Fe Wt Research Articles

Effect of Cr-Rich Phase Precipitation on Magnetic and Mechanical Properties of Fe-20% Cr Alloy

Magnetic Hysteresis Loop (MHL) and micro-Vickers hardness measurements were carried out in isothermal aged Fe-20 wt. % Cr alloy. The results were compared with the existing atom probe data at similar heat treated conditions. Coercivity and hardness of the alloy was increased and remanence of the alloy was decreased with the increase in ageing time. Such increase in the magnetic and mechanical hardness was due to the nucleation and growth of Cr rich α' phase. The size of the Cr rich α' phase precipitates were increased and the number density of the precipitates were decreased with the increase in ageing time observed by atom probe analysis. In this work a good correlation between hardness (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> ) and coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) was found with the combined effect of precipitate size (r) and number density (n). A linear relationship was found with the change in coercivity and hardness of the alloy indicating that the MHL technique would be a good Non-Destructive Evaluation (NDE) tool for the evaluation of thermal embrittlement in structural components made of Fe-Cr alloys.

Microstructure and texture evolution of strip casting 3 wt% Si non-oriented silicon steel with columnar structure

An Fe-3 wt%Si strip with columnar structure and pronounced {0 0 1}〈0 v w〉 texture was produced using a twin-roll strip caster. Then the as-cast strip was cold-rolled and annealed. The microstructure and texture evolution along the processing steps was investigated. It is found that inhomogeneous microstructure is produced in both cold-rolled and final annealed samples due to the large initial grains. The cold rolling texture is dominated by pronounced a-fiber texture and relatively strong γ-fiber texture. The final recrystallization texture is characterized by {0 0 1}〈0 1 0〉, {0 0 1}〈2 1 0〉, {1 1 0}〈0 0 1〉 texture and a slightly shifted {1 1 1}〈1 1 2〉 component. The microstructural inhomogeneity plays an important role in the texture evolution.

Effects of Residual Elements Arsenic, Antimony, and Tin on Surface Hot Shortness

Scrap-based electric arc furnace (EAF) steelmaking is limited by a surface cracking problem in the recycled steel products, which is known as surface hot shortness. This problem originates from the excessive amount of copper (Cu) in the steel scrap, which enriches during the oxidation of iron (Fe) and consequently melts and penetrates into the austenite grain boundaries. In this article, the effects of arsenic (As), antimony (Sb), and tin (Sn) on surface hot shortness were investigated. A series of Fe-0.3 wt pct Cu-x wt pct (As, Sb, or Sn) alloys with x content ranging from 0.06 to 0.10 wt pct was oxidized in air at 1423 K (1150 °C) for 60, 300, and 600 seconds inside the chamber of a thermogravimety analyzer (TGA) where heat is supplied through infrared radiation. Scanning electron microscopy (SEM) investigations show that (1) the presence of Sb and Sn results in severe grain boundary cracking, whereas the presence of As does not, (2) open cracks with Fe oxides were found beneath the oxide/metal interface in the Sb and Sn alloys, and (3) the oxide/metal interfaces for all As, Sb, and Sn alloys are planar. Penetration experiments of pure Cu and Cu-30 wt pct Sn liquid were also conducted in the chamber of a hot-stage confocal laser scanning microscopy (CLSM) in nonoxidizing atmosphere: (1) on the Fe-35 wt pct manganese (Mn) alloys to study the correlation between cracking and grain boundary characters, and (2) on the pure Fe substrates to exclude the bulk segregation effects of Sn on grain boundary cracking. It was found that grain boundary cracking rarely took place on low-energy grain boundaries. The results also suggest that the bulk segregation of Sn in the substrate is not necessary to promote significant grain boundary cracking, and as long as the liquid phase contains Sn, it will be highly embrittling.

SPS densification behavior of W-5.6Ni-1.4Fe heavy alloy powders

Spark plasma sintering (SPS) method was used to sinter two different types of 93W-5.6Ni-1.4Fe (wt pct) heavy alloy powders which were respectively prepared by simple mixing and high-energy ball milling (HEBM) for 40 h. In SPS processing, the powder compacts were heated at 100 °C/min to the desired sintering temperature with 5 min holding. The SPS densification behavior of the two types of powders was investigated. For the simple mixed powders, the compacts start to shrink around 850 °C, and the densification is enhanced by diffusion and plastic deformation with the increase of temperature. Consequently the compacts shrink effectively and obtain nearly full density around 1230 °C. While for the as-milled powders, recovery and recrystallization occur between 700–850 °C due to the crystal lattice distortion and defects resulted from HEBM, causing the soften of particles and a slight shrink of compacts. When increasing temperature, nanosintering of W crystallines in the matrix occurs in the inside of the composite powders, and the densification rate accelerates and maximizes at about 1050 °C. Owing to the improved activity of powders from HEBM, the tungsten grains coarsen rapidly in the sintering, simultaneously, the harmful intermetallic phases Ni2W4C and Fe6W6C are generated.

The Use of Fe-30% Ni and Fe-30% Ni–Nb Alloys as Model Systems for Studying the Microstructural Evolution during the Hot Deformation of Austenite

The development of physically-based models of microstructural evolution during thermomechanical processing of metallic materials requires knowledge of the internal state variable data, such as microstructure, texture, and dislocation substructure characteristics, over a range of processing conditions. This is a particular problem for steels, where transformation of the austenite to a variety of transformation products eradicates the hot deformed microstructure. This article reports on a model Fe-30 wt% Ni-based alloy, which retains a stable austenitic structure at room temperature, and has, therefore, been used to model the development of austenite microstructure during hot deformation of conventional low carbon–manganese steels. It also provides an excellent model alloy system for microalloy additions. Evolution of the microstructure and crystallographic texture was characterized in detail using optical microscopy, X-ray diffraction (XRD), SEM, EBSD, and TEM. The dislocation substructure has been quantified as a function of crystallographic texture component for a variety of deformation conditions for the Fe-30% Ni-based alloy. An extension to this study, as the use of a microalloyed Fe-30% Ni–Nb alloy in which the strain induced precipitation mechanism was studied directly. The work has shown that precipitation can occur at a much finer scale and higher number density than hitherto considered, but that pipe diffusion leads to rapid coarsening. The implications of this for model development are discussed.

Compositional depth profile investigation of plasma nitriding by multiple analyses techniques

Compositional depth profile in plasma nitriding is investigated by several experimental techniques including EDS, GDOES and SIMS as well as a calculated method. Plasma nitriding was carried out on high purity iron substrate at a temperature of 550 °C in an atmosphere of 75 vol.% H 2–25 vol.% N 2 for time periods of 1, 2, 5 and 10 h. SEM and XRD methods were used for microstructural evaluation and phase identification. According to EDS, GDOES and calculated data, composition of the compound layer reached nearly to Fe-8 wt% N and Fe-6 wt% N indicating ε-Fe 2–3N and γ′-Fe 4N nitrides were formed, respectively. Although nitrogen concentration was decreased to nearly zero close to the nitrided surface, calculated data and SIMS profiles show very smooth gradient in diffusion zone down to several hundreds of micrometers. The results of compositional depth profiling by EDS, GDOES and SIMS indicated good agreement between experimental findings and, thus, the techniques completed one another. It was found that EDS and GDOES are appropriate for analysis of Fe and N in the compound layer, but both have limitations for profiling of nitrogen in the diffusion zone. SIMS, on the other hand, was distinguished as a professional technique for accurate measurement of nitrogen within the diffusion zone. The experimental depth profiles indicated good consistency with calculated diffusion profiles for all treatment cycles.

Structural and phase transformations in ferromanganese alloys during deformation under pressure

Using optical metallographic, TEM, Mossbauer spectroscopy, and X-ray analysis the structural and phase transformations in Fe-(3–55) wt % Mn alloys during shear deformation under pressure were investigated. It is established that a large deformation under high pressure causes the formation of a nanocrystalline structure with grain sizes of 40–60 nm. Nanostructure increases the hysteresis of inverse (hcp-fcc) transformation and stabilizes the (hcp) ɛ phase in alloys containing more than 40 wt % Mn, up to normal conditions. The Fe-3 wt % Mn alloy after shear under pressure treatment became nanostructured, retaining the original bcc phase state.

Characterization of electrodeposited Ni–Fe–SiC alloys for microelectromechanical applications

Ni–Fe–SiC alloy is a promising material for the fabrication of microactuators. In this article, the electrolytic codeposition technique is used to deposit the Ni–Fe–SiC composite onto stainless-steel substrates, where nickel becomes alloyed with iron as the binder phase, and SiC becomes alloyed as dispersed particles. Analysis of the morphology indicates that the deposited SiC nanoparticles are compact, with the orientation of the deposited crystal planes indexed as (111), (200), (220), (311), and (222). The resistivity of the deposited SiC nanoparticles is about 30×10−8 Ω m. When the loading of Fe (wt %) ranges from 10% to 50% in the deposit, the electrodeposit shows a strong paramagnetism with a lowest value of coercivity of 2.75×10−2 A/m. In addition, the remanence shows a monotonic decrease with an increasing iron content in the deposit. It is demonstrated that the electroformed Ni–Fe–SiC alloy has better electromagnetic properties and a higher corrosion resistance (with a corrosion rate of 0.17 mg/dm2 h 2M HCl) than the electroformed Ni–Fe alloy (with a corrosion rate of 0.23 mg/dm2 h).

The effect of strain path reversal on high-angle boundary formation by grain subdivision in a model austenitic steel

The effects of large strain and strain path reversal on deformation microstructure development in austenite below recrystallization temperature were studied by hot torsion using an Fe-30 wt.% Ni model alloy. Results show that high-angle boundaries (HABs) can be generated by both dislocation accumulation and subgrain rotation. Multiple strain reversals lead to less well-developed HABs in the original grains compared to single reversal deformed to the same strain. This is attributed to subgrain rotation mechanism being less effective at small strains.

Anelastic Behavior of Nanocrystalline Fe-Cr Alloy Obtained by Mechanical Alloying

Anelastic behavior of nanocrystalline Fe-17 wt.%Cr alloy obtained by mechanical alloying was investigated using a multifunctional internal friction apparatus. Internal friction (Q-1) and relative dynamic modulus (f2) have been measured as a function of temperature by free-decay method from room temperature to 400oC for the ball-milled Fe-17 wt.%Cr alloy The specimens with different milling time were examined by XRD to determine the solid solubility of Fe and Cr atoms and detect the lattice strain of the compacted specimen before and after annealing. TEM observation was employed to obtain further information about the morphology and microstructure, especially crystalline size, of the milled Fe and Cr mixture powders. It has been suggested that the anelastic behavior of ball-milled nanocrystalline Fe-17 wt.%Cr alloy origins from the viscoelastic sliding at the interfaces resulting from the thermally-activating process. The damping increasing of the specimen with smaller grain sizes is larger than that of the specimen with larger grain sizes with increasing temperature since the former contains more interfaces. The increase in the relative dynamic modulus is attributed to the structural reordering with the lowering of lattice micro-strain that is produced during milling when temperature is over 300oC.

Thermal Stability in Nanocrystalline Fe-30 Wt Pct Ni Alloy Induced by Surface Mechanical Attrition Treatment

By means of surface mechanical attrition treatment (SMAT), a nanocrystalline surface layer is produced in Fe-30 wt pct Ni alloy, accompanying the formation of the strain-induced martensite. The thermal stability of nanocrystalline martensite and parent phase austenite in Fe-30 wt pct Ni alloy is studied by X-ray diffraction (XRD) and transmission electron microscope (TEM). The grain growth kinetics parameters, time exponent, n, and activation energy, Q, for both martensite and austenite, are determined, respectively. The TEM observations indicate that abnormal grain growth occurs during annealing at high temperatures.

Magnetic characteristics of HPT deformed soft-magnetic materials

Five sets of soft-magnetic metals, such as pure Fe, pure Ni, Fe-3 wt% Si, Fe-6.5 wt% Si and Fe-17 wt% Co, were subjected to high pressure torsion (HPT) up to strain levels where a saturation of the microstructural refinement is observed. Following HPT at 77, 293 and 723 K, transmission electron microscopy (TEM) was used to study the grain size and grain shape of the severely deformed metals. The coercivity H C was characterized in a magnetic closed system by using ring shaped samples. Magnetic measurements obtained on ring shaped samples give a much higher accuracy for determining the coercivity. Depending on the material the mean microstructural sizes in the steady state vary from 300 nm at 723 K to 30 nm at 77 K, respectively. The coercivity of the deformed materials first increases with decrease in grain size. Once the crystallite size is far below 100 nm the coercivity shows a strong decrease.

Characterisation of the Portevin-Le Châtelier effect affecting an austenitic TWIP steel based on digital image correlation

When strained in tension, high-manganese austenitic TWIP steels achieve very high strength and elongation before necking. They also present serrated flow within a certain range of temperatures and strain rates. A consequence of this jerky flow is the appearance of strain localisation in the form of narrow deformation bands apparent on the surface of the sample. This phenomenon arises from the dynamic interaction between solute atoms and mobile dislocations, otherwise known as dynamic strain ageing (DSA). In this study, the heterogeneous deformation of a Fe–20wt.%Mn–1.2wt.%C grade has been investigated at room temperature and at different strain rates by means of digital image correlation (DIC) for spatially resolved strain measurements made in situ during tensile tests. Simple tensile tests have also been conducted at different temperatures in order to investigate the evolution of the type of serrations and their influence on the bulk mechanical properties. The results of tests performed at room temperature and at two different strain rates, indicate that the plasticity is entirely governed by the appearance of localised deformation bands, similar to those observed in materials that exhibit the Portevin-Le Châtelier (PLC) effect. However, no critical strain for the onset of the phenomenon could be determined. The origin of these observations is discussed in this paper. It is proposed that the mode of propagation of the bands is dependent on the strain rate and the strain level. Moreover, it is shown that the band propagation is well correlated with the different types of serrations appearing on the stress–strain curve. These results match the characteristics of a classical DSA effect and help to shed light on the remarkable properties achieved by this material.

Electrical and optical properties of iron-doped CdO

Thin films of Fe-doped CdO with 1.3, 2.0, 2.3, 3.0, and 5.7 wt.% were prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence and diffraction. Results show that doping of CdO with Fe enhances the film's [111] preferred orientation and causes slight shifts in the (111) Bragg angle towards higher values. The samples were investigated with a UV–VIS–NIR absorption spectroscopy and dc-electrical measurements. It was observed that there is a complicated dependence of bandgap on the Fe wt.% content in the film. In addition, light doping with Fe improves the dc-conduction parameters of CdO, so that with 1.3 wt.% Fe doping, the mobility increases by about 6 times, conductivity by 24 times, and carrier concentration by about 4 times, relative to undoped CdO film. The observations were analysed by using the available models (with a slight modification) for the coexistence of bandgap widening and bandgap narrowing.

Fe-8 wt%Ni 나노합금분말 사출성형체의 소결특성 및 표면조도

Development of nanoparticulate materials technology is essential to processing of highly functional nanoparticulate materials and components with small and complex shape. In this paper, the effect of particle size on surface roughness and shrinkage of sintered Fe-8 wt%Ni nanopowder components fabricated by PIM were investigated. The Fe-8 wt%Ni nanopowder was prepared by hydrogen reduction of ball-milled Fe<TEX>$_2$</TEX>O<TEX>$_3$</TEX>-NiO powder. Feedstock of nanopowder prepared with the wet-milled powder was injection molded into double gear shaped part at 120<TEX>$^{\circ}C$</TEX>. After sintering, the sintered part showed near full densified microstructure having apparently no porosity (98%T.D.). Surface roughness of sintered bulk using nanopowder was less than 815 nm and it was about seven times lower than 7 <TEX>$\mu$</TEX>m that is typically obtainable from a sintered part produced from PIM.

Single-Walled Carbon Nanotube Materials as T2-Weighted MRI Contrast Agents

With their unique nanoscalar properties, single-walled carbon nanotube (SWNT) materials are widely studied for various biological applications. Herein, we report the efficiency of full-length HiPco SWNTs and ultra-short SWNTs (US-tubes) as T2-weighted MRI contrast agents. Analysis has concluded that the superparamagnetic SWNT materials (especially US-tubes) are a new class of high-efficacy contrast agents having performance contributions from both the iron catalyst nanoparticles (originating from the synthesis of SWNT materials) and the carbon SWNT material itself. The superparamagnetic US-tubes with their short length (<100 nm), negligible metal content (<1% Fe (wt %)), and superior T2 relaxation efficiency (T2 = 31.7 ms per mg SWNT at 3 T and 37 °C) are the most promising candidates for advanced applications such as molecular and cellular imaging using MRI.

Study on the Si penetration into Fe sheets using PVD method and its application in the fabrication of Fe-6.5wt.% Si alloys

Abstract FeSi (12 wt.% Si) and Si were alternatively deposited on pure iron (Fe) substrates by direct current magnetron sputtering. Subsequent annealing in vacuum at 1150–1190 °C results in penetration of Si into the substrate. Cross-sectional microstructure and Si concentration were investigated by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The penetration mechanism is found to depend greatly on Si amount in the as-deposited films. When FeSi/Si/FeSi/Si/FeSi was deposited on the Fe substrate, the Si penetration is controlled by phase-boundary migration, while a diffusion-controlling penetration is observed in FeSi/Si/FeSi deposited samples. Fe-6.5 wt.% Si sheet with thickness of 0.35 mm is obtained through the deposition of FeSi/Si multilayer on a Fe-3 wt.% Si sheet together with subsequent annealing at 1180 °C for 2 h.

Fe-Si/Fe 혼합분말의 온간성형 및 자성특성

3-D shape soft magnetic composite parts can be formed by general compaction method of powder metallurgy. In this study, the results on the high density nanostructured Fe-Si/Fe composite prepared by a warm compaction method were presented. Ball-milled Fe-25 wt.%Si powder, pure Fe powder and Si-polymer were mixed and then the powder mixture was compacted at various temperatures and pressures. Pore free density of samples up to 95% theoretical value has been obtained. The warm compacted sample prepared at 650 MPa and 240<TEX>$^{\circ}C$</TEX> had highest compaction properties in comparison with other compacts prepared at 300, 400 MPa and room temperature and 120<TEX>$^{\circ}C$</TEX>. The magnetic properties such as core loss, magnetization saturation and coercivity were measured by B-H curve analyzer and vibration sample magnetometer.

Transient Behavior of Inclusion Chemistry, Shape, and Structure in Fe-Al-Ti-O Melts: Effect of Titanium Source and Laboratory Deoxidation Simulation

In the present study, laboratory-scale deoxidation experiments in a vacuum-induction furnace (VIF) were carried out to elucidate the evolution of inclusions during transient stages after a titanium addition. Three different titanium sources (Fe-70 wt pct Ti, Fe-30 wt pct Ti, and titanium granules) were employed and the results were compared in terms of the inclusion chemistry, structure, and morphology. It was found that, immediately after titanium additions to an aluminum-killed melt, titanium-containing inclusions, which are either single-phase or dual-phase particles having a certain amount of titanium and are contrary to melt equilibrium predictions, were formed. Analysis by transmission electron microscope (TEM) suggested that these inclusions could be Al2TiO5. The change in the inclusion chemistry was accompanied by a shift in the inclusion morphology from spherical to irregular. With time, the inclusion chemistry shifted back toward the thermodynamically stable Al2O3, but the change in morphology remained. The temporary Al2TiO5 inclusions were formed as a result of local high content of titanium immediately after and at the vicinity of the titanium addition. When comparing the different titanium sources, it was found that they can be ranked as Ti > Fe-70 pct Ti > Fe-30 pct Ti, in terms of the amount of titanium-containing inclusions produced during the transient stage.

Removal of Tin and Copper from Liquid Iron by Al2O3-Saturated Ca-CaCl2 Slags at 1448 to 1648 K

The removal of tin and copper from liquid iron by Al2O3-saturated Ca-CaCl2 slags was carried out in separate alumina crucibles at 1448 to 1648 K that showed small partition ratios of less than 1. The tin content of the liquid iron typically decreased from its initial value of 50 to 40 wt pct and the (gross) copper content of the iron-copper mixture from 50 to 45 wt pct, at equilibrium. The small refining efficiencies (37 pct, maximum) of the slags, the initial composition of which were, in most cases, Ca-50 wt pct CaCl2, may be attributed to the significant dissolution in them of alumina, up to 42.0 wt pct (29.6 mol pct), in experiments with Sn, and up to 54.4 wt pct (38.6 mol pct), in experiments with Cu. Treating Ca as the solvent, a number of interaction coefficients such as $$ \varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }} ,\,\varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{{{\text{CaCl}}_{ 2} }} ,\,\varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{\text{Sn}} ,\,\varepsilon_{{{\text{CaCl}}_{ 2} }}^{{{\text{CaCl}}_{ 2} }} ,\,\varepsilon_{{{\text{CaCl}}_{ 2} }}^{\text{Sn}} , $$ and $$ \varepsilon_{\text{Sn}}^{\text{Sn}} $$ as well as the activity coefficient $$ \gamma_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{0} $$ were all determined at 1448 K. The activity of Ca (relative to pure liquid Ca) was obtained as approximately 0.65 to 0.75 in the system. Further, the two partial molar mixing/excess properties of alumina $$ \bar{H}_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{M} $$ and $$ \bar{S}_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{XS} $$ in the alumina-saturated Ca-17 pct CaCl2- ~37 pct Al2O3 (molar basis) slag were evaluated and found to be −118.3(±10.8) kJ/mol and −0.062(±0.007) kJ/K·mol, respectively, at 1448 to 1648 K. In addition, in view of the reported success of CaC2 as a refining agent, some experiments were carried out with CaC2-CaF2 mixtures in alumina, magnesia, and graphite crucibles at 1873 K, to remove tin from liquid Fe-2 wt pct Sn. However, alumina and magnesia crucibles leaked owing to their dissolution in calcium fluoride; in graphite crucibles, only a small transfer of tin, 3 to 7 pct of its initial mass, to the slag phase took place.