Thermodynamics of Mn–Fe–C and Mn–Si–C system

The solubility of C in Mn melts with different contents of Si and Fe at 1400 and 1500°C was determined. With these data the interaction coefficients e^Si_C, e^Fe_C, e^C_C as well as γ^o_C were evaluated. The standard free energy of solution of C in liquid Mn based on 1 wt.% solution standard at 1400 and 1500°C were calculated, respectively. The solubility of C in liquid Mn formulated in relation to temperature was made as to the conformability of the present results with those given in the literature.     

The solubility of Ca in Mn melt and the third-element interaction effects

Solubility experiments of Ca in Mn melt were carried out in a Mo-wire-heated furnace. Small CaO crucibles, charged with the Mn alloys with small amount of Ca chips on top, were placed in an iron crucible, its lid being tightly sealed under red-hot conditions. Relation of the solubility of Ca in pure Mn with temperature was formulated between 1 250 and 1 380°C. The effects of 3rd elements upon the solubility of Ca in Mn at 1 350°C were studied. Diagram showing the relation of Ig f^j_Ca with [%j] (j = Si, Cr, Ni, Fe, Al, C and Ca) was drawn and e^j_Ca evaluated. With the formula of Wagner, In γ_Ca⁰ and ε_Ca^Ca were found by regression analysis from the experimental data. The standard free energy of solution of Ca in Mn, based on the 1 wt.% standard at 1350°C was calculated, and its relation with T estimated.     

Microstructures and Mechanical Properties of High‐Strength Fe‐Mn‐Al‐C Light‐Weight TRIPLEX Steels

High‐strength TRIPLEX light‐weight steels of the generic composition Fe‐xMn‐yAl‐zC contain 18 ‐ 28 % manganese, 9 ‐ 12 % aluminium, and 0.7 ‐ 1.2 % C (in mass %). The microstructure is composed of an austenitic γ‐Fe(Mn, Al, C) solid solution matrix possessing a fine dispersion of nano size κ‐carbides (Fe,Mn)₃ AlC_1‐x and α‐Fe(Al, Mn) ferrite of varying volume fractions. The calculated Gibbs free energy of the phase transformation γ_fcc → ?_hcp amounts to ΔG^γ→? = 1757 J/mol and the stacking fault energy was determined to Γ_SF = 110 mJ/m². This indicates that the austenite is very stable and no strain induced ?‐martensite will be formed. Mechanical twinning is almost inhibited during plastic deformation. The TRIPLEX steels exhibit low density of 6.5 to 7 g/cm³ and superior mechanical properties, such as high strength of 700 to 1100 MPa and total elongations up to 60 % and more. The specific energy absorption achieved at high strain rates of 10³ s^?1 is about 0.43 J/mm³. TEM investigations revealed clearly that homogeneous shear band formation accompanied by dislocation glide occurred in deformed tensile samples. The dominant deformation mechanism of these steels is shear band induced plasticity ‐SIP effect‐ sustained by the uniform arrangement of nano size κ‐carbides coherent to the austenitic matrix. The high flow stresses and tensile strengths are caused by effective solid solution hardening and superimposed dispersion strengthening.     

The Thermodynamic Properties of Fe‐Mn‐C Melt at Reduced Pressure

The solubility of carbon in the Fe‐Mn‐C system was measured under reduced pressure of 1 Pa at 1573 K and 1673 K, respectively. The carbon solubility in terms of mole fraction in the iron based solution was found varying with manganese mole fraction in the solution and with temperature, as x_C= 0.1819 + 0.2531 x_Mn at 1573 K and x_C = 0.1981 + 0.2515x_Mn at 1673K. Manganese has a stronger influence on the carbon solubility at lower pressure than it has at higher pressure. The pressure was found to have an insignificant effect on the carbon solubility when manganese in the melt was absent. The activity interaction parameters between manganese and carbon in the alloy were determined from carbon solubilities at 1573 and 1673 K. Analysis of the experimental results showed that under vacuum conditions, the activity interaction parameter of manganese with carbon is higher than that at atmospheric pressure.     

Microstructure and properties of a C–Mn–Si–dual-phase steel

A study has been carried out on an Fe–0.11% C–1.58% Si–0.4% Mn-dual phase steel. The dual-phase microstructures and properties are significantly affected by both the intercritical temperature and cooling rate from (α + γ) field. Upon rapid cooling (water or oil quench) from the temperature range 735–820°C, the structure comprises ferrite + martensite. On the other hand, slow cooling (air cooling) from the temperature range 735–820°C produces microstructures containing ferrite + martensite + pearlite/bainite and more favourable mechanical properties as: σ_0,2 = 281–296 MPa, σ_UTS = 632–690 MPa, TE = 26–30% and continuous yielding behaviour.     

Spinel deoxidation equilibria in the Fe—Mn—Al—O system – experiment and computation

The concentration and chemical potential of oxygen in liquid Fe—Mn alloys equilibrated with the spinel solid solution, (Fe, Mn)Al_2+2xO_4+3x, and α-Al₂O₃ have been determined at 1873 K as a function of manganese concentration. The composition of the spinel phase has been determined using electron probe microanalysis. The results are compared with data reported in the literature. The deoxidation equilibrium has been computed using data on free energy of solution of oxygen in liquid iron, free energies of formation of hercynite and galaxite, and interaction parameters reported in the literature. The activity-composition relationship in spinel solid solution was derived from a cation distribution model. The model is in excellent agreement with the experimental data on oxygen concentration and potential and the composition of the spinel phase.     

A microstructural characterization of scale formed on austenitic Fe–29.7Mn–8.7Al–1.04C and duplex Fe–29Mn–10Al–0.4C alloys in oxidizing-sulfidizing environments

Austenitic Fe–29.7Mn–8.7Al–1.04C and duplex Fe–29Mn–10Al–0.4C alloys were exposed to the SO₂–O₂ mixed gas environments at 900 °C. The morphology of the scales formed on these alloys under oxidizing-sulfidizing conditions were examined by SEM and X-ray mapping techniques. The results showed that the addition of carbon up to 1 wt.% to the Fe–29.7Mn–8.7Al–1.04C alloy led to the formation of internal sulfidation and intergranular oxidation in the mixed oxidant gas environments. On the other hand, no evidence of intergranular oxidation could be detected in the duplex Fe–29Mn–10Al–0.4C alloy with lower carbon concentration.     

Thermodynamics of manganese distribution between liquid iron and the CaO–Al2O3–SiO2–FeO–MnO system

The thermodynamics of distribution of constituents between liquid iron and the CaO–Al₂O₃–SiO₂–FeO–MnO system at 1600°C was studied using electrochemical indication of the equilibrium partial pressure of oxygen in both phases. The results show that oxidation potential of the Fe(l)–CaO–Al₂O₃–SiO₂–FeO–MnO system, expressed in terms of log p(O₂), is directly proportional to log (x(MnO) · x(FeO)/w| Mn |). Manganese distribution coefficient, L'_mn, in intersection CaO/Al₂O₃ = 1 decreases with increasing slag basicity expressed in terms of activity a(CaO) or 1/γ(MnO). Experimentally determined equilibrium constant K_Mn/Fe is equal to 2.7 for 1600°C. The number of exchanged electrons between Fe-O-Mn-Si electrode and the slag approaches the theoretical value.     

The Development of a Processing Window for the Continuous Galvanizing of a Mn–Cr–Si Martensitic Steel

Martensitic or complex phase steels are leading candidates for automotive impact management applications. However, achieving high strengths while obtaining high quality coatings via continuous galvanizing is a challenge due to cooling rate limitations of the processing equipment and selective oxidation of alloying elements such as Cr, Mn, and Si adversely affecting reactive wetting. The galvanizability of a Cr? Mn? Si steel with a target tensile strength above 1250 MPa was investigated within the context of the continuous galvanizing line. The continuous cooling transformation behavior of the candidate alloy was determined, from which intercritical and austenitic annealing thermal cycles were developed. The evolution of substrate surface chemistry and oxide morphology during these treatments and their subsequent effect on reactive wetting during galvanizing were characterized. The target strength of 1250 MPa was achieved and high quality coatings produced using both intercritical (75% γ) and austenitic (100% γ) annealing using a conventional 95%N₂–5%H₂, ?30°C dew point process atmosphere and 0.20 wt% dissolved (effective) Al bath, despite the presence of significant Mn and Cr oxides on the substrate surfaces. It is proposed that complete reactive wetting by the Zn(Al, Fe) bath was promoted by in situ aluminothermic reduction of the Mn and Cr‐oxides by the dissolved bath Al.     

The activity coefficient of oxygen in binary liquid metal alloys

The Wagner model with one energy parameter,h, for describing the effect of alloying elements on the activity coefficients of nonmetallic solutes in liquid metals is extended to have two energy parameters,h ₁andh ₂. The validity of both the Wagner one-parameter equation and the newly derived two-parameter equation is tested using data available in the literature for twelve ternary metal-oxygen systems. In order to have consistent thermodynamic data, all the relevant binary, as well as the twelve ternary metal-oxygen systems are evaluated using the same thermodynamic values for the reference materials which were used in carrying out the experimental measurements. It is found that the twoparameter equation is capable of quantitatively accounting for the compositional dependences of the activity coefficients of oxygen in all twelve ternary systems while the Wagner one-parameter equation is not. A correlation between the Wagner parameter,h, and the thermodynamic properties of the respective binary metal-oxygen and binary metals systems is found, from which the value of this parameter may be predicted without referring to any ternary data. Accordingly, the two-parameter equation is more useful in evaluating ternary experimental data while the Wagner one-parameter equation in connection with the correlation betweenh and binary data is capable of predicting ternary data without any experimental investigation in the ternary region. Based on the one-parameter and the two-parameter equations, theoretical equations for the first-order and second-order free energy interaction parameters,(∈ ₀ ^j )_sand(ρ ₀ ^j )_s, are derived in terms of the model parameters. The values of(∈ ₀ ^j )_s and(ρ ₀ ^j )_s for all the systems are derived and are found to vary linearly with the reciprocal of temperature. Furthermore, linear relationships between these two interaction parameters and their slopes with 1/T are found, from which the temperature dependence of the interaction parameters may be estimated in the absence of experimental data.     

Thermodynamic behaviour of phosphorus in Mn-Si-Ca-P melts

Thermodynamic experiments of Mn-Si-Ca-P melts were carried out in Mo-wire-heated furnace. With these experimental data, the first and second order activity interaction coefficients of Ca, Si and P upon P under the conditions of the same activity and the same concentration method were evaluated. The standard free energy of solution of P in liquid Mn based on 1 wt.% solution standard formulated in temperature was given and it only holds near 1623 K.     

Thermodynamic Properties of Dilute Aluminum in Liquid Zinc

Abstract

The thermodynamic properties of the liquid zinc-aluminum system in the range of 0 to 0.36 mole fraction of aluminum and over a temperature range of 430 to 530 °C were investigated by using an electromotive force (EMF) cell of the type

Al(s)|LiCl–KCl–AlCl₃|Zn–Al(l),Mo

The activity of aluminum was found to show a significant positive deviation from Raoultian behaviour. The activity coefficient of aluminum in the dilute solution range (γ°) and the free energy of solution of aluminum based on the one weight percent (1 wt %) standard state were determined as a function of temperature and found to follow the relationships:

logγ°=(1195/T)?0.874

ΔG_s=5457?11.4T (cal/mole)

Over the temperature range investigated, the self-interaction coefficient of aluminum in liquid zinc (e^Al_Al) was found to be approximately constant at ?0.01.

On a étudié les propriétés thermodynamiques du système liquide zinc-aluminium, entre 0 et 0.36 fraction molaire d'aluminium, à des températures de 430 à 530 °C, en utilisant une cellule à force électromotrice (FEM) du type:

Al(s)|LiCl–KCl–AlCl₃|Zn–Al(l),Mo

On a trouve que l'factivite de l'faluminium montrait une deviation positive importante du comportement Raoultien. On a determine le coefficient d'factivite, γ°, de l'faluminium pour une solution diluee ainsi que l'fenergie libre de solution de l'faluminium, base sur l'fetat standard de un pour-cent en poids (1%), en fonction de la temperature. On a trouve que ceux-ci suivaient les relations suivantes:

logγ°=(1195/T)?0.874

ΔG_s=5457?11.4T (cal/mole)

Dans le domaine de température étudié, on a trouvé que le coefficient d'auto-interaction de l'aluminium dans le zinc liquide (e_Al^Al) était approximativement constant à ?0.01.     

A comparison of the molecular interaction volume model with the subregular solution model in multicomponent liquid alloys

The molecular interaction volume model (MIVM) is a two-parameter model, meaning it can predict the thermodynamic properties in a multicomponent liquid alloy system using only the coordination numbers calculated from the ordinary physical quantities of pure liquid metals and the related binary infinite dilute activity coefficients, γ _∞ ⁱ and γ _∞ ^j , which avoids somewhat adjustable fitting for the binary parameters of B _ji and B _ij. In comparison with the subregular solution model (SRSM), the prediction effect of the MIVM is of better stability and safety because it has a good physical basis.     

Activity of MnO in MnO‐CaO‐MgO‐SiO2‐Al2O3 Slags at 1500 °C

A thermodynamic study was made on the MnO‐CaO‐MgO‐SiO₂‐Al₂O₃ slags that are typical of the production of ferromanganese in submerged arc furnaces. The Al₂O₃ content of the slags was kept constant at 5 per cent by mass. The activity‐composition relationship in Pt‐Mn binary alloys were re‐determined for calibration purposes at 1300, 1400 and 1500°C and po₂ values between 5.40×10^?6 and 4.54×10^?13 atm. A linear regression equation was derived to predict the activity coefficients of manganese, in Pt‐Mn alloys at 1500°C. The effect of concentration, basicity ratio and CaO‐to‐MgO ratio on MnO activities in above mentioned complex slags was investigated at 1500 °C and at two different po₂ values of 4.76×10^?7 and 5.80×10^?8 atm. It was found that a_Mno values increase with increasing MnO, and tend to increase with an increasing CaO‐to‐MgO ratio. The a_MnO values also increase with increasing basicity ratio. The activity coefficient of MnO increases with an increase in its mole fraction in the slag. Quadratic multivariable regression model equations which represent the activity data successfully and which can be used to predict the MnO activities in the compositional range of this study were developed. The MnO activity data was interpreted in terms of a slag model which describes the thermodynamic properties of the slag successfully.     

On the Formation of Vanadium Ferrites in CaO–SiO2–FeO–V2O5 Slags

Selective extraction of valuable elements (such as V, Cr, Mn, etc.) and their compounds from metallurgical slag is in a focus of many researchers. Although vanadium may be present in slag as oxides and/or complex spinels with Fe, Mn, etc. during an alloyed steel production, the majority of vanadium in metallurgical slags typically exists as V₂O₅, which comprises up to 3–5 wt% of the slag in some cases. Due to the vanadium toxicity, these slags are forbidden in many civil engineering applications. As a result, hundreds of thousand tonnes of V₂O₅‐bearing slags are landfilled every year. In the present work, the formation of vanadium ferrites (FeV₂O₄ and Fe₂VO₄) in synthesized CaO–SiO₂–FeO–V₂O₅ slags containing 5 wt% V₂O₅ was examined under different partial pressures of oxygen. For the current slag chemistry range, an XRD analysis confirmed the presence of vanadium ferrite in slag samples treated at 1773 K in an argon atmosphere (PO₂ = 10^?1–10^?2 Pa) while no solid was noted in samples treated in air. Results were discussed based on thermodynamic consistency.     

Speciation of the Fe(II)–Fe(III)–H2SO4–H2O system at 25 and 50 °C

This work presents theoretical and experimental results on the speciation of the Fe(II)–Fe(III)–H₂SO₄–H₂O system in concentrated solutions (up to 2.2 m H₂SO₄ and 1.3 m Fe). The aim was to study the chemical equilibria of iron at 25 and 50 °C in synthetic aqueous sulphuric acid solutions that contain dissolved ferric and ferrous ion species. Raman spectroscopy, volumetric titration and conductivity measurements have been carried out in order to study the presence of specific ions and to characterize the ionic equilibrium. A thermochemical equilibrium model incorporating an extended Debye–Hückel relationship was used to calculate the activities of ionic species in solution. Model calculations were compared with experimental results. Model simulations indicate that anions, cations and neutral complexes coexisted in the studied system, where the dominant species were HSO₄⁻, H⁺, Fe²⁺ and FeH(SO₄)₂⁰. This indicated that these solutions showed a high buffer capacity due to the existence of bisulphate ions (HSO₄⁻), which presented the highest concentration. A decrease in the concentration of H⁺ and Fe³⁺ took place with increasing temperature due to the formation of complex species. Standard equilibrium constants for the formation of FeH(SO₄)₂⁰ were obtained in this work: log K_f⁰ = 8.1 ± 0.3 at 25 °C and 10.0 ± 0.3 at 50 °C.     

Development and characterization of high strength impact resistant Fe-Mn-(Al-, Si) TRIP/TWIP steels

Iron manganese steels with Mn mass contents of 15 to 30 % exhibit microstructural related superior ductility and extraordinary strengthening behaviour during plastic deformation, which strongly depends on the Mn content. This influences the austenite stability and stacking fault energy γ_fcc and shows a great impact on the microstructure to be developed under certain stress state or during severe plastic deformation. At medium Mn mass contents (15 to 20 %) the martensitic γ-ε-ά phase transformation plays an important role in the deformation mechanisms of the TRIP effect in addition to dislocation glide. With Increasing Mn mass content large elongation is favoured by intensive twinning formation. The mechanical properties of plain iron manganese alloys are strongly influenced by the alloying elements, Al and Si. Alloying with Al Increases the stacking fault energy and therefore strongly suppresses the martensitic γ-ε transformation, while Si sustains the γ-ε transformation by decreasing the stacking fault energy γ_fcc. The γ-ε phase transformation takes place in Fe-Mn-X alloys with γ_fcc ≤ 20 mJm⁻². The developed light weight high manganese TRIP and TWIP (twinning induced plasticity) steels exhibit high ultimate tensile strength (600 to 1100 MPa) and extremely large elongation of 60 to 95 % even at high strain rates of έ = 10³ s⁻¹. Particularly due to the advanced specific energy absorption of TRIP and TWIP steels compared to conventional deep drawing steels high dynamic tensile and compression tests were carried out in order to investigate the change in the microstructure under near crash conditions. Tensile and compression tests of iron manganese alloys with varying Mn content were performed at different temperatures and strain rates. The resulting formation of γ twins, ά- and ε martensite by plastic deformation was analysed by optical microscopy and X-ray diffraction. The deep drawing and stretch forming behaviour at varying deformation rates were determined by performing cupping tests and digitalised stress-strain-analysis.     

Thermodynamics of MnO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MnS Liquid Oxysulfide: Experimental and Thermodynamic Modeling

The activities of MnO and MnS in a MnO-SiO₂-Al₂O₃(or AlO_1.5)-MnS liquid oxysulfide solution were investigated by employing the gas/liquid/Pt-Mn alloy chemical equilibration technique under a controlled atmosphere at 1773 K (1500 °C). Also, the sulfide capacity, defined as C _S = (wt pct S)(pO₂/pS₂)^1/2, in MnO-SiO₂-Al₂O₃ slag with a dilute MnS concentration was obtained from the measured experimental data. As X _SiO2/(X _MnO + X _SiO2) in liquid oxysulfide increases, the activity coefficient of MnO decreases, while that of MnS first increases and then decreases. As X(AlO_1.5) in liquid oxysulfide increases, the activity coefficient of MnS increases, while no remarkable change is observed for the activity coefficient of MnO. The behavior of the activity coefficient of MnS was qualitatively analyzed by considering MnO + A _x S _y (SiS₂ or Al₂S₃) = MnS + A _x O _y (SiO₂ or Al₂O₃) reciprocal exchange reactions in the oxysulfide solution. The behavior was shown to be consistent with phase diagram data, namely, the MnS saturation boundary. Quantitative analysis of the activity coefficient of the oxysulfide solution was also carried out by employing the modified quasichemical model in the quadruplet approximation.     

Thermodynamics of the System Fe−Mn−S: Part III. Equilibria Involving Solid and Liquid Phases in the Temperature Range 1100 to 1300°C

The equilibria between cubic (Fe,Mn)S solid solutions and sulfur rich liquid have been measured in the temperature range 1100 to 1300°C, and those between cubic (Fe,Mn)S and hexagonal ‘FeS’ at 1100°C. Gas phases consisting of H₂S-H₂ mixtures were used as atmospheres. Further, isosulfur-activity lines in the liquid phase region and the composition of the liquid at saturation with γ-iron were determined. The data were used to delineate the liquidus surfaces of γ-iron, (Fe,Mn)S, and ‘FeS’, and the location of the pertinent univariant lines in the 1100 to 1300γC range of the Fe?Mn?S system.