Increasing Chromium Content Research Articles

The Importance of Phase Composition for Corrosion Resistance of Borided Layers Produced on Nickel Alloys.

The plasma paste boriding process was used for production of the borided layers on pure nickel and nickel-chromium alloys. The produced layers consisted of nickel borides only (in the case of nickel) or a nickel and chromium borides mixture (in the case Ni–Cr alloys). The objective of this investigation was to indicate the importance of the presence of chromium for corrosion resistance of non-borided alloys, as well as to indicate the influence of phase composition of borided layers on their corrosion resistance. Pure nickel was characterized by higher corrosion resistance, in comparison to the nickel-based alloys. Increased chromium content in nickel alloys resulted in their high susceptibility for pitting corrosion. All borided samples were characterized by higher corrosion resistance than the non-borided samples. However, the phase composition of borided layers influenced their corrosion resistance. Due to the microstructure which consisted of one type of borides (nickel borides), borided nickel had the highest resistance to corrosion, whereas the presence of chromium borides in layers produced on nickel-chromium alloys caused a decrease in corrosion resistance.

ИССЛЕДОВАНИЕ УПРОЧНЕННОГО СЛОЯ СТАЛИ 40Г2 ПОСЛЕ ЭЛЕКТРОДИФФУЗИОННОЙ ОБРАБОТКИ

The electrodiffusion processing is considered, which creates conditions for "upward diffusion" of alloying elements into the hardened surface. It has been found out that an increase in the microhardness of the surface of 40Mn2 steel was 1,18-1,51 times up to a depth of 250-350 μm with an increase in chromium concentration by 1,9 times.

Influence of Chromium on the Phase Composition and Specific Features of Hardening of the MnFeCoNiCu High-Entropy Alloy

A six-component system of CoNiCuCrx high-entropy alloys with different contents of chromium (where x = 0, 0.5, 1.0, 2.0, and 3.0 mole) is obtained by the method of argon-arc melting in a МІFІ-9 study. By the methods of X-ray diffraction analysis, scanning-electron microscopy, and indentation, we investigate the influence of chromium on the crystalline structure, microstructure, and hardness of these alloys in the as-cast state. In their structure, depending on the chromium content, we detect a mixture of the following phase components: two face-centered cubes + a body-centered cube + an intermetallic σ-phase (FCC1 + FCC2 + BCC + σ). It is also established that, as the chromium content increases, we observe the formation of the bcc structure and the σ-phase, which is the predominant factor of hardening of the alloy.

The influence of chromium content on wear and corrosion behavior of surface alloyed steel with Fe(16−x)Crx(B,C)4 electrode

In this study, the electrodes containing Fe(16−X)CrX(B,C)4 (X = 3,4,5) were used for surface alloying on an AISI 1010 steel substrate. The alloy structure of the coating exhibits in-situ composite structure with a large amount of reinforcing carbides and borides phases as to be hypoeutectic and hypereutectic structure in the surface alloyed layer. The obtained composition of the alloy shows that it contains much more interstitial hard phases in the alloyed layer than the conventional hardfacing alloys used in the industrial applications for the hardfacing of the steels. The morphological and microstructural properties showed that layer microstructure changed from hypoeutectic to hypereutectic structure with an increase in chromium content. The results of these studies revealed that the microstructure of hardfacing layers consists of interstitial phases of α(Fe-Cr) and (Fe,Cr)23(C,B)6 as major phases, (Fe,Cr)2(C,B) and (Fe,Cr)7(C,B)3 as minor phases in the in-situ composite structure. The composite hardness’ in the alloyed surface layers of the Fe(16−X)CrX(B,C)4 alloys ranged from 711 HV to 1164.3 HV. Wear test against alumina ball shows that the friction coefficients of the surface alloyed layers decreased with increase in applied loads and decrease in chromium content in the Fe(16−X)CrX(B,C)4 alloy composition. Coefficient of friction ranged from 0.55 to 0.79 in the present study. Wear rates of the surface alloyed steels caused to increase with decrease in chromium content and increase in applied loads. The wear rates of the alloyed layer changed between 3.07 × 10 and 5 mm3/m and 6.95 × 10−5 mm3/m. The corrosion resistance of the alloyed layers was measured by a potentiostatic polarization test. Icorr and Ecorr of the coated layers changed from 1.813 to 9.965 µA/cm2 and −704.786 to −745.792 mV, depending on alloyed layer compositions. With increasing chromium content, the corrosion resistance of the coating layer has changed in a nobler side.

Cations distribution by Rietveld refinement and magnetic properties of MgCrxFe2−xO4 spinel ferrites

Magnesium–chromium ferrites MgCrxFe2−xO4 (0 ≤ x ≤ 1) were studied using X-ray diffraction and magnetization measurements. Rietveld refinement of XRD patterns confirmed the cubic spinel structure in the space group Fd-3m and enabled to obtain the cations’ distribution amongst octahedral and tetrahedral sites of this structure. Magnetization measurements were performed using vibrating sample magnetometer (VSM) in the temperature range of 300–700 K and superconducting quantum interference device (SQUID) in the range of 10–300 K. Hysteresis loops for each concentration x at 300 K, show non-linear variation of saturation magnetization (MS) with chromium content. Both coercitive field and remanence decrease with increasing chromium content. MS variations with temperature indicate that the Curie temperature TC decreases with increasing chromium content. On the basis of Neel’s two sub-lattice crystal field model, the cations’ distribution enabled to calculate the theoretical magnetic moments at 0 K which are compared and discussed with those extracted by extrapolation to 0 K from MS experimental data.

Effect of chromium substitution on structural, electrical and magnetic properties of NiZn ferrites

Ni0.5Zn0.5Fe2−xCrxO4 (0≤x≤0.5) ferrites were successfully prepared by conventional solid state reaction method to investigate the effect of chromium substitution on the structural, electrical and magnetic properties. X-ray powder diffraction results demonstrate that all the prepared samples are well crystallized single-phase spinel structures without secondary phase. As chromium concentration increases, the lattice parameter and crystallite size gradually decrease. The magnetic measurement indicates that saturation magnetization is substantially suppressed by Cr3+ doping, changing from 73.5 A·m2/kg at x=0 to 46.3 A·m2/kg at x=0.5. While the room-temperature electrical resistivity is more than four orders of magnitude enhanced by Cr3+ substitution, reaching up to 1.1×108 Ω·cm at x=0.5. The dielectric constant monotonously decreases with rising frequency for these ferrites, showing a normal dielectric dispersion behavior. The compositional dependence of dielectric constant is inverse with that of electrical resistivity, which originates from the reduced Fe2+/Fe3+ electric dipole number by doping, indicating inherent correlation between polarization and conduction mechanism in ferrite.

Effect of Chemical Composition and Heat Treatments on the Microstructure and Wear Behavior of Manganese Steel

The present paper analyzes the effect of the chemical composition and heat treatments on the microstructure and wear resistance of manganese steels. The studied steels are melted in an electric arc furnace. Alloying elements (Cr + Ni + Nb) are added as ultra-fine powder in a well-heated ladle. Samples are subjected to two heat treatments: one at 1100 °C and the other at 1050 °C, and then quenched in water. Optical microscopy, scanning electron microscopy and X-ray diffraction are used to evaluate the microstructural changes. Hardness and microhardness measurements, mass loss and friction coefficient were also performed to determine the wear behavior of the studied steels. The results indicated that the microstructure of the manganese steel in the as-cast state consists of an austenitic matrix and cementite alloyed with manganese and chromium ((Fe,Mn,Cr)3C). Increasing chromium content increases the size of the alloyed cementite (Fe,Mn,Cr)3C. Addition of niobium leads to the apparition of new secondary carbide (NbC). The heat-treated microstructures consist of martensite, retained austenite and a small quantity of precipitates. Increasing in heat treatment temperature and addition of alloying elements (Cr + Ni + Nb) increase the hardenability of the studied steel and favor the martensitic transformation. As a result, addition of niobium and increasing in chromium and nickel contents improve hardness and wear resistance of the studied manganese steel.

Regeneration of native collagen from hazardous waste: chrome-tanned leather shavings by acid method.

The collagens (COL2, COL4, and COL5) were extracted from chrome-tanned leather shavings via three distinctive routes of acid method. The dechroming degree of COL2 extracted with the easiest operation was the highest (95.6% ± 1.2%) and the yield exceeded 90%; however, the total amount of acid was the most and the cost was the highest. In the second route, although the three-step dechroming process brought cumbersome operation, the dechroming degree and yield of COL4 were 90.5% ± 0.8% and 92.2% ± 0.6%, respectively, and the acid amount was less than that in the first route. For COL5, the dechroming degree and yield was the lowest; nevertheless, this route had the advantages of lowest cost and simpler operation. Electrophoretic patterns showed that all the collagens contained α1, α2, and β chains without low molecular weight components and were close to those of type I collagen. Compared with native collagen extracted from fresh calf skin, the regenerated collagens also maintained unique triple helix conformation determined via ultraviolet, infrared spectra and X-ray diffraction, confirmed by the similar values of AIII/A1455 and Δν. Additionally, the collagens existed in the form of fibrils with D-period pattern of ~ 67nm. Furthermore, the denaturation temperatures of COL2, COL4, and COL5 were 71.2, 79.1, and 85.4°C, respectively, which were relevant to the tighter arrangement of fibrils with the increased chromium content.

Influence of a Chromium-rich Industrial Waste on the Hydration and Hardening Processes of Portland Cements with Slag and Limestone Additions

This research work assesses the influence of a chromium-rich waste (from potassium dichromate manufacture) on the hydration and hardening processes of two types of Portland cements with limestone filler and slag additions. Therefore, mixtures of Portland cement and chromium-rich waste, corresponding to 0.5% wt. and 1% wt. Cr, were prepared and tested. The analyses performed on cement pastes with chromium waste content, showed that chromium immobilization is mainly due to the formation of Ca6Al2Cr3O18�32H2O (CrEt); this compound results by the substitution of [SO4]2- groups from ettringite lattice of with [CrO4]2-. CrEt crystals growth on the surface of clinker particles forms a diffusion barrier which explains longer setting times for cements with chromium content. The increase of chromium content in the studied systems decreases the compressive strength values but these remain above the lower limits imposed for this type of materials. The chromium content in leachates prepared according to the method described in SR EN 12457-2, was well below the legal limit of 70 mg/Kg established by Romanian legislation. A better chromium immobilisation was achieved in the cement with slag content, in good correlation with the nature and amount of formed hydrates.

Acute effects of chromium on hemato-biochemical parameters and morphology of erythrocytes in striped catfish Pangasianodon hypophthalmus

Chromium is considered the most detrimental pollutant to the aquatic organisms. The present experiment was conducted to determine the acute toxicity of chromium in view of its effects on hemato-biochemical parameters and the structure of erythrocytes in striped catfish, Pangasianodon hypophthalmus. Fish were exposed to seven different concentrations (0, 10, 20, 30, 40, 50 and 60 mg/L) of chromium, each with three replications for 96 h. After 96 h of exposure, the survived fish were sacrificed to measure hemato-biochemical parameters (hemoglobin, Hb; red blood cell, RBC; white blood cell, WBC; packed cell volume, PCV; mean corpuscular volume, MCV; the mean corpuscular hemoglobin, MCH and blood glucose). In addition, erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) of peripheral erythrocytes were assayed. No mortality was observed up to 10 mg/L, but 90% and 100% mortality was observed at 50 mg/L and 60 mg/L, respectively after a 96 h exposure period. The 96 h LC50 value through probit analysis was 32.47 mg/L. Hb (%), RBC (×106/mm3) and PCV (%) significantly decreased at 20, 30 and 40 mg/L of chromium, whereas WBC (×103/mm3), MCV (μm3) and MCH (pg) showed the opposite scenario. Blood glucose (mg/dL) levels significantly increased at 10, 20, 30 and 40 mg/L of chromium compared to 0 mg/L. Frequencies of ECA and ENA significantly increased with increasing chromium concentrations. This study indicates that chromium is highly toxic to striped catfish.

Chromium effects on the microstructural, mechanical and thermal properties of a rapidly solidified eutectic Sn-Ag alloy

PurposeThis study aims to investigate the chromium (Cr) effects on the microstructural, mechanical and thermal properties of melt-spun Sn-3.5Ag alloy.Design/methodology/approachTernary melt-spun Sn-Ag-Cr alloys were investigated using X-ray diffractions, scanning electron microscope, dynamic resonance technique, instron machine, Vickers hardness tester and differential scanning calorimetry.FindingsThe results revealed that the Ag3Sn intermetallic compound (IMC) and ß-Sn have been refined because of the hard inclusions’ (Cr atoms) effects, causing lattice distortion increasing these alloys. The tensile results of Sn96.4-Ag3.5-Cr0.1 alloy showed an improvement in Young’s modulus more than 100 per cent (42.16 GPa), ultimate tensile strength (UTS) by 9.4 per cent (23.9 MPa), compared with the eutectic Sn-Ag alloy due to the high concentration of Ag3Sn and their uniform distribution. Shortage in the internal friction (Q−1) of about 54 per cent (45.1) and increase in Vickers hardness of about 7.4 per cent (142.1 MPa) were also noted. Hexagonal Ag3Sn formation led to low toughness values compared to the eutectic Sn-Ag alloy, which may have resulted from the mismatching among hexagonal Ag3Sn phase with orthorhombic Ag3Sn and ß-Sn phases. Mechanically, the values of Young’s modulus have been increased, with increasing chromium content, whereas the UTS and toughness values have been decreased. The opposite of this trend appeared in Sn95.8-Ag3.5-Cr0.7 alloy, which may have been due to high lattice distortion (ƹ = 16.5 × 10−4) compared to the other alloys. Increase in the melting temperature Tm, ΔH, Cp and ΔT was because of Ag3Sn IMC formation. The low toughness of Sn96-Ag3.5-Cr0.5 and Sn95.8-Ag3.5-Cr0.7 (109.56 J/m3 and 35.66 J/m3), relatively high melting temperature Tm (223.22°C and 222.65°C) and low thermal conductivity and thermal diffusivity (32.651 w.m−1.k−1 and 0.314 m2/s) make them undesirable in the soldering process. The high UTS, high E, high thermal conductivity and diffusivity, low creep rate and low electrical resistivity, which have occurred with “0.1 Wt.%” of Cr, make this alloy desirable and reliable for soldering applications and electronic assembly.Originality/valueThis study provides chromium effects on the structure of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors compared the elastic modulus of the melt-spun compositions, which have been resulted from the Static method with that have been resulted from the Dynamic method. This paper presents new improvements in mechanical and thermal performance.

Cr3+ substituted Zn-Al layered double hydroxides as UV–Vis light photocatalysts for NO gas removal from the urban environment

The ZnAl-CO3, ZnAlCr-CO3 and ZnCr-CO3 LDH samples were studied as De-NOx photocatalysts in this work. Samples without Cr and increasing the presence of Cr3+ in the LDH framework in the 0.06, 0.15 and 0.3 Cr/Zn ratio were prepared by co-precipitation method, all of them constituted by pure LDH phase. The increase of chromium content in the LDH framework leads to lower crystallinity and higher specific surface area in the samples. Moreover, the CrO6 octahedron centres expand the photo-activity from UV to Visible light and assist to decrease the recombination rate of the electrons and holes. The favourable textural, optical and electronic properties of Cr-containing LDH samples explain the good NO removal efficiency (55%) and outstanding selectivity (90%) found for the analysed De-NOx process.

Characterization of Microstructure and Mechanical Properties of CuCr Alloy Produced by Stir Casting

The relatively low mechanical properties of pure copper at low and high temperature made it very limited applications. The mechanical properties of the copper can be improved by adding a small amount of elements such as Cr. This work consists of four CuCr alloy castings (0.3, 0.8, 1.2 and 1.5%) by using the stir casting method in an argon atmosphere. Then, the heat treatment was done for these alloys which included solution treatment and aging. Heat treatment was treated at 980 ° C for 1 hour, then water-quenching, followed by an aging treatment at 480 ° C for 2.4 and 6 hours. The Optical Microscopy and the Scanning Electron Microscopy (SEM) with (EDS) were used to study the microscopic structure of the produced alloys. The results showed that the mechanical properties of copper increased with increasing chromium content. The microstructure of the castings consist of the dendiritic structure, columinar and segregation. It has been also indicated that after heat treatment and aging, the microstructure changed to fine grains and the clusters disappeared. XRD showed a α-Cu phase and a small amount of CrO2 in microstructures. The highest value of hardness and the ultimate tensile were 101 Hv and 239.12 MPa, respectively. They were achieved at 1.5wt% addition of Cr at 480oC and 4hrs aging

The content of petroleum products, benzo(a)pyrene and heavy metals in soils of yamalnenets autonomous district and heavy metals in the hair of children

The paper presents information about the content of benzo(a)pyrene in soil samples of petroleum products and the content of heavy metals (iron, copper, lead, arsenic, manganese, chromium, cadmium and mercury) in the soil and hair samples of children. Soil samples and hair were taken in October 2014 in the north-western part of the Yamal-Nenets Autonomous District. The values obtained were compared with the approximately permissible levels and maximum allowable concentrations adopted in the Russian Federation. Levels are determined compounds in the soil in general do not exceed the allowable concentrations. In hair samples there was noted marked exceeding of the recommended values for zinc, copper, chromium and iron 10%, 16.7%, 83.3% and 100% samples, respectively. The cause of the high iron content in the hair samples may be due to the quality of consumed water, which is characterized by low mineralization and high iron content. Increased chromium content of more than 80% of the hair samples can be caused, as in the case of iron, the quality of water consumed, but also a high proportion of local foods in the diet of people, rich by chromium. A conducted study on the state of the environment in the village, away from areas of hydrocarbon production, indicates to the low importance of anthropogenic impact.

Effect of secondary phases on 475 °C embrittlement of 1.4462 and 1.4501 duplex stainless steels at short-term heat treatment conditions

Duplex stainless steels (DSSs) are classified according to their chemical composition. Also, the formation of the secondary phases can be defined as a main problem of the DSSs. In this study, decomposition of chromium and iron was studied at short-term heat treatment conditions, and also the effect of the intermetallic phase on the decomposition of chromium and iron was investigated. 1.4462 duplex stainless steel (DSS) and 1.4501 super duplex stainless steel were used in experimental studies. Both alloys were aged at 800 °C for 30 min for obtaining the intermetallic based sigma phase. Then, sigma-free and sigma-containing samples for both 1.4462 and 1.4501 alloys were treated at 475 °C for 24 h and 75 h, respectively. Samples were characterized by an optical microscope (OM) and scanning electron microscope (SEM). Effect of sigma phase on the formation of 475 °C embrittlement was conducted by electron diffraction analysis (EDS) and Vickers hardness measurements. It was determined that decomposition of the chromium and iron in a ferrite grain is accelerated by the presence of sigma phase. Sigma phase morphology and the ratio of the alloys did not change for both alloys during the heat treatment processes at 475 °C. Also increasing chromium content promoted the decomposition of chromium and iron in the ferrite phase. It was clearly shown that the sigma is more detrimental to the corrosion properties compared to the decomposition of chromium/iron at 475 °C.

Effect of Chromium Content on Microstructure, Hardness, and Wear Resistance of As-Cast Fe-Cr-B Alloy

The effects of chromium content on microstructure, hardness and wear resistance of as-cast Fe-xCr-1.0B (x = 0, 4, 8, 12, 16, 20) alloys were investigated by means of optical microscope (OM), scanning electron microscope (SEM), x-ray diffractometer (XRD), hardness tester and ring block wear tester. The results showed that the microstructures of chromium-free alloy were mainly composed of pearlite, ferrite, and eutectic borocarbides, and the hardness was very low, only 18.8 HRC. With the increase in chromium content, the matrix of as-cast Fe-Cr-B alloy gradually began to transform from pearlite and ferrite to lath martensite, and the type of borocarbides changed from Fe2(B, C) to M2(B, C), M7(C, B)3 and M23(C, B)6 (M = Fe, Cr). When the chromium content was 12 wt.%, the hardness of alloy reached the highest value of 61.1 HRC, and the wear resistance of alloy was the best. The results of worn surface analysis showed that the wear failure of as-cast Fe-Cr-B alloy was mainly caused by multiple plastic deformation and micro-cutting.

Structural transition, electrical and magnetic properties of Cr doped Bi0.9Sm0.1FeO3 multiferroics

The structural, vibrational, electrical and magnetic properties of Bi0.9Sm0.1Fe1-xCrxO3 (0.02 ≤ x ≤ 0.1) ceramics have been investigated in the vicinity of the morphotropic phase boundary (MPB) between the rhombohedral and orthorhombic structures. X-ray diffraction (XRD) patterns reveal a gradual formation of the orthorhombic phase and Bi14CrO24 impurity with increasing chromium concentration. The Rietveld refinement and Raman scattering analysis confirm the structural transformation from the polar R3c to the anti-polar Pnam phases. The Cole-Cole plots show two relaxation regimes which are attributed to gain and grain boundary responses above room temperature. The slim magnetic hysteresis loops are observed in samples with x = 0.02–0.08, while a robust loop with the coercivity field of Hc ≈ 1200 Oe is observed for x = 0.1 sample where the canted antiferromagnetic phase is significantly contributed to the total magnetization. This result approves that the cycloidal spin structure cannot be suppressed by Cr doping.

Effect of Cr and C on microstructure evolution of medium carbon steels during friction stir welding process and their mechanical property

The aim of the present study was to investigate the effect of chromium and carbon in medium carbon steels on the microstructure evolution during FSW process and their mechanical property. The materials are dynamically recrystallized in austenite during FSW followed by phase transformation from austenite to ferrite, pearlite, bainite, and martensite. In the case of 0.2%C, the microstructure of the stir zone transited from pearlite and ferrite to bainite and martensite with the increase in chromium content. On the other hand, in the case of 0.4%C, the microstructure transited from pearlite to martensite with the increase in chromium content. The specimens of 0.2%C-4%Cr, 0.4%C-2%Cr and 0.4%C-4%Cr showed high tensile strength of over 1.5 GPa. In addition, even though the microstructures in the stir zones of the specimens are martensite, the elongation of 0.2%C-4%Cr was 31%while those of the others were less than 5%. TEM observation revealed that many tiny carbides precipitated in martensite of the stir zone of 0.2%C-4%Cr and micro twin formed in martensite in those of 0.4%C-2%Cr and 0.4%C-4%Cr. Thus, it was considered that auto-tempering occurred in the stir zone of 0.2%C-4%Cr during FSW process. The carbide precipitation in martensite is more effective to improve the tensile elongation compared with micro twin formation.

The peculiarities in oxidation behavior of the ZrB2-SiC ceramics with chromium additive

ZrB2-SiC-Cr powder sintering at 1600 °C and its oxidation behavior at 1000–1500 °C in air were studied as a function of chromium content. It was shown that the relative density of the ZrB2-SiC ceramics increases with an increase in chromium content in the powdered mixture. This is related to the formation of the liquid Cr-Si-C-B phase during the high-temperature interaction of SiC with chromium and ZrB2.It was stated that the mechanism of ZrB2-SiC-Cr ceramics oxidation is changed from bulk to passive. The oxidation resistance is improved for the ceramics with 13% of chromium or less, which can be explained by a decrease in its porosity. The ceramics with higher chromium content demonstrates the opposite effect, namely, large-size Cr2O3 crystals are formed during oxidation, this promotes microcracking in the oxidizing layer and causes damage of surface integrity. As a result, the oxidation resistance of the ZrB2-SiC-Cr ceramics with high chromium content is decreased.

Magnetocaloric behavior of chromium doped Pr0.5Sr0.5MnO3 system

The magnetocaloric behavior of chromium doped Pr0.5Sr0.5MnO3 manganite system has been studied by synthesizing a series of samples using the citrate sol–gel route. The samples were characterized structurally by XRD and found to be crystallized in orthorhombic structure with Pnma space group. A systematic investigation of magnetization over a temperature range 80–300 K was carried out mainly to understand their magnetic behavior and the transition temperatures are found to decrease with increase in chromium concentration. This may be due to change in Mn3+ and Mn4+ ratio. Further, from the fittings (using a theoretical model) of M-T data at 500 Oestered magnetic field, curie constant has been calculated. It has been observed that due to chromium doping ferromagnetic phases were induced in the charge ordered system and this gave rise to interesting phenomena.