Fe Cr Ni Alloys Research Articles

Dissolution Behavior of δ-ferrite in Continuously Cast Slabs of SUS304 during Heat Treatment

The dissolution of δ-ferrite in continuously cast slabs of SUS304 has been studied during heat treatment in the temperature range of 1373 to 1473 K. The dissolution behavior can be expressed by Kolmogorov–Johnson–Mehl–Avrami equation. The dissolution rate is affected by annealing temperature and secondary dendrite arm spacing. Moreover, the numerical methodology for multi-phase field method has been performed in Fe–Cr–Ni alloy. It is thought that dissolution behavior of δ-ferrite during heat treatment can be also predicted by this method.

Prediction of Martensite Volume Fraction in Fe–Cr–Ni Alloys

Prediction of Martensite Volume Fraction in Fe–Cr–Ni Alloys

Magnesium Deoxidation Equilibrium of Molten Fe–Cr–Ni Alloy Expressed by Quadratic Formalism and Redlich-Kister Type Polynomial

Magnesium deoxidation equilibrium of molten Fe–Cr–Ni alloy was determined by a chemical equilibrium method at temperature of 1873 to 1973 K. Extreme care was taken of oxygen analysis of the samples. Numerical analysis on Mg deoxidation of molten Fe–Cr–Ni alloy has been carried out by utilizing the model based on Darken's quadratic formalism and Redlich-Kister type polynomial. Magnesium deoxidation equilibrium can be expressed in wide composition region of the Fe–Cr–Ni alloy.

Design and characterization of new Cu alloys to substitute Cu–25%Ni for coinage applications

As the material and manufacturing cost of coins approached or even exceeded the face value of coins over the last 10years, the needs to develop less-expensive alloys to replace the current coinage materials increased. The objective of this study is to develop new cost-effective alloys with the same vending machine acceptability and similar color tone as Cu–25%Ni coins. Cu–Zn–Ni–Fe and Cu–Zn–Ni–Fe–Cr alloys developed in this study were found to have the electrical conductivity close to and color similar to that of Cu–25Ni. The strengths of the annealed Cu–25.5%Zn–12%Ni–1.5%Fe and Cu–25.5%Zn–12%Ni–1.5%Fe–0.28%Cr alloys were observed to be 451MPa and 512MPa, respectively, with excellent ductility, suggesting that these alloys could be substitutive to Cu–25%Ni alloy for other general structural applications as well as coinage application. Both alloys exhibited the typical ductile fracture surfaces. Cu–Zn–Ni–Fe alloy was found to be a better candidate for coins because of the better formability and machinability associated with its moderate strength and excellent ductility.

Rare earth effect on the microstructure and tribological properties of FeNiCr coatings

FeNiCr alloys with various amounts of La2O3 powders were thermally sprayed onto steel substrate. Electron probe microscopy analysis (EPMA), X-ray photoelectron spectroscopy (XPS), and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration were employed to investigate the properties of the sprayed coatings. The results show that rare earth can refine the microstructure effectively and make the element distribution uniform, which leads to the improvement in the properties of the coatings. Meanwhile, the wear rate of the FeNiCr alloy with 1.5% La2O3 is smaller than those of the other coatings. Interestingly, the rare earth can reduce the friction coefficient and act as a self-lubricant in the oxide debris layer formed on the worn surface in friction. The wear mechanism of the coatings is oxidation wear, and a large amount of counterpart material is transferred to the coatings.

Microstructure selection of Fe–Cr–Ni alloy during directional solidification

Phase and microstructure selection in directionally solidified AISI 304 stainless steel has been theoretically studied using the highest interface temperature criterion to explore primary phase prediction during rapid directional solidification. It is found that competitive growth exists between the stable phase (δ) and the metastable phase (γ) because of different solidification conditions. For the alloy calculated, metastable phase (γ) dendrites begin to precipitate as the primary phase when the growth rate is higher than 4·2 cm s–1 at the given temperature gradient of 300 K mm–1. Strip casting experiments on 304 using a symmetrical water cooled copper mould confirmed the theoretical prediction. The influence of temperature gradient on the velocity scope and the interface temperatures of planar growth and dendrite/cellar growth in directionally solidified stainless steel are also discussed.

Intermediate-temperature embrittlement induced by non-equilibrium grain-boundary segregation of sulfur in Ni–Cr–Fe alloy

Intermediate-temperature embrittlement (ITE) for a Ni–Cr–Fe alloy has been experimentally studied by Auger electron spectroscopy and elevated-temperature tension tests. Results show both the grain boundary concentration of sulfur and the degree of embrittlement reach maxima at 500°C. The peak of the grain boundary concentration of sulfur during aging at 500°C occurs at about 20 min, which is close to the holding time prior to the start of tension at the test temperature. It can be concluded from these results that ITE of this alloy is induced by non-equilibrium grain-boundary segregation of sulfur.

Analysis and characterization by electron backscatter diffraction of microstructural evolution in the adiabatic shear bands in Fe–Cr–Ni alloys

The microstructural evolution inside adiabatic shear bands in Fe–Cr–Ni alloys dynamically deformed (strain rates > 104 s−1) by the collapse of an explosively driven, thick-walled cylinder under prescribed strain conditions was examined by electron backscatter diffraction. The observed structure within the bands consisted of both equiaxed and elongated grains with a size of ∼200 nm. These fine microstructures can be attributed to recrystallization; it is proposed that the elongated grains may be developed simultaneously with localized deformation (dynamic recrystallization), and the equiaxed grains may be formed subsequently to deformation (static recrystallization). These recrystallized structures can be explained by a rotational recrystallization mechanism.

Analysis of second-harmonic generation of Lamb waves using a combined method in a two-layered solid waveguide

Within the second-order perturbation treatment, the present work analyzed the complex second-harmonic generation of Lamb waves in a two-layered solid waveguide by combining the modal analysis method and the nonlinear reflection of acoustic waves at interfaces. The formal solution of the second-harmonic field is obtained on the basis of the modal analysis approach, from which a phase matching modification factor can be determined. The solution of the cumulative second-harmonic displacement field derived from the nonlinear reflection of acoustic waves at interfaces can be modified by multiplying the phase matching modification factor, and then be more general and applicable for the total second-harmonic field of Lamb wave propagation. Numerical computation results show that amplitude of the second-harmonic displacement increases clearly with propagation distance when the phase velocity of a double frequency Lamb wave (DFLW) component is exactly or approximately equivalent to that of the primary Lamb wave propagation, and reveal that the amplitudes of the second harmonics exhibit a decreasing tendency when the relative deviation of phase velocity between the primary Lamb wave and the DFLW component increases. Primary experimental measurements have been performed to verify the results of the numerical simulations in a FeCrNi alloy steel specimen. The research provides a further understanding for the physical process of the cumulative second-harmonic generation in a two-layered solid waveguide.

Quantitative evaluation of carbon nanotubes by the scanning atom probe

In order to evaluate the impurity levels in carbon nanotubes, single walled carbon nanotubes (SWCNT) grown by the high pressure carbon monoxide process (HiPCO), SWCNT synthesized by a direct-current arc-discharge method in He gas with Fe∕Ni∕S catalysis and multiwalled carbon nanotubes (MWCNT) formed on a substrate of Ni–Cr–Fe alloy by thermal chemical vapor deposition are mass analyzed at atomic level by utilizing the unique capability of the scanning atom probe. Since the largest number of ions detected from the analyzed CNTs is C2+ and C+∕C22+ is the second largest, the binding between carbon atoms is uniform and nondirectional. No metal ions except sodium ions are detected from the HiPCO SWCNT. Hydrogen ions detected from the HiPCO SWCNT is significantly smaller than two other CNTs. Metal ions detected from the dc arc SWCNT and MWCNT are localized in a range of a few nanometers.

Formation of a blocky ferrite in Fe–Cr–Ni alloy during directional solidification

Formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that a coupled growth microstructure, consisting of lathy ferrite and austenite, forms first from the melt. At solid-state transformation stage, most lathy ferrite disappears due to the phase transformation from ferrite to austenite. With further decreasing of the temperature, plenty of fine ferrite colonies occur in the original austenite region. The formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place. This transformation is due to the segregation and the instability of austenite during the growth of austenite under low cooling rate. The fine ferrite colonies transform into blocky ferrite at room temperature. TEM and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.

Modeling solute-vacancy trapping at oversized solutes and its effect on radiation-induced segregation in Fe–Cr–Ni alloys

Rate theory modeling was used to simulate the effects of oversized solute additions on radiation-induced segregation in austenitic stainless steels. The purpose was to understand the effects of a solute-vacancy trapping mechanism on radiation-induced segregation and to define key parameters that most affect segregation behavior. Sensitivity analysis of the model showed the solute-vacancy binding energy to be the most important model parameter. Binding energies from ab initio first principles were calculated for oversized solutes of Pt, Ti, Hf and Zr, with energies of 0.31, 0.39, 0.71 and 1.08 eV, respectively. Differences in binding energies, despite similar sizes of the atoms, suggests that the short-range electronic interactions play an important role in determining binding energy. The model results show oversized solutes to be most effective at reducing grain boundary Cr depletion at temperatures of 450–500 °C for a dose rate applicable to proton irradiations. The reduction increases with increasing oversized solute concentration, where it saturates at approximately 0.1 at.%.

The properties of samarium doped ceria oxide thin films grown by e-beam deposition technique

One of the main challenges in today's solid oxide fuel cell (SOFC) technology is the reduction of their operating temperature. New types of oxygen ion conducting materials are currently under investigation to overcome the problems which SOFC faces at high temperatures. Samarium doped ceria oxide (SDC) was the material of investigation in this work. Optical quartz (SiO 2) and Fe–Ni–Cr alloy (Alloy 600) were the two types of chosen substrates onto which SDC thin films were deposited by e-beam evaporation technique. The bias voltage was applied to the substrate during film growth. It had an influence on film formation, its microstructure and density because of the ionized particles presence in the SDC vapor stream. Changes in crystallite size and surface morphology were determined from X-ray diffraction data and scanning electron microscopy images. Influence of bias voltage on porosity of formed SDC thin films on optical quartz were calculated from transmittance spectra data by using Swanepoel method. The porosity decreases up to 12% by decreasing bias voltage from 0 to −150 V.

Structural and magnetic characterization of plasma ion nitrided layer on 316L stainless steel alloy

In this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430°C for 72min under a gas mixture of 60% N2–40% H2. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γN phase, [γN-(Fe,Cr,Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γN layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γN layer is found to be ∼6μm. According to the MFM and VSM analyses, ferromagnetism in the γN layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γN phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.

Microstructural and mechanical characterization of nitrogen ion implanted layer on 316L stainless steel

Nitrogen ion implantation can be used to improve surface mechanical properties (hardness, wear, friction) of stainless steels by modifying the near-surface layers of these materials. In this study, a medical grade FeCrNi alloy (316L stainless steel plate) was implanted with 85keV nitrogen ions to a high fluence of 1×1018N2+/cm2 at a substrate temperature <200°C in an industrial implantation facility. The N implanted layer microstructures, thicknesses and strengths were studied by a combination of X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS), atomic force microscopy (AFM) and nanohardness measurements. AFM was also used for the surface roughness analysis of the implanted as well as polished materials. The CEMS analysis indicate that the N implanted layer is ∼200nm thick and is composed of ε-(Fe,Cr,Ni)2+xN-like nitride phase with mainly paramagnetic characteristics. The nanohardness measurements clearly indicate an enhanced hardness behaviour for the N implanted layer. It is found that the implanted layer hardness is increased by a factor of 1.5 in comparison to that of the substrate material. The increased hardness resulting from nitrogen implantation is attributed to the formation of ε nitride phase.

Ti Deoxidation Equilibrium in Molten Fe–Cr and Fe–Cr–Ni Alloys at Temperatures between 1823 K and 1923 K

Titanium deoxidation equilibria between Ti and O in molten Fe–Cr and Fe–Cr–Ni alloys were investigated at temperatures of 1823 to 1923 K. Titanium oxides equilibrated with molten Fe–Cr and Fe–Cr–Ni alloys have been determined by EBSD (Electron Backscatter Diffraction) pattern analysis using FE-SEM (Field Emission Scanning Electron Microscope). Deoxidation product changes from Ti2O3 to Ti3O5 with decrease of Ti content in Fe–Cr and Fe–Cr–Ni alloys.Binary interaction parameters of Redlich–Kister type polynomial between Cr and O was assessed by using the previous experimental result in the Fe–Cr–O system. Experimental result of titanium deoxidation in molten Fe–Cr alloy has been numerically analyzed by the excess Gibbs free energy change of mixing Fe–Cr–Ti–O system with Redlich–Kister type polynomial. Validity of evaluated parameters between Cr–O (ΩCr–O) and Cr–Ti (ΩCr–Ti) was confirmed by comparison with experimental result for Fe–Cr–Ni alloy.Binary interaction parameters of Redlich–Kister type polynomial in present work were evaluated as follows,0ΩCr–O = −52870−24.10T J/mol (XO<0.0015, 1823≤T≤1923 K)1ΩCr–O = −498200+234.7T J/mol (XO<0.0015, 1823≤T≤1923 K)0ΩCr–Ti = 365700−206.3T J/mol (XTi<0.003, 1823≤T≤1923 K)1ΩCr–Ti = 432900−208.8T J/mol (XTi<0.003, 1823≤T≤1923 K)

The Effect of Alloy Solidification Path on Sulfide Formation in Fe–Cr–Ni Alloys

Solidification and sulfide precipitation in Fe–Cr–Ni alloys were investigated. Five samples containing 0.3 wt% S and 1.5 wt% Mn were investigated and each sample chemistry was adjusted to solidify as primary austenite, primary ferrite or eutectic by tailoring the Cr and Ni contents. The solidification was observed in-situ in a Confocal Scanning Laser Microscope (CSLM) equipped with a gold-image furnace, and the morphology and distribution of sulfides were characterized through SEM and Optical Microscopy. For high Ni and low Cr alloys which solidified in the primary austenite field, sulfides formed in the enriched melt ahead of the dendrite fronts as a eutectic metal-sulfide structure. On the other hand, for high Cr and low Ni alloys which solidified in the primary ferrite field, liquid sulfide phase precipitated in the inter-dendritic enriched melt first, and it appeared to deform and to concentrate in the dendrite boundaries during cooling. In the near eutectic intermediate Cr and Ni containing alloy, sulfides formed in the solid state. The sulfides formed in all the alloys were Mn and/or Cr rich.

Lengthening, Cracking and Weldability Problems of Fe–Ni–Cr Alloy Tube

Ethylene pyrolysis furnace tubes which are made of high Cr-Ni alloys often become difficult to weld after few years in service due to carburization and creep damage. The presence of carburization, often attempted to detect by magnetic permeability, can escape detection due to high Cr-Ni content of the alloy. Based on optical microstructural analysis and supported by scanning electron microscopy, this paper establishes that carburized material becomes difficult to weld due to carburized internal layers of the tube and cause hot shortness. To provide a practical way out for ethylene furnace operators, a solution annealing heat-treatment is recommended to have a successful weld.

Investigation of a novel porous anodic alumina plate for methane steam reforming: Hydrothermal stability, electrical heating possibility and reforming reactivity

A plate-type alumina support was synthesized through a novel anodization technology followed by a hot water treatment, which resulted in the drastically enlargement of support BET surface area from 16.5 to 204.6 g/m 2, and such BET value is even comparable to some commercial alumina supports. A high thermal stability of this kind of porous anodic alumina support was shown because as much as 63% of surface area remained after the support subjected to 700 °C air calcination for 50 h. Innovatively, an electrical heating pattern was allowed over this plate support due to the existence of Fe–Cr–Ni alloy interlayer among the support. Our work showed that the utilization of electrical heating pattern would shorten the reformer start-up time from 1 to 2 h to just a few minutes. With the porous anodic alumina support, a 17.9-wt% Ni catalyst with nickel aluminate layer was synthesized and its reforming reactivity was investigated during stationary and DSS SRM at 700 °C, under usual and electrical heating pattern. It showed excellent SRM reactivity and no deactivation was evidenced during 500 h stationary test and 100 times start–stop cycles DSS SRM test. Nevertheless, for the industrialization, some efforts should be made to alleviate the sintering of anodic supports, because after subjected to a hydrothermal treatment at 700 °C for 50 h, only 36% of surface area was kept.

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO4 · 7H2O and CrCl3 · 6H2O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.