Fe-C System Research Articles

The modeling of crystallization kinetic of Fe-C alloy

The work is aimed on studying the influence of melt state and cooling rate on the solidification processes in model alloys of Fe-C system. The processes, proceeding during the solidification are investigated by a method of the differential thermal analysis. The analysis of the results has shown that the increase of cooling rate results in downturn of liquidus and solidus temperatures and expansion of solidification interval. The formation of equilibrium and microhomogeneous melt promotes the increase of a supercooling degree, downturn of phase transaction temperatures, expansion of the interval of eutectic formation. It is established, that the formation of equilibrium melt has favorably affected the formation of casting structure and properties: the large plates of graphite disappears; the linear sizes of flake graphite decrease, its amount increases. On the basis of the results obtained the physical model for Fe-C–alloys solidification, taking into account a melt structural state, is offered.

Study on the HPHT synthetic diamond crystal from Fe-C(H) system and its significance

Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C(H) system indicate that most of them have an octahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic diamond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to differences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy (E) of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitrogen into a nitrogen-pair is shortened because of the existence of hydrogen. Therefore, aggregate nitrogen (A-centers) may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues (e.g. growth mechanism, etc.) in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a “bridge” for explaining the formation of HPHT synthetic and natural diamond.

Improvement of dispersion tolerance using wavelength-interleaving and forward error correction

In this paper, we first derived the BER expression of an optical channel with chromatic dispersion impairment. The derived BER expression takes into account the influence of pulse spreading, transmitter rise/fall times, receiver Q-factor and noises. It is simpler and hence easier to use than many existing channel BER models. Then we proposed a wavelength-interleaved FEC scheme to mitigate the chromatic dispersion impairment in optical transmission system and analyzed its decoding performance. The minimum wavelength separation required for such a wavelength-interleaving FEC system to obtain the highest coding gain is also determined. Based on this design, the chromatic dispersion tolerance of the proposed system with 2-wavelength and 4-wavelength-interleaving are shown to improve by about 13% and 22%, respectively, over a non-interleaved system. In essence, wavelength-interleaving averages out the performances of a set of channels experiencing higher and lower dispersion, hence the interleaved channels have better performance than the non-interleaved channels experiencing higher dispersion, and worse performance than the non-interleaved channels experiencing lower dispersion. However, since WDM systems are typically designed based on the worst-case channel, the overall system performance is improved by wavelength-interleaving.

Modelling of Precipitation Kinetics with Simultanous Stress Relaxation

AbstractMisfit strain connected with the formation of large internal stresses may drastically influence the precipitation kinetics. A new model for the simultaneous precipitate growth and misfit stress relaxation in binary systems has been developed based on the idea that the internal stresses are relaxed by generation or annihilation of vacancies at the matrix/precipitate interface. The model is applied to the Fe-C system by considering the growth of the cementite precipitate in the ferritic matrix. The influence of the stress relaxation on the precipitate growth kinetics is demonstrated.

Contribution to the influence of chemical composition and cooling conditions on the eutectic solidification range of Fe–C–X-melts

The eutectic solidification range (ESR) is the difference between the eutectic temperature of the stable Fe–C-system (iron–carbon, iron–graphite) and the eutectic temperature of the metastable Fe–Fe 3C-system (iron–ironcarbide, iron–cementite). This range is a key to graphitization. The size and the location of the range are important to determine the solidification system: grey or mottled or white. Quantitative investigations by thermal analysis (TA) with croning-sand and steel crucibles at the Technical University Clausthal in Germany gave the following results: Si and Al expand the range, the stable system is promoted. Cu and Ni have no significant influence. P, Mn, Cr, Mo and S contract the range, the metastable system is promoted. Increasing cooling rate normally decreases the transformation temperatures. Concerning these results a combination of thermal analysis and the spectrometric analysis could be very useful. Variations in chemical composition can be taken into account to evaluate temperature–time curves and graphitization tendency more accurately.

A Performance Comparison of Different FEC System Architectures for ATM over Wireless Multi-Carrier Modulation

In multi-carrier modulation (MCM) systems multiple relatively narrowband sub-carriers are used to alleviate the undesirable influence of frequency selective fading. This paper analyses the performance of MCM data links when forward error correction is employed either in each sub-carrier or in the main stream of bits. The influences on system performance of interleaving and suppression of the poorest sub-carriers are also analysed.

Occurrence and regulation of the ferric citrate transport system in Escherichia coli B, Klebsiella pneumoniae, Enterobacter aerogenes, and Photorhabdus luminescens

In Escherichia coli K-12, transcription of the ferric citrate transport genes fecABCDE is initiated by binding of diferric dicitrate to the outer membrane protein FecA which elicits a signaling cascade from the cell surface to the cytoplasm. The FecI sigma factor is only active in the presence of FecR, which transfers the signal across the cytoplasmic membrane. In other bacteria, fecIRA homologues control iron transport gene transcription by siderophores other than citrate. However, in most cases, the FecI homologues are active in the absence of the FecR homologues, which might function as anti-sigma factors. Since not all E. coli strains contain a fec system, we determined the occurrence of fec genes in selected Enterobacteriaceae and the dependence of FecI activity on FecR. Incomplete FecIRA systems were chromosomally encoded in Enterobacter aerogenes strains and plasmid-encoded in K. pneumoniae. E. coli B, Photorhabdus luminescens and one of three Klebsiella pneumoniae strains had a functional FecIRA regulatory system as in E. coli K-12. The cytoplasmic N-terminal FecR fragments caused constitutive FecI activity in the absence of ferric citrate. The PCR-generated mutant FecI(D40G) was inactive and FecI(S15P) was partially active. FecR of E. coli K-12 activated FecI of all tested strains except FecI encoded on the virulence plasmid pLVPK of K. pneumoniae, which differed from E. coli K-12 FecI by having mutations in region 4, which is important for interaction with FecR. The C-terminally truncated FecR homologue of pLVPK was inactive. pLVPK-encoded FecA contains a 38-residue sequence in front of the signal sequence that did not prevent processing and proper integration of FecA into the outer membrane of E. coli and lacks the signaling sequence required for transcription initiation of the fec transport genes, making it induction-incompetent but transport-competent. The evidence indicates that fecIRABCDE genes are acquired by horizontal DNA transfer and can undergo debilitating mutations.

Reconfigurable Adaptive FEC System Based on Reed-Solomon Code with Interleaving

This paper proposes a reconfigurable adaptive FEC system based on Reed-Solomon (RS) code with interleaving. In adaptive FEC schemes, error correction capability t is changed dynamically according to the communication channel condition. For given error correction capability t, we can implement an optimal RS decoder composed of minimum hardware units for each t. If the hardware units of the RS decoder can be reduced for any given error correction capability t, we can embed as large deinterleaver as possible into the RS decoder for each t. Reconfiguring the RS decoder embedded with the expanded deinterleaver dynamically for each error correction capability t allows us to decode larger interleaved codes which are more robust error correction codes to burst errors. In a reliable transport protocol, experimental results show that our system achieves up to 65% lower packet error rate and 5.9% higher data transmission throughput compared to the adaptive FEC scheme on a conventional fixed hardware system. In an unreliable transport protocol, our system achieves up to 76% better bit error performance with higher code rate compared to the adaptive FEC scheme on a conventional fixed hardware system.

Monte carlo-method simulation of the deformation-induced ferrite transformation in the Fe-C system

A Monte Carlo (MC) technique has been used to model deformation-induced ferrite transformation (DIFT) in an Fe-C binary system on a mesoscale. The effects of strain rate, strain, and recrystallization of the matrix on DIFT are investigated. Increasing the strain rate slightly retards the onset of DIFT. The volume fraction of ferrite increases gradually as the strain increases before the volume fraction of ferrite reaches its saturation value. After the volume fraction of ferrite becomes saturated, it oscillates around its saturation value. The recrystallization of austenite slightly retards the onset of the DIFT. Although the recrystallization of austenite reduces the equilibrium volume fraction of ferrite significantly, it cannot completely suppress DIFT. The stress concentration has been shown to induce the nucleation of ferrite near the grain boundaries and phase boundaries. The significance of the reverse transformation has been investigated. We found that there is a temporal oscillation of the volume fraction of ferrite and the stored energy after they arrive at their saturation values. We conclude that this oscillation and the effect of the strain rate on DIFT are both brought about by the reverse transformation from induced ferrite to undeformed austenite. The diffusion behavior of carbon atoms in the systems is different for different strain rates. The simulation shows that the dynamic recovery of austenite cannot occur in the system during deformation under the present conditions. The results of the simulation show that, other than the oscillation of the equilibrium volume fraction of ferrite and the unusual diffusion behavior of carbon atoms, the simulation agrees well with the corresponding experimental results. The temporal oscillation of the volume fraction of ferrite and stored energy and the unusual diffusion behavior are two new phenomena that have not been reported by other researchers.

Reactions, Coalescence of Reduced Iron Particles, and Liberation of Carbon Particles in Carbon Composite Iron Ore Pellets

Reactions in carbonaceous material composite iron ore pellets of 18 mm heated at elevated temperatures were studied. The overall reduction rate is controlled by a complex combination of direct reactions and indirect reactions and never by gasification reaction. The final reduction of iron oxide is controlled by carburized carbon. The carburization of the reduced iron is mainly progressed by the direct carburization reaction, C(s)=[C]. As the carbon content approaches to the solidus line of the phase diagram of Fe-C system, the reduced iron particles are gradually forced to coalesce to grow in much larger particles. The coalescing rate is increased with temperature. Its driving force is the large surface energy of reduced iron due to its large specific surface area. Due to the coalescence, the particles of carbon are apt to lose the contact state with the reduced iron particles and to lose the ability to carburize the reduced iron. Therefore, the carburization exceeding the solidus line can be severely depressed. Consequently, the carburization up to the solidus line can be achieved at relatively lower temperatures, i.e. 1 200-1 250°C. As a result, the carbon content of reduced iron decreases with increasing temperature. Since the coal char has a very poor ability to directly carburize reduced iron, the carbon contents of reduced iron were very low and increased with increasing temperature. Graphite and coke possess the strongest and the intermediate carburizing abilities, respectively. And the carbon contents of the shell part and core part of reduced iron decreases with increasing temperature.

C—Fe—Mo (Carbon‐Iron‐Molybdenum)

AbstractFor Abstract see ChemInform Abstract in Full Text.

Carbon Pickup Phenomenon of Fe-C System Alloys in Evaporative Pattern Casting Process

Carbon Pickup Phenomenon of Fe-C System Alloys in Evaporative Pattern Casting Process

Fe-C System Alloys Prepared by Mechanical Alloying and Powder Metallurgy

Fe-C system alloys were prepared by mechanical alloying and powder metallurgy (MA-PM). Elemental powders of iron and graphite with various carbon concentrations were mechanically alloyed (MAed) by using a planetary ball mill in argon atmosphere. The MAed powders were then characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). During MA, the particle refinement, formation of super-saturated solid solution and Fe/C amorphous occur and their degrees are influenced by carbon concentration in the mixed powders. The MAed powders with 4-10 mass% carbon concentration were hot isostatic pressed (HIPed) and with 0.4-2 mass% were hot pressed (HPed) at both lower and higher temperatures than the eutectoid transformation point A1. The sintered compacts were characterized by Vickers hardness test, tensile test and scanning electron microscopy (SEM). Both the HIPed and HPed compacts obtained in the present study have very fine microstructures in which very fine cementite dispersed in very fine ferrite matrix. Mechanical properties of the HPed compacts of Fe-C system with hypo-eutectoid composition are comparable with those of standard steels. Thus, MA and PM is a new technique of near net-shape to gain steels with excellent mechanical properties without thermal refining and alloying elements.

Error control for receiver-driven layered multicast of audio and video

We consider the problem of error control for receiver-driven layered multicast of audio and video over the Internet. The sender injects into the network multiple source layers and multiple channel coding (parity) layers, some of which are delayed relative to the source, Each receiver subscribes to the number of source layers and the number of parity layers that optimizes the receiver's quality for its available bandwidth and packet loss probability. We augment this layered FEC system with layered pseudo-ARQ. Although feedback is normally problematic in broadcast situations, ARQ can be simulated by having the receivers subscribe and unsubscribe to the delayed parity layers to receive missing information. This pseudo-ARQ scheme avoids an implosion of repeat requests at the sender and is scalable to an unlimited number of receivers, We show gains of 4-18 dB on channels with 20% loss over systems without error control and additional gains of 1-13 dB when FEC is augmented by pseudo-ARQ in a hybrid system, Optimal error control in the hybrid system is achieved by an optimal policy for a Markov decision process.

Parallel FEC code in high-speed optical transmissionsystems

Parallel FEC code transmission is proposed, in which check bits are transmitted on a different wavelength. The signal format is perfectly compatible with SDH in terms of signal wavelength. A smooth upgrade to the FEC system is possible by connecting additional modules. High FEC capability is obtained such that the BER of 10–6 can be improved to 10–11 with a decoding delay of several bits. When the parallel processing number is 8, the GVD tolerance is extended by a factor of 2.5, while the number of L-REPs possible in an optical link is doubled.

Nanocomposite powders of Fe-C system produced by the flowing gas plasma processing

Nanometer-sized α-Fe particles formed by the gas evaporation method were transferred into the microwave plasma region with a carrier gas of Ar including a small amount of CH 4. Particles collected after the plasma region were found to show a composite phase of Fe-C system that consisted of α-Fe and γ-Fe (Austenite) and Fe 3C. Moessbauer spectroscopy was used to estimate the relative yield of these three phases. An increase of γ- Fe is followed by the decrease of α-Fe with increasing CH 4 content. Formation of Fe 3C was recognized at 0.5 vol% of CH 4 in Ar gas and became more remarkable when the CH 4 content was increased. HRTEM observation revealed the individual particles to be a concentric shell structure composed of the Fe-C system.

Spacing arrangement of dispersed particles in thin foil : M.Besterci et al. (Ustav Materialoveho Vyskumu SAV, Kosice, Czech. Republic) Pokroky Praskove Metal., vol 34, no 4, 1996, 10–16. (In Czech.)

The complex model developed by Hoch and Arpshofen is used to describe the thermodynamic behavior of the liquid iron-carbon and iron-silicon systems; the standard states are the pure liquids. We have ΔGexm = n(x − xn)W where n is the size of the complex (number of atoms), W is the interaction parameter, and x is the atom fraction of the component with the lower binding capacity. The data used were taken from the compilation of Hultgren, and the phase diagrams from Hansen. In both systems, x is the atom fraction of Fe, and n = 3.The data used in the Fe-C system were gDGexC, ΔGexFe at 1873 K, the eutectic composition at 1426 K, and the carbon liquidus from 1426 K to 3148 K. In this system W = −(2.336 ± 0.033) + (0.6374 ± 0.020)T in kK.For the Fe-Si system, ΔGexSi at 1873 K, ΔHm, and ΔHexSi were used, and from the phase diagram four points: three points FeSi(s) in equilibrium with liquid, and Si(s) in equilibrium with liquid. In the Fe-Si system W = −(4.014 ± 0.144) + (.7758 ± 0756)T in kK.

Sir William Chandler Roberts-Austen — His role in the development of binary diagrams and modern physical metallurgy

This biographical sketch of Sir William Chandler Roberts-Austen was motivated by the centennial anniversary of his famous report of 1897. In the discussion session, Roberts-Austen presented his so-called “first” T-x diagram for the Fe-C system. Though not itself an equilibrium phase diagram, it became one in 1899 when H.W.B. Roozeboom modified an updated (“second”) version in accordance with the phase rule of J.W. Gibbs. In 1875 Sir William pioneered the use of T****-x diagrams for alloy systems, even before reliable thermocouples were available. Eventually, after Chatelier’s Pt, Pt-10% Rh thermocouple proved reliable for high temperature work, Roberts-Austen incorporated it in his own revolutionary invention: a mechanical autographic temperature recorder. Electronic versions are still used in all modern industrial plants and research labs.

アトマイズ法により作製された亜共晶Ｆｅ‐Ｃ系鋳鉄粉末のパルス通電焼結特性 ＩＩ アトマイズ鋳鉄粉末多孔質焼結体のヤング率

アトマイズ法により作製された亜共晶Ｆｅ‐Ｃ系鋳鉄粉末のパルス通電焼結特性 ＩＩ アトマイズ鋳鉄粉末多孔質焼結体のヤング率

アトマイズ法により作製された亜共晶Ｆｅ‐Ｃ系鋳鉄粉末のパルス通電焼結特性 Ｉ 焼結体の気孔率制御と内部組織

We studied the pulse electric current sintering behavior of the atomized cast-iron powder of Fe-C system containing hypo-eutectic carbon and the microstructures of sintered bodies. The results were as follows:(1) The porosity control of the atomized cast-iron sintered body, which was very difficult by the vacuum sintering method, could be done by the pulse electric current sintering method with several sintering conditions, that is, the sintering temperature and the sintering pressure.(2) The microstructure of the sintered body was depending on the sintering temperature, and was independent of the sintering pressure.