Percent Chromium Research Articles

Analisa Pengecoran Logam dengan Pengujian Mekanik dan Metalografi

The Ball Valve Axle is an axle that functions as a handle for the balls on HPD and HPS type hydrants produced by a metal foundry factory in Tegal, Central Java. This Ball Valve Axle is made from gray cast iron which consists of 2.746 percent carbon, 0.247 percent silicon, 0.708 percent manganese, 0.001 percent phosphorus, 0.058 percent sulfur, 0.007 percent chromium, 0.046 percent nickel, 0.172 percent molybdene, 0.000 percent vanadium, tungsten 0.007 percent, copper 0.122 percent, aluminum 0.003 percent, titan 0.003 percent, boron 0.00 percent, tin 0.026 percent, lead 0.000 percent and the element iron itself. In the casting process, porosity has occurred which causes the cast product to fail and cannot be used. To determine the condition of the failed object, tests are carried out, namely mechanical testing and metallographic testing. Mechanical tests carried out include material wear testing, material hardness with a hardening process through a heat treatment process at a temperature of 870 degrees Celsius which is then tempered at temperatures of 100 degrees Celsius, 200 degrees Celsius, 300 degrees Celsius and 400 degrees Celsius. Wear level The casting yield is 0.0001 mm2/kg and the hardness level is 166,360 kg/mm2. This cast iron experiences high hardness after being tempered at 100 degrees Celsius where the hardness becomes 418.347 kg/mm2 but experiences a decrease in hardness if we temper it to 400 degrees Celsius where the hardness becomes 270.813 kg/mm2.

ATI 301

Abstract ATI 301 (UNS S30100) is an austenitic stainless steel with a nominal composition of 17 percent chromium and 7 percent nickel. The high strength of this grade of steel in the six available conditions or tempers, its resistance to atmosphere corrosion, and its bright, attractive surface make it an excellent choice for decorative structural applications. This datasheet provides information on composition, physical properties, elasticity, tensile properties, and compressive strength as well as creep and fatigue. It also includes information on high temperature performance and corrosion resistance as well as forming and heat treating. Filing Code: SS-1359. Producer or source: ATI.

Impacts of Anthropological Activities on Soils of Some Parts of Rivers State, Nigeria

The study is a post project implementation Environmental Monitoring (EM) of impacts of anthropological activities on levels of soil physicochemical parameters. The study evaluates levels of physicochemical parameters in soils of 9 locations in Port Harcourt and its environs in Rivers State, Nigeria, grouped into 3 categories; urbanized, industrialized and agricultural. Composite soil samples were collected between April to October 2018. Concentration levels of Benzene, Toluene, Ethyl-benzene, and Xylene (BTEX), Total Petroleum Hydrocarbon (TPH), Percent Total Organic Carbon (% TOC), Lead (Pb), Iron (Fe), Copper (Cu), Cadmium (Cd), Zinc (Zn), Calcium (Ca), Nickel (Ni), Sodium (Na), Potassium (K), Chromium (Cr), Magnesium (Mg), Manganese (Mn), and Sulphur (S) in soil was measured using standard analytical procedures. The study evaluates the impact magnitude (IM) of the obtained test values against control values. In industrial area, BTEX recorded the highest Impact Magnitude (IM) of 100% while TOC and TPH recorded 100.00% and 88.89% respectfully, and were classified as severely impacted (S). In the agricultural areas, TOC and Ni recorded IM of 88.89% while BTEX had an IM of 77.78% which were highest and were classified as severe impact (S). In urbanized areas, Ni and (Phosphate) PO43- recorded the highest IM of 88.89% and were classified as severe (S). The study establishes that urbanization, industrialization and agricultural activities do affect the level of physicochemical parameters in the study areas. Activities in industrial areas negatively impact on levels of BTEX, % TOC and TPH in soils. Activities in agricultural areas negatively impacted on levels of BTEX, NO3-, NO2- and SO42- in soils, and activities in urban areas negatively impact on levels of Ni, PO43-, Zn, Mn, TPH, % TOC and Ca in soils of the study areas. These findings form a reliable baseline data for future researchers in EM in the study areas. The study recommends EM of soil physicochemical parameters in the study area in order to ensure a healthy soil for food production in order for realization of Sustainable Development Goals (SDGs); Good Health and well-being, and sustainable cities and communities.

Quantifying Void Formation and Changes to Microstructure During Hydrogen Charging: A Precursor to Embrittlement and Blistering

Hydrogen diffusion into the microstructure is a key first step for both hydrogen embrittlement and hydrogen blistering. Previous research has suggested that an increase in voids pre-loading can significantly affect the void growth and failure of samples during loading. However, there is a lack of knowledge on the effect of hydrogen alone on initial void fraction. Therefore, the microstructures of six samples of 13 pct chromium stainless steel were imaged using a computed tomography technique before and after hydrogen charging. These images were then formed into a 3D model to quantify the total void volume fraction before and after charging. Overall, charging was shown to increase void fraction by 18 times. This work provides support to the theory that an important role of hydrogen in promoting failure is to increase void production through recombination into H2.

Effect of Compositional Changes of Laves Phase Precipitate on Grain Boundary Embrittlement in Long-Term Annealed 9 Pct Cr Ferritic Steel

In 9 to 12 pct chromium steels, the high-temperature mechanical properties are known to be strongly dependent on the formation and coarsening of Laves phase precipitates at boundaries. During high-temperature deformation, the Laves phase precipitate coarsening to over a critical size has been considered to trigger cavity formation at the precipitate-matrix interfaces. This coarsening, accompanied by the diffusion of W, Mo, and Cr, should change the mechanical properties and chemical composition of both Laves phase precipitates and the matrix. In this study, we aimed to clarify the effects of compositional changes of Laves phase precipitates on cavity formation during coarsening. The values of the Fe/Cr and W/Mo ratios in Laves phase precipitates were shown to induce different levels of strain energy in the vicinity of the Laves phase precipitate, consequently promoting the formation of cavities. Therefore, the compositional change of Laves phase precipitates was found to play a critical role in the grain boundary embrittlement of high Cr steel at elevated temperature.

Efficient Separation and Extraction of Vanadium and Chromium in High Chromium Vanadium Slag by Selective Two-Stage Roasting–Leaching

Vanadium and chromium are important rare metals, leading to a focus on high chromium vanadium slag (HCVS) as a potential raw material to extract vanadium and chromium in China. In this work, a novel method based on selective two-stage roasting–leaching was proposed to separate and extract vanadium and chromium efficiently in HCVS. XRD, FT-IR, and SEM were utilized to analyze the phase evolutions and microstructure during the whole process. Calcification roasting, which can calcify vanadium selectively using thermodynamics, was carried out in the first roasting stage to transfer vanadium into acid-soluble vanadate and leave chromium in the leaching residue as (Fe0.6Cr0.4)2O3 after H2SO4 leaching. When HCVS and CaO were mixed in the molar ratio CaO/V2O3 (n(CaO)/n(V2O3)) of 0.5 to 1.25, around 90 pct vanadium and less than 1 pct chromium were extracted in the first leaching liquid, thus achieving the separation of vanadium and chromium. In the second roasting stage, sodium salt, which combines with chromium easily, was added to the first leaching residue to extract chromium and 95.16 pct chromium was extracted under the optimal conditions. The total vanadium and chromium leaching rates were above 95 pct, achieving the efficient separation and extraction of vanadium and chromium. The established method provides a new technique to separate vanadium and chromium during roasting rather than in the liquid form, which is useful for the comprehensive application of HCVS.

Microstructural Characterization of the Heat-Affected Zones in Grade 92 Steel Welds: Double-Pass and Multipass Welds

The microstructure in the heat-affected zone (HAZ) of multipass welds typical of those used in power plants and made from 9 wt pct chromium martensitic Grade 92 steel is complex. Therefore, there is a need for systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds manufactured using the traditional arc welding processes in order to understand possible failure mechanisms after long-term service. In this study, the microstructure in the HAZ of an as-fabricated two-pass bead-on-plate weld on a parent metal of Grade 92 steel has been systematically investigated and compared to a complex, multipass thick section weldment using an extensive range of electron and ion-microscopy-based techniques. A dilatometer has been used to apply controlled thermal cycles to simulate the microstructures in distinctly different regions in a multipass HAZ using sequential thermal cycles. A wide range of microstructural properties in the simulated materials were characterized and compared with the experimental observations from the weld HAZ. It has been found that the microstructure in the HAZ can be categorized by a combination of sequential thermal cycles experienced by the different zones within the complex weld metal, using the terminology developed for these regions based on a simpler, single-pass bead-on-plate weld, categorized as complete transformation, partial transformation, and overtempered.

Dynamic Strain Aging Phenomena and Tensile Response of Medium-Mn TRIP Steel

Dynamic strain aging (DSA) and rapid work hardening are typical behaviors observed in medium-Mn transformation-induced plasticity (TRIP) steel. Three alloys with manganese ranging from 10.2 to 13.8 wt pct with calculated room temperature stacking fault energies varying from − 2.1 to 0.7 mJ/m2 were investigated. Significant serrations were observed in the stress-strain behavior for two of the steels and the addition of 4.6 wt pct chromium was effective in significantly reducing the occurrence of DSA. Addition of chromium to the alloy reduced DSA by precipitation of M23(C,N)6 during batch annealing at 873 K (600 °C) for 20 hours. Three distinct DSA mechanisms were identified: one related to manganese ordering in stacking faults associated with e-martensite and austenite interface, with activation energies for the onset and termination of DSA being 145 and 277 kJ/mol. A second mechanism was associated with carbon diffusion in γ-austenite where Mn-C bonding added to the total binding energy, and activation energies of 88 and 155 kJ/mol were measured for the onset and termination of DSA. A third mechanism was attributed to dislocation pinning and unpinning by nitrogen in α-ferrite with activation energies of 64 and 123 kJ/mol being identified. Tensile behaviors of the three medium manganese steels were studied in both the hot band and batch annealed after cold working conditions. Ultimate tensile strengths ranged from 1310 to 1404 MPa with total elongation of 24.1 to 34.1 pct. X-ray diffraction (XRD) was used to determine the transformation response of the steels using interrupted tensile tests at room temperature. All three of the processed steels showed evidence of two-stage TRIP where γ-austenite first transformed to e-martensite, and subsequently transformed to α-martensite.

The Influence of Thermal Cycles on the Microstructure of Grade 92 Steel

The microstructure in the heat-affected zone (HAZ) of welds made from the 9 wt pct chromium martensitic Grade 92 steel is complex and has not yet been completely understood. There is a lack of systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds as a function of the welding process. In this study, the microstructure in the HAZ of an as-fabricated single-pass bead-on-plate weld on a parent metal of Grade 92 steel was systematically investigated by using an extensive range of electron and ion-microscopy-based techniques. A dilatometer was used to apply controlled thermal cycles to simulate the microstructures in the different regions of the HAZ. A wide range of microstructural properties in the simulated materials were then characterized and compared with the experimental observations from the weld HAZ. It was found that the microstructure in the HAZ of a single-pass Grade 92 steel weld can be categorized as a function of a decreasing peak temperature reached as (1) the completely transformed (CT) region, in which the original matrix is completely reaustenitized with complete dissolution of the pre-existing secondary precipitate particles; (2) the partially transformed (PT) region, where the original matrix is partially reaustenitized along with a partial dissolution of the secondary precipitate particles from the original matrix; and (3) the overtempered (OT) region, where the pre-existing precipitate particles coarsen. The PT region is considered to be the susceptible area for damage in the commonly reported HAZ failures in weldments constructed from these types of steels.

Comparative Tensile Flow and Work-Hardening Behavior of 9 Pct Chromium Ferritic-Martensitic Steels in the Framework of the Estrin–Mecking Internal-Variable Approach

The comparative tensile flow and work-hardening behavior of P9 steel in two different product forms, normalized and tempered plate and thick section tube plate forging, and P91 steel were investigated in the framework of the dislocation dynamics based Estrin–Mecking (E–M) one-internal-variable approach. The analysis indicated that the flow behavior of P9 and P91 steels was adequately described by the E–M approach in a wide range of temperatures. It was suggested that dislocation dense martensite lath/cell boundaries and precipitates together act as effective barriers to dislocation motion in P9 and P91 steels. At room and intermediate temperatures, the evolution of the internal-state variable, i.e., the dislocation density with plastic strain, exhibited insignificant variations with respect to temperature. At high temperatures, a rapid evolution of dislocation density with plastic strain toward saturation with increasing temperature was observed. The softer P9 steel tube plate forging exhibited higher work hardening in terms of larger gains in the dislocation density and flow stress contribution from dislocations than the P9 steel plate and P91 steel at temperatures ranging from 300 K to 873 K (27 °C to 600 °C). The evaluation of activation energy suggests that the deformation is controlled by cross-slip of dislocations at room and intermediate temperatures, and climb of dislocations at high temperatures. The relative influence of initial microstructure on flow and work-hardening parameters associated with the E–M approach was discussed in the three temperature regimes displayed by P9 and P91 steels.

Stainless Steel for Dairy and Food Industry: A Review

Stainless steels (SS) were invented to overcome the problem of corrosion which is a major concern of food and many other industries. The alloy of steel containing iron-chromium-nickel is known as stainless steels. Stainless steels typically contain between 9 and 30 percent chromium and varying amounts of nickel, molybdenum, copper, sulfur, titanium, niobium, etc., may be added to obtain the desired mechanical properties and service life. Stainless steel is considered noble metal for use in dairy industry. Stainless steels are classified based on the chemical composition and it provides information to overcome many types of corrosion. Some of the limitations of SS employed in food and dairy industry are attack by lactic and malic acids at elevated temperature and poor thermal conductivity. However, these limitations may be overcome by carefully selection and fabrication, optimized operating condition, care and maintenance of the equipment. Stainless steels of various grades are widely used as engineering material for the fabrication of equipment. Stainless steels are corrosive resistant but under certain conditions the materials can stain and can corrode. Dairy and food industries are concerned with reliability of equipment and product purity. To achieve these, stainless steels are often the economical and practical materials of choice for process equipment. It is necessary to select most suitable grade of SS depending on the requirements for the specific application. The understanding of metallurgy and ways of fabrication are very essential to select right grade of SS. The food and dairy processing industries, corrosion becomes a critical factor directly influencing equipment and indirectly, overall equipment longevity. Key to minimizing corrosion impact needs better understanding of factors affecting corrosion as early as the equipment design phase and throughout subsequent processing operation.

An Assessment of Milling Time on the Structure and Properties of a Nanostructured Ferritic Alloy (NFA)

The tensile properties of a 14 wt pct chromium nanostructured ferritic alloy (NFA) are assessed as a function of attrition time. Small angle X-ray scattering results show quantitatively that the number density of precipitated oxides increases as a function of milling time. This difference in oxide density alone is not enough to describe the tensile behavior of the NFA as a function of temperature. As a result, a previously proposed root mean square strengthening model is applied to the current study where direct dispersion strengthening, grain boundary strengthening, dislocation forest hardening, and matrix hardening are all considered. When an optimization routine is conducted, the fitting results suggest that the precipitated oxides are soft obstacles to dislocation motion.

Interphase precipitation of Fe2Hf Laves phase in a Fe–9Cr/Fe–9Cr–Hf diffusion couple

Periodically arrayed rows of fine Fe2Hf Laves phase particles were found to form in ferritic matrix containing 9 weight percent chromium and a few weight percent hafnium. Microstructural investigation suggests that the particles were formed on cooling through interphase precipitation during the phase transformation from δ ferrite to austenite, and the austenite was subsequently transformed into the α ferrite. The interphase precipitation mode may be effectively used to strengthen ferritic heat resistant steels with Laves phase.

Biosorption of Cr(VI) from aqueous solution by chemically modified potato starch: Equilibrium and kinetic studies

The biosorption capacity of chemically modified potato starch (CPS) for Cr(VI) from aqueous solution was investigated. The materials derived from carbohydrates are biodegradable and are generally regarded as safe and environmentally acceptable. The hydroxyl, carboxyl and carbonyl groups are responsible for the biosorption process. In the present study, the influence of various important parameters such as pH, time, biosorbent dose and initial Cr(VI) concentration on the biosorption capacity were investigated. The isotherms such as Langmuir, Freundlich and Tempkin were studied. The Freundlich and the Redlich–Peterson isotherms had been well fitted the biosorption of Cr(VI) with chemically modified potato starch. The kinetics of Cr(VI) removal using chemically modified potato starch was well explained by second-order kinetic model. The thermodynamic parameters were also evaluated from the biosorption measurements. Among the various desorbing agents tested, 98.2 percent chromium recovery was achieved with 0.1molL−1 NaOH.

Anomalous surface segregation profiles in ferritic Fe-Cr stainless steel

The iron-chromium alloy and its derivatives are widely used for their remarkable resistance to corrosion, which only occurs in a narrow concentration range around 9 to 13 atomic percent chromium. Although known to be due to chromium enrichment of a few atoms thick layer at the surfaces, the understanding of its complex atomistic origin has been a remaining challenge. We report an investigation of the thermodynamics of such surfaces at the atomic scale by means of Monte Carlo simulations. We use a Hamiltonian which provides a parameterization of previous ab initio results and successfully describes the alloy's unusual thermodynamics. We report a strong enrichment in Cr of the surfaces for low bulk concentrations, with a narrow optimum around 12 atomic percent chromium, beyond which the surface composition decreases drastically. This behavior is explained by a synergy between (i) the complex phase separation in the bulk alloy, (ii) local phase transitions that tune the layers closest to the surface to an iron-rich state and inhibit the bulk phase separation in this region, and (iii) its compensation by a strong and non-linear enrichment in Cr of the next few layers. Implications with respect to the design of prospective nanomaterials are briefly discussed.

Effect of Boron on Carbide Coarsening at 873 K (600 °C) in 9 to 12 pct Chromium Steels

The addition of small amounts of boron to 9 to 12 pct chromium steels has been found to decrease their creep rate at 823 K to 923 K (550 °C to 650 °C). In this article, the behavior of boron during austenitizing, tempering, and isothermal heat treatment at 873 K (600 °C) is studied using high-resolution microscopy and microanalysis as well as using atomistic modeling. It was found that increasing the boron content from 9 to 40 ppm decreased the coarsening constant of M23C6 by a factor of almost 2. Most of the added boron was incorporated in M23C6. Atomistic modeling showed that boron diffusion in ferrite is dominated by an interstitial mechanism at 873 K (600 °C). However, the generation of vacancies when carbide precipitates dissolve may promote a distribution with substitutional boron atoms. The absence of a fast mechanism for the transition from substitutional to interstitial occupancy will make the slow substitutional boron diffusion in the matrix rate controlling for the coarsening process.

High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr3C2-NiCr Coating

High-velocity oxy-fuel (HVOF) sprayed coatings have the potential to enhance the high-temperature oxidation, corrosion, and erosion-corrosion resistance of boiler steels. In the current work, 75 pct chromium carbide-25 pct (nickel-20 pct chromium) [Cr3C2-NiCr] coating was deposited on ASTM SA213-T22 boiler steel using the HVOF thermal spray process. High-temperature oxidation, hot corrosion, and erosion-corrosion behavior of the coated and bare steel was evaluated in the air, molten salt [Na2SO4-82 pct Fe2(SO4)3], and actual boiler environments under cyclic conditions. Weight-change measurements were taken at the end of each cycle. Efforts were made to formulate the kinetics of the oxidation, corrosion, and erosion-corrosion. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM)/energy dispersive spectroscopy (EDS) techniques were used to analyze the oxidation products. The coating was found to be intact and spallation free in all the environments of the study in general, whereas the bare steel suffered extensive spallation and a relatively higher rate of degradation. The coating was found to be useful to enhance the high-temperature resistance of the steel in all the three environments in this study.

Correlation between morphology, chemical environment, and ferromagnetism in the intrinsic-vacancy dilute magnetic semiconductor Cr-doped Ga2Se3/Si(001)

Chromium-doped gallium sesquiselenide, Cr:Ga${}_{2}$Se${}_{3}$, is a member of a new class of dilute magnetic semiconductors exploiting intrinsic vacancies in the host material. The correlation among room-temperature ferromagnetism, surface morphology, electronic structure, chromium concentration, and local chemical and structural environments in Cr:Ga${}_{2}$Se${}_{3}$ films grown epitaxially on silicon is investigated with magnetometry, scanning tunneling microscopy, photoemission spectroscopy, and x-ray absorption spectroscopy. Inclusion of a few percent chromium in Ga${}_{2}$Se${}_{3}$ results in laminar, semiconducting films that are ferromagnetic at room temperature with a magnetic moment $\ensuremath{\geqslant}4{\ensuremath{\mu}}_{B}/\text{Cr}$. The intrinsic-vacancy structure of defected-zinc-blende $\ensuremath{\beta}\ensuremath{-}$Ga${}_{2}$Se${}_{3}$ enables Cr incorporation in a locally octahedral site without disrupting long-range order, determined by x-ray absorption spectroscopy, as well as strong overlap between Cr $3d$ states and the Se $4p$ states lining the intrinsic-vacancy rows, observed with photoemission. The highest magnetic moment per Cr is observed near the solubility limit of roughly one Cr per three vacancies. At higher Cr concentrations, islanded, metallic films result, with a magnetic moment that depends strongly on surface morphology. The effective valence is Cr${}^{3+}$ in laminar films, with introduction of Cr${}^{0}$ upon islanding. A mechanism is proposed for laminar films whereby ordered intrinsic vacancies mediate ferromagnetism.

Microstructure of a Creep-Resistant 10 Pct Chromium Steel Containing 250 ppm Boron

The microstructure of a trial martensitic chromium steel containing a high content of boron (250 ppm) was characterized in detail in the as-tempered and aged conditions. This steel has a similar composition and heat treatment as the TAF steel that still is unsurpassed in creep strength among all 9 to 12 pct chromium steels. Characterization was performed by using scanning electron microscopy, energy-filtered transmission electron microscopy, secondary ion mass spectroscopy, and atom probe tomography. Focus was placed on investigating different types of precipitates that play a key role in improving the creep resistance of these steels. The low tempering temperature of 963 K (690 °C) is enough for the precipitation of the full volume fraction of both MX and M23C6. A high boron content, more than 1 at. pct, was found in M23C6 precipitates and they grow slowly during aging. The high boron level in the steel results in metal borides rather than BN with the approximate formula (Mo0.66Cr0.34)2(Fe0.75V0.25)B2. Two families of MX precipitates were found, one at lath boundaries about 35 nm in size and one dense inside the laths, only 5 to 15 nm in size.

Formation of Delta Ferrite in 9 Wt Pct Cr Steel Investigated by In-Situ X-Ray Diffraction Using Synchrotron Radiation

In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling.