Fe-C System Research Articles

A further determination of the austenite solidus of the Fe-C system

A further determination of the austenite solidus of the Fe-C system

Partition of Carbon between Solid and Liquid in Fe-C Binary System

Synopsis : In order to investigate carbon distribution between solid and liquid phases in Fe-C binary system, austenite-liquid phases equilibrated in the temperature range from 1150 to 1 400•Ž were quenched and the carbon concentrations in each phase were determined by EPMA analysis. The results obtained are summarized as follows : (1) Solidus and liquidus obtained coincided well with the curves given in other recent works. (2) Diffusion distance of carbon from liquid-solid interface into solid phase during quenching was calculated. From the results of the calculation, it became clear that carbon concentration in the center of solid phase was not influenced by the carbon diffusion during quenching. (3) Equilibrium distribution coefficient of carbon in Fe-C system was determined thermodynamically. Solidus corresponding to the liquidus obtained experimentally was calculated by using the above coefficient and it was in good agreement with the experimental one.

Effects of Ti and Nb on the Nucleation of Primary Austenite in Hypoeutectic Cast Iron of Fe-C System

Effects of Ti and Nb on the Nucleation of Primary Austenite in Hypoeutectic Cast Iron of Fe-C System

Experimental Determination of the Austenite + Liquid Phase Boundaries of the Fe-C System

Differential thermal analysis has been employed to achieve an accurate determination of the solidliquid equilibria for γ-Fe at temperatures between 1147 °C and 1430 °C and compositions in the range 1.5 to 4.42 wt pct C. Several small but significant changes to the established phase diagram have been proposed. In particular, the liquidus in the vicinity of the eutectic has been raised by approximately 15 °C and the temperature of the graphite eutectic lowered to 1150.5 °C. Consequently, the eutectic compositions have been increased to 4.39 and 4.42 wt pct C for the graphite and cementite eutectics, respectively. The possibility of some modification to the γ-solidus has also been suggested, and a revised phase diagram is presented.

Fe-C2元系におけるCの固液間の分配

Synopsis : In order to investigate carbon distribution between solid and liquid phases in Fe-C binary system, austenite-liquid phases equilibrated in the temperature range from 1150 to 1 400•Ž were quenched and the carbon concentrations in each phase were determined by EPMA analysis. The results obtained are summarized as follows : (1) Solidus and liquidus obtained coincided well with the curves given in other recent works. (2) Diffusion distance of carbon from liquid-solid interface into solid phase during quenching was calculated. From the results of the calculation, it became clear that carbon concentration in the center of solid phase was not influenced by the carbon diffusion during quenching. (3) Equilibrium distribution coefficient of carbon in Fe-C system was determined thermodynamically. Solidus corresponding to the liquidus obtained experimentally was calculated by using the above coefficient and it was in good agreement with the experimental one.

The Nucleation of Graphite Eutectic in White Cast Iron of Fe-C System Molten below Graphite Eutectic Temperature

The Nucleation of Graphite Eutectic in White Cast Iron of Fe-C System Molten below Graphite Eutectic Temperature

Effect of small additions of a third component on the eutectic and peritectic temperatures of binary systems

The effect of additions of a third component on the temperature and composition of the eutectic or peritectic point of a binary system, at infinite dilution of this component, has been derived analytically. The depression of the eutectic temperature and the raising of the peritectic temperature are found to have an upper limit that no ternary element can exceed. The determination of the effect of a given solute on a eutectic or peritectic temperature hinges on the values of the activity coefficients of that solute at infinite dilution in the three phases in mutual equilibrium. In the absence of these data, various estimation methods can be used. Several of these methods have been illustrated in detail through the study of the effects of Sn, Zn and Au on the Ag-Cu eutectic temperature, and of the effects of Si on the peritectic and eutectoid temperatures of the Fe-C system. At least on a semiquantitative basis, the results are in very satisfactory agreement with data in the literature.

Structure and phase composition of surface zones of carburized and carbonitrided layers

1. Mossbauer spectroscopy makes it possible to detect the following iron-containing phases in the surface layers of carburized and carbonitrided samples: martensite, austenite, cementite, and iron oxides. 2. The quantities of these phases depend on the conditions of the chemicothermal treatment and can be used to judge the quality of the treatment with the proper correction factor. 3. The layer nearest the surface is most sensitive to the quality of the chemicothermal treatment (a layer ∼0.1 μ deep) in which the spectra of iron oxides are observed along with those of compounds characteristic of the Fe-C system. 4. With chemicothermal treatment in an endothermal atmosphere, a high concentration of iron oxides is observed in surface zones as thick as 1 μ. The higher the concentration of alloying elements with a large affinity for oxygen in the solid solution, the larger the total concentration of oxides. 5. No oxides are observed on the surface of samples carburized in an atmosphere of methane at a pressure of 10−3 mm Hg.

Thermodynamics and solubility of carbon in ferrite and ferritic Fe-Mo alloys

A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of α-Fe, Fe-0.48 wt pct Mo and Fe-1.16 wt pct Mo specimens which were equilibrated with a series of methane-hydrogen gas mixtures. The equilibria investigated involved the ferrite phases of the alloys between 682 and 848‡C. The experimental results permitted direct calculation of the activities of carbon in the samples, relative to graphite as unity, and of other thermodynamic functions, without the necessity for any correction factors. The results have been compared with the experimental measurements of a number of other investigators. In ferrite, the partial molar enthalpy and entropy of solution of carbon are found to be 26,800 cal/mole, (112, 130 J/mole), and 30.59 cal/K-mole, (127.99 J/K-mole) respectively at temperatures below about 727‡C. Above this temperature, the values are 25,200 cal/mole and 29.13 cal/K-mole, respectively. The addition of molybdenum results in an increase in these properties below 727‡C and a decrease in the values above 753‡C, and the changes are found to be proportional to the molybdenum content. The solubility of carbon in α-Fe is found to be 0.0176 wt pct at the eutectoid temperature. Molybdenum increases the solubility relative to the Fe-C system at temperatures above the eutectoid and decreases it below the eutectoid.

Thermodynamics of carbon in austenite and Fe-Mo austenite

A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of iron, iron-0.48 wt pct molybdenum and iron-1.16 wt pct molybdenum specimens which were equilibrated with a series of methane-hydrogen gas mixtures of constant composition. The equilibria investigated involved the austenite phases of the alloys at 783, 813 and 848‡C. The experimental results permit direct calculation of the activities of carbon in the samples, relative to graphite as unity, and of the enthalpy and entropy of solution of carbon. The results are compared with the experimental measurements of a number of other investigators. The results are in excellent agreement with those of Smith and Schenck and Kaiser for the Fe-C system at 800‡C, and indicate -HC/M values of 9700 ± 500 cal/mole for pure Fe, 10,030 ± 500 cal/mole for an Fe-0.48 wt pct Mo alloy, and 10,150 ± 500 cal/mole for an Fe-1.16 wt pct Mo alloy. The effect of molybdenum in austenite is to decrease the activity coefficient of carbon in austenite.

凝固鋼の熱間割れにおよぼす炭素含量の影響

In order to clarify the effect of the peritectic reaction in Fe-C system on the hot cracking in steel weld metal, the hot cracking tendency of the solidified steel specimens, of which carbon content were in the range of 0.01-0.54%, were investigated by means of the simple cast tear tests. The microsegregations in the cast steeel specimens were also examind by the electron-probe microanalyser.It was found that the hot cracking tendency of the solidified steel specimen with more than 0.1% of carbon content increases remarkably, because the sulphur is more segregated during solidification.This could be explained as follows;Through the peritectic reaction the crystallized δ iron has the surface skin of r iron, of which sulphur solubility is much lower than that of δ iron, and the solidification may terminate while the sulphur-enriched melt is sorrounded by r phase.Therefore it is important for the prevention of the hot cracking in steel weld metal to keep the carbon content under 0.1% as well as to reduce the sulphur content.

A stability analysis of the plate-to-needle morphological transition

The plate-to-needle morphological transition was investigated by means of a stability analysis of a growing platelet. Conditions were found for the evolution of a parallel array of needles from a sinusoidal perturbation of the plate tip. The theory was applied to the Fe-C system using recently obtained kinetic data and the transition region was shown on the Fe-C phase diagram. On the basis of the maximum growth rate postulate the evolving needle spacing was determined by the fastest growing perturbation wavelength. This spacing was plotted vs the dimensionless supersaturation for transformation temperatures of 700°, 650°, and 550°C. A multiple-sectioning technique was used to experimentally determine the morphology of Widmanstatten precipitates in four samples and good agreement was found with theory. Blade or lath-like precipitates, rather than needles, were found to be the result of platelet instability.

Thermodynamics and phase diagram of the Fe-C system

A critical review of published data provides a fairly accurate knowledge of the thermodynamic properties of all of the phases of the system Fe-C that are stable or metastable at atmospheric pressure. Selected data are shown as tables and equations. A proposed phase diagram differs only slightly from others recently published but has the following features. Peritectic compositions and the α-γ equilibrium are shown to agree with measured values of the activity of iron in the solid and liquid solutions and the thermodynamic properties of pure iron. Of all the reported carbides of iron only two may be studied under equilibrium conditions. The solubilities of cementite and of χ-carbide in α-Fe are deduced from measured equilibria. Both are metastable at all temperatures with respect to graphite and its saturated solution in iron. The χ-carbide becomes more stable than cementite below about 230° Certain published data on e-carbide permit an estimate of its free energy as a precipitate during the aging process.

Futher studies on the effect of C-content on the corrosion and passivity of Fe

The anodic and cathodic behaviour of pure Fe, five different steels of C-content ranging from 0·15 to 1·38 %, cast Fe containing 3·2 % C and 18-8 stainless steel was studied in 0·1N borax solution in absence and presence of Versene. The anodic behaviour of the steels investigated is markedly influenced by the nature of the separate phases in the Fe-C system and by Versene. In addition to pure Fe and 18-8 stainless steel, steel having a composition corresponding to the eutectoid structure shows the highest corrosion resistance. In presence of Versene and at low c.d.s ≤ 10μA/cm 2, the potential remains constant at values corresponding approximately to the formation of Fe(OH) 2. Increase of c.d. leads to passivity without manifesting the intermediate step obtained in absence of Versene.

Calculations of partial molal volumes in Fe-C system

Calculations of partial molal volumes in Fe-C system

Dynamic Polymorphism of Some Binary Iron Alloys

Investigations of the pressure-induced polymorphism of the Fe-V, Fe-Mo, Fe-Co, and Fe-C alloy systems have been carried out by dynamic techniques. The addition of vanadium to iron is found to raise the transition pressure very strongly, to some 575 kbar for 25 wt% vanadium content. The Fe-Co study indicates that long-range order does not have an appreciable effect on the transformation. The initial mixed phase state of the Fe-Mo system is clearly manifested in the transition behavior, generally fulfilling expectations. Variations of the transition parameters by various sample heat treatments are demonstrated in the Fe-C system investigation. The dynamic transformation parameters for pure iron have been reappraised, and are found to be Pb=129±1 kbar, v/v0=0.9360±0.0005. A summary of transition pressures for binary iron alloys is provided.

鋳鉄の黒鉛化におよぼす焼鈍雰囲気の影響

From the viewpoint of protective atmosphere for heat treatment, the effects of annealingatmospheres on the primary and secondary graphitization in making black heart malleablecast iron were studied. Namely, the relations between the graphitizing process of cementitein ledeburite or pearlite structures and the annealing atmospheres were investigated by observingthe graphitizing behaviour of several single atmospheres such as Ar, N2, H2 CO, CO2, H20 and CH4, as well as some practical furnace atmospheres which contain hydrogen as acomponent such as the mixed gas of N2-H2 system, the charcoal gas generated by blowingwet air and the exothermic gas produced through partial burning of propane. Results obtainedare as follows.When heated in the elemental gas which contains hydrogen such as 112, H20 or CH4, atomichydrogen penetrated quickly into the cast iron. In these atmospheres, the number of graphiteparticles formed was decreased and simultaneously the diffusion of carbon in austeniteor ferrite matrix was lowered because the meta-stable cementite in Fe-C system was stabilizedremarkably with dissolved hydrogen. In consequence, primary graphitizing was retardedand secondary graphitizing almost stopped. In the other annealing atmospheres the penetrationinto the cast iron was so sluggish that the difference from that in the argon atmosphere wasnot recognized.In every annealing atmosphere except hydrogen, the “bull's eyes” structure was formed bythe furnace being cooled after primary graphitization was completed. However, it was foundthat free ferrite phase was not precipitated in the hydrogen atmosphere. It was observedthat the degree of super cooling and the dilatic value at Al transformation became lowerthan in the other atmospheres.When heated in various practical furnace atmospheres, both primary and secondary graphitizationwere disturbed rapidly with rising hydrogen and water vapor contents. The particularpreventive tendency of dissolved hydrogen was very remarkable at the secondary graphitizing stage.

Effect of carbon content on the corrosion and passivity of iron

Anodic and cathodic polarization experiments were made on spectroscopically pure iron six carbon steels of carbon contents ranging between 0·15 and 1·3 percent and on 18-8 Cr-Ni stainless steel. The electrochemical behaviour of these steels in 1·4 N NaOH has been correlated with the phase diagram of the Fe-C system. Steels with a carbon content below 0·9 per cent behave in a manner similar to that of pure iron, in contradistinction from steels with higher carbon contents. With steels < 0·9 % C stages corresponding to the oxidation of iron to ferrous hydroxide and of this to ferric compounds are disclosed by the anodic polarization curves, while with steels > 0·9 %C only the second stage is indicated. The presence of ferrite or cementite as separate phases in addition to pearlite raises the number of C/cm 2 necessary to passivate the metal. On interrupting the anodic current imposed on passivated samples or on cathodically reducing them, potentials corresponding to the Flade potential are obtained in the former case (below 0·9 %C). Other samples on the other hand yield much more active potentials corresponding to the thermodynamically calculated value for the system Fe/Fe 3O 4/Fe 2O 3. The stability of the anodically formed passivating films decreases with decrease of ferrite as a separate phase.

Fe-Cr-N系状態図について

The tentative phase diagram of an Fe-Cr-N system in the composition range of 12 to 60% Cr, N up to about 2% at the partial pressure of nitrogen in air has been constructed by thermal analyses of Fe-Cr-N alloys which contained less nitrogen in the previously reported experimental formula [Cr] =32.9 log [N] +4.1.5, and X-ray analyses as well as microscopic examinations. Besides molten alloys, Fe-Cr-N alloys were prepared by the nitrogen-absorption at 1250°C and at one atmospheric preesure of pure nitrogen, and their structures have been examined. The denitrogenization of the nitrogen-absorbed alloys during the heating in the vacuum has also been clarified. The results are summarized as follows.(1) It was presumed from the study of the heterogeneous equilibrium of the Fe-Cr-N system that a peritectic reaction L+δ γ exists in the Fe-rich melt of the Fe-N system as seen in that of the Fe-C system, and it was also assumed that a eutectic reaction L δ+Cr2N exists in the range up to 11.6%N at Cr2N in the Cr-N system.(2) The peritectic reaction at the Fe-N alloy-side lowers the temperatures as the Cr content in the melt increases, and the eutectic reaction at the Cr-Cr2N alloy-side also decreases the temperatures as the Fe content in the melt increases. The above two mono-variant reactions meet at the point s in Fig. 1, which is found to exist at 16%Cr and 0. E9%N and at 1328.., and a peritecto-eutectic reaction L+δ γ+Cr2N is formed, the composition range of the non-variant reaction being in the hatched area formed by the following four points: q (δ), u (γ), s (L) and Cr2N.(3) It is presumed from x-ray diffraction analyses of alloys quenched immediately after their solidification that Cr2N does not dissolve Fe, Cr or N; the nitride primarily separated from melts may be shown as the simple form of Cr2N.(4) When Fe-Cr alloy sheets are heated at 1250°C at one atmospheric pressure of nitrogen, the higher the chromium content of the alloys, the more the nitrogen-absorption and the shorter the time for the saturation of the absorbed nitrogen.(5) When Fe-Cr alloys in the composition range of 12 to 40%Cr are nitrogen-absorbed at 1250°C, austenite is formed irrespective of the concentration of chromium in the alloys, and the phase containing chromium up to 23% decomposes into martensite on quenching and decomposes into α + Cr2N on slow cooling to room temperature, while the austenite containing above 23% Cr is retained as austenite without being decomposed by water-quenching from high temperatures.(6) Nitrogen-absorbed Fe-Cr-N alloys are denitrogenized by heating in the vacuum, the degree being less in higher chromium alloys.

鋼の変態理論

Heat treatment of steel is one of the most important matters in productive engineering. Many authorities have already made an effort to establish the theory of transformation of steel. But these theories are not completely able to explain the phenomena of phase change of steel in both cases of quenching and slow cooling.The author has endeavoured to certify the transformation of austenite→martensite and austenite→ferrite + cementite from different points of consideration. As a result he has proposed the following two important theories concerning the transformation.1. A homogeneous γ solid solution is stable to Ar point in cooling but carbon atoms do not move to aggregate locally or to settle in compounds. In this case the austenite-martensite transformation is concluded as a single component system and an iron-carbon alloy of a certain composition is transformed from austenite to martensite at a certain temperature.2. If it is assumed that carbon atoms in γ solid solution are allowed to move freely, they distribute themselves to keep the equal relative stability in crystals even in a transient state of transformaton. In this case it is explained as the phase change of two component Fe-C system. The equiliorium diagram shows the ideal case of this change.Theory 1 and 2 are confirmed by experimental facts. And in the case of slow cooling, carbon atoms in γ crystal move previous to a lattlice change of γ→a or separation of Fe3C from γ solid solution. In quenching, carbon atoms can not be transferred and only a lattice change takes place at Ar point. This change is considered a partial equilibrium change of transformation neglecting the movement of carbon atoms whose migration is very slow compared to lattice change.After quenching the secondary change of transformation in tempering or aging isM→a+Fc3Cand reversible changeγ Mis not realized in ordinary conditions.Dr. K. Honda has an opinion that the change of A1 transformation is always passed through the following steps :γ→M→a+Fe3Cand that cementite is to be separated after lattice changeγ→MAccording to the author's theory the carbon atom is to move in a solid solution before the Iattice change and therefore the change ofγ→αand separation of Fe3C from γ are direct ones as follows:γ→αα→Fe3CDr. K. Iwase's theory that the locus of Ar points concerning the composition of steel, is presumed as the extension of A3 solidus line GP, is not considered to be correct.