Graphite Precipitation Research Articles

Evaluation of ductile iron casting material quality using ultrasonic testing

The study presents the influence of pouring delay time on the decay of spheroidisation effect and magnesium content in the alloy, as well as the influence of magnesium content on the shape and number of graphite precipitations in bar samples. For one particular set of production conditions, it was observed that 17 min after completing the spheroidisation and modification process, the magnesium content had decreased from 0.07% to 0.04%. This resulted in a decrease in the graphite precipitation shape index S s from 0.081 to 0.067, as well as a decrease in the average number of graphite precipitations N A from 568 to 305 mm −2. Dependencies have been worked out to describe the influence of time passed after the end of spheroidisation and modification on the amount of magnesium in the ductile iron, as well as the influence of magnesium content on the graphite shape index S s and number of graphite precipitations N A. It has been found that a reduction in magnesium content of approximately 0.027% corresponds to a reduction in graphite precipitation shape index S s of about 0.014, as well as a reduction in the average number of graphite precipitations N A of 255 mm −2. On the basis of the longitudinal ultrasonic wave velocity measurements c L, as well as the measurement of the graphite shape index S s and the number of graphite precipitations N A in the analyzed ductile iron, dependencies have been worked out: c L = 3218.4 S s + 5407.6, R = 0.99, c L = 0.1887 N A + 5567.6, R = 0.99, where: S s is the graphite shape index, N A is the number of graphite precipitations, mm −2, c L is the ultrasonic velocity, m/s. Changes in the shape and number of graphite precipitations are accompanied by a decrease in the average longitudinal ultrasound wave velocity c L of 45 m/s. This resulted in establishing nomograms to evaluate the graphite shape index and the number of graphite precipitation from a measured ultrasonic wave velocity in control samples. Obtained dependencies are only valid in the conditions of the specific foundry, for which they have been developed. The applied methodology allowed the achievement of dependencies with high correlation coefficient values, which demonstrates its suitability for industrial use.

The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism

The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C–O–H fluids. The δ 13C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous metapelites of the Skiddaw Group by andesite magmas of the Borrowdale Volcanic Group. The graphite mineralization occurred as the fluids migrated upwards through normal conjugate fractures forming the main subvertical pipe-like bodies. The mineralizing fluids evolved from CO 2–CH 4–H 2O mixtures (XCO 2 = 0.6–0.8) to CH 4–H 2O mixtures. Coevally with graphite deposition, the andesite and dioritic wall rocks adjacent to the veins were intensely hydrothermally altered to a propylitic assemblage. The initial graphite precipitation was probably triggered by the earliest hydration reactions in the volcanic host rocks. During the main mineralization stage, graphite precipitated along the pipe-like bodies due to CO 2 → C + O 2. This agrees with the isotopic data which indicate that the first graphite morphologies crystallizing from the fluid (cryptocrystalline aggregates) are isotopically lighter than those crystallizing later (flakes). Late chlorite–graphite veins were formed from CH 4-enriched fluids following the reaction CH 4 + O 2 → C + 2H 2O, producing the successive precipitation of isotopically lighter graphite morphologies. Thus, as mineralization proceeded, water-generating reactions were involved in graphite precipitation, further favouring the propylitic alteration. The structural features of the pipe-like mineralized bodies as well as the isotopic homogeneity of graphite suggest that the mineralization occurred in a very short period of time.

Insights into the origin of mantle graphite and sulphides in garnet pyroxenites from the External Liguride peridotites (Northern Apennine, Italy)

Abstract This paper describes a rare occurrence of graphite in non-cratonic mantle rocks. Graphite has been found in garnet clinopyroxenite layers from the External Liguride peridotites that represent slices of subcontinental lithospheric mantle exhumed at the ocean floor in Mesozoic times. The high-pressure assemblage of the pyroxenites is characterized by garnet+Al–Na-rich clinopyroxene, and testifies to an early stage of equilibration at approximately 2.8 GPa and 1100 °C. Graphite occurs as small dispersed euhedral flakes and stacks of flakes. Structural characterization by microRaman spectrometry indicates a highly ordered structure, compatible with a high-temperature mantle origin. C isotope composition of graphite has a typical mantle signature. Fe–Ni–Cu sulphides occur as accessory phases, both as blebs enclosed in silicates (E-Type) and interstitial grains (I-Type). The sulphide assemblage (Ni-free pyrrhotite, pentlandite, Cu–Fe sulphides) mainly reflects subsolidus exsolution from high-temperature Fe–Ni–Cu monosulphide solid solutions with variable Ni (up to 18 wt%) and Cu content (up to 7 wt%). The origin of E- and I-Type sulphides requires the existence of an immiscible Fe–Ni–Cu sulphide liquid, which segregated from the partial melt of the garnet pyroxenite. Graphite precipitation in the pyroxenite was presumably related to the reduction of a more oxidized carbon species interacting with the sulphide liquid as a reducing agent.

Quality Control by Means of Ultrasonic in the Production of Ductile Iron

The paper presents several concepts of physical substantiation for the rationale of building the relationships between mechanical properties and ultrasonic inspection indicators. Special emphasis is put on assessing the influence of graphite shape number SS and the number of graphite precipitations NA on the tensile strength and longitudinal ultrasound wave velocity of ductile iron manufactured under production conditions. Tests were conducted on wedge casts which were used as samples for tensile tests and a map of the structure and longitudinal ultrasound wave velocity was determined for the cast wedges. The tensile tests were conducted and values of graphite shape number, average number of graphite precipitations and longitudinal wave velocity were determined in the place where the sample was broken. Relations between the mechanical properties, graphite shape number, number of graphite precipitations and the velocity of longitudinal ultrasonic wave were determined.

Sintering of binderless tungsten carbide

The most widely used mold materials for optical glass molding processes are cemented tungsten carbide and silicon carbide. In this research, tungsten carbide with minor addition of TiC and TiN as the second phase has been studied. The powders were ball-milled and pre-formed under a temperature of 200 °C and a pressure of 130 MPa. The specimens were sintered in a graphite lined furnace at a temperature of 1600 °C. A density of 15.43 g/cm 3, a Vickers hardness number of 23.14 GPa, and a fracture toughness of 6.56 MPa m 1/2 was found for the sintered specimen fabricated by this process. The result of X-ray analysis revealed no trace of precipitated graphite during sintering, nor the brittle eta-phase as a result of decarburization. Through scanning electron microscopy, spherical air bubbles have been found to precipitate inside the grains, because the activation energy for grain-boundary diffusion is lower than that of the air inside the grains. Therefore it is advisable that the pre-form process is carried out in vacuum.

Low-density CO 2-rich fluid inclusions from charnockites of southwestern Madurai Granulite Block, southern India; implications on graphite mineralization

Characterization of fluid inclusions in graphite-bearing charnockites from the southwestern part of the Madurai Granulite Block in southern India reveals a probable relation with the formation and break down of graphite during the high-grade metamorphism. The first-generation monophase pure CO 2 inclusions, the composition of which is confirmed by laser Raman spectroscopy, recorded moderate density (0.77–0.87 g/cc) corresponding to low tapping pressure (around 2 kb) than that of the peak granulite-facies metamorphism. The precipitation of graphite, as inferred from graphite inclusions and δ 13C values of the graphite from the outcrops, is interpreted as the cause of this lowering of fluid density. An intermediate generation of pseudosecondary inclusions resulted from the re-equilibration or modification of the first-generation fluids and the CO 2 formed is interpreted to be the oxidation product from graphite. The youngest generation of fluids which caused widespread retrogression of the granulites is a low-temperature (∼350 °C) high-saline (32.4–52.0 wt% NaCl equivalent) brine. Carbon isotope data on the graphite from the charnockites show δ 13C values ranging from −11.3 to −19.9‰, suggesting a possibility of mixing of carbon sources, relating to earlier biogenic and later CO 2 fluid influx. Combining the information gathered from petrologic, fluid inclusion and carbon stable isotope data, we model the fluid evolution in the massive charnockites of the southwestern Madurai Granulite Block.

Nanostructuring in Ni/SiC reaction layers, investigated by imaging of atomic columns and DFT calculations

Formation and structuring of the product phases of solid state reactions between nickel and silicon carbide were evidenced by high resolution electron microscopy (HREM), as well as by high angle annular dark field scanning transmission technique (HAADF-STEM) allowing the element-sensitive Z-contrast. The observed preferential orientation relationships between precipitated graphite and δ-Ni 2Si as well as between the silicide and the 6H-silicon carbide substrate could be explained by epitaxial relations between the corresponding phases. The diffusion-related mechanisms of the carbon precipitation were investigated in the framework of density functional theory (DFT), yielding information on the diffusion barriers and preferential diffusion directions of carbon atoms in δ-Ni 2Si. The calculated driving forces for solution and precipitation of carbon within the silicide phase are discussed.

Effect of Ni powder characteristics on the consolidation of ultrafine TiMoCN cermets by means of SPS and HIP technologies

Fully dense titanium carbonitride cermets have been consolidated from Ti(C,N)–Ni–Mo 2C–TiAl 3 powder mixtures either by spark plasma sintering or hot isostatic pressing techniques. Carbonyl Ni powders enhance the densification of the cermets produced by SPS (spark plasma sintering), a phenomenon likely related to a more efficient dissolution of Mo 2C additions and the possible precipitation of α″ phase. Both SPS and HIP (hot isostatic pressing) processes lead to materials with a bimodal Ti(C,N) grain size distribution containing a considerable fraction of nanometric grains. Unlike SPS, HIP induces significant graphite precipitation which could be explained by the destabilization of the carbonitride phase under high isostatic pressures at high temperature. Optimized compositions processed by SPS exhibit a combination of hardness and toughness close to the range covered by ultrafine WC–Co hardmetals of similar binder contents.

Effect of presintering treatments on TiMoCN–Ni based cermets processed from different powder mixtures

Abstract Different powder mixtures have been used to analyse the effect of presintering heat treatments on the composition and microstructure of TiMoCN–Ni based cermets. When methane is present in the atmosphere C contents after presintering can be associated to the C activity calculated from the C + 2H 2 = CH 4 equilibrium. H 2 based atmospheres produce high C losses whereas N 2 –CH 4 –H 2 gas mixtures induce strong carburization of the compacts. When no methane is present in the atmosphere, the C activity could be related to the C content of the compacts by the Boudouard equilibrium. Changes in C and N contents are also observed to depend critically on the phases present in the powder mixtures. Those containing free C, TiC, Mo 2 C or TiMoC phases show higher C and N changes after presintering than those based on quasi-monophasic TiMoCN powders. These data confirm that presintering treatments can be designed to modify the C/N ratio of TiMoCN–Ni cermets in order to avoid graphite precipitation and to have a closer control on the composition of carbonitride and metallic binder phases after sintering.

Manganese distribution and effect on graphite shape in advanced cast irons

The manganese contribution to a change of the graphite shape (in nodular graphite cast irons) has never been revealed. We made obvious the negative action of this element on the nodularization of graphite. Using SEM, we observe a significant change of the shape of the precipitated graphite (decrease of the shape coefficient values), depending on the cooling rate, the nature and the quantity of the nodularizing elements. The distribution of manganese and silicon in the metallic matrix and in the nodular graphite of cast irons with various amounts of manganese was studied using Castaing Scanning X-ray Microprobe. The distribution profiles of (K α Mn and K α Si) show that polycarbides appear on the graphite periphery in the cast iron with manganese contents over 1.0% (confirmed by SEM-EDX analysis). These chemical compounds influence the slowing down of the expected growth of graphite during the austenitic decomposition. This allows us to suggest that manganese would be added to the referenced antinodularizing elements group (O, S, halogens and Pb, Te, Ti, Cu, Al, Sn, Sb, Bi).

A Model for High-Temperature Pitting Corrosion in Nickel-Based Alloys Involving Internal Precipitation of Carbides, Oxides, and Graphite

The present investigation is concerned with fundamental studies of the mechanisms of pitting corrosion in the Ni-based alloys 602 and 693, following long-term exposure to syngas at 540 °C and a 35-bar total pressure. The 4-years’ plant-exposed alloys were examined using synchrotron X-ray diffraction (XRD) in combination with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is concluded that the pitting corrosion attacks start when carbon diffuses into the bulk of the alloys following the breakdown of the protective Cr2O3-Al2O3 surface oxide layer. During the incubation period, this oxide layer provides an effective barrier against carbon intrusion by virtue of its ability to restore cracks and flaws through diffusion. The corrosion pits then grow by a process of internal carburization and oxidation, in which carbides, oxides, and graphite form separately within an approximately 30-μm-thick belt in front of the pits (referred to as the white zone). In particular, the oxidation of the internal Cr3C2 carbides occurring close to the white zone/pit interface is associated with large volume changes. This volume expansion results in the buildup of high mechanical stresses within the white zone and, eventually, to the complete disintegration of the original alloy matrices into a layered pit microstructure consisting of Ni + Fe and Cr2O3 + Al2O3 + graphite. The observed microstructural changes have been rationalized through detailed modeling of the physical reactions involved, leading to the development of new and comprehensive models for high-temperature pitting corrosion in Ni-based alloys.

Ventilation of CO2 from a reduced mantle and consequences for the early Martian greenhouse

Because much or all of the Martian mantle is apparently quite reduced, with oxygen fugacities within 1 order of magnitude of the iron–wüstite (IW) buffer, the stable form of carbon in Martian basalt source regions is likely to be graphite. The presence of graphite limits the liberation of CO2 from Martian mantle-derived magmas and thereby constrains volcanogenic fluxes of CO2 to the Martian atmosphere. Thermodynamic calculations for graphite-saturated basalt indicate that dissolved CO2 concentrations near the Martian mantle solidus range from 5 ppm at IW−1 to 500 ppm at IW+1 and vary little with pressure along the solidus, but increase with increasing temperature (and melt fraction) above the solidus. For oxygen fugacities between IW−1 and IW+1, formation of the ancient (4.5 Ga) 50 km-thick Martian crust could therefore have produced a CO2 atmosphere ranging from 70 mbar to 13 bars, depending chiefly on the mean oxygen fugacity during melting and, to a lesser extent, on temperatures and pressures of partial melting. Subsequent volcanogenic outgassing of CO2 associated with post-4.5 Ga magmatism could have contributed from 40 mbar up to 1.4 bars of CO2 to the atmosphere, depending on oxygen fugacity and the details of melting conditions. However, for both early (~4.5 Ga) and subsequent volcanic activity, large CO2 fluxes outgassed to the mantle are probable only at the more oxidized and higher temperature extrema of plausible ranges. If the oxidation state of the Martian mantle is and has been more similar to more reduced estimates, ventilation of CO2 to the Martian atmosphere has been quite limited and may not be sufficient to account for greenhouse conditions apparently required to support liquid surface waters. Finally, low concentrations of CO2 in graphite-saturated magmas under reducing conditions suggest that carbon in the Martian mantle may have originated by precipitation of graphite (or diamond) during solidification of a magma ocean.

Identification and quantification of active manufacturing factors for graphite formation in centrifugally cast Nihard cast irons

The present research arises from the need to gain knowledge to control the precipitation of interdendritic dispersed graphite in mottled Nihard cast irons used in the outer ring layer of industrial duplex work rolls. Industry desires a volume fraction of 2.5–4% graphite, distributed homogeneously across the layer thickness, with a reasonably constant, high number of particles across the layer, with a predominantly short flake-graphite shape. The objective was to ascertain the role of metallurgical manufacturing parameters and their interaction with graphite precipitation in the layer, and in the outer and inner sections of the roll collar. These rolls, used in the finishing stands of hot strip steel mills, were processed by a double pour method using vertical centrifugal casting machines. Analysis was conducted using a fractional Design of Experiments (DOE) program consisting of 16 industrial trials based on the study of 7 manufacturing factors at 2 levels. The analyzed responses, obtained by quantitative metallographic techniques, were: the volume fraction, V V, number per unit area, N A, and the graphite morphology across the layer thickness. The results confirmed that an increase from 0.5 to 0.8 kg/T of SiCaMn added as a bath inoculant in the ladle increased the fraction of precipitated graphite without affecting N A. An outstanding result was that the addition of 1 kg/T of FeTi as a bath inoculant did not modify the amount of precipitated graphite but significantly affected the morphology, favouring the development of elongated graphite shapes.

Modelling the role of graphite in development of a mineralised mid-crustal shear zone, Macraes mine, New Zealand

The Hyde–Macraes Shear Zone (HMSZ) is a mineralised low-angle shear within the Otago Schist traceable for ∼ 30 km with a NW strike. It is being actively mined along 12 km of this strike, producing > 6 Moz of gold. The shear zone formed under lower greenschist facies conditions as the host schist was uplifted through the brittle–ductile transition. Sheared rocks consist of greenschist facies schists with mineralogy only subtly different from that of the host schist. Pervasive fluid flow has occurred along grain boundaries and within microshears whose development has been enhanced by the deposition of hydrothermal graphite. We model the development of these microshears using a three-dimensional numerical code. For an inhomogeneous initial rock with lithostatic fluid pressures and a dynamic permeability deformed under dextral non-coaxial flow, deformation is distributed into weak shear bands. Graphite deposition and associated reaction-softening have a dramatic effect on the development of model shear zones. Graphite is deposited into a shear band, weakening it and further localising the deformation into that shear band, producing an anastomosing and interconnected shear zone structure such as observed in the HMSZ. The degrees of graphite precipitation and graphite-induced weakening are varied in the models. Graphite precipitation with a low degree of reaction-softening results in more diffuse shear bands. In contrast less graphite deposition but with a high degree of reaction-softening leads to the development of more focused shear bands. Graphite deposition has clearly controlled the formation of the HMSZ structure, and is an important indicator of potentially mineralised mid-crustal structures elsewhere.

Improvement of Magnetic Characteristic in Spheroidal Graphite Cast Iron

The spheroidal graphite cast iron is widely used as a structural material in an industrial field. Possibility to be able to use by improving magnetic characteristic of spheroidal graphite as magnetic circuit material of product related to electromagnetism besides structure material. In this study, the influence that the amount of graphite precipitation , the matrix organization, and the structure gave to a magnetic characteristic was investigated in the spheroidal graphite cast iron that makes matrix ferrite by compounding C element and the Si element and heat-treatment. The graphite was completely precipitated at the heat-treatment temperature of 1173K or more, the organizatiom became a ferrite, and permeability rose. Moreover, Rough making by heat-treatment the size about the particle size of the ferrite and the appearance of the Fe-Si phase have raised permeability.

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere.

Highly cracked and isomerized archaeal lipids and bacterial lipids, structurally changed by thermal stress, are present in solvent extracts of 2,707- to 2,685-million-year-old (Ma) metasedimentary rocks from Timmins, ON, Canada. These lipids appear in conventional gas chromatograms as unresolved complex mixtures and include cyclic and acyclic biphytanes, C36-C39 derivatives of the biphytanes, and C31-C35 extended hopanes. Biphytane and extended hopanes are also found in high-pressure catalytic hydrogenation products released from solvent-extracted sediments, indicating that archaea and bacteria were present in Late Archean sedimentary environments. Postdepositional, hydrothermal gold mineralization and graphite precipitation occurred before metamorphism (approximately 2,665 Ma). Late Archean metamorphism significantly reduced the kerogen's adsorptive capacity and severely restricted sediment porosity, limiting the potential for post-Archean additions of organic matter to the samples. Argillites exposed to hydrothermal gold mineralization have disproportionately high concentrations of extractable archaeal and bacterial lipids relative to what is releasable from their respective high-pressure catalytic hydrogenation product and what is observed for argillites deposited away from these hydrothermal settings. The addition of these lipids to the sediments likely results from a Late Archean subsurface hydrothermal biosphere of archaea and bacteria.

Fluid chemistry of the Palaeoproterozoic Fäboliden hypozonal orogenic gold deposit, northern Sweden: Evidence from fluid inclusions

A new ore province, the Gold Line, southwest of the Skellefte District, northern Sweden, is currently under exploration. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. The mineralization is hosted by arsenopyrite-bearing quartz veins, within a steep shear zone in amphibolite facies metagreywacke host rocks. Gold occur in fractures and as intergrowths in arsenopyrite-löllingite, and as free grains in the silicate matrix of the host rock. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. Primary fluid inclusions in the Fäboliden quartz veins show a CO2-CH4 or a H2S (±CH4) composition (the latter recognized for the first time in a Swedish ore deposit). The primary fluid inclusions are associated with arsenopyrite-löllingite (+gold) and the CO2-CH4 fluid was also involved in precipitation of graphite. A prevalence of carbonic over aqueous fluid inclusions is characteristic for a number of hypozonal high-temperature orogenic gold deposits. The Fäboliden deposit, thus, shows fluid compositions similar to other hypozonal orogenic gold deposits. The proposed main mechanism for precipitation of gold from the fluids, is a mixing between H2S-rich and H2O?-CO2±CH4 fluids. Fluid inclusion data indicate arsenopyrite-löllingite and graphite deposition at a pressure condition of about 4 kbar. Graphite thermometry indicates maximum temperatures of 520-560°C for the hydrothermal alteration at Fäboliden, suggesting that at least the late stages of the mineralizing event took place shortly after peak-metamorphism in the area, i.e. at c. 1.80 Ga.

Production of carbonic fluids during metamorphism of graphitic pelites in a collisional orogen—An assessment from fluid inclusions

Fluid inclusions in quartz veins within Proterozoic metamorphic rocks in the Black Hills, South Dakota, were examined by microthermometry and Raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic-rich shales and late-orogenic magmatism, both of which were related to the collision of the Wyoming and Superior crustal blocks. Fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet-grade conditions, and in veins within the aureole of the Harney Peak Granite (HPG), where temperatures reached second-sillimanite grade conditions. Early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early CH 4 or CO 2 and N 2-dominated inclusions. These fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase. They are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fO 2 conditions. Most inclusions in the quartz veins are, however, secondary CO 2-bearing. They imply a transition to higher fO 2 conditions with increasing temperature of regional metamorphism. The fO 2 conditions may have been controlled by the mineral assemblage in the host metapelites. The prevalence of bimodal distributions of trapped CO 2–N 2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism. In the aureole of the HPG, graphite was evidently consumed by influx of magmatic fluids. CO 2–H 2O fluid inclusions dominate, but they have significantly less N 2 than inclusions at lower metamorphic grades. All inclusions define secondary trails in mostly unstrained quartz. The bimodality of inclusion compositions is not as well defined as at lower grades, with many inclusions containing intermediate CO 2–H 2O compositions. This suggests that a single fluid phase existed at the high temperatures in the granite aureole, but then unmixed during cooling. A set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains CH 4-bearing inclusions with little N 2. The existence of CH 4 in these inclusions is attributed to complexing of magmatic B with hydroxyl anions taken from the CO 2–H 2O fluid phase, effectively causing reduction in fO 2 and promoting precipitation of graphite.

Crystallization and Breakdown of Metasomatic Phases in Graphite-bearing Peridotite Xenoliths from Marsabit (Kenya)

Mantle-derived xenoliths from the Marsabit shield volcano (eastern flank of the Kenya rift) include porphyroclastic spinel peridotites characterized by variable styles of metasomatism. The petrography of the xenoliths indicates a transition from primary clinopyroxenebearing cryptically metasomatized harzburgite (light rare earth element, U, and Th enrichment in clinopyroxene) to modally metasomatized clinopyroxene-free harzburgite and dunite. The metasomatic phases include amphibole (low-Ti Mg-katophorite), Na-rich phlogopite, apatite, graphite and metasomatic low-Al orthopyroxene. Transitional samples show that metasomatism led to replacement of clinopyroxene by amphibole. In all modally metasomatized xenoliths melt pockets (silicate glass containing silicate and oxide microphenocrysts, carbonates and empty vugs) occur in close textural relationship with the earlier metasomatic phases.The petrography, major and trace element data, together with constraints from thermobarometry and fO2 calculations, indicate that the cryptic and modal metasomatism are the result of a single event of interaction between peridotite and an orthopyroxene-saturated volatile-rich silicate melt. The unusual style of metasomatism (composition of amphibole, presence of graphite, formation of orthopyroxene) reflects low P^ T conditions (� 850^10008 Ca t51� 5 GPa) in the wall-rocks during impregnation and locally low oxygen fugacities. The latter allowed the precipitation of graphite from CO2.The inferred melt was possibly derived from alkaline basic melts by melt^rock reaction during the development of the Tertiary^Quaternary Kenya rift. Glassbearing melt pockets formed at the expense of the early phases, mainly through incongruent melting of amphibole and orthopyroxene, triggered by infiltration of a CO2-rich fluid and heating related to the magmatic activity that ultimately sampled and transported the xenoliths to the surface.

Saturated Fractional Design of Experiments: Toughness and Graphite Phase Optimizing in Nihard Cast Irons

The aim of the present research is to identify the manufacturing factors that exert an active influence on the graphite phase formation in mottled Nihard cast irons constituting the roll shells of duplex work rolls processed by the double pour method during centrifugal casting. The studied rolls, referred to as alloy indefinite chill, were processed at industrial scale and had a core consisting of spheroidal graphite cast iron with a matrix of ferrite and pearlite. An additional aim of this study was to evaluate the effect and extent of these factors on the dynamic toughness response of the roll shell material.The research methodology employed consisted of the application of a saturated design of experiments with seven factors, eight experiments, and resolution III. The measured responses for graphite were: the volume fraction, count number per unit area, and morphology, determined by quantitative metallography. Impact testing was characterized by Charpy tests on U-notched specimens at 350 °C. The manufacturing factors studied were: the final weight percent of silicon, sulfur, and manganese; the liquidus and the casting temperatures; and, finally, inoculation with SiCaMn and A-type FeSi (with Zr).The statistical experimental method conducted allowed us to confirm the significance of factors such as the %Si, the liquidus temperature and inoculation with SiCaMn on the precipitation of graphite in a white cast iron such as the Nihard irons used in the roll shell, in agreement with the precipitation of graphite in gray cast irons widely reported in the literature. It was also shown that the development of lamellar graphite shapes were favored by an increase in the total equivalent carbon and also by the increase in the amount of A-type FeSi added. Furthermore, the impact toughness was shown to improve with the increase in both the %Si and the liquidus temperature.