Papers by Keyword: Grain

Abstract: This paper presents an experimental study on the influence of solidification cooling rate on the evolutions of microstructural morphologies of a high strength low alloy steel. To this end, solidification samples (cylindrical form with 10 mm diameter and 120 mm length) were prepared from 30 cm below the ingot/hot-top interface, at the center, of a 40 MT (Metric Ton) ingot. Solidification experiments were carried out by using Gleeble^® 3800 thermo-mechanical simulator. Two solidification cooling rates of 1 and 50°C/s were chosen. For microstructural characterization, samples were prepared by mounting, polishing and etching with 3% Nital solution. Also, an optical microscope was employed for microstructural observations. The obtained results showed that for 1°C/s, the microstructure is composed with dendrites and grains. Here, the grain morphology is the dominant one. In the case of 50°C/s, the dendrites were localized at the sample surface and the grains were present more into the depth of the sample. Moreover, the increase of solidification cooling rate results in finer dendrites. The results are discussed in the framework of solidification mechanisms.

Abstract: The paper proposes an approach to assessing the grinding wheel wear, which includes the wear of grains and pulling them out of the bond, based on fatigue failure under cyclic loads caused by cutting forces, with a period of the order of microseconds. This approach is implemented on the basis of stress life calculation in the ANSYS Fatigue module using loading data obtained from the numerical simulation of grain-workpiece interaction. The simulation results allows to obtain the grain wear area, the level of bond fatigue fracture and the possibility of self-sharpening of the grinding wheel for a given grain size and operation conditions.

Abstract: Based on the interaction of solid and liquid phases in metallic systems, the paper deals with the properties of grain boundary propagation (migration) in solid-state alloys. Using the effect of surface solid-state dispersion enables to obtain composite materials and brazed joints with a required set of physical and mechanical properties. For the first time, the authors investigate the features of boundary migration in type II systems, in which, in accordance with the thermodynamic criterion σ_ss< 2 σ_SL, the grain-boundary propagation is not basically allowed.

Abstract: The morphological and crystallographic characteristics of noble metal nanoisland films play an important role in determining their properties, performance, and reliability. In this work we have applied a rapid three-dimensional orientation mapping technique in the transmission electron microscope (3D-OMiTEM) in the characterization of a gold nanoisland film. A volume of 200×1024×1024 nm³ has been analyzed, generating a 3D orientation map composed of more than 500 nanoislands and 7000 grains constituting the islands. The 3D shapes and sizes of individual islands and grains have been analyzed, revealing their true 3D morphological features and the correlation between the number of grains within individual islands and the size of the islands. The crystallographic orientations of the grains and the misorientations across the grain boundaries have been quantified, revealing a weak texture but a preferential presence of Σ3 and Σ9 grain boundaries in the gold nanoisland film.

Abstract: An important factor in solving the problem of stainless steel corrosion resistance is carbon concentration reduction. However, a decrease in carbon content of austenitic steels leads to a drop in level of their strength properties. Theoretically, nitrogen alloying can lead to a strength increase in all types of austenitic corrosion-resistant steels. Practically, nitrogen alloying is effectively only with low-carbon compositions. This work shows the effect of nitrogen on the mechanical properties of middle-alloying nitrogen, containing stainless steel, and a study of AISI 304L and pilot steel with different nitrogen content (from 0.16 to 0.30 wt. %). Nitrogen increases strength of steel, which is approximately 30-60% higher than for steel without nitrogen, but reduces technological plasticity. Pilot steels show high corrosion resistance and fine austenite grains.

Abstract: Drawing is characterized by non-uniform character of plastic deformation, which is transferred from the die to the processed wire. Such impact causes specific change of wire microstructure. In the surface area the thin layer with highly deformed grains is observed. It is important to measure the thickness of this thin layer. For this purpose it is proposed in this paper to use the value of coefficient of anisotropy, which is calculated as the ratio of mean quantity of phase particles, crossed by secant line perpendicular to deformation axis on the unit of secant line length to the mean quantity of phase particles, crossed by secant line parallel to deformation axis on the unit of secant line length. Distribution of coefficient of anisotropy, both for low and high carbon steel wire after drawing, was obtained by Thixomet PRO software. It made it possible to calculate the thickness of highly deformed area automatically taking into consideration the difference of steels microstructure.

Abstract: The paper presents the influence of chemical compositions and structure of the deposited metal on its hardness and wear resistance in abrasive-shock conditions. Metal Was deposited by the arc powder wire automatic welding. The studies have shown that increasing nikel contain to 0.65% in the surfaced steel and cobalt additive while reducing carbon contain to 0.17-0.23%, provides martensite and former austenite grain size disintegration. In consequence of multivariate correlation analysis, it was determined dependence to the hardness of the deposited layer and the wear resistance of the mass fraction of the elements included in the flux-cored wires of the system Fe-C-Si-Mn-Cr-Mo-Ni-V-Co. Obtained dependences could be used in predicting hardness and wear resistance of the deposited metal while changing welding metal chemical composition.

Abstract: This study aims to review variation pattern of moisture content ratio of grains in deep-bed drying process, guide the drying technology design, realize real-time tracking and regulation in drying process, improve the quality of drying process and reduce energy consumption. Based on the moisture diffusion model in thin layer drying process, the principle of mass conservation of deep drying process, state function and irreversible thermodynamics analytic method, we have established and solved basic equations of deep-bed drying of grains, obtained the moisture content ratio of grains and analysis formula of drying velocity distribution in processes of concurrent flow drying, counter flow drying, cross-flow drying and standing drying and resolved the sustained decreasing drying process of grains in the concurrent flow drying and extreme point of drying rate in the counter-flow drying. Under the same conditions of temperature, humidity and air output, the drying velocity in counter-flow drying significantly higher than that in the concurrent flow drying. It means the energy utilization effects in counter-flow drying is better than that in the concurrent flow drying. Drying characteristics of grains in cross-flow drying and standing flow drying are the same, while drying rates in inlet-air side and outlet-air side vary widely. It means that when the layer thickness is 0.5m and the moisture content is over 20%, the drying rate in outlet-air side is nearly zero and the drying uniformity is bad. Tests on 5HP-3.5 recirculation drier shows that maximum deviation between analytic value and measured value in deep drying process is 0.69% and the range scope is -0.27%-0.69%. From the drying characteristics of grains, deviations mainly come from instrument detection deviations. The analytic method has important significance for realizing real-time tracking and regulation in drying process, guiding drying technology design, reducing energy consumption, increasing drying rate and drying machine capacity.

Abstract: Crack propagation after low-cycle fatigue (LCF) deformation has been studied in the chromium martensitic structural steel. Although the study of a fundamental mechanism of fatigue crack growth has received much attention over the last decade, it still remains a sufficiently complex problem and needs full understanding. Moreover, the recent studies show that the cracks propagate discontinuously even on the millisecond timescale, and their growth rate significantly depends on a microstructure of the material. In the present work the boundaries of the former austenitic grains were revealed on the polished surfaces of the thermally treated samples, which subsequently were undergone low-cycle fatigue tests. The experimental studies show that fatigue macrocracks mainly grow along the boundaries of the former austenitic grains, and changetheir propagation direction when crossing the grain boundary, however, remain within 45 ̊ interval with regard the cycling axis. In particular cases, when the boundaries of a martensite packets and those of the former austenite grains lay along the length of a packet, the macrocrack is better formed and with regular borders. After a macrocrack reaches a definite length ~30-50μ, a microcrack is nucleated ahead of the macrocrack tip, and is oriented along the substructure element of the steel. Further deformation tests provide an increase in the length of the main crack via aggregation of microcracks initiated ahead of it during the LCF. In the cases when the macrocrack is deviated, slip bands are formed in martensitic structures along the boundaries of martensite packets (laths). A correlation is revealed between the microcrack components and the substructure elements of the steel as well. The same results were obtained by fractography of the tested and fractured samples. However, in the latter case correlation was established between the cleavage facets and the dimensions of packets.

Abstract: In this paper weldability study of low-alloyed thermal resistant conductor alloys of Al-Cu-Mn and Al-Mg-Si alloying systems with different content of B, Sc, Fe, Zr and ability to resist corrosion in the welding area is presented. The effect of large intensive deformation in the welding area on the phase composition and the size of phases was determined.