The density of liquid iron-carbon alloys

The density of liquid Fe-C alloys at temperatures ranging from 1250 °C to 1550 °C was measured by the sessile drop profile method. An accurate method of digital image processing was de-veloped to capture, enhance, and determine the coordinates of the X-ray shadow image of the droplet. Laplace's equation was then solved to obtain the volume and density of the droplet. The density of iron-carbon alloys was then determined as a function of carbon content (from 0 to 4 wt pct) and temperature (1250 °C to 1550 °C). A least-squares analysis of our data points gives an equation for the density of liquid iron-carbon alloys as a function of temperatureT [K] and carbon content [pct C] [wt pct]: ρ[g/cm³] = (7.10 - 0.0732[pct C]) - (8.28 - 0.874[pct C]) × 10^-4(T - 1823) These results will give a value to within ±1.5 pct of the data of Lucas, [3] Widawski and Sauerwald, [2] and the present work.     

Decarburization of iron-carbon alloys by argon-oxygen mixtures

Abstract

Liquid iron which contained up to 4% carbon was decarburized at temperatures of 1335 – 1445°C in argon containing up to 1.16% oxygen. Rates were measured by following the O₂ consumption by an electrochemical cell, or the CO₂ production by a mass spectrometer. The crucible was arranged so that the depth of alloy could be varied without altering the pattern of gas flow. The rate of decarburization did not depend on the crucible-melt interfacial area or the roughness of the crucible. It was concluded that heterogeneous nucleation of CO at the walls of the crucible was not an important rate-controlling step. The effects of carbon content of the melt, oxygen content and flow rate of the gas, and temperature on the rate of decarburization, support previous suggestions that the rate-determining step for the range of conditions studied is diffusion of oxidant in the gas phase.

Résumé

Du fer liquide contenant jusqu' à 4% de carbone fut décarburé à des températures variant de 1335 à 1445°C dans de l'argon comprenant jusqu'à 1.16 % d'oxygéne. Le processus de décarburation était suivi soit en mesurant la consommation d'oxygène par une cellule électrochimique, soit en mesurant au spectromètre de masse la production de CO₂. Le dessin du creuset permettait de faire varier le niveau de métal liquide sans pour autant changer l'écoulement du gaz. Le taux de décarburation est independent de l'interface creuset-bain liquide et de la rugosite du creuset. Les auteurs en concluent que la germination heterogene du CO sur les parois du creuset n'est pas un mecanisme determinant le taux de reaction. L'effet de la teneur en carbone du bain, de la teneur en oxygene du gaz, et de la temperature sur le taux de décarburation confmne les idees précédemment emises que le facteur déterminant le taux de reaction, pour les conditions expérimentales étudiées, est la diffusion de l'oxydant dans la phase gazeuse.     

Intergranular embrittlement of iron-carbon alloys by impurities

It is shown that plain Fe-C alloys can be embrittled by certain heat treatments if they are doped with Sb, Sn, As or P. Embrittlement occurs when these elements are rejected from precipitating carbides during cooling, and it results from a piling-up of the elements ahead of the carbide and the concomitant lowering of cohesion along the carbide-ferrite interface. It is a transient (non-equilibrium) condition and disappears upon continued holding at elevated temperatures. Embrittlement by equilibrium segregation of these impurities in unalloyed ferrite apparently does not occur. A model for this transient embrittlement is proposed and tested. This model is relevant to the phenomenon of “500°F” embrittlement in alloy steels, and it is also consistent with most aspects of temper embrittlement. J.R. RELLICK, formerly Research Fellow, Department of Metallurgy and Materials Science, University of Pennsylvania     

The densities of high-purity iron-carbon alloys in the spheroidized condition

The densities were determined for a series of spheroidized then slowly cooled, high-purity iron-carbon alloy specimens containing from 0 to 4.17 pct C. They were found to follow the relationshipρ ^-1 (cc/g at 23°C) = 0.12698₈ + (5.03₆ × 10^-4) (wt pct C). Whereas the intercept value coincided with the x-ray specific volume of iron, the extrapolated value at the Fe₃C composition was slightly greater than published X-ray specific volumes for Fe₃C. The results suggested that the cementite phase in these specimens was slightly iron-rich with respect to Fe₃C. Assuming a vacancy-defect structure for the cementite, we were able to roughly estimate its composition. This appears to be a promising method for determining the cementite/(cementite + ferrite) saturation boundary.     

Thermomechanical properties of iron and iron-carbon alloys: density and thermal contraction

For the modelling of strains und stresses arising during solidification data on the mechanical and thermal properties of the steel are needed. Data on density and on related properties of iron and iron-carbon alloys in the literature were evaluated giving the thermal contraction as a function of temperature and carbon content.     

Effects of precipitation on the thermoelectric power of iron-carbon alloys

The thermoelectric power (T.E.P.) of iron-carbon alloys and its variations due to carbide precipitation are studied and analysed. The carbon in solid solution decreases the T.E.P. of iron by reducing the lattice component. An increase of T.E.P. is always observed during carbide precipitation; it is essentially due to the decrease of solute content in the residual solid solution. The kinetics of T.E.P. variation for isothermal ageing from ambiant temperature to 500°C have been determined. Their analysis permits to separate the two stages of precipitation corresponding to Fe₃C phase and ϵ-phase. Moreover it is shown that ϵ precipitates reversion can be obtained by a short ageing at 275°C. The particular aspect of kinetics at low temperature (20°C) seems to show that the precipitation is different from ϵ -phase precipitation at 100°C. These results are confirmed by internal friction measurements and by transmission electron microscopy observations.     

Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

The processes of nucleation and growth of alloys during solidification are linked to the level of gravitational force. In a low-gravity environment, buoyancy-induced convection becomes negligible, resulting in lower convection as compared to normal or high gravity. In this paper, heterogeneous nucleation and grain multiplication during solidification of gray cast iron, and the effect of gravitational level on them, have been studied by means of directional solidification on ground and under low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It has been assumed that the final number of eutectic grains results from the contribution of heterogeneous nucleation,N _h , heterogeneous nucleation induced by inoculation,N _i , and heterogeneous nucleation induced by convection,N _c . In turn,N _c has two components, a grain multiplication component,N _c ^m , and a kinetics of chemical reactions component,N _c ^k . In all cases, it was found that a higher number of grains are obtained when solidifying in highg as compared with lowg. This was attributed to higher convection in highg. It was demonstrated that grain multiplication due to convection can contribute 20 to 23 pct from the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was shown that the contribution to the convection-induced nucleation of the kinetics of chemical reactions can be as high as 30 pct but can be zero at very low or very high grain numbers. A possible mechanism and an explanation have been given to those findings. The silicon distribution, graphite morphology, and the influence of soak time on experimental results have also been discussed.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15?_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15ƒ_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal. This paper is based on a presentation made at the G. R. Fitterer Symposium on Nitrogen in Metals and Alloys held at the 114th annual AIME meeting in New York, February 24–28, 1985, under the auspices of the ASM-MSD Thermodynamic Activity Committee.     

The diffusion of carbon in iron-carbon alloys at 1560°C

Measurements have been made of the rate of absorption of carbon from CO-CO₂ mixtures into stagnant liquid iron and of the rate of unidirectional dissolution of graphite into stag-nant liquid iron and iron-carbon alloys at 1560°C. Total absorptions and concentration pro-files were found to be consistent with a composition dependent chemical diffusivity given byD = 1.1 (1 + wt pct CJ5.3) X 10∼⁴ cm²Js with an uncertainty of about ±0.2 x 10^-4. It is shown that many of the previous determina-tions of the chemical and self-diffusivity are consistent with this suggested dependence. Formerly graduate student at the University of Pennsylvania     

The effect of microstructure on fatigue crack propagation in iron-carbon alloys

The dependence of fatigue crack growth rate on the cyclic stress intensity factor was determined for six iron-carbon alloys ranging in carbon content from 0.23 to 1.08 wt pct carbon. Both ferrite/pearlite and ferrite/free iron carbide microstructures were studied. Scanning electron microscope fractography studies correlated the fatigue mechanism with microstructure. It was found that when the predominant mode of crack growth was ductile, the crack growth rateda/dN could be related to the cyclic stress intensity factor ΔK by an equation of the formda/dN = (ΔK)_m where andm are constants. The constantm was approximately equal to four when the crack growth mechanism presumably was the blunting and resharpening of the crack tip by slip processes. The constantm was greater than four when the crack growth mechanism was void coalescence in the interlamella ferrite of pearlite colonies. The preferred fatigue crack path through the pearlitic alloys was through the free ferrite phase. formerly Research Assistant at Materials Science and Engineering Department and Materials Research Center, Northwestern University.     

Evolution of damage and plasticity in

The inelastic deformation mechanisms were evaluated for a model titanium-based, fiber-reinforced composite: a beta titanium alloy (Ti-15V-3Al-3Cr-3Sn) reinforced with SiC (SCS-6) fibers. The primary emphasis of this article is to illustrate the sequence in which damage and plasticity evolved for this system. The mechanical responses and the results of detailed microstructural evaluations for the [0]₈, [90]₈, and [±45]_2s, laminates are provided. It is shown that the char- acteristics of the reaction zone around the fiber play a very important role in the way damage and plasticity evolve, particularly in the microyield regime of deformation, and must be included in any realistic constitutive model. Fiber-matrix debonding was a major damage mode for the off-axis systems. The tension test results are also compared with the predictions of a few con- stitutive models.     

An Evaluation of the summation of cyclic plastic strain damage in two high strength aluminum alloys

A damage equation based upon the integration of low cycle fatigue plastic strain ranges was verified experimentally for two high strength aluminum alloys 2024-T4 and 7075-T651. The damage equation which has been used extensively for many fatigue crack propagation theories assumes cyclic damage under increasing plastic strain ranges. In order to verify the damage equation, low cycle fatigue specimens were subjected to a fully reversed strain cycle in which the total strain-range was increased linearly by a constant amount Δ[Δε_d] per cycle. An excellent agreement was obtained between the predicted and observed fatigue lifetimes. The stress-strain response of these alloys was also measured. The experimental results showed that these two alloys cyclically harden substantially and that the single strain increment stress-strain curve is a fair lower bound approximation of the cyclic stress-strain curve.