Increasing Chromium Content Research Articles

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.

Change of growth performance, hematological parameters, and plasma component by hexavalent chromium exposure in starry flounder, Platichthys stellatus

The study investigated the changes in growth performance, hematological parameters, plasma components, and stress indicators of juvenile starry flounder, Platichthys stellatus, depending on varying exposure to hexavalent chromium. P. stellatus was exposed to waterborne chromium at 0, 50, 100, 200, and 400 ppb for 4 weeks. The result showed that Cr exposure resulted in decreased daily length gain (DLG), daily weight gain (DWG), condition factor (CF), and hepatosomatic index (HIS) in P. stellatus. In terms of hematological parameters, red blood cell (RBC) count, hematocrit (Ht), and hemoglobin (Hb) significantly decreased at 400 ppb after 2 weeks. In terms of plasma components, inorganic analysis was unchanged and cholesterol, an organic component, considerably increased at 400 ppb after 4 weeks. Plasma enzyme components including glutamic oxalate transaminase (GOT) and glutamic pyruvate transaminase (GPT) were significantly increased. Stress indicators such as cortisol and glucose were notably increased over 100 ppb after 4 weeks with increasing chromium concentration. The results indicate that exposure to waterborne Cr induced toxic effects on growth, hematological parameters, plasma components, and stress indicators.

Influence of grinding media, pyrite mineralogy and water chemistry on the galvanic interaction between grinding media and pyrite

ABSTRACTThe purpose of this study was to investigate the role of grinding media type, water chemistry and pyrite mineralogy on the galvanic interaction between grinding media and pyrite during grinding of a gold ore. The galvanic current between pyrite and grinding media increased with the electrochemical activity of the grinding media, while it decreased as a function of increasing chromium content in the media. Furthermore, changing the pyrite-based electrode from pure pyrite to a gold-bearing pyrite electrode increased the galvanic current between the pyrite and the grinding media electrodes; therefore, the gold-bearing pyrite electrode is more active than the pure pyrite one. In addition, using process water instead of tap water increased the galvanic current density between pyrite and the high-chromium grinding media electrode (30% chromium). However, when the forged steel or the low-chromium grinding media electrodes were used, the galvanic current decreased compared to the tap water condition. In addition, the results obtained from SEM-EDX analysis showed that in both tap and process water conditions, oxide species were identified on the surface of the forged steel and low chromium electrodes. However, no oxygen was detected on the surface of the 30% chromium grinding media.

Corrosion Resistance Behavior of Cr–Cu Alloyed Thermo-Mechanically Treated Reinforced Bars in 3.5% NaCl Solution

The corrosion resistance of reinforcing steels are of interest to the building and construction industry as it decides the durability of structures. These steels passivates under very high alkaline pore solution (leached solution from concrete). However, they corrode once they come in direct contact with chlorides ions (near sea coast and/or de-icing material) causing premature deterioration of the entire concrete structure. To protect steel bar from corrosion, they are alloyed with chromium (up to 0.50%) in steps to steel and their corrosion resistance behavior are compared with unalloyed rebar in chloride environment. In general, chromium addition in steel provides better corrosion protection through surface passivation than unalloyed one. However, in the present study, increase in chromium content in steel did not show a direct relationship to the corrosion protection of thermo mechanically treated (TMT) rebars. To ensure the corrosion protection of TMT rebars, the critical limit of chromium addition should be 0.3%. The corrosion resistance of the TMT with varying chromium content followed the following trends: TMT-0.5Cr > TMT-0.3Cr > TMT > TMT-0.1Cr.

Investigation of Spectral Properties of Potassium Aluminoborate Glasses Doped with Chromium

Spectral properties of potassium aluminoborate glasses activated by various concentrations of trivalent chromium compounds are studied. The temperatures of glass transition (434°C) and bulk crystallization of the glass matrix (600°C) are determined. The heat treatment of the glass at the crystallization temperature results in the appearance of intensive narrow luminescence bands in the area of 685–715 nm that is connected with the crystallization of the LiAl7B4O17:Cr3+ phase in the glass matrix; in this phase chromium is located in a highly symmetrical octahedral surrounding. Concentration dependences of lifetime and quantum yield show the existence of the concentration luminescence quenching at increasing chromium content in the glass from 0.05 to 0.2 mol %. The maximum value of quantum yield is 30%.

Field exposure of FeCrAl model alloys in a waste‐fired boiler at 600°C: The influence of Cr and Si on the corrosion behaviour

AbstractThe aim of this study was to examine the performance of FeCrAl model alloys in a waste‐fired boiler and investigate the influence of chromium and silicon content on the corrosion behaviour. The investigation was executed by utilising an air‐cooled probe, giving a material temperature of 600°C throughout a 672 hr exposure. The material loss measurements were performed by utilizing an ultrasonic thickness gauge in combination with scanning electron microscopy analysis. It was found that increasing the chromium content significantly reduced the overall material loss of the FeCrAl model alloys but further accelerated the corrosion attack on the windward side. Simultaneously, the increased chromium content caused embrittlement of the material. Minor additions of silicon drastically reduced the material loss of the FeCrAl model alloys, whereas the sample ring with no silicon present was completely deteriorated. The trends observed in this field study correlated well with what has been observed in previous laboratory studies. A state‐of‐the‐art alloy in the present environment, Inconel 625, was simultaneously exposed and showed similar performance to the silicon‐containing FeCrAl model alloys with ≥10 wt% Cr.

Effect of Cr content on corrosion behavior of AlCrxFeNi2Cu1.6 high entropy alloys

This paper investigates the microstructure, hardness, and corrosion behavior of AlCrxFeNi2Cu1.6 (x = 0.5, 1.5, 2.5) high entropy alloys (HEAs). There are two simple phases, face-centered cubic (FCC) and body-centered cubic (BCC) phases, in all high entropy alloys. The result shows that the Icorr decreases from 3.76 to 1.25 μA cm−2, and the breakdown potential (Eb) increases from −0.155 to −0.021 V with the addition of chromium. Microstructure of the corroded surface indicates that the number of the pits decreases as the increase of chromium content. Cr element has the capacity to enhance the corrosion resistance of the alloys.

Effect of Cr3+ Substitution on the Structural, Electrical and Magnetic Properties of Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 Ferrites

In this work, Ni0.7Zn0.2Cu0.1Fe2−xCrxO4 (x = 0.02, 0.04, 0.06, 0.08 and 0.1) ferrites were synthesized by using the solid state reaction method and how relevant properties of the samples were modified accordingly. The structural, morphological, magnetic and electrical features of the ferrites were evaluated by using X-ray diffraction, scanning electron microscopy, Fourier transmission infrared (FTIR) spectra, vibrating sample magnetometry, electron spin resonance and network analyser. The lattice constant decreases with increasing chromium concentration and the decrease in the lattice constant is attributed to the ionic radius of chromium being smaller than that of iron. The distribution of metal cations in the spinel structure was estimated from the X-ray diffraction data and showed that along with Ni2+ ions, most of the Zn2+ and the Cu2+ ions additionally occupied the octahedral [B] sites. The FTIR spectra revealed two prominent frequency bands in the wave number range 400–600 cm−1 which confirm the cubic spinel structure. The magnetic properties, such as the initial permeability, saturation magnetization and coercivity, were investigated at room temperature. The frequency-dependent dielectric constant was observed to decrease with increasing chromium concentration. This behavior was using Koops phenomenological theory.

Chromium-modified cobalt molybdenum nitrides as catalysts for ammonia synthesis

AbstractThe influence of chromium compounds on the properties of cobalt molybdenum nitrides was studied. CoMoO4 obtained by precipitation from cobalt and molybdenum salts was modified by the addition of chromium(III) nitrate. A mixture of cobalt-molybdenum nitrides, Co2Mo3N and Co3Mo3N, was formed by ammonolysis of modified CoMoO4. The concentration of Co2Mo3N decreases with increasing chromium content. The specific surface area of cobalt molybdenum nitrides consisting of 2 wt% of Cr atoms increased by 50% in comparison to pure cobalt molybdenum nitrides. The catalytic activity of obtained catalysts in ammonia synthesis process decreases with rising of chromium concentration.

The influence of chemical composition of Ni-based alloys on microstructure and mechanical properties of plasma paste borided layers

Plasma paste boriding at temperature of 800 °C (1073 K) for 3 h was applied in order to produce hard ceramic phases on the surface of Ni-based alloys with various chromium concentrations. The microstructure of boride layer depended on the chemical composition of substrate material. The increase in chromium concentration was the reason for reducing the average thickness of the boride layers. Hence, the average thicknesses were as follows: 54.24 ± 3.07 μm for Nickel 201-alloy, 44.41 ± 2.24 μm for Inconel®600-alloy, 41.31 ± 1.56 μm for Nimonic®80A-alloy. The chemical and phase composition of the investigated layers strongly influenced their hardness (HVIT), Young's modulus (EIT) and fracture toughness (Kc). The boride layer, produced on Nickel 201-alloy, was characterized by lowest average hardness of 17.97 ± 1.59 GPa and Young's modulus of 217.89 ± 20.72 GPa. The highest values of HIT and EIT (22.96 ± 4.30 GPa and 291.95 ± 25.64 GPa, respectively) were obtained for boride layer on Nimonic®80A-alloyin which the highest chromium concentration occurred. It was also confirmed that the increase in chromium concentration in substrate material strongly influenced the fracture toughness of the produced layers. The plasma-paste borided layer, in which only nickel borides were identified, was characterized by the highest average fracture toughness (Kc) of 1.477 ± 0.86 MPa·m1/2. Whereas, the boride layer on Nimonic®80A-alloy (Cr content of 19.52 wt%) was characterized by about tree time lower fracture toughness (Kc = 0.534 ± 0.44 MPa·m1/2).

Response of Artemisia herba alba to hexavalent chromium pollution under arid and semi-arid conditions

The aim of this work is to study and evaluate in situ, the Artemisia herba alba responses to hexavalent chromium stress in the arid and semi-arid steppe Algerian soil. This metallic pollutant was selected to its high toxicity and to its great release from several industrial and agricultural activities emissions in the area of the study region. Artemisia herba alba is a medicinal plant but also a forage species widely used in pasture. It has dominated then adapted to the arid and semi-arid climate of Algerian steppe region, due principally to their morphological and physiological characteristics.To establish this work, A. herba alba species were selected in the Algerian steppe region, and their soils were treated weekly with K2CrO4 solution for about three months. Chromium concentrations were determined in the soil and in the different plants’ parts to verify its absorption and translocation with and without pollution simulation.This study demonstrated that A. herba alba has a strong resistance to high concentrations of hexavalent chromium. An increase in chromium concentrations at the different parts of plant’s has been noticed, without affecting its growth and vegetative development. The results of physiological and elementary analysis indicated that chromium was absorbed by A. herba alba. Cr (VI) accumulation in plant increase when they are increasing in soil. Translocation factor results indicated that Cr (VI) was mainly accumulated by A. herba alba roots. Particle size analysis showed that the soil is poor in organic substances and mostly sandy loams with 79.77% of sand and 9.76% of clay minerals.

Nodulation, nitrogen uptake and growth of lima bean in a composted tannery sludge-treated soil

ABSTRACT: This study evaluated the responses of lima bean (Phaseolus lunatus L.) to application of composted tannery sludge on nodulation, N uptake and plant growth. For eight years, the compost was applied at rates of: 0, 2.5, 5, 10, and 20 Mg ha-1 (dry basis). Plants of lima bean showed higher nodulation in treatments with compost; however, nodules reported in these treatments presented lower biomass, size and diversity than those reported in treatment without compost. Accumulation of N increased with the application of the highest rate (20 Mg ha-1), while there was an increase in chromium content in shoot with the increase in compost rates. Thus, the use of composted tannery sludge, in long-term, increases the accumulation of chromium in plants, increasing nodulation, while decrease rhizobia diversity in nodules.

Structural, magnetic and dielectric properties of chromium substituted copper ferrite ceramics

Abstract Chromium-copper ferrite (CuCrxFe2-xO4, 0 ≤ x ≤ 0.8) ceramics were prepared by simple sol-gel process using ethylene glycol as a cross-linking agent. X-ray diffraction patterns showed a tetragonal spinel structure for the samples with x ≤ 0.2 and cubic spinel structure for the samples with x > 0.2. Structural transformation was probably due to Jahn-Teller effect of copper ion. The magnetic properties of the CuCrxFe2-xO4 samples were also measured using a vibrating sample magnetometer. All samples showed hysteresis loops, corresponding to ferromagnetic behavior. The Cr content has an influence on magnetic properties. Both saturation magnetization and coercivity were decreased with increasing Cr content. The dielectric properties (er and tanδ) of the ferrite as a function of Cr content were also studied at room temperature in the frequency range from 100 Hz to 1 MHz using impedance analyzer. The result showed that the er and tanδ were decreased with increasing frequency that corresponded to Maxwell-Wagner interface polarization. The er values of CuCrxFe2-xO4 samples were increased with increasing chromium content, due to increasing of relative density. However, their er values were lower than that of pure CuFe2O4. The substitution of Cr ion on octahedral site of ferrite structure leads to the decrease of Fe2+ ↔ Fe3+ electron hopping, resulting in the decrease of er value.

Dynamic Impact of Chromium on Nutrient Uptake from Soil by Fluted Pumpkin (<i>Telfairia occidentalis</i>)

Pot experiments were conducted to investigate the impact of chromium on nutrient uptake by fluted pumpkin (<i>Telfairia occidentalis</i>) in soil. The study was conducted with a sandy loam soil for three weeks on a slightly acidic soil. Stratified sampling method was used. Soil samples were collected before and after planting to determine soil nutrient concentrations using Atomic Absorption Spectrophotometer and Hach Spectrometer. The result showed a maximum uptake of 27.5%, 17.57%, 17.07%, 9.76%, 18.44% and 3.66% for N, P. Mg, Fe, Ca, and K respectively. Excellent morphological characteristics were observed at 2.5ppm chromium concentration with average height, average number of leaves and average distance between nodes as 33.0cm, 10 and 4.8cm in contrast with 21.0cm, 8 and 2.3cm respectively. The impact of chromium concentration showed no specific trend on all nutrients considered, but had varying effects on the uptake of individual nutrient. The result also showed that increasing chromium concentration inhibit the uptake of Mg, Fe, Ca and P possibly due to competition for sorption site, masking and the formation of insoluble complexes.

Designing a Novel Graphitic White Iron for Metal-to-Metal Wear Systems

Metal-to-metal wear systems are widely used in various industries, but heat-induced adhesive wear has been limiting the lifetime of the components for many years. An idea of introducing interconnected flake graphite networks into white iron was developed by the authors, which can potentially solve this problem by increasing the overall thermal conductivity. To optimize the thermal conductivity and wear resistance, five alloys with different chromium and carbon contents were designed, produced, and investigated to develop the first generation of graphitic white iron. Mathematical models were developed to correlate the graphite phase concentration and cooling rate with carbon equivalent. It was shown that graphite volume percent needs to be higher than 7 pct to have a consistent thermal conductivity increase. Hardness model developed in this article suggested that M7C3 has a higher hardness than the plate cementite, and hardness increases with increasing chromium content in the carbides. The as-solidified microstructure was characterized using a SEM, and solidification sequence was established for this novel alloy system. Unexpectedly, for the first time, study of alloy with 11 wt pct Cr shows that M7C3 was formed during eutectic reaction and then transformed into cementite at a lower temperature.

PERILAKU SENSITASI PADA LOGAM STAINLESS STEEL SERI J4 AKIBAT PERLAKUAN PANAS

The failure of austenitic stainless steel during the industrial aplications is place sensitization due to heat treatment. The investigation of that failure has been investigated by researchers in particular for stainless steel 2XX and 3XX types, while there isno or little investigation for stainless steel J4 type.Furthermore, the investigation of the presence of sensitization on stainlees steel was conducted by referring to American Society for Testing and Materials (ASTM) A262-02a, which the caracterization of metal surface morphologies dan chrom content used optical microscope andscanning electron microskop, and Energy-dispersive X-ray spectroscopy, respectively. The results elucidate that sensitization is produced in temperature range from700 o C up to 900 o C .There isgrain boundaries attack onsurface morphologies after sensitization test in the temperature range from700 o C up to 900 o C ,whichis unlikely to happenat temperature of 600 o C. The possibility of chromium difusion to grain boundaries took place from the decrease of chromium content adjancent with grain boundaries and the increase of chromium content in grain boundaries, whichimplies the formation of intermetallic compound of carbide.

Thermal analysis, crystal structure and magnetic properties of Cr-doped Ni–Mn–Sn high-temperature magnetic shape memory alloys

The superiority of NiMnSn alloy on NiMnGa alloy is far ahead in term of some physical characteristics, and therefore, the development of this alloy group is very important. In this work, Ni50Mn45−xSn5Crx magnetic shape memory alloys were produced for x = 0, 4, 6, 10 and 12. Thermal analysis was performed on produced alloys in a wide range (200–1000 °C) by using differential scanning calorimetry, thermogravimetric and differential thermal analysis. According to the thermal analysis results, the austenite ↔ martensite transformation temperatures of the NiMnSn alloy decreased with increasing chromium content. Furthermore, the increase in the chromium ratio caused single-phase transformation due to the multiple phase transformation that was observed in the NiMnSn alloy. In addition, the crystal structure and microstructure analyses of the alloys were determined by using X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy. In all cases, martensite and gamma phase were encountered and the gamma phase ratio was found to be increased by chromium addition. The magnetization characteristics were studied by using physical properties measurement systems device, and it was found that the alloys have a considerably small response to magnetic flux.

Cation distribution, magnetic and structural properties of CoCrxFe2-xO4: Effect of calcination temperature and chromium substitution

Abstract The influence of chromium doping and the calcination temperature on the structural, morphological, cation distribution and magnetic properties of CoCrxFe2−xO4 where x = 0.0, 0.25, 0.5, 0.75 and 1 were investigated in detail. The X-ray diffraction (XRD) analysis using the Rietveld refinement technique proved the nanocrystalline single-phase, chromium doped cobalt ferrite samples. It is observed that the lattice parameter 'a' decreases with increasing the chromium concentrations, while lattice parameter gradually enhances with increasing of calcination temperature. The cation distribution was inferred from the analysis of intensity of XRD as well magnetic properties. Magnetic measurements informed that both of the coercivity (HC) and saturation magnetization (MS) overall decrease with increasing chromium substitution. Also, with rising of calcination temperature from 350 to 1000 °C, for un-doped cobalt ferrite sample, MS is increased from 31 to78 emu/gr, respectively. These magnetic behaviors could be explained by the cation distribution and crystallite size enhancement. The HC enhancement for the heat-treated samples until 700 °C can be attributed to the crystal growth within the single domain region, while decreasing HC by further increasing calcination temperature to 1000 °C, is due to the transformation of single domain nanoparticles to multi-domain particles. The reduced hysteresis loops due to decreasing MS and HC with increase in chromium concentration, which in turn lowered the coercive field and softened the material, favoring its application in high-frequency transformers.