Iron-chromium Alloys Research Articles

Study of Fe-Ni(Cr) Alloy and Nano-Al2O3 Particles Composite Coating Prepared by Laser Cladding

The experiments of laser cladding Ni-coated nano-Al2O3 powder were made on 2Cr13 stainless steel using 7kW CO2 laser processing system. The microstructure and mechanical characteristics of composite coating were tested by scanning electronic microscope (SEM), X-ray diffraction (XRD), energy dispersion analyzer of X-ray (EDAX) and microhardness tester. The results showed that the composite coating was composed of superfine cellular dendritic structure. The X-ray diffraction data revealed that the cellular grains were composed of nano-Al2O3 particles, iron nickel alloy and iron chromium alloy. The mechanical characteristics of composite coating greatly increased. Compared with parent metal, the average hardness of composite coating increased by 1 time, and its wear property increased by 1.25 times.

Oxygen reduction on strontium-doped LaMnO 3 cathodes in the absence and presence of an iron–chromium alloy interconnect

Oxygen reduction on a Sr-doped LaMnO 3 (LSM) electrode of a solid oxide fuel cell (SOFC) is investigated in the absence and the presence of a Fe–Cr alloy interconnect. The results show that oxygen reduction is controlled by a surface exchange reaction that involves dissociative adsorption and diffusion of oxygen on the LSM electrode surface, and migration of oxygen ions from the LSM to the yttria stabilized zirconia (YSZ) electrolyte lattice at the three-phase boundary (TPB). In the presence of Fe–Cr alloy, the reaction order and activation energy of the surface exchange process are similar to those in the absence of Fe–Cr alloy. This indicates that the presence of gaseous chromium species simply reduces the active sites for the surface exchange reaction by blocking oxygen vacancy formation on the LSM electrode surface. On the other hand, the Cr 2O 3/(Cr,Mn) 3O 4 solid species deposited on the YSZ electrolyte surface primarily inhibits the migration of oxygen ions into the YSZ electrolyte, as indicated by a significant increase in the activation energy of the migration process of the oxygen ions into YSZ electrolyte.

Magnetically Induced Immiscibility in the Ising Model of FeCr Stainless Steel

The iron-chromium alloy system has an unexplained anomaly: although there is a broad miscibility gap it appears to be favorable for chromium to dissolve in iron. This is consistent with ab initio calculation, but no simpler physically intuitive picture has been presented. Here it is shown that the Ising model, based on the bcc lattice with antiferromagnetic and ferromagnetic species, has the potential to exhibit similar behavior, with a skew miscibility gap arising from the solubility of antiferromagnetic species on nonadjacent sites. Essential characteristics of stainless steel (high Cr solubility and surface segregation) are correctly reproduced. Under some conditions, magnetization increases with temperature. The equilibrium miscibility gap due to mixed magnetism and segregation-driven positive dM/dT are fundamental features of the bcc Ising model itself, not just FeCr.

Effect of surface deposited rare earth oxide gel characteristics on cyclic oxidation behavior of Fe20-Cr alloys

Rare earths have been used to increase high temperature oxidation resistance of many chromium dioxide and alumina forming alloys. These rare earths can be added as elements (or as oxide dispersions) to the alloys or applied as an oxide coating to the alloy surface. The sol-gel technique is considered to be very efficient to apply fine oxide particle coatings. Oxide gel coatings of various rare earths such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, yttrium, erbium and ytterbium have been applied to an iron-chromium alloy to determine their influence on the cyclic oxidation behavior (RT-900 °C) of the alloy. The morphology and coverage of the rare earth oxide gels varied with the type of rare earth. The cyclic oxidation resistance of the alloy increased with increase in time at temperature required to reach a specific chromium dioxide layer thickness and this in turn was influenced by the rare earth ion radius and characteristics of the rare earth oxide coating such as morphology, stability, coverage, resistance to thermal stresses and consequently adhesion.

Effect of alloying additions and preoxidation on high temperature sulphidation resistance of iron–chromium alloys

High temperature corrosion of structural alloys in sulphur bearing environments is many orders of magnitude higher than in oxidising environments. Efforts to increase sulphidation resistance of these alloys include addition of alloying elements. This paper reports the effect of yttrium, aluminium and yttrium plus aluminium addition on the sulphidation behaviour of an Fe–20Cr alloy in H2–2%H2S at 700 and 800°C. The effect of preoxidation of these alloys on sulphidation behaviour was also investigated. The initial stages of sulphidation of these alloys were observed and overall sulphidation kinetics was determined. In the presence of yttrium, the sulphidation rate of the alloy decreased by an order of magnitude, and the sulphide layer on the FeCrY alloy was significantly thinner than that formed on the FeCr alloy. Aluminium addition increased sulphidation resistance even more. The FeCrAl and FeCrAlY alloys exhibited parabolic sulphidation kinetics at the two temperatures. On both alloys, initial chromium sulphide (Cr2S3) formation at grain boundaries and Al2S3 and FeCr2S4 formation over the grains was followed by formation of an outer Cr2S3 layer over a mixed sulphide layer. Preoxidation of the two alloys resulted in an ‘incubation period’ with practically no sulphidation during subsequent exposure to S bearing environments. After this incubation period, the sulphidation behaviour of the FeCr alloy was similar to that when the alloy was not preoxidised. The incubation period of the FeCrAl alloy was significantly longer, over 45 h, compared with 2 h for the Al free alloy. Based on thermogravimetric as well as SEM, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) data, sulphidation mechanisms have been proposed for the alloys before and after preoxidation.

Effect of Rhenium Addition on Tungsten Diffusivity in Iron-Chromium Alloys

The Alloying effect of Re on the diffusivity of W in Fe-15 mol%Cr based alloys was investigated experimentally using the Fe-15Cr/Fe15Cr-5W and Fe-15Cr-1Re/Fe-15Cr-5W diffusion systems. In these systems, a single ferrite phase existed stably at 1473 K, and Fe and W atoms interdiffused at 1473 K without any attendant changes in the Cr concentration of 15 mol% in them. The measured diffusion length of W atoms was shorter in the Re-containing diffusion system than the Re-free one. Following the binary Boltzmann-Matano method, an apparent interdiffusion coefficient at 1473 K was estimated to be 7:1 � 10 � 15 m 2 /s in the Re-free diffusion system and 1:5 � 10 � 15 m 2 /s in the Recontaining diffusion system. Thus, the presence of Re in the alloy worked to suppress the atomic diffusion of W in a ferrite phase. [doi:10.2320/matertrans.47.2106]

Initial Stages of Iron-Chromium Alloys Passivation in Acid Sulfate Solutions

Upon jumpwise applied “maximal critical passivation potential” (that is, the most positive potential at which Fe-Cr alloys still remain in the state of active-passive transition), chromium can continuously accumulate at the surface because of the selective dissolution of iron atoms. This probability can actualize at a chromium content in the alloy of up to 27.7% and pH < 1.2. Oxygen-containing compounds of bivalent chromium are the passivating agents at pH < 1.2 those of trivlent chromium, at pH ≥ 1.2.

Corrosion rate of iron and iron–chromium alloys in CO 2 medium

In the present paper corrosion of iron (99.95%) and iron–chromium alloys (1–5% Cr) were investigated by mass loss and ac impedance. These low-chromium content alloys have been proposed as an intermediate corrosion-performance material between C-steel and stainless steels to be used in oil plants. It was observed that small contents of chromium in the alloy decrease the corrosion attack only in very specific pH range 4 < pH < 5. In CO 2 medium, mass loss showed a linear behaviour with respect to time whereas in the presence of acetate the results were not monotonic. By ac impedance, it was found that R p - 1 and R t - 1 vary proportionally with respect to mass loss. A discussion concerning the online monitoring of the corrosion rate is presented.

Influence of bovine serum albumin in sulphuric acid aqueous solution on the corrosion and the passivation of an iron–chromium alloy

The adsorption of bovine serum albumin (BSA), and its influence on the electrochemical behaviour in deaerated 0.05 M H 2SO 4 solution of a ferritic stainless steel, Fe–17Cr, was studied by electrochemical methods (time dependence of the corrosion potential E cor, polarization curves, EIS) and surface analysis techniques (PM-IRRAS, XPS). The electrochemical measurements show a corrosion inhibition by the BSA at E cor. The charge transfer resistance decreases and hence the corrosion current of the alloy increases with immersion time at E cor, but this phenomenon is much less marked in the presence of BSA. Impedance measurements performed after passivation of the alloy at 0 V versus SSE show that the presence of protein has no effect on the electrochemical behaviour of the passivated alloy surface. Surface analysis of the stainless steel samples by PM-IRRAS and XPS shows that chemically intact BSA molecules are adsorbed on the surface at E cor and 0 V. The amount of adsorbed BSA is quite similar at both potentials. All these results demonstrate that the adsorption of BSA takes place on the Fe–17Cr surface both at the corrosion potential and in the passive region, and the BSA has a corrosion inhibition effect when the surface is not fully passivated.

Classical Many-Body Potential for Concentrated Alloys and the Inversion of Order in Iron-Chromium Alloys

Atomistic simulations of alloys at the empirical level face the challenge of correctly modeling basic thermodynamic properties. In this Letter we propose a methodology to generalize many-body classic potentials to incorporate complex formation energy curves. Application to Fe-Cr allows us to correctly predict the order vs segregation tendency in this alloy, as observed experimentally and calculated with ab initio techniques, providing in this way a potential suitable for radiation damage studies.

Corrosion studies of different ferrous alloys for rolling cylinders

The aim of this work is to study the corrosion behaviour in chloride media of a high chromium iron alloy. The influence of the surface finishing as well as the heat treatment was analysed. The technique employed for measuring the corrosion behaviour was the Electrochemical Impedance Spectroscopy, an electrochemical technique that allows the observation not only of the corrosion rates but also the changes on the corrosion mechanism of the alloy. The results showed that it is worth performing a double tempering and a having smoother surface finishing only for long exposure periods. A comparison between different oxidising conditions was also performed simulating the life in service of the hot rolling cylinders and revealed an increase in the protective properties as the oxidising time increased due to the chromium present on the alloy (18%).

CARPENTER GLASS SEALING 27

Abstract Carpenter Glass Sealing 27 is a ductile chromium-iron alloy that has been used for strong glass-to-metal seals in electronic and vacuum tubes, and incandescent and fluorescent lamps. It exhibits no phase transformation up to 1150 deg C (2100 deg F). This datasheet provides information on composition, physical properties, and elasticity. It also includes information on corrosion resistance. Filing Code: FE-136. Producer or source: Carpenter Technology Corporation.

Corrosion behaviour of different hot rolled steels

The oxidation–corrosion behaviour of hot rolled alloys was examined by electrochemical impedance spectroscopy. The corrosion behaviour of the non-oxidised alloys was first determined in order to have a reference behaviour. Then, each alloy was oxidised for 1 and 3 days at 650 °C in air and its corrosion behaviour was also determined. For all the alloys, Fe 2O 3 was formed at the scale–gas interface. However, the Fe 2O 3 crystallographic structures varied as a function of the alloy composition. Differences in the corrosion behaviour are due to the thickness, the microstructure and the porosity of the scale. The new graphite chromium iron alloy (Hi-Cr + C) have an oxidation–corrosion behaviour close to the indefinite chill double paired (ICDP) one and is therefore thought to be a good candidate to replace the ICPD alloy. In the case of the high speed steel (HSS) alloy, the oxidation–corrosion kinetics are too slow to prevent sticking problems. The Co addition decreases the corrosion–oxidation rates for the non-oxidised and oxidised samples but this effect is limited in time.

プラズマ窒化した鉄‐クロム合金中の固溶窒素濃度に関する研究

プラズマ窒化した鉄‐クロム合金中の固溶窒素濃度に関する研究

Oxide reduction and diffusion in Fe-Cr alloy honeycombs

The goal of this study is to develop practices for evaluating and predicting the microstructural evolution of directly reduced iron-chromium alloys. This fundamental knowledge is being applied to a process developed at the Georgia Institute of Technology to fabricate metal honeycomb extrusions. A paste composed of oxide powders, binders and lubricants is extruded through a die of the desired cross-section and subsequently reduced to metal with hydrogen. The effects of time, temperature and composition on the extent of reduction and diffusion in reducing Fe2O3-Cr2O3 powder mixtures is investigated. The thermodynamics and kinetics of Fe2O3-Cr2O3 reduction are evaluated in terms of the free energy of formation as well as reducing species. The kinetics of the microstructural changes are evaluated through diffusion measurements. A thermodynamic model for Fe2O3-Cr2O3 was developed and used to determine the maximum amount of Cr2O3 that would reduce when in contact with iron as a function of the $\frac{P_{H_{2}}}{P_{H_{2}O}}$ ratio . Diffusion studies consisted of Fe-Cr2O3 couples held at temperature in a reducing atmosphere. Cr diffusion in Fe showed a concentration dependence for the geometries investigated.

The nitriding kinetics of iron-chromium alloys; the role of excess nitrogen: Experiments and modelling

To investigate the morphology and the growth kinetics of nitrided layers of Fe-Cr alloys, nitriding experiments were performed for alloys with 4.3, 7.7, 14.0, and 21.5 at. pct Cr. The precipitation morphology of the nitrided samples was investigated with light optical microscopy and scanning electron microscopy (SEM). The elemental compositional variation was determined with electron probe microanalysis. To describe the evolution of the thickness of the nitrided layers, a numerical model was developed that has as important (fit) parameters: the surface nitrogen content, the solubility product of chromium and nitrogen dissolved in the ferrite matrix, and a parameter defining the composition of the precipitated chromium nitride. Fitting of the model to the experimental data demonstrated for the first time that mobile and immobile excess nitrogen is present in the nitrided layers and that the mobile excess nitrogen considerably influences the nitriding rate.

Modeling of the Interaction of an Aqueous Electrolyte with Metals: Molecular-Dynamic Approach

We develop a computer model of the electrochemical behavior of a metal-electrolyte interface based on the joint application of the MNDO semiempirical quantum-chemical and molecular-dynamic methods. We consider the evolution of metal-environment systems and study in detail the thermodynamic and kinetic features of establishing the adsorption-desorption equilibrium for the cluster systems FeCu-aqueous electrolyte and FeCr-aqueous electrolyte. We calculate the following electrolytic micropotentials: absolute for a hydrogen electrode and relative for copper, zinc, iron, α-brass, and iron-chromium alloy, which are in good agreement with experimental data.

Oxidation Kinetics and Scale Spallation of Iron-Chromium Alloys with Different Titanium Contents

Oxidation Kinetics and Scale Spallation of Iron-Chromium Alloys with Different Titanium Contents

Hydrogen Permeation Through Fe-16Cr Alloy Interconnect in Atmosphere Simulating SOFC at 1073 K

Iron-chromium ferritic alloy is a candidate for the interconnect of solid oxide fuel cells (SOFCs). Gastightness is one of the most important properties of the interconnect in a planar-type SOFC. Hydrogen permeation in an iron-chromium alloy was measured in an atmosphere simulating an SOFC at 1073 K. Hydrogen permeability of the oxide scale, which was mainly composed of was estimated by comparison between experimental results and calculation. The result was approximately at 1073 K, which is about four orders of magnitude lower than that of iron. This study revealed quantitatively that the oxide layer, mainly consisting of that formed on the alloy suppressed hydrogen permeation. © 2004 The Electrochemical Society. All rights reserved.

Interaction of iron-chromium alloys containing 10 and 25 mass% chromium with liquid aluminium Part II Formation of intermetallic compounds

Two intermetallic layers Fe2Al5 and Fe2Al7 occur at the interface between the iron-chromium alloys containing 10 and 25 mass% Cr and the saturated aluminium melt at 700°C. Under conditions of simultaneous dissolution in pure liquid aluminium only the Fe2Al5 phase forms an adherent continuous layer, while the Fe2Al7, FeAl3, FeAl6, CrAl7 and other phases exist as inclusions in the aluminium matrix. Dissolution of the Fe—Cr alloy base into pure aluminium causes a three-fold decrease in layer thickness compared with the case where no dissolution occurs. A simple equation for evaluating the Fe2Al5 layer thickness during dissolution is proposed. Making the Fe—Cr alloy-to-aluminium transition joints, with the mechanical strength of the joint greater than or equal to that for pure aluminium (70–80 MPa), appears to be feasible.