that high microwave transmission can only be achieved in a refractory with a small thickness corresponding to a slight transmission peak shift in the entire microwave heating (less than one eighth wavelength in the refractory).