Graphite Precipitation Research Articles

Lattice Parameter of Austenite in Silicon Cast Irons

Upon solidification, graphitic cast irons undergo a volume change whose amplitude depends on two opposite terms, the contraction associated with austenite formation and the expansion due to graphite crystallization. During cooling after solidification, further precipitation of graphite occurs that continuously changes the physical properties of the material and possibly affects the eutectoid transformation that transforms the matrix from austenitic to ferritic or ferritic-pearlitic. This work intended to study the density of graphitic cast irons at high temperature, i.e., in the temperature range where the matrix is austenitic. High-temperature laboratory X-rays have been carried out on several alloys containing various carbon and silicon contents to characterize the austenite mean lattice parameter. By complementing these results with literature data, a statistical analysis was carried out that expresses the austenite mean lattice parameter as a function of temperature and composition, evidencing the high uncertainty related to the austenite carbon content. Finally, one of the investigated alloys was submitted to a simultaneous dilatometry and X-ray analysis in a synchrotron from room temperature to 1050 °C. The data are used to discuss the austenite lattice parameter prediction and the possibility of density prediction.

Experimental Simulation of Directional Crystallization of SiMo Cast Iron Alloyed with Al and Cr.

SiMo ductile cast iron combines ease of part fabrication with good mechanical properties, including a usable plasticity range. Its poor corrosion resistance inherited from grey cast iron could be alleviated through alloying with Al or Cr additions capable of forming a dense oxide scale protecting the substrate. However, the presence of Al and Cr in cast iron tends to make the material brittle, and their optimum alloying additions need to be studied further. The present work was aimed at investigating the effect of crystallization rates on microstructure changes during directional crystallization of SiMo-type alloys with up to 3.5% Al and 2.4% Cr. The experiment was performed using the Bridgman-Stockbarger method. The tubular crucible was transferred from the hot section to cold section at rates ranging from 5 mm/h to 30 mm/h with a 4/5 crucible length and then quenched. The introduced Al promoted graphitization up to a point, wherein, at the highest applied addition, the graphite precipitation preceded crystallization of the rest of the melt. A rising level of Cr in these alloys from 1% to 2.4% resulted in the formation of low and high contents of pearlite, respectively. The higher crystallization rates proved effective in increasing the ferrite content at the expense of pearlite. In the investigated cast iron samples with smaller applied alloying additions, Widmanstätten ferrite or ausferrite, i.e., fine acircular phase, were often found. The switch from directional crystallization to quenching caused a transition from a liquid to solid state, which started with nucleation of islands of fine austenite dendrites with chunky graphite eutectic separating them. As these islands expanded, they pushed alloying additions to their sides, promoting carbide or pearlite formation in these places and forming a super-cell-like structure. The performed experiments helped gather information concerning the sensitivity of the microstructure of SiMo cast iron modified with Al and Cr to crystallization rates prevailing in heavy cast structures.

Analysis of the Microstructure and Hardness of Flake Graphite Cast Iron Using the Barkhausen Noise Method and Conventional Techniques

The new brake disc was evaluated for microstructure and hardness by the conventional destructive tests and non-destructive Barkhausen noise method (BNM). Ten non-destructive measurements were carried out in different areas of a brake disc, which were then cut out and made into metallographic test samples. Qualitative and quantitative analysis of graphite precipitates was performed to assess their volume in material matrix, anisotropy and size. Subsequently, graphs showing the relationships between selected stereological parameters of graphite precipitates and parameters determined from the RMS envelope of Barkhausen noise were elucidated. Similar relationships between hardness and parameters coming from non-destructive tests were carried out. Magnetic parameters that specified the size of a graphite precipitate was selected. In addition, repeatability studies using BNM were carried out in the areas of the material with the smallest and largest average size of graphite precipitates. A linear relationship between amplitude of BN and length of graphite flakes was found. The paper presents the possibilities of assessing the volume and size of graphite precipitates, as well as cast iron hardness using BNM.

Viscosity and structure studies of iron-based quaternary melts: The effect of P

This study systematically investigates the underlying principles and mechanisms governing viscosity across the entire range for the Fe-4.5C-0.1Ti-xP (in wt.%) melts. The viscosity profile exhibits distinct variations in different phases. In the solid–liquid transition region, the primary determinant of viscosity is the presence of solid phase particles, while in the region characterized by liquid phase, the primary influencing factor is the number of clusters. Notably, the impact of P content demonstrates a contrasting effect on low-temperature solid phase precipitation and high-temperature liquid phase structure. During the low-temperature solid phase precipitation stage, an increase in P content serves as a catalyst for graphite precipitation, resulting in an increase in system viscosity and, by extension, impacting an increase in system viscosity. In contrast, within the high-temperature liquid phase, the interaction of P with iron (Fe) results in the breakdown of mid-range clusters in the original system, leading to the formation of smaller clusters with a reduced overall cluster volume. Consequently, an increase in P content is associated with a decrease in viscosity. These findings provide a nuanced understanding of the interplay between P content and viscosity throughout different phases of the melt.

Microstructural Evolution During Welding of High Si Solution-Strengthened Ferritic Ductile Cast Iron Using Different Filler Metals

The paper deals in depth with characterizing bead-on-plate welds on EN-GJS-500-14 base metal, utilizing two filler metals: a pure Ni wire and a NiFe wire containing 45 wt pct Ni. The welds were conducted using the same heat input to ensure comparability in microstructure analysis. The microstructural observations were carried out using optical and scanning electron microscopies, X-ray tomography, X-ray diffraction analysis, and microhardness testing. Thermodynamic simulations using the non-equilibrium Scheil solidification model provide insights into the solidification process and the underlying metallurgical factors associated with the observed microstructural evolution. The observations revealed that the pure Ni wire deposited a softer fusion zone with graphite precipitation, while cementite precipitated in the fusion zone of NiFe alloy. The formation of martensite structures with different morphologies was the predominant microstructural evolution in the heat-affected zone of both welds. The partially melted zone of the pure Ni weld is narrower than the NiFe weld because more diffusion of Ni avoids widening the brittle structures in the partially melted zone. An unmixed zone in the form of a peninsula was exclusively observed in the fusion zone of the NiFe weld because of inadequate diffusion of Ni into the liquified materials along the fusion boundary.

Usage of the Cast Iron Cylindrical Liner in an Automobile Engine Block

This study addresses the issues related to the quality of the connection between cast iron liners and inserts in a pressure die-cast automotive engine block, along with the macro and micro wear of the cylinder bearing surface. it was found that the commonly used HPDC high-pressure casting technology of Al-Si alloy engine blocks with cast iron liners, in which the cylinder liner is then recreated, does not ensure their metallic connection. The micro-gap created there becomes thicker as the engine is used, which worsens the conditions for heat dissipation from the sleeve to the block. Locally, on the surface of the cylinder bearing surface, reductions in honing effects and longitudinal cracks were observed. The presented literature mechanism of micro wear of the cylinder bearing surface, dependent on the morphology of graphite segregations, was confirmed. The mechanism of creating micro-breaks in the area of phosphoric eutectic and graphite precipitation occurrence was presented, initiated by the formation of microcracks in the eutectic and delaminations at the eutectic-matrix boundary.

Microstructure and Properties Variation of High-Performance Grey Cast Iron via Small Boron Additions

A study was undertaken to investigate the effects of small boron additions on the solidification and microstructure of hypo-eutectic alloyed grey cast iron. The characteristic temperatures upon crystallisation of the treated metal melt were recorded, specifically those concerning small boron addition by using thermal analysis with the ATAS system. Additionally, a standardised wedge test was set to observe any changes in chill performance. The microstructures of thermal analysis samples were analysed using a light optical microscope (LOM) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS), which reveal variations in graphite count number with the addition of boron within observed random and undercooled flake graphite. The effect of boron was estimated by the classical analytical and statistical approach. The solidification behaviour under equilibrium conditions was predicted by a thermodynamic approach using Thermo-Calc. Based on all gathered data, a response model was set with boron for given melt quality and melt treatment using the experimentally determined data. The study reveals that boron as a ferrite and carbide-promoting element under the experimental set shows weak nucleation potential in synergy with other heterogenic nuclei at increased solidification rates, but no considerable changes were observed by the TA samples solidified at slower cooling rates, indicating the loss of the overall inoculation effect. The potential presence of boron nitride as an inoculator for graphite precipitation for a given melt composition and melt treatment was not confirmed in this study. It seems that boron at increased solidification rates can contribute to overall inoculation, but at slower cooling rates these effects are gradually lost. In the last solidification range, an increased boron content could have a carbide forming nature, as is usually expected. The study suggests that boron in traces could affect the microstructure and properties of hypo-eutectic alloyed grey cast iron.

Thermotopes-COH—A software for carbon isotope modeling and speciation of COH fluids

Carbon-bearing fluids and condensed carbon are common on and inside planetary bodies. Understanding the mechanisms capable of transferring carbon from fluids into solids and vice-versa is central in many fundamental and applied research targets within the Earth and Planetary Sciences. A broad range of applications can benefit from the thermodynamic properties of carbon-oxygen-hydrogen (COH) systems. As an example, the precipitation of natural graphite or diamond can be modeled within the COH thermodynamic systems. Because the evolution of COH fluids implies isotopic fractionation among different species, carbon stable isotopes can be used in conjunction with thermodynamic calculations to reconstruct graphite or diamond formation mechanisms, or the evolution of fluid species such as carbon dioxide or methane.Thermotopes-COH is a Python-based graphical user interface (GUI) software for computation of thermodynamic and carbon isotopic modeling in the C–O–H system within the 0.1–5 GPa and 300–900 °C range. The software allows generic and process-oriented thermodynamic and carbon stable isotope calculations including fluid mixing, fluid-graphite/diamond interactions with changing pressure or temperature, and fluid desiccation. This versatile numerical tool is designed to model processes of dissolution/precipitation of graphite or diamond. Along with a description of the software functions, this contribution also provides practical examples.

Certain investigation on feasibility of developing riser less ductile iron castings

The solidification mechanism of ductile iron is a bit complex due to the precipitation of graphite and silicon. These elements change the solidification pattern of cast iron. Density of these elements is less than iron leads to occupying more volume consequently increase the overall metal volume. There are two aspects on this increase in metal volume. One is, reducing this volume increase to reduce the creation of porosities at the earlier stage of solidification and second is, using this volume increase to remove porosity at the later stage of solidification. Proper understanding of this graphite expansion in cast iron solidification will bring insights on reducing or removing of the risers. The current study focus on correlating the net contraction and austenitic liquidus point with shrinkage. The average contraction found through this study is 1.36 % which is more than the net expansion of 0.25 % (without riser) reported in literature. The study found that properly balancing graphite precipitation, pouring temperature and mold strength can enable riserless casting of ductile iron by compensating for liquid contraction through graphite expansion.

The Influence of Boron (B), Tin (Sn), Copper (Cu), and Manganese (Mn) on the Microstructure of Spheroidal Graphite Irons

Most spheroidal graphite irons (SGIs) have a matrix consisting of ferrite, pearlite, or a mix of the two. To achieve the desired matrix composition, pearlite promoters such as Mn, Cu, or Sn, are added to the molten metal. Among these elements, Sn is the most potent pearlite promoter. However, each has a different impact on the solidification, graphite precipitation, eutectoid transformation, and ultimately the final structure of the material. Research has shown that B promotes ferrite in fully pearlitic grades where Cu and Mn were used to promote pearlite. The present work investigates the effect of B in SGI with additions of Sn, Cu, and Mn, and the effects of varying amounts of the different pearlite promoters on the matrix composition. The results show that Mn alone at levels of approximately 0.9 wt% is not enough to promote a fully pearlitic matrix, while 0.5 wt% Cu combined with 0.67 wt% Mn is sufficient. Likewise, a fully pearlitic microstructure can be obtained by alloying with 0.06 wt% Sn and 0.67 wt% Mn. B was found to promote ferrite in fully pearlitic SGI alloyed with Sn or Cu. However, in the absence of those elements, B promoted pearlite when alloyed with just Mn. Graphite protrusions were observed on the graphite nodule surface only for B-added alloys with Sn and Cu. In these cases, it is believed B promotes ferrite by changing the growth mechanism of graphite after solidification from spherical to lamellar. However, a different graphite morphology is observed when B is added with just Mn. Thermal analysis data is in agreement with the microstructural observations regarding the ferrite promoting effect of B.

Michael James Stowell. 10 July 1935—27 February 2022

Mike Stowell was a Bristol physicist turned metallurgist who led the development of practical aluminium-based superplastic alloys by showing how to retain grains small enough, at temperatures high enough, to allow almost unlimited shape changes in forming operations. He can be regarded as the father of SUPRAL alloys, as these are now called. At the Tube Investment laboratory in Hinxton Hall, Essex, he led teams that made effective use of the novel electron-optical equipment invented there to solve numerous fascinating problems of technical importance, among them the sequence of growth by evaporation of thin metallic films and the mechanisms controlling the precipitation of graphite in cast iron. He was dedicated to science at the heart of industrial metallurgy, so that when the laboratory closed, rather than retire, he became research director at Alcan, interacting with a laboratory in Italy as well as managing disparate laboratories in England and Canada to develop coatings for the electrodes used in aluminium production. He was a founder member of what we now know as the ‘Cambridge Phenomenon’, the close interaction between innovative, high-tech industry and the university. In connection with these activities, he made long-lasting fundamental contributions to the understanding of precipitation both of two-dimensional islands in the growth of thin films and in three dimensions in the bulk solid state.

Complexity of graphite formation in response to metamorphic methane generation and transformation in an orogenic ultramafic body

The fate of carbon in subduction is explored by considering fluid-rock interactions in a body of metamorphosed ultramafic rocks from the Appalachian belt as potential proxies for metasomatism and carbon recycling (e.g., infiltration, solution, precipitation) in the mantle wedge at convergent margins. Ultramafic rocks may record intense redox variations affecting the exchanges between solid and fluid carbon-bearing phases. The Belvidere Mountain Complex (BMC) in Vermont, USA is an ultramafic body that underwent Ordovician Taconic subduction metamorphism up to 510–520 °C and 0.9–1.3 GPa. Previous investigations indicate that the BMC experienced partial serpentinization and carbon recycling in the subduction zone. Here bulk δ11B, 87Sr/86Sr and δ13C, data, in-situ microRaman spectroscopy and bulk δ13CCH4 and δ2HCH4 on fluid inclusions, and numerical modeling results aim to constrain the origin and formation mechanisms of carbon-bearing solid and fluid phases in the BMC. Bulk 87Sr/86Sr ratios and δ11B of the BMC rocks suggest infiltration of metasediment-derived fluids inside the mafic/ultramafic body. Carbonates present in the studied ultramafic and mafic rocks have δ13C values ranging from −7.26 to −1.27 ‰. This range was found to record progressive reduction of an initial isotopically light carbonate to methane under reducing conditions. MicroRaman spectroscopy on fluid inclusions confirms CH4-rich gaseous compositions, along with N2, NH3, and S-H compounds, which support a metasedimentary origin for the fluid infiltrating the BMC. Methane-rich fluid inclusions were observed in partially serpentinized peridotites, in carbonate veins, and in amphibolite bodies associated with the ultramafic body, and as well in the surrounding metasedimentary rock units. The δ13C and δ2H of methane in fluid inclusions show a wide range of values in ultramafic rocks from −45.2 ‰ to −12.6 ‰ for carbon and −226 ‰ to −140 ‰ for hydrogen. The methane stable isotope data suggest the presence of two types of methane preserved in studied samples, formed by high-temperature thermogenic processes of metamorphosed graphitic carbon and by abiotic conversion of more oxidized carbon bearing species in the presence of H2-rich fluids produced during metamorphic serpentinization. The BMC also hosts a remarkable example of graphite deposit, with up to 3.90 wt% graphite, along a ∼ 6 m-thick zone within the serpentinized ultramafic body and along lithologic contacts. The δ13C composition of the graphite clusters at −15 ‰ (VPBD), which is consistent with the composition of graphite precipitating from the mixing of the two types of methane-bearing fluids identified in fluid inclusions. The mixing between metasediment-derived and serpentinization-related methane-rich fluids is proposed as the mechanism leading to graphite precipitation. Further complexity is suggested by carbonate reduction evidenced in the samples, which may have locally contributed to the formation of graphite on the precursor carbonate domains. The BMC rocks highlight the variability of carbon recycling processes, including carbon mobilization from multiple solid sources, and mixing of multiple carbon-bearing fluids in a dynamic fluid-rock system, with carbon mobilization and sink adapting to evolving redox conditions.

Hydrothermal Graphite as a Trigger for High-Temperature Orogenic Gold Mineralization at Haoyaoerhudong, Northern China

Abstract Carbonaceous materials are a key factor controlling mineralization processes in many world-class gold deposits. Haoyaoerhudong is the largest carbonaceous metasediment-hosted gold deposit on the north margin of the North China craton. Gold-bearing orebodies are hosted in carbonaceous slates and schists belonging to Mesoproterozoic rift-related successions. Typical hydrothermal minerals are pyrrhotite, quartz, biotite, graphite, apatite, titanite, and native gold. The ore mineralogy, combined with microthermometry and Raman spectra on fluid inclusions, has demonstrated three stages of hydrothermal activity: (I) quartz-biotite ± sulfide stage associated with gold mineralization (315°–510°C; ~4.8 wt % NaCl equiv; H2O-NaCl-CO2 ± CH4 ± N2 system); (II) quartz-sulfide stage, including quartz-sulfide stringers (IIa, 250°–334°C; ~5.4 wt % NaCl equiv; H2O-NaCl-CH4 ± CO2 ± N2 system) and fractured quartz-sulfide ores (IIb, 234°–308°C; ~4.1 wt % NaCl equiv; H2O-NaCl-N2 ± CH4 system); and (III) post-ore quartz-calcite stage (70°–219°C; ~4.8 wt % NaCl equiv; H2O-NaCl system). The molar ratios of CO2 and CH4 progressively decreased from stage I to II, consistent with the occurrence of graphite in alteration zones. Microscopic observation and Raman spectra suggest that the fine-grained graphite from altered schist (Gr-1/2) and coarse-sized graphite from gold-bearing veins (Gr-3/4) are of high crystallinity and exhibit characteristics indicating a hydrothermal origin. The δ13C values of graphite, varying from −27.1 to −26.0‰ Vienna-Pee Dee Belemnite (V-PDB), suggest that the carbon was of biogenetic origin. Apatite Sr isotopes (87Sr/86Sr: 0.708293–0.708842) and titanite Nd isotopes (εNdt: –11.76 to –14.84) also indicate contributions from carbonaceous rocks during mineralization. Thermodynamic modeling demonstrates that graphite may have precipitated at Haoyaoerhudong due to cooling and reduction of the H2O-CO2-CH4 fluids at high temperatures. Graphite precipitation would significantly consume CO2 and effectively destabilize Au bisulfide complexes, facilitating the codeposition of pyrrhotite, graphite, and native gold at high temperatures (≥379°C). We infer that deposition of hydrothermal graphite is a crucial process for mesothermal-hypothermal mineralization in sediment-hosted orogenic gold deposits.

On the constitution and cobalt alloy formation in WC-1.4 wt% Ru-9.5 wt% Co cemented carbides

Our work confirms that the addition of Ru to Co-based cemented carbides significantly broadens the carbon processing window. Using a WC-10.9 wt% (Co-12.8Ru) alloy, the width of the two-phase window is extended from about 0.16 wt% C (Ru-free) to about 0.21 wt% C on addition of Ru.According to semi-quantitative EDS analysis, the amount of W dissolved in the Co binder is significantly higher in Ru-containing materials at all carbon contents. This higher degree of solubility is also reflected in the lattice parameter. When decreasing the carbon content (from precipitation of graphite to the formation of eta carbides), the lattice parameter increases steadily from 3.585 Å to 3.609 Å respectively. In contrast, Ru-free materials present 3.548 Å in equilibrium with graphite, and 3.576 Å in equilibrium with eta carbides.The relative magnetic saturation value of the alloys with Ru was significantly lower when compared to Ru-free alloys (from 80.2% at graphite precipitations to 41.4% with dendritic eta phase), which is also in agreement with the higher W solubility observed in these alloys.DTA measurements of WC-4.4 wt% Ru-30 wt% Co samples (same Ru to Co ratio in the nominal composition) demonstrated a similar melting and solidification regime as compared to Ru-free WC-30 wt% Co materials.

Analysis of the structure and viscosity of iron melts containing titanium at various concentration

This study aims to investigate the correlation between viscosity and liquid structure in Fe-4.5 wt%C-xTi melts. As the temperature decreases, Free-Fe and A-Fe species undergo a transformation into B-Fe, resulting in a significant reduction in free volume. This leads to the aggregation and growth of existing clusters as well as the formation of new clusters, thereby increasing both the number and average volume of atomic clusters. Consequently, the viscosity of the melt experiences a substantial increase as the temperature decreases. In the high-temperature liquid phase region, an elevated titanium content enhances the abundance of titanium-centered clusters within the melt, promoting the stable growth of atomic clusters. Additionally, the increased presence of titanium facilitates the binding of a greater number of carbon atoms and enhances the occupation of free space by iron atoms. As a combined effect, the viscosity of the molten iron rises with an increase in titanium content. At temperatures below the liquidus temperature, a higher titanium content decreases the precipitation temperature of graphite. Consequently, melts with a greater titanium content exhibit a pronounced increase in viscosity at a lower temperature threshold. The primary factor influencing viscosity is the mass fraction of graphite precipitation, and the impact of titanium content diminishes as the titanium content increases.

Graphitization in Paleoproterozoic granulites from the Taihua Complex, North China Craton: Constraints from laser Raman spectroscopy, carbon isotopes and geochronology

The presence of graphite as a refractory form of solid carbon in high grade meta-sedimentary rocks serves as a valuable tool for identifying carbon sources and assessing the movement of carbon through the Earth's interior. In this study, we investigate the graphite formation processes from different lithologies (marbles, metapelites) from the Paleoproterozoic granulites in the southern margin of North China Craton. By utilizing a range of analytical techniques, including petrographic, mineral-chemical, laser Raman spectroscopic, carbon stable isotopic, and geochronological studies, we characterize the textural and isotopic variety of graphite and the timing of metamorphism associated with graphitization. The results suggest a progressive growth and graphitization of graphite during medium to high temperature metamorphic facies. The δ13C values of crystalline graphite in metapelites and marble range in −24.00‰ to −20.10‰, and − 22.50‰ to −21.60‰, respectively, both close to organic carbon averages. The calcite from the graphite-bearing marble shows δ13C values in the range of −2.90‰ to −2.80‰, which corresponds to marine carbonates. In contrast, graphite-bearing quartzo-feldspathic gneiss and diopside/augite-bearing marble show heavier isotopic values of −14.4‰ to −16.5‰, suggesting graphite precipitation from fluids of both organic and magmatic origin. The spectral and isotopic signatures of graphite in these rocks indicate a dominant biogenic signature with mixture of abiogenic carbon sources. Zircon UPb geochronology marks the timing of high-grade metamorphism at ca. 1.93 to 1.92 Ga, associated with graphite formation during subduction and accretion process associated with the final assembly of the North China Craton. We propose that crystalline graphite was formed during the continental collision-triggered medium to high temperature metamorphic event, consistent with a global graphite metallogenic event in the Paleoproterozoic.

Reduction of dislocation density in single crystal diamond by Ni-assisted selective etching and CVD regrowth

The development of large-area diamond films with low dislocation density plays a key role in diamond-based devices. In this study, we present a straightforward and reasonably priced Ni-assisted etching and re-growth method to decrease the dislocation density of diamond. By adjusting the annealing temperature, a high-density inverted pyramid and/or trapezoidal pit can be effectively exposed because the interaction between carbon and Ni metal. The Ni tends to dissolve the diamond surrounding the dislocation at high temperature while maintaining the surface's flatness. The precipitated graphite layer is removed using wet etching, and the step flow mode is then restored via the re-growth procedure. It shows that the dislocations located beneath the etching pits are partially annihilated during the lateral coalescence, resulting in a decrease in dislocation density.

Graphitic inclusions in zircon from early Phanerozoic S-type granite: Implications for the preservation of Hadean biosignatures

A biotic origin of isotopically light graphite in Hadean zircon remains contested, in part because it is unclear how biogenic carbon in sediments behaves during diagenesis, metamorphism and anatexis, and how it can be preserved as inclusions in zircon. Here, we report the discovery of graphitic inclusions in zircon from Rumburk granite in the Lusatian Block of eastern central Europe as the first example of such inclusion-bearing zircon in a well-constrained geological and petrological context. Most graphite inclusions are trapped at the interface between inherited zircon interiors of early Cambrian–Proterozoic age and late Cambrian (496.2 ± 2.3 Ma; 95% confidence) zircon overgrowths that crystallized at ∼700 °C under highly reducing conditions (typically −4.6 log units relative to the fayalite-magnetite-quartz buffer). Zircon overgrowths are also enriched in xenotime component (up to 93 µmol/g P) and δ18O (average δ18O = 7.7‰), both typical for S-type granitic melts. Raman microspectroscopy reveals crystalline and disordered graphitic carbon, but because overgrowth temperatures reached >700 °C, sufficient for complete graphitization, disordering is presumably secondary and caused by in-situ irradiation from the zircon host. Because organic materials were avoided during sample preparation, and inclusions were excavated by ion beam sputtering, exposure to potential C-bearing contaminants can be dismissed. Inclusions range in δ13C from −44.6 to −7.5‰ with a dominant mode at δ13C = −34‰ that is positively skewed. Rayleigh-type graphite precipitation from a CO2-CH4 fluid with a starting composition equivalent to regional black shale (δ13C = −32‰) explains inclusion carbon isotopic range and distribution. Collectively, these observations suggest that graphite was initially trapped in voids formed via dissolution-reprecipitation of trace element enriched, and possibly metamict, detrital zircon in metasedimentary protoliths when exposed to C-O-H fluids during prograde metamorphism. Subsequently, graphite-filled voids in inherited zircon became enclosed when zircon rims crystallized from highly reduced S-type granitic melts. Besides partial disordering of graphitic carbon due to irradiation, there is no indication for post-entrapment alteration, demonstrating that graphitic inclusions in zircon can preserve isotopic biosignatures over hundreds of millions of years.

Effect of Ni and Mo on microstructure and mechanical properties of grey cast iron

ABSTRACT Alloying elements (Ni, Mo) were added to grey cast iron, and the effect of Ni, Mo on microstructure and mechanical properties were analysed in this study. When Ni was added alone, the precipitation of graphite was inhibited at the early stage of solidification, and part of graphite was formed between the dendrites, resulted in an uneven distribution of graphite. Ni played a role of solution strengthening and reduced the pearlite interlammer spacing, improved the mechanical properties. The addition of Mo refined the austenite dendrites and made the carbon unevenly distributed, which led to the abnormal growth of graphite. Mo increased the eutectoid supercooling degree, reduced the pearlite interlammer spacing and improved tensile strength. When Ni and Mo were added together, the elements beneficial to strength (Mo, Sn) were not uniformly distributed, and the influence on graphite size and pearlite interlammer spacing was not obvious, resulted in poor mechanical properties.

Direct Evidence for Phase Transition Process of VC Precipitation from (Fe,V)3C in Low-Temperature V-Bearing Molten Iron

V-bearing molten iron was obtained by adding Na2CO3 in the smelting process of vanadium titanomagnetite at low temperature. Two forms of V-rich carbides ((Fe,V)3C, VC) were detected in the V-bearing pig iron products. Once the smelting temperature was above 1300 °C, most of the V in the raw ore was reduced into molten iron. Owning to the high content of V, the unsteady (Fe,V)3C solid solution decomposed along with the precipitation of graphite and VC during the solidification process. The presence of VC cluster and VC precursor in (Fe,V)3C was detected by transmission electron microscopy, which confirmed the possibility of this transition process at the atomic perspective. The transformation dramatically affected the compositions and properties of V-bearing pig iron and had important guiding significance for the actual production process.