Compacted Iron Research Articles

Contribution of shear deformation to grain refinement and densification of iron powder consolidated by high pressure torsion

High Pressure Torsion (HPT) experiments were performed for consolidation of water-atomized pure iron powder (99%) with initial particle sizes of 20-100 gm. The experiments were carried out successfully at room temperature, achieving both low level of residual porosity and significant grain refinement, thanks to the intense shear strain and hydrostatic pressure applied in HPT. X-ray diffraction analysis was carried out on the consolidated samples which revealed no significant proportion of oxides. Considering the inherent heterogeneity of the imposed shear strain in HPT, different positions across the diameters of sample disks were selected for mechanical property and microstructure investigations. The effect of shear deformation on the microstructure and texture was investigated by metallography, scanning electron microscopy, electron backscattered diffraction (EBSD). The micro-hardness and porosity of the samples as a function of shear strain at constant hydrostatic pressure were also measured. The grain size distributions showed homogeneous microstructures with significant grain refinement due to shear deformation. The texture measurements revealed that a shear texture typical to the shear of bcc iron was obtained during HPT compaction of iron powder.

Investigation and optimization of properties of sintered iron/recycled grey cast iron powder metallurgy parts

In this work, the preparation of iron/grey cast iron powder metallurgy parts by recycling machining scraps using target jet milling method is studied. Cast iron powder percentage, compaction pressure, sintering temperature and sintering time are selected as input process parameters. The effects of selected parameters on the response density, transverse rupture strength and hardness of the sintered samples are investigated by response surface methodology, and optimal combinations of input parameters are obtained. Analysis of variance and regression analysis are used to determine the main and interaction effects of input parameters, develop mathematical models and evaluate the validity of the models. Scanning electron microscopy and optical microscopy micrographs are provided to discuss the obtained responses. The results evidenced that the combination of iron/jet-milled grey cast iron is promising for producing powder metallurgy parts with diverse properties and economical considerations. Also, by comparing the optimized results obtained from the proposed models to that from the confirmation tests, the models errors were found to be in a range of 1%−8%.

Structural and magnetic properties of Fe–Al2O3 soft magnetic composites prepared using the sol–gel method

Abstract In this work, powder metallurgy was performed for preparation of iron-based soft magnetic composites (SMCs). For this purpose, iron powders were coated with a thin alumina insulating layer using the sol–gel process, and then compacted for characterization. Microstructural analysis confirmed the formation of an alumina insulating layer with high thermal stability and uniform coverage on the powder surfaces. The alumina coating increased the magnetic permeability of the composites at high frequencies as a result of increased electrical resistivity and decreased eddy current loss. In addition, the different components of the total loss factor were calculated by means of a loss separation method. It was found that by addition of 8 wt.% insulation, the hysteresis loss coefficient increased from 2.7 × 10−3 to 4 × 10−3 while the eddy current loss coefficient decreased from 3.00 × 10−6 to 1.53 × 10−6 as compared with pure iron compacts.

Use of wood as a wrapper for dry isostatic pressing

The regularities of the process of hard and soft wood pressing are studied in the paper, with the purpose of determining the possibility of using wood as a wrapper for dry isostatic pressing, as it meets the basic wrapper requirements. The advantage of this material is a sufficiently low cost, lack of iron powder adhesion and easy removal after pressing. It is shown that the use of soft wood as the wrapper material allows to obtain products from iron powder mixtures with high density and strength. It is found that the use of additional heat treatment improves the wood pressing, as well as the absence of pressing friction on the matrix walls improves the iron powder compaction. The results of the conducted studies can be used in creating powder products of complex shape, which operate under medium and heavy loads.

Model Predictions for New Iron Ore Sintering Process Technology Based on Biomass and Gaseous Fuels

In this paper a new technology for a compact iron ore sintering machine is analyzed. The compact sintering process is based on the massive injection of gaseous fuels and the solid fuel is only agglomerated fine charcoal obtained by biomass. The solid fuel used in this study is obtained by agglomeration of fine charcoal produced from elephant glass which has very short period for production and CO2 capture (less than 6 months in tropical climate). To overcome the lower heat supply into the combustion front of the sintering process the simultaneous injection of oxygen and gaseous fuel is proposed. The proposed methodology is to combine the solid fuel (agglomerated fines charcoal) and steelworks gases in a compact machine to enhance heat and mass transfer with high productivity (about 5 times the conventional large machine). A multiphase mathematical model based on transport equations of momentum, energy and chemical species coupled with chemical reaction rates and phase transformations is used to analyze the inner process parameters. A base case representing a possible actual industrial operation of the sintering machine is used in order to compare different scenarios of practicable operations which represents advanced operations techniques. The model was used to predict six cases of combined operation with biomass and fuel gas utilization: a) Scenario 01 and 02: Wind boxes inflow from N01-N10 of rich mixture of natural gas (NG) +Air +O2, b) Scenario 03 and 04: Wind boxes inflow from N01-N10 of rich mixture of coke oven gas (COG)+Air + O2, c) Scenario 05 and 06: Wind boxes inflow from N01-N10 of mixture of COG+BFG+Air+O2. The model predictions indicated that for all cases, the sintering zone is enlarged and the solid fuel consumption is decreased. In order to maximize the steelworks gas utilization it is recommended the use of mixture of COG and BFG with optimum inner temperature distribution within a compact sintering machine (in this study was the scenario 05), which enhance the productivity keeping good inner temperature distribution which promotes formation of calcium ferrites of structural shape which confers adequate metallurgical properties for blast furnace sinter. This technology is also expected to decrease considerably the specific CO2 emissions, as demonstrated by scenarios simulated. It worthy to mention that, although the solid fuel considered in this work is produced from biomass the gas utilization is attractive due to decrease of the CO2 emissions and the gas mixtures can easily be obtained by using inner steelworks gas.

Residual Stresses in Shot Peened Grey and Compact Iron

AbstractGrey cast iron and compacted graphite iron with a pearlitic matrix are investigated in this study after shot peening using twelve unique combinations of parameters, namely shot size, peening intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from heavy truck cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between −245 MPa to −565 MPa and from 280 μm to 770 μm in depth. Resultant surface compressive stresses decrease with increasing shot size, peening intensity or coverage whereas the affected depth increases with increasing intensity. The increased affected depth is a result from the increased extent and magnitude of plastic deformation. The compacted graphite iron was more affected by shot peening than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

Kinetics of graphite expansion during eutectic solidification of cast iron

The paper introduces a new linear displacement analysis (LDA)/thermal analysis (TA) experimental device for measuring linear displacement during the solidification of cast iron. The experimental device comprises a sand mould encased in a steel shell that prevents mould wall movements. Thus, only the linear displacement caused by the shrinkage or expansion of the metal is recorded by the transducers. Two quartz rods introduced directly at different heights into the liquid metal and connected to two transducers record the linear displacement during the liquid–solid transformation and subsequent cooling. Two thermocouples positioned at the same height with the quartz rods allow for the concomitant TA and LDA and thus for the direct correlation between expansion/contraction and the temperature change during solidification events such as graphite formation. The LDA device was used to study the differences in the solidification mechanisms of irons with different graphite morphologies (lamellar, compacted/vermicular and spheroidal) at carbon equivalent in the range of 3·7–4·4%. The analysis included the LDA and TA curves and full metallographic characterisation of the cast irons. In general, graphite expansion increased as the graphite shape changed from lamellar, to compacted and then to spheroidal. The most important process variables are the magnesium and carbon contents. Higher Mg residual and C in the iron produced more graphite expansion. Compacted graphite (CG) iron was particularly sensitive to the Mg residual. Indeed, the high Mg CG irons exhibited similar graphite expansion to that of spheroidal graphite (SG) iron, while the low Mg CG iron expansion was closer to that of the lamellar graphite (LG) iron. Graphite expansion increased for all data with the time interval over which graphite expansion occurred. It also increased with both carbon and carbon equivalent. The time for graphite expansion increased noticeably with the carbon content of the iron. It did not depend on the graphite shape. By combining TA and LDA, it was possible to plot the evolution of graphite expansion as a function of the fraction solid and thus to understand the kinetics of graphite expansion. The amount of expansion available at the end of solidification was quantified. Such data, when correlated with process variables, will be useful in decreasing microshrinkage and in producing riserless compacted and SG irons.

ВЛИЯНИЕ ТЕМПЕРАТУРЫ ДИНАМИЧЕСКОГО ПРЕССОВАНИЯ НА СТРУКТУРУ И МЕХАНИЧЕСКИЕ СВОЙСТВА КОМПАКТОВ

The results of studies of the effect of pulse compression temperature on the structure and properties of the reduced iron powder compacts with the addition of tungsten carbide nanopowder. It is shown that an increase in temperature leads to an increase in compression quality obtained compacts, forming a perfect fine-grain structure, increased density and microhardness. Keywords: pulse compression, powder materials, pressing temperature, nanopowders, structure.

Investigation of green properties of iron/jet-milled grey cast iron compacts by response surface method

Grey cast iron powder was produced from grey cast iron scraps by jet milling method and mixed with commercial pure iron powder. The morphology of the produced powders and characteristics of the powder mixtures were investigated. The mathematical models were successfully developed to predict green properties of iron/jet-milled grey cast iron compacts using response surface methodology. Using response surface methodology, the effects of the percentage of jet-milled cast iron powder and compaction pressure on green density, green strength, and hardness of the green compacts were analyzed and the optimal combinations of the input process parameters were obtained to maximize the responses. The main and interaction effects of the input process parameters and also the validity of the models were evaluated by using analysis of variance method. Scanning electron microscopy micrographs of the powders and the fracture surfaces were provided to discuss the obtained responses. The results indicated that in addition to fast production rate and economical considerations, the iron/jet-milled grey cast iron powder compacts have adequate green properties for most of the different combinations of the input process parameters.

Structure and Properties of Iron–High-Carbon Ferrochrome Powder Composites

The physical and process properties of ferrochrome powder produced by grinding of lump high-carbon ferrochrome FKh800 are examined. It is found that the ferrochrome is pulverized sufficiently well, and its physical and process properties allow its use to make wear-resistant powder materials. The effect of ferrochrome content on the structure and properties of materials sintered in vacuum from iron powder compacts and powdered FKh800 is studied. The materials containing 30 wt.% FKh800 are found to have high density, bending strength, hardness, and resistance to abrasive wear.

Effect of heat treatment on magnetic properties of iron-based soft magnetic composites with Al2O3 insulation coating produced by sol–gel method

In this study, influences of the annealing process on the magnetic properties of new soft magnetic composite (SMC) materials with alumina insulator coating were investigated. Iron powders were coated with alumina by the sol–gel process at room temperature. The results of energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and density measurements showed that the iron powders were uniformly coated by a thin layer of alumina coating with high thermal stability. Magnetic measurements indicated that the annealing treatment increased the permeability of the composites at low and medium frequency ranges. It was shown that the annealed composites exhibited noticeably higher frequency stability of the magnetic permeability compared to the heat treated pure iron compacts at the same annealing temperature. The results of the loss separation implied that the heat treatment suppressed the hysteresis loss coefficient while it increased the eddy current loss coefficient of the SMCs. The annealed SMCs showed a lower eddy current loss and higher hysteresis loss coefficients compared to the relaxed pure iron compacts due to the preservation of the alumina coating after heat treatment.

Plasmodynamic synthesis of ultradispersed iron oxides

Results of a pilot study of direct plasmochemical synthesis of ultradispersed crystalline iron oxide phases in a high-speed pulse jet of iron-containing electrodischarge plasma that effluxes into a closed volume with the air atmosphere are presented. The synthesized powder contains all main oxide phases, including magnetite Fe3O4, maghemite γ-Fe2O3, and hematite α-Fe2O3. An important feature of the method is the formation of the metastable e-Fe2O3 phase under normal conditions. The minimum average size of coherently diffracting domains (CDD) (particles) of the magnetic phases is observed when they are synthesized at air pressure of 1.0 atm. The powders have high magnetic properties comparable with those of compact iron oxides.

702 鉄粉圧縮成形時におけるDLC被覆工具および異種配合潤滑剤適用時の壁面摩擦挙動について(GS-4 機械材料)

702 鉄粉圧縮成形時におけるDLC被覆工具および異種配合潤滑剤適用時の壁面摩擦挙動について(GS-4 機械材料)

Effect of heating mode on sinterability of carbonyl iron compacts

In recent years, microwave processing has gained wide acceptance as a novel method for sintering metal powders. As compared to conventional sintering, microwave sintering provides rapid and volumetric heating involving conversion of electromagnetic energy into thermal energy within the material. This results in finer microstructures, thereby providing improved mechanical properties and quality of the products. This study examines the dependence of densification, microstructure and mechanical properties on the heating mode of Fe–2%Cu and Fe–2%Cu–0·8%C. The powdered compacts were sintered in conventional (radiation mode) and microwave (2·45 GHz, multimode) furnaces at 1120°C in 90N2–10H2 atmosphere, and comparative analysis of the properties was investigated.

Estimation and optimization of shear strength for compacted iron powders by means of soft computing paradigms

The artificial neural network methodology presented in this paper was trained to predict the green shear strength of compacted samples made from iron powder. Iron powders of three different morphologies admixed with three types of lubricants in different amounts were considered. Green compacts were pressed uniaxially in a square floating die. The more or less cubic slugs were sheared to fracture perpendicularly and parallel to the direction of compaction. From the maximum loads at the start of decohesion the green shear strengths were calculated. Compaction parameters together with corresponding shear strength records were used as sets of data for the training process. The performance of the network was verified by putting aside one set of data and testing the network against it. Comparison of the predicted and experimental data confirmed the accuracy of the model.

Robust 3D gravity gradient inversion by planting anomalous densities

We have developed a new gravity gradient inversion method for estimating a 3D density-contrast distribution defined on a grid of rectangular prisms. Our method consists of an iterative algorithm that does not require the solution of an equation system. Instead, the solution grows systematically around user-specified prismatic elements, called “seeds,” with given density contrasts. Each seed can be assigned a different density-contrast value, allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals. In real world scenarios, some sources might not be targeted for the interpretation. Thus, we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources. In our iterative algorithm, the estimated sources grow by the accretion of prisms in the periphery of the current estimate. In addition, only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations. Therefore, the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place, greatly reducing the demand for computer memory and processing time. Tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources, even when interfering signals produced by nontargeted sources are present. Inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of Quadrilátero Ferrífero, southeastern Brazil, we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations.

Empirical Determination of the Diffusion Coefficient of Carbon in Austenite in Carburizing Phase of the Gas-Carburizing-Sintering Process

Numerical simulation of a mass-diffusion analysis requires several parameters in order to comply with experimental method of gas – carburizing of iron powder compacts. Among the known parameters of mass-diffusion process, the diffusivity is an uncertain parameter in terms of its value. Different formulas can be found in literature but most of them are empirical determined since different results of carbon content are obtained by numerical mass-diffusion analysis. For iron powder compacts with rectangular shape subjected to gas – carburizing – sintering process it was determined the average carbon content in several layers. Based on these determinations and on the characteristics of mass diffusion analysis using Abaqus software it was empirically determined the diffusivity dependency on the carburizing time.

Thermal processes during high-voltage electric discharge consolidation of powder materials

The results of a simulation of the thermal processes occurring within interparticle contacts of powder materials under high-voltage electric discharge consolidation are presented. The thermal processes in the contacts between powder particles are characterized by significant spatial inhomogeneity and time dependence. The determination of the behavior of the interparticle contact zones enables optimization of the pulse electrical current parameters. A good correlation between the modeling and experimental data for compacted iron and heat-resistant steel powders is demonstrated.

The Effects of Sintering Schedule to the Final Properties of Iron Powder Compacts Formed through Warm Compaction Route

Powder forming at above ambient temperature with admixed lubricant to obtain the high quality green compacts is recently discovered, however the effects of sintering schedule to the mechanical properties and microstructures of final products are not explored yet. Therefore, a lab scale warm compaction rig is designed and fabricated to generate green compacts at different forming parameters. Iron ASC 100.29 is used as main powder constituent during this investigation. The defect-free green compacts were sintered in an argon gas fired furnace at different sintering schedule. The mechanical properties and microstructures of sintered parts were evaluated. The results revealed that the mechanical properties and microstructures of sintered products are affected by the forming temperature and sintering schedule. Therefore, the suitable forming temperature and sintering schedule are identified for the production of high quality components.

Enhanced electromagnetic characteristics of porous iron particles made by a facile corrosion technique

For the first time, detailed investigation into the formation of porous iron particles (PIPs) via a facile corrosion technique is reported. The complex permittivity, permeability, and electromagnetic (EM) wave absorption properties of the products were characterized at 2–18GHz. Compared with compact iron particles, PIPs had higher complex permittivity and permeability, which were strongly dependent on their microstructure. Wax composites containing 20vol% PIPs showed a strong absorption peak of −42.2dB at 13.2GHz, a low area density of 0.387gcm−2, and a bandwidth (≤−20dB) of about 10.0GHz. The enhanced multipolarization, multiple dispersion, and interference of EM waves in pores led to excellent EM wave absorption properties. The PIPs may be candidates for EM wave absorption materials with thinness, lightness, width, and strength.