Carbon Content Of Alloy Research Articles

Quenched and Partitioned CMnSi Steels Containing 0.3 wt.% and 0.4 wt.% Carbon

The effect of partitioning parameters on mechanical properties and carbon partitioning in quenching and partitioning (Q&P)-treated C-1.5Mn-1.5Si steels was studied using 0.3 wt.% and 0.4 wt.% carbon compositions. Fully austenitized specimens were quenched to a fixed quenching temperature followed by partitioning at 400°C and 450°C for varying times. In most cases, increasing the partitioning temperature decreased UTS and increased TE, and both UTS and TE decreased with increasing partitioning times. Similar ultimate tensile strength levels were obtained for the 0.3C alloy partitioned at 400°C and the 0.4C alloy partitioned at 450°C. Increasing alloy carbon content increased retained austenite fractions. Mossbauer effect spectroscopy results were used to investigate carbon redistribution after Q&P processing in the 0.4C alloy.

Effect of carbon content on the mechanical properties and microstructural evolution of Fe–22Mn–C steels

Abstract A Fe–22Mn–0.6C (wt%) sheet steel was decarburized and heat treated to obtain four Fe–22Mn–C alloys with carbon contents of 0, 0.2, 0.4 and 0.6 wt% with similar grain sizes, with the objective of determining the effect of varying the alloy stacking fault energy (SFE) on the microstructural evolution and mechanical properties of these alloys as a function of applied strain. Microstructural observations determined the deformation products to be mechanical twins for the 0.6C alloy and mechanical e-martensite for the 0C and 0.2C alloys. For the 0.4C alloy, both mechanical twins and e-martensite were observed during deformation. As expected, the ultimate tensile strength and uniform elongation increased with increasing alloy carbon content. For the e-martensite dominated 0C and 0.2C alloys, the critical damage mechanism was determined to be void formation at matrix/inclusion and austenite/e-martensite boundaries, leading to cleavage-like features on the fracture surface. For the twinning dominated 0.4C and 0.6C alloys, the critical damage event was void nucleation at grain and matrix/inclusion boundaries, leading to ductile tearing features on the fracture surfaces. In the case of the higher SFE (i.e. SFE≥15 mJ/m 2 ) 0.4C and 0.6C twinning dominated alloys, it was determined that the sum of the volume fractions of mechanical twins and e-martensite saturated at higher strains, where the sum of the saturation volume fraction of these two deformation products was approximately 0.37 for all experimental alloys and was found to be consistent with similar systems in the high-Mn twinning induced plasticity (TWIP) steel literature. From this data, it was concluded that the combined twinning and e-martensite formation kinetics determined the initiation of critical damage in the higher SFE, mechanical twinning dominated alloys. It was also found that the saturated volume fraction of e-martensite had a sigmoidal decay relationship with increasing values of the SFE for the present alloys and for a variety of high-Mn steel systems taken from the literature. It was further determined that the volume fraction of e-martensite in the low SFE (i.e. SFE≤10 mJ/m 2 ) alloys at fracture was independent of SFE, suggesting that the e-martensite formation kinetics, as dictated by the alloy SFE, dominate the critical damage processes in these alloys. Finally, it was found that the stress for the activation of twinning and the related increase in work hardening rates for the higher SFE, twinning dominated alloys could be described by a simple linear relationship with the SFE, leading to the conclusion that the observed work hardening characteristics and properties of high-Mn TWIP alloys are largely determined by the alloy twinning kinetics.

Preparation of TiFe based alloys melted by CaO crucible and its hydrogen storage properties

The carbon contamination of alloys prepared by the electro graphite crucible is impossible to avoid due to the inherit reaction between the melt and the crucible. In this study, the TiFe-based alloy is prepared by VIM process using CaO crucible as well as the electro graphite crucible. The samples are examined by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrometer (EDS), and the PCT curves are also measured. It is resulted that, the oxygen content of alloys melted by CaO crucible is almost equal to the one melted by graphite crucible and without the carbon contamination, meanwhile the carbon content of alloys obtained by the electro graphite crucible is 1860ppm, which exceeds the tolerance of the commercial alloy (1000ppm). The microstructure of the alloy melted by CaO crucible is dendrite, while it is composed of the equiaxed crystal with the lamellar structure and the spherical TiC particles distributed along grain boundaries or within the grain when melted by the graphite crucible; the interfacial reaction of the electro graphite crucible with TiFe alloy melt is serious and the interaction layer is formed up to 200μm in thickness, the carbon in TiFe-based alloys forms TiC. The hydrogen desorption plateau pressure of alloys melted by CaO crucible is (0.11–0.4)×105Pa, and that by the graphite crucible is (0.6–1)×105Pa. This may imply that the CaO crucible may be the promising candidate for melting the high performance TiFe based hydrogen storage alloys.

Effect of Carbon Gradient on the Microstructure and Mechanical Properties of Fe-22Mn-C TWIP/TRIP Steels

High-manganese austenitic steels are promising emerging automotive steels demonstrating high strength and ductility. The main deformation products observed in these steels are mechanical twins and ε-martensite, where the dominant deformation products vary quite strongly with stacking fault energy (SFE), which in turn is a very strong function of the alloy carbon content. In this research, a Fe-22Mn-0.6C sheet steel was decarburized to achieve a variety of through-thickness C gradients, thereby varying the dominant deformation products through the sheet thickness, with the overall objective of producing unique microstructures and mechanical properties. Microstructural analyses after interrupted tensile testing indicated that the amount of both mechanical twins and ε-martensite increased with increasing true strain, where the deformation products changed from mechanical twins at the higher-C core to ε-martensite at the lower-C surface. The spring-back properties of the C graded steels were also compared with reference to the effect of differential carbon concentration gradient.

High temperature oxidation behavior of chromium-rich alloys containing high carbides fractions. Part I: Nickel-base alloys

Six wear-resistant alloys based on nickel, containing 30 wt.% Cr and from 2.5 to 5.0 wt.% C, were elaborated by foundry and subjected to oxidation by air at 1000, 1100, and 1200 °C, for evaluating the oxidation behavior of hard bulk alloys. Their microstructures are rich in chromium carbides, eutectic, or pro-eutectic, and they also contain graphite for the highest carbon contents of interest. All the studied alloys obviously display a chromia-forming behavior, despite the initial low chromium content in the matrix. During oxidation, carbides disappear over an increasing distance from the oxidation front, with the consequence of the enrichment of the neighbor matrix in chromium. The minimal chromium content on the surface after oxidation decreases when the alloy is richer in carbon and increases with the oxidation temperature. The carbide-free zone tends to be deeper when the oxidation temperature increases, and also when the alloy's carbon content increases, in contrast with low-C Ni-30Cr alloys previously studied. The disappearance of carbides means a carbon loss as gaseous oxidized species. This probably disturbs the oxide scales growing on the external surface and may influence the oxidation behavior of the alloys. When present, graphite does not deteriorate dramatically the oxidation resistance of the alloys. The hardness of the alloys are lowered by the exposures to high temperature and by the presence of graphite.

Chromia-Assisted Decarburization of W-Rich Ni-Based Alloys in Impure Helium at 1273 K (1000 °C)

The microstructure and surface stability of two experimental W-rich Ni-based alloys have been studied at 1273 K (1000 °C) in an impure-He environment containing only CO and CO2 as impurities. The alloy Ni-2.3Al-12Cr-12W contained 0.08 wt pct carbon in solution, whereas the second alloy Ni-2.3Al-3Mo-12Cr-12Co-12W contained M6C carbides at the same carbon level. Both alloys, which were preoxidized with ~2.3 μm Cr2O3 layer, were decarburized completely within 50 hours of exposure to the helium gas mixture at 1273 K (1000 °C) via the following chromia-assisted decarburization reaction: Cr2O3 (s) + 3Calloy (s) → 2Cr (s) + 3CO (g). Microstructural observations, bulk carbon analysis, and microprobe measurements confirmed that the carbon in solid solution reacted with the surface chromium oxide resulting in the simultaneous loss of chromia and carbon. The Cr produced by the decomposition of the Cr2O3 diffused back into the alloy, whereas CO gas was released and detected by a gas chromatograph. Once the alloy carbon content was reduced to negligible levels, subsequent exposure led to the uninterrupted growth of Cr2O3 layer in both alloys. In the preoxidized alloys, chromia-assisted decarburization rates were slower for an alloy containing carbides compared with the alloy with carbon in solid solution only. The formation of Cr2O3 is shown to be the rate-limiting step in the chromia-assisted decarburization reaction. Exposure of as-fabricated alloys to the impure-He environment led to the formation of a thin layer of Al2O3 (<1 μm) between the substrate and surface Cr2O3 oxide that inhibited this decarburization process by acting as a diffusion barrier.

Effects of Carbon Content in Alloys and Cr3C2 Addition on Corrosion Characteristics of WC-10%Co Alloys

In order to evaluate corrosion characteristics of cemented carbides in wide pH range of aqueous solutions from strong acidity to strong alkalinity, the effects of carbon content in the alloy and Cr3C2 addition on corrosion characteristics of WC-10%Co alloys were investigated by mainly measuring potentiodynamic polarization curves of them. The results obtained were as follows; (1) In the case of aqueous solutions of strong acidity and weak acidity close to neutrality, corrosion speed in pseudo-passive region decreased with the decrease of carbon content in the alloy. (2) The effect of corrosion repression by Cr3C2 addition was small in the strong acid solution, but so big in the weak acid one. (3) The corrosion in the strong and weak acid solutions was mainly due to the dissolution of the cobalt phase. (4) In the case of strong alkali solution, the alloys showed almost same polarization curves with no relation to carbon content in the alloy and Cr3C2 addition because the corrosion was due to the dissolution of WC phase.

Microstructure Role in Passivation and Local Activation Processes of Carbon Steels

The regularity of carbon steels passivation and local activation in borate-sulphate solutiones at room temperature were analyzed. Pits on iron are initiating on ferrite/cementite interface. On carbon steel surface was observed the spots representing the uniformly dissoluble pearlite grain. So necessary to note that high carbon content in alloys decrease their corrosion stability under local destruction conditions.

Effect of microstructure on the cleavage fracture strength of low carbon Mn–Ni–Mo bainitic steels

The effects of the microstructure on the cleavage fracture strength of low carbon Mn–Ni–Mo bainitic steels were examined. A four-point bend test and double-notched bend specimens were used to measure the cleavage fracture strength of the alloys and identify the cleavage initiating micro-cracks, respectively. The cleavage fracture strength and DBTT of Mn–Ni–Mo bainitic steels were strongly affected by the alloy carbon content. The decrease in the alloy carbon content resulted in a decrease in the inter-lath cementite-crowded layers and higher cleavage fracture strength. Micro-cracks that formed across the inter-lath cementite-crowded layers were observed to initiate cleavage fracture. The width of these inter-lath cementite-crowded layers was accepted as a cleavage initiating micro-crack size in the micro-mechanical modeling of the cleavage fracture, and the measured cleavage strength values of the bainitic Mn–Ni–Mo steels were well represented by the modified Griffith relationship.

Quantitative analysis of the wear and wear debris from low and high carbon content cobalt chrome alloys used in metal on metal total hip replacements.

The biological reactions to polyethylene wear debris have been shown to result in osteolysis and loosening of total hip arthroplasties. This has led to renewed interest in the use of metal on metal bearings in hip prostheses. This study employed uniaxial and biaxial multistation pin on plate reciprocators to assess how the carbon content of the cobalt chrome alloy and the types of motion affected the wear performance of the bearing surfaces and the morphology of the wear debris generated. The low carbon specimens demonstrated higher wear factors than both the mixed carbon pairings and the high carbon pairings. The biaxial motion decreased the wear rates of all specimens. Plate wear was significantly reduced by the biaxial motion, compared to pin wear. The metal wear particles isolated were an order of magnitude smaller than polyethylene particles, at 60-90 nm, and consequently, 100-fold more particles were produced per unit volume of wear compared to polyethylene. The low carbon specimens produced significantly larger particles than the other material combinations, although it is thought unlikely that the difference would be biologically significant in vivo. The volumetric wear rates were affected by the carbon content of the cobalt chrome alloy, the material combination used and type of motion applied. However, particle morphology was not affected by the carbon content of the alloy or the type of motion applied.

Hydrogen-containing chemically active gas medium for controlling carbon content of tungsten-base hard alloys

The interaction between components of tungsten-base hard alloys and hydrogen which is used in sintering as a protective gas medium has been theoretically and experimentally studied, Thermodynamic possibility of reactions responsible for variations in carbon content of alloys has been analyzed. It has been found that when the alloy interacts with hydrogen, the former is decarburized both by hydrogen proper and moisture and oxygen impurities present in it. Equilibrium constants K P and equilibrium compositions for the above reactions have been calculated at 300–1500 K. It is shown that methane added to hydrogen in amounts exceeding its equilibrium concentration with respect to WC but not exceeding its equilibrium concentration with respect to graphite not only slows down the process of WC decarburization, but recarburizes W and W 2C impurities present in initial powders to WC with no risk of free carbon liberation. Compositions of methane-hydrogen mixture have been found, which allow a reliable control of the carbon content of sintered hard alloys. The above gas medium has permitted us to devise a peculiar sintering procedure which allows two-phase alloys uniform with respect to carbon content, as well as alloys having special-purpose properties to be fabricated.

Thermodynamics of the iron-carbon-zinc system

A two-zone isopiestic experimental technique was used to determine the solubility of zinc vapor in liquid and solid iron-carbon alloys as a function of zinc partial pressure (0.1 to 1 atm), carbon content (0 to 4.6 wt Pct), and temperature (1473 to 1873 K). The solubility of zinc at a given partial pressure decreases with both increasing temperature and carbon content in both liquid alloys and solid austenite; its activity in these solutions, and in pure δ-ferrite, deviates more positively from ideality than previous model-based predictions have suggested. The Bale-Pelton unified interaction parameter formalism was successfully applied to the results of liquid-alloy experiments, but the degree of experimental scatter in the austenite equilibrations was too great to allow its application in the calculation of solid-solution iron-carbon-zinc thermodynamic parameters. Using the available results, values were calculated for the equilibrium partition coefficientK zn in solidifying iron-carbon alloys as a function of alloy carbon content; the results suggest that significant segregation of zinc between solid and liquid phases is not likely.

板状ＷＣ相を含むＷＣ‐βｔ‐Ｃｏ超硬合金

The factors affecting the structure having sheet-like WC phases were studied in WC-βt-Co cemented carbide. It was found that the sheet-like phases were apt to form in the structure as the grain size of starting WC powder decreased by ball-milling and as the carbon content of alloy increased, in close relation to sintering temperatures and binder and βt contents. It was noted that the sheet-like phases formed also in the alloy prepared by solid-phase sintering.

Formation of a metastable ferromagnetic τ phase during containerless melt processing and rapid quenching in Mn-Al-C alloys

Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable τ (L10) phase formed directly from the melt. Complete solidification to τ phase was interrupted by the competitive evolution of an equilibrium ε phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic τ phase in a Mn0.55Al0.433C0.017 alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034 alloy), a transition in structure development occurred so that the samples exhibited γ2 phase formation as well as τ and ε phases. Both microstructural observations and x-ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable τ phase from the melt may be facilitated by containerless processing.

Partition Coefficients of Alloying Elements to Primary Austenite and Eutectic Phases of Chromium Irons for Rolls.

The partition coefficients of chromium and carbon to primary austenite were measured on Fe-Cr-C ternary alloys containing 1.1 to 3.6 mass% C and 1.5 to 26 mass% Cr. Each alloy specimen was held for 1 h at a temperature just below the liquidus and then quenched in water cooled copper mold. Partition coefficients were in the range of 0.53 to 0.80 for chromium and 0.25 to 0.38 for carbon. Partition coefficients of third elements to primary austenite were also evaluated on 5 and 15 mass% Cr quaternary alloys. The coefficients of silicon, nickel and copper were larger than unity and increased with an increase in carbon content, while those of molybdenum, manganese and vanadium were smaller than unity and decreased with increasing carbon content of alloy. The partition coefficient of chromium was little influenced by the third elements.The partitions of alloying elements between liquid and eutectic phases were evaluated on eutectic alloy specimens with 2, 5, 15 and 30 mass% Cr that were quenched during freezing unidirectionally at 10 mm/h. The irons containing 2 and 5 mass% Cr froze in austenite+(Fe, Cr)3C eutectic, and the 15 and 30 mass% Cr irions crystallized into austenite+(Cr, Fe)7C3 eutectic. In each alloy system chromium, molybdenum, manganese and vanadium were distributed preferentially to eutectic carbide, white silicon and nickel dissolved selectively into eutectic austenite. The partition coefficient of each alloying element to eutectic, defined as the ratio of the average eutectic composition at cell tip to alloy content of liquid near freezing front, were also determined in this study.

ＷＣ‐Ｃｏ超硬合金の表面酸化による強度低下

The transverse-rupture strength of WC-(10, 20)%Co alloys oxidized in air at the temperature of 973-1173 K for the time of 0.3-1.8 ks was studied as a function of Co content, carbon content of alloys, WC grain size and r-domain size. It was found that the strength of the alloy decreased owing to the surface oxidation and the strength decrease became larger with rising temperature and increasing time. It was noted that the strength decrease was enhanced with increasing r-domain size. It was also found that the rate of oxidation was faster in the domain boundary than inside the domain, so that the domain boundary after oxidation acted as a notch during transverse-rupture test, leading to the strength decrease.

ＷＣ‐１５％Ｎｉの二相域に及ぼすＣｒ３Ｃ２添加の影響

The WC-Ni alloy containing Cr3C2 has been widely used for non-magnetic or corrosion resisting parts. However, the (WC+γ) two-phase region of WC-Ni alloy affected by the Cr3C2 addition seems not to have been studied. The present work was concerned with this subject for WC-Cr3C2-15%Ni alloy. It was found that the two-phase and the adjacent (WC+γ+Cr3C2) three-phase regions shifted markedly to the high carbon side. It was also found that the solid solubility of Cr in the binder phase varied according to the carbon content of alloy and it showed a maximum value of about 16% for the alloy containing about 5.8%C.

The effect of carbon on the high temperature oxidation of Fe-31 Mn-9Al-0.87C alloy

The alloy with the composition Fe-31Mn-9Al-0.87C was employed to investigate the effects of carbon on the oxidation behaviour at 800, 900 and 1000° C in dry air. Electron and optical microscopy were applied to examine the morphology and elemental redistribution in the oxide scale. Oxidation kinetics of the alloy oxidized at 800 and 900° C exhibited three-stage and two-stage parabolic rate laws, respectively. For the alloy oxidized at 1000° C, a carbon-induced breakaway three-stage oxidation mechanism developed. The carbon addition had a detrimental effect on the oxidation resistance and resulted in a porous initial oxide layer, which was favourable to the oxidation of manganese as well as the formation of a uniform and bulky oxide. As the oxidation temperature was increased, the diffusion rates of the metallic elements and the healing ability of oxide scales were enhanced. However, when the carbon content in alloy was above the saturation value, a breakaway scaling may have occurred due to the carbon-induced oxidation.

超硬合金の表面部に生じる結合相の富化層

For the purpose of increase in toughness of coated cemented carbides, studies on the formation of binder enriched layer near the surface (BEL) were carried out.It was found that the BEL having lamellar structure of binder phase was apt to form when the alloy was cooled in decarburizing atmosphere after sintering. The BEL formation became easy with higher carbon content of alloy, slower cooling rate and higher sintering temperature. The formation mechanism of BEL, which would closely relate to rapid liquid flow during cooling from sintering temperature, was in detail examined.

The microstructural response of mill-annealed and solution-annealed INCONEL 600 to heat treatment

Samples of INCONEL* 600 were examined in the mill-annealed and solution-annealed states, and after isothermal annealing at 400 °C and 650 °C. The corrosion behavior of the samples was examined, analytical electron microscopy was used to determine the microstructures present and the chemistry of grain boundaries, and Auger electron spectroscopy was used to measure grain boundary segregation. Samples of different alloys in the mill-annealed state were found to have quite different microstructures, with Cr-rich M7C3 carbides occurring either along grain boundaries or in intragranular sheets. The corrosion behavior of the samples correlated well with the occurrence of grain boundary chromium depletion. Solution annealing at 1190 °C caused dissolution of all carbides, whereas at 1100 °C the carbides either dissolved or the grain boundaries moved away from the carbides, depending upon alloy carbon content. Low-temperature annealing at 400 °C had little effect on millannealed or fully solutionized samples, but in samples with intragranular carbides present, the grain boundaries moved until intersecting or adjacent to the carbides. Isothermal annealing at 650 °C caused carbide nucleation and growth at grain boundaries in fully solutionized samples. Chromium depletion at grain boundaries accompanied carbide precipitation, with a minimum chromium level of 6 wt pct achieved after 5 hours. Healing was found to occur after 100 hours. Solution-annealed samples with intragranular carbides present had more rapid corrosion kinetics since the grain boundaries moved back to the existing carbides. Thermodynamic analysis of the chromium-depletion process showed good agreement with experimental measurements. The Auger results found only boron present at grain boundaries in the mill-annealed state. Aged samples had boron, nitrogen, and phosphorus present, with phosphorus and nitrogen segregating to the greatest extent. The kinetics of phosphorus segregation are much slower at 400 °C compared with 650 °C.