Fe-3 Mass Research Articles

Development of Cell Structure and Crack Initiation during Fatigue of an Fe-3 mass%Si Alloy

A cell structure development and a crack initiation during a fatigue of an Fe-3 mass%Si alloy was investigated through electron channeling contrast imaging in a scanning electron microscope and electron back-scatter diffraction analysis. The crystal rotation regions (CRRs), deformation bands (DBs), and cell bands (CBs) together formed a hierarchy in the dislocation structures. In the early stage of fatigue, deformation is constrained near grain boundaries; this impedes further dislocation propagation. This restriction is attributed the formation of CRRs with a width of several hundred micrometers. Further, DBs that were several microns wide were developed inside the CRRs, and CBs with a width of several hundred nanometers were formed inside the DBs. Meanwhile, a crack was initiated from a CRR near a grain boundary. At the crack tip, a DB penetrating the CRR was formed parallel to the crack-propagation direction. It was elucidated that the cell boundary in the DB had a high misorientation angle of approximately 10 degrees, which greatly affected to the crack initiation. In addition, the penetrating DB was composed of elongated cells and cell bands. Prior to crack initiation, the boundaries of the cell bands evolved in proportion to the increasing dislocation density during fatigue. The elongated direction of the cell boundary, which was almost parallel to the {110} plane with a tilt boundary feature, dominated the crack-propagation direction. The formation plane and the cell boundary development process can be explained by analyzing the geometrical relationship of the activated slip systems between adjacent cells.

Transient Evolution of Inclusions during Al and Ti Additions in Fe-20 Mass pct Cr Alloy

The transient evolution of inclusions during Al and Ti additions in a Fe-20 mass pct Cr alloy was investigated using polished cross sections and electrolytic extraction. After Al addition, the evolution of Al2O3-based inclusions based upon the area and particle size passed through the following three main stages with time: Particle agglomeration, inclusion floating, and a slow decrease of the remaining Al2O3-based inclusions. Titanium wire was fed into the steel at the end of the floating stage after Al addition when the Ostwald ripening process was finished. Immediately after Ti addition, the transient phase of Ti oxide was readily generated on the existing Al2O3-based inclusion and disappeared due to Al reduction as time progressed. The formation of the transient TiOx phase was affected by the low disregistry between Al2O3 and TiOx and the local Ti supersaturation, which cannot be predicted by the equilibrium relations of Ti–O–N or Ti–Al–O in the high-Cr-containing melt. Because of the local supersaturation of dissolved [%Ti] and [%N] shortly after Ti addition, TiN associated with existing inclusions and three types of individual TiN including single cubes, twinned inclusions, and clusters were identified. In order to minimize the Ti loss caused by the formation of Ti-rich zones during the transient stages, the removal of large Al2O3-based particles including aggregates, clusters, and flower-shaped inclusions should be promoted by stirring before Ti addition. After Ti addition, Brownian and turbulent were the major factors affecting the collision of particles smaller than the threshold of 2.7 μm. The agglomeration of inclusions larger than this threshold was mainly dominated by turbulent and Stokes’ collisions.

Magnetic and Mechanical Properties of the High Purity Fe-3 mass%Si Alloy by Cold Crucible Levitation Melting

Magnetic and Mechanical Properties of the High Purity Fe-3 mass%Si Alloy by Cold Crucible Levitation Melting

Bcc Fe-3 mass%Al合金単結晶の繰返し変形挙動と転位組織の発達

Bcc Fe-3 mass%Al合金単結晶の繰返し変形挙動と転位組織の発達

Application of Different Extraction Methods for Investigation of Nonmetallic Inclusions and Clusters in Steels and Alloys

The characterization of nonmetallic inclusions is of importance for the production of clean steel in order to improve the mechanical properties. In this respect, a three-dimensional (3D) investigation is considered to be useful for an accurate evaluation of size, number, morphology of inclusions, and elementary distribution in each inclusion particle. In this study, the application of various extraction methods (chemical extraction/etching by acid or halogen-alcohol solutions, electrolysis, sputtering with glow discharge, and so on) for 3D estimation of nonmetallic Al2O3inclusions and clusters in high-alloyed steels was examined and discussed using an Fe-10 mass% Ni alloy and an 18/8 stainless steel deoxidized with Al. Advantages and limitations of different extraction methods for 3D investigations of inclusions and clusters were discussed in comparison to conventional two-dimensional (2D) observations on a polished cross section of metal samples.

Effects of Primary Oxide and Oxide-Nitride Particles on the Solidification Structure in a Fe-20 mass%Cr Alloy Deoxidised with Ti and M (M = Zr or Ce)

The ratio of equiaxed grains on a cross section and the size of equiaxed grains in a Fe-20 mass% Cr alloy deoxidised with Ti/M (M = Zr or Ce) were studied as function of nitrogen content and particle characteristics such as size distribution, morphology and composition. Fe-20 mass% Cr alloys were melted at 1 600 degrees C, deoxidised, and cooled to 1 400 degrees C followed by water quenching. Thereafter, the particles were separated from the matrix using electrolytic extraction using a 10%AA electrolyte and collected on a film-filter surface. The inclusion characteristics were determined using SEM. It was found that the number of particles increases with an increased N content. Furthermore, that the solidification structure was clearly affected by the number of primary oxide and oxide-nitride particles in the Ti/Zr deoxidation experiments. However, a similar effect could not be detected in the Ti/Ce deoxidation experiments.

Effect of Secondary Nitride Particles on Grain Growth in a Fe-20 mass% Cr Alloy Deoxidised with Ti and Zr

The pinning effects of different particles on grain growth were investigated in Fe-20 mass% Cr alloys deoxidised with Ti and Zr. More specifically, in-situ observations of the specimen surface were made during heat treatment at 1 200 and 1 400 degrees C in a High Temperature - Confocal Scanning Laser Microscope (HT-CSLM). Initially, primary and secondary particles were investigated using thermodynamic equilibrium calculations and the SEM/EDX observations. Thereafter, the pinning effect of secondary nitride particles on grain boundary migration and the kinetics of the grain growth process were investigated. It was found that secondary nitride particles generally have a considerable effect on the pinning of grain boundary migration during heating treatment. This is especially true for heat treatment at 1 400 degrees C. Despite that the pinning effect of TIN particles decreases due to dissolution of these particles, the implicit pinning effects of ZrO2, ZrO2-ZrN and ZrO2-ZrN-TiN particles appear. Thus, despite that TIN individually is ineffective in causing grain-boundary pinning at high-temperature, TiN is effective as a compound with ZrO2 and ZrN in pinning grain-boundaries at high temperatures. The changing of the uniformity of grain size distributions during grain growth at different N contents and temperatures was discussed based on the consideration of the geometric standard deviation of the grain size distribution (sigma(g)).

Evolution of Different Inclusions during Ladle Treatment and Continuous Casting of Stainless Steel

As the requirements on material properties increase, there has been a demand on an additional knowledge on the effect of impurities in the ferroalloyson the steel cleanness. Thus, the number, morphology, size and composition of inclusions in sixdifferent ferroalloys (FeTi, FeNb, FeSi,SiMn, LC and HC FeCr) were investigatedin this study. This was done in three dimensions (3D) by using a SEM in combination with EDS after electrolytic extraction of the ferroalloy samples. Theresults show that thenon-metallic and metallic inclusions can besuccessfully analyzed on the surface of a film filterafter a separation of the inclusions from the matrix. Overall, the inclusions canbe divided into two categories depending on the melting point. Furthermore, the possible transformation of different kinds of inclusions after their addition to the liquid steel canalso be determined.The inclusions and clusters in steel samples of two similar steel grades of high-silicon non-calcium treated (HSiNC) stainless steels were also investigated and compared during ladle treatment and continuous casting. Samples of liquid steel and slag were taken at different stages of the ladle treatment and casting during two plant trials: a low Al steel (LAl) and a high Al steel (HAl). Spherical (SP), irregular and regular (IR) inclusions and clusters (CL) were observed in the samples from both heats. It wasfound that the morphology and composition of inclusions and clusters in both heats were significantly changed during the ladle treatment and casting. Most of inclusions (44-98%) in a low Al steel are MgO-CaO-SiO2-Al2O3spherical inclusions. The compositions of irregular and regularinclusions and clusters in steel samples of a high Al steel were mostly MgO·Al2O3spinel, but also complex sphericalinclusions containing Al2O3-MgO-CaO-SiO2. In addition, the phase stabilitydiagram based on Darken’s quadratic formalism and Redlich-Kister type polynomial was estimated for both heats at a non-infinite solution.It is known that clusters in liquid steel have a harmful effect on the casting process and the quality of the final steel product. Therefore, clusters of rare earth metals (REM) were investigated in steel samples of a S30185 stainless steel grade from a pilot trial (PT, 250 kg) and from an industrial heat (IH, 100 t). Samples were taken from the liquid steel at differentholding times after the addition of a mischmetal. The morphology, composition, number and size of clusters in PT and IH steel samples were analyzed and compared as a function of the holding time. It was found that typical clusters with regular and irregular inclusions were the main type of clusters (69%-98%) in all PT and IH steel samples. The composition of inclusions in clusters corresponded mostly to REM-oxides. The size of clusters that were observed in different samples varied mainly from 2 to 23 μm. In addition, the size and number of most clusters in PT are larger than those in IH samples.Largesize inclusions are recognized to be crucially harmful for the mechanical properties of steel products. Therefore, predictionsof the maximum size of Al2O3-CaO spherical inclusions in an Fe-10 mass% Ni alloy have been examined based on two dimensional (2D) and three dimensional (3D) investigations. The effects of the number of measurements and unit volume on the estimated 3D results were also investigated.

Effects of Permeability on DC Biased Properties of Powder Cores and Modeling

DC biased magnetic properties of Fe-3 mass % Si powder cores have been measured and compared with calculated values using a nonmagnetic grain boundary (NMGB) model. Aluminum oxide fine powder was added into magnetic powder in order to change permeability and the amount of the powder was 0, 0.25, 0.4, 0.7, 1.0 mass %. DC initial B-H loops were measured and differential permeability was calculated at each magnetic force H. The values were compared with calculated one using the NMGB model which was taken account of gap width distribution. Best agreement of relative inaccuracy was additive amount 0.4 mass %. In that case relative inaccuracy of the powder core was from -0.4 % to 8.4 % with non gap distribution and from -3.00 to 4.00 % with gap distribution. The most improved case was additive amount 0 %. Relative inaccuracy was from -6.0 % to 22.8 % with non gap distribution and from -4.40 to 9.20 % with gap distribution.

DC-Biased Properties of Powder Cores using a Nonmagnetic Grain Boundary Model

DC-biased magnetic properties of Fe-3 mass % Si powder cores were investigated using a nonmagnetic grain boundary (NMGB) model. The powder was prepared by gas atomization. DC initial BH loops were measured and differential permeability was calculated at each magnetic force H. The values were compared with the NMGB-model considered from particle size distribution, body-centered cubic lattice situation and gap width distribution. The calculated values were in good agreement with measured values, which had intrinsic permeability: 3000, aspect ratio: 1.0 and geometric mean gap width: 0.41 μm. The relative inaccuracy of differential permeability was from -5.5 to 5.3 % between H=0.6 and 16 k A/m.

Characteristics of Fine Oxide Particles Produced by Ti/M (M=Mg and Zr) Complex Deoxidation in Fe–10mass%Ni Alloy

Characteristics of Fine Oxide Particles Produced by Ti/M (M = Mg and Zr) Complex Deoxidation in Fe-10 mass% Ni Alloy

Ｆｅ‐３ ｍａｓｓ％Ｓｉアトマイズ粉末を用いた圧粉磁心の磁気特性

Magnetic cores made by compaction with soft magnetic powder have been used for conventional chock coils of switched mode power supplies. A new application of these powder cores to motor cores is recently focused. In this paper the authors have studied the magnetic properties, especially magnetic flux density and core loss at 400 Hz of Fe-3 mass%Si powder cores made with changing atomizing process, gas atomization, modified water atomization, and conventional water atomization. And we concluded as follows. 1) Gas atomized powder has the best magnetic properties, high magnetic flux density and low core loss compared with the others. 2) At 400 Hz excitation hysteresis loss is dominant, and eddy current loss is very small. 3) Water atomized powder has small grain size, because it is suggested that Si oxide inclusions suppress the grain growth. 4) Eddy current loss decreases with increasing core resistivity, and over about 10-4Ωm the loss is approximately constant. It is considered that over the critical resistivity eddy current generates only in the particle, but under the resistivity eddy current flows particle to particle.

Characteristic Microstructure and Grain Boundary Motion in Secondary Recrystallization of Fe-3%Si Alloys

The microstructure of Fe-3 mass% Si alloys before secondary recrystallization has been characterized by analyzing precipitates and grain boundary segregated elements. The samples used were mainly sheets of Fe-3%Si alloys containing manganese, sulfur, aluminum, nitrogen and tin, which were decarburized and annealed up to secondary recrystallization. Grain boundary segregation in primarily recrystallized samples was studied using Auger electron spectroscopy (AES), and precipitates were analyzed using transmission electron microscopy (TEM) with an energy dispersive X-ray spectrometer (EDX). AES spectra showed that tin and nitrogen were enriched on grain boundaries in the Fe-3 mass% Si alloys. TEM/EDX analysis showed that the morphology and distribution of the fine precipitates such as manganese sulfide and aluminum nitride were influenced by addition of tin. The characteristic structure formed by secondary recrystallization of grain oriented silicon steel is considered to be influenced by the fine precipitates and segregation of a small amount of elements, as the abnormal motion of grain boundaries of the silicon steel was correlated with the precipitation and segregation of the alloying elements.

Formation Mechanism of Spinel-Type Inclusions in High-Alloyed Stainless Steel Melts

Fundamental thermodynamics of the relationship between high-alloyed stainless steel melts (Fe-20 mass pct Cr-13 mass pct Ni-3 mass pct Si) and the inclusions were investigated. The formation mechanism of the inclusions containing the spinel crystals was developed based on the experimental results and from the compositions of the inclusions in the steel samples taken during plant operations. The molar content of alumina in the inclusions was found to be linearly proportional to the increase of aluminum content, indicating that the inclusions could contain alumina even with less than about 200 ppm aluminum in the steel melt, e.g., steel melts that were mainly deoxidized by silicon. Furthermore, the composition of the inclusions is shown to be a function of the activity of the deoxidizers such as aluminum and silicon in the steel melt. From the analysis of the plant samples, it was found that the contents of MgO and Al2O3 in the calcium silicate type inclusions increased continuously as the steel melt transfers from the argon oxygen decarburization (AOD) converter to the tundish. This composition change in the inclusions originated from the reduction of MgO and Al2O3 in the slags or refractories by silicon in the steel melt. Increases of MgO and Al2O3 contents were prominent in tundish samples, and thus, the spinel phase could be crystallized in the calcium silicate inclusion matrix in the tundish; and finally the spinel crystals grew during cooling of the steel melt through the continuous casting (CC) mold and in the slabs. On the other hand, manganese silicate type inclusions containing chromium oxide were observed after tapping of the molten steel to the ladle. The MnO and Cr2O3 in these inclusions was initially reduced by silicon in the steel melt in the ladle treatment (LT) process, followed by further reduction by aluminum through the LT to the CC mold. The fractions of inclusions containing spinel crystals in cast slabs were negligible at the alumina content of less than about 20 mass pct, while they critically increased at alumina contents greater than about 20 mass pct.

Fracture Behavior of Micro-Sized Fe-3%Si Alloy Single Crystals

Fracture tests have been performed for both millimeter-sized and micro-sized specimens prepared from a Fe-3 mass%Si alloy single crystal, and the size effects on fracture behavior have been considered. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For millimeter-sized specimens, cleavage fracture occurred during introducing a fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. This phenomenon is discussed based on the plastic zone at crack tip and the ligament size. The results obtained in this investigation provide important information for designing actual MEMS devices.

Fe-3 mass%Si 合金単結晶の微小試験片における破壊挙動とその試験片寸法効果

Fracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the size effects on fracture behavior have been considered. Micro-sized cantilever beam specimens with dimensions of 10 μm×10 μm×50 μm were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 mm×2 mm×10 mm were also cut from same Fe-3%Si alloy single crystal. Notches with a depth of 1 mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In constant, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material. The results obtained in this investigation provide important information for designing actual MEMS devices.

Ｆｅ‐Ｓｉ系圧粉磁心の電気抵抗率および磁心サイズと磁心損失の関係

Compressed cores made with Fe-Si-Al or Fe-Si alloys are widely used for smoothing and boost choke coils of switching regulators and DC-DC converters. In this study, the relationship between resistivity and eddy current loss was investigated for Fe-3 mass% Si compressed cores by changing heat treatment temperature and height. Furthermore, eddy current losses were calculated electromagnetically by finite element method, and they were compared to the experimental results. Following conclusions were obtained. (1) Eddy current loss rapidly increases with increase in heat treatment temperature above 1173 K. (2) Resistivity decreases monotonically with increase in heat treatment temperature. (3) Eddy current loss is almost constant and independent of core height in higher resistivity than about 0.1 Ωm. When the resistivity is lower than 0.1 Ωm, eddy current loss increases with decrease in resistivity and increase in core height. (4) The above behavior of eddy current loss was explained as follows. Eddy current generates only inside of each particle and eddy current loss does not depend on core size in higher resistivity than 0.1 Ωm. On the other hand, eddy current flows particle to particle and causes large eddy current loss dependent on resistivity and core size in lower resistivity than 0.1 Ωm. (5) Calculated inter-particle eddy current losses based on homogeneous bulk model show good agreements with experimental data. The fact suggests that the behavior of inter-particle eddy current in the compressed core is same as that of homogeneous bulk material.

Ｈ２‐Ｎ２混合ガスによるＦｅ‐Ｃｒ合金の窒化に関する熱力学的研究

In order to evaluate dissolved nitrogen concentration penetrated during nitriding reaction of Fe-(5, 10, 14, 20 and 30)mass%Cr alloys, the specimens of 1 mm in thickness were nitrided at various partial pressures of nitrogen (pN2: 0.081, 0.051, 0.020, 0.002 and 0.001 MPa) for 36 ks at 1023 and 1223 K, respectively. Only CrN was precipitated in the nitrided layer of the Fe-5 mass%Cr alloy, nitrided at 1023 K under any pN2 studied, whereas CrN and Cr2N were for the alloy more than 10 mass%Cr at 1023 K. On the other hand, only CrN was precipitated for the alloys with 14 and 20%Cr nitrided at higher pN2 than 0.051 MPa at 1223 K. CrN and Cr2N were detected for the alloys with 20 and 30%Cr at 1023 K. Furthermore, some Fe-Cr alloys had no precipitation after nitriding them under a definite condition of pN2 and mass%Cr. Based on these experimental results, foils of Fe-Cr alloys with about 100 μm in thickness were nitrided at 1223 K to measure nitrogen solubility. Using the standard Gibbs energy of formation of CrN after the literature, the solubility limits of nitrogen in Fe-Cr alloys were obtained as; 0.12 mass%N for Fe-3 mass%Cr alloy, 0.15 mass%N for Fe-5 mass%Cr alloy.

Gold Penetration Correlated with Selective Oxidation of Silicon in Fe-3 mass%Si Single Crystal

Secondary ion mass spectrometry (SIMS) has been used for characterizing penetration of gold, which was deposited on the surface of Fe– 3 mass%Si (011) single crystal and subsequently penetrated into its bulk by annealing under the low partial pressure of oxygen. The degree of gold penetration was evaluated using an effective diffusion coefficient of gold in Fe–3 mass%Si, which was apparently estimated from a SIMS depth profile. The effective diffusion coefficients of gold in the surface layer of Fe–3 mass%Si were found to be larger than those in the bulk iron. The gold penetration is likely to be correlated with the distribution of silicon oxides, which is formed by selective oxidation of silicon in the surface layer of Fe–3 mass%Si. This indicates that silicon oxides formed in the surface layer of Fe–3 mass%Si act as a path for the gold penetration, which is presumably the interface between the iron matrix and a network of silicon oxides.

Grain boundary self-diffusion in high-purity Fe-50 and 60 mass % Cr alloys

Grain boundary diffusivity of 51 Cr and 59 Fe in high purity Fe-50 mass% Cr and Fe-60 mass% Cr alloys have been measured in the temperature range from 473 to 1273 K by use of a serial lathe sectioning technique. Below 653 K, the grain boundary diffusivity has been determined from the type C kinetics, whereas above 923 K it has been obtained from the type B kinetics. Linear Arrhenius lines have been observed for both types of B and C kinetics. Putting the grain boundary width δ at 5.10–10 m for the type B kinetics, the Arrhenius lines for the grain boundary self-diffusion coefficients Dgb in Fe-50 mass% Cr alloy obtained from both types kinetics are smoothly expressed as a single line. They can be expressed as :[math] for chromium and[math] for iron.The grain boundary diffusivities of 51 Cr and 59 Fe in Fe-60 mass% Cr alloy measured above 973 K are only slightly larger than those in Fe-50 mass% Cr alloy. The ratio of the activation energy for grain boundary diffusion to that for volume diffusion in the Fe-50 mass% Cr alloy is 0.35 which is much smaller than 0.6-0.7 observed in many metals and alloys.