Browsing by Department "Department of Materials Science and Rock Engineering"

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  • The effect of dissolved ozone on the corrosion behaviour of some stainless steels
    (2001-12-14) Pehkonen, Antero
     Doctoral dissertation (monograph)
    The corrosion behaviour of some stainless steels and pure metals has been investigated in solutions with dissolved ozone. The pH of the test solution was 1, 2, 3 and neutral (adjusted by H2SO4). 2.3 and 23 g/l Na2SO4 was added to increase the conductivity in anodic and cathodic polarisation measurements. The temperature of the test solution was 20, 50 and 75 °C. Test materials were four different stainless steels: ferritic stainless steel Polarit 815 and austenitic stainless steels Polarit 720, Polarit 752 and Ralloy 654MO. Also Armco iron, pure Mo, Ni and Cr were tested. The general electrochemical behaviour of stainless steels and pure metals was studied with potentiodynamic cyclic polarisation experiments at scanning rates 1, 10 and 100 mV/min and pitting behaviour at 10 mV/min. Potentiostatic experiments were also used. Immersion tests were also carried out mainly to produce test samples for surface examination but also to measure the weight losses. The structure and thickness of the oxidized surfaces were examined and analysed using optical microscope, SEM, GDOS, ESCA and X-ray diffractometer methods. Dissolved ozone increases the redox-potential of test solutions to about +1200 mV vs. SCE and the corrosion potential of stainless steel to the transpassive region, below the oxygen evolution potential. The current densities of stainless steels in this region increase as the amount of alloying elements increases. On the other hand, dissolved ozone increases current densities only slightly compared to oxygen bubbled solution. Higher ozone concentration obtained under high pressure has no effect on the corrosion behaviour of stainless steels. The corrosion of stainless steels is general but peeling of oxide layers was also observed. Shallow corrosion damages are formed in immersion. In cyclic polarisation experiments pits are formed in Ralloy 654MO. The pits formed are similar to those formed by chloride induced pitting. As the pH of the solution is decreased, the current density of higher alloyed steels increases at higher pH than lower alloyed steels. Dissolved ozone increases the thickness of the oxide layers greatly. In oxygen bubbled solution at pH 3 the thickness of the layers is a few nanometers and in ozonated solution 60 - 260 nm. The compositions of these oxide layers has been found to vary greatly. Cr concentration is negligible in the oxide layers especially for Ralloy 654MO and P752. Molybdenum concentrates in the outer layer, even more so with lower alloyed steels. Iron and alloying elements have oxidised to their highest valencies. The main components in the oxide layers are iron oxides and on the surfaces also MoO6 occurs.
  • High temperature oxidation of metal, alloy and cermet powders in HVOF spraying process
    (2004-12-03) Korpiola, Kari
     Doctoral dissertation (monograph)
    In thermal spraying, the coatings, alloys and metals oxidise during the spraying process. Oxidation often results in a decrease in the mechanical and corrosion properties of the coating. In this study, oxidation of HVOF coatings is examined. In the beginning of the study, the HVOF spraying process is analysed, including the combustion process, gas temperature, oxygen concentration, gas velocity, and gas momentum. Temperature and velocity of the spray particles are measured. Thermodynamic and kinetic equations of metal oxidation are introduced. In the experimental part of the work, calculations and coating experiments were carried out. Thermodynamic calculations of metal oxidation were done in the HVOF spray gun environment using different fuel/oxygen ratios, fuel quality and metals. The metal oxidation calculations were performed with HSC thermodynamic software. The thermodynamic calculations showed that Ni and Co can be sprayed without any oxidation in the HVOF gun nozzle whereas Cr, Ti, Al and Mg are always oxidised. No significant differences were found in the oxidizing potential of fuels such as H2 and kerosene. In the spraying experiments, oxidation of WC-Co17 and NiCr80/20 coatings was studied. It was shown experimentally that the short process dwell time does not enable coatings to oxidise completely. It was also found that spray powder oxidation occurs in three steps. First, primarily in the HVOF gun nozzle, second, to a small extent in the plume and third, hardly at all on the surface being coated. The thermodynamic calculations, reaction kinetics and experimental work showed that oxidation of spray powder is a complex phenomenon involving selective and volatile oxidation, and formation of solid oxide. Oxidation of the coating is strongly related to the temperature of the particles and combustion gas. Oxidation of the spray powder can take place in solid or molten state. Experimental work showed that the oxidation processes in the HVOF spray process can not be completely prevented, but can be controlled. The degree of oxidation is reduced by lowering the temperature of the flame, by using a higher gas velocity and density, and employing effective substrate cooling.
  • Investigation of particle-bubble interactions with a new experimental setup
    (2003-11-28) Schreithofer, Nóra
     Doctoral dissertation (monograph)
    Flotation is one of the most widely used processes in mineral beneficiation industry. Research on flotation circuit modelling and optimisation has for long time been of major importance. Flotation is mainly driven by surface chemical properties of the particles attaching to air bubbles. Earlier flotation models are based solely on dynamic consideration, but in the recent years serious research effort has been focused on finding surface chemical parameters, which may improve the existing flotation models. Parameters were mainly obtained from measurements performed with surface force apparatus, thin film balance techniques and atomic force microscopy. This thesis work aimed to design and develop a new experimental apparatus, suitable for in-depth study of particle-bubble interactions. The experimental results of this work provide additional data for the improvement of existing, and development of new flotation models. The new experimental setup named Colloidal Interaction Force Measurement Apparatus (CIFMA) is based on AFM force measurement principle. The apparatus eliminates the limitations caused by the small measurement range of commercial instruments and provides several new features that facilitate the in-depth investigation of particle-bubble interactions. In connection with the instrument design, the errors and problems associated with the technique are reviewed. The experiments conducted with CIFMA were focused on ultrapure, electrolyte containing and gas saturated aqueous systems. In addition the effects of approach velocity, applied load and contact time on the particle-bubble adhesion were studied. The results among others revealed, that the particle-bubble interaction process is time dependent, highly dynamic phenomena. The jump-in force and the adhesion decrease with time. Increased load and contact time enhance the adhesion of the particle to the air bubble even if no three-phase contact is formed. The nanometer-sized roughness of the particle surfaces has a significant effect on the particle-bubble adhesion. In ultrapure system a very long-range jump of the bubble towards the particle occurred, that was detected by optical means. With increasing electrolyte concentration this effect disappeared. These results emphasize the importance of reassessment of existing flotation models and development of new ones by taking into consideration the observed effects.
  • Lessons from nature : the behaviour of technical and natural barriers in the geological disposal of spent nuclear fuel
    (2002-12-16) Marcos, Nuria
     Doctoral dissertation (article-based)
    This work deals with the study of the long-term performance of materials and elements involved in the near- and far-field of an underground nuclear waste repository. Materials and elements occurring in nature are similar, or at least analogous, to the materials and elements manufactured or processed by man. Also, natural processes may be similar to those envisaged as occurring in a nuclear waste repository. This similarity makes it possible to study the behaviour of those materials in nature and to compare it with the behaviour of the manufactured materials to be used in a repository. As many materials and elements have been in the natural environment for long time periods (thousands to million of years), the data obtained can be extrapolated to estimate the future evolution of similar components in a nuclear waste repository. Thinking by analogy is the process of comparison, with those materials, elements and environments used to perform the studies that allow the comparison to be regarded as natural analogues. The Hyrkkölä U-Cu mineralisation (SW Finland) was studied as an analogue to the behaviour of copper canisters in crystalline bedrock. This analogue could also address the interaction between copper corrosion products and uranium. Copper sulphides are shown to retain up to 25% of uranium as U (IV) even if oxidizing conditions prevail. Furthermore, uranium was observed in smectite (main component of bentonite) associated with native copper and cuprite, which constitutes an analogue to the behaviour of the repository near-field materials in a natural oxidizing environment. In addition to the Hyrkkölä analogue, the issue of irreversible sorption or uranium immobilization is also addressed, in the studies of the boulder rock near Hämeenlinna. The behaviour of U, Th, and rare earth elements (REE) as analogues to the long-lived actinides is also evaluated in groundwater and rock samples at Olkiluoto (SW Finland). U and Th were shown to be released more easily from clean fracture surfaces than from fracture surfaces covered with calcite or kaolinite. From the studies presented here, it may be seen that the Hyrkkölä analogue has been applied so far in safety assessments, mainly to demonstrate the canister lifetime and to a lesser extent to confirm the interactions between copper corrosion products and uranium. Up to the present, the issues of irreversible sorption or immobilization and the analogy between REE and actinides have not been taken into account in safety assessments. The results of the studies presented here indicate strong prospects that these issues could be new and powerful tools indispensable to safety assessments. More research and understanding is required, however, to form them into operational tools for this application.
  • Novel Ni-Mn-Ga alloys and their magnetic shape memory behaviour
    (2004-12-10) Söderberg, Outi
     Doctoral dissertation (article-based)
    The ternary Ni-Mn-Ga system has already been studied for several decades. Although the present work concentrates on the alloys with the 7-layered near-orthorhombic martensite structure (7M) and the non-modulated tetragonal martensite structure (T), it introduces 37 alloys altogether, including materials that have the 5-layered tetragonal martensite (5M) at ambient temperature. The dissertation shows briefly how the different compositions of ternary Ni-Mn-Ga alloys affect the phase transformations and the crystallographic structures of various phases. This thesis presents new alloys with the 7M structure and, for the first time, the Curie point of such a martensitic structure (TC7M). This TC7M is mainly detected in the cooling of the alloys, showing the co-occurrence of the magnetic transition and the double-step reverse transformation where the hysteresis of the Curie point is connected to the two martensitic phases. The service temperature region of the MSM alloy depends on the existence of the proper ferromagnetic twinned martensite. Consequently, the transformation sequence of the studied 7M and T alloys is investigated in more detail. According to the magnetic and crystalline transformation, the alloys are divided into six groups: A (7M ambient), B (7M above), C (7M co-transition), D (T high), E (T low) and F (T co-transition). In the groups A, B, D and E, the magnetic and crystalline transitions are separated, while in the groups C and F they co-occur. The pre-straining processes for obtaining the single-variant state in the 7M and the T martensite are presented. In the compression of the 7M alloys, three deformations to two crystallographic directions are needed, while the T alloys require three deformations to three crystallographic directions. However, it is also shown that with the tensile/compressive cycling of the T phase the full single-variant state has been obtained already, during the second cycle. The twinning stresses (σtw) needed for the martensite variant reorientation could be lowered by pre-straining close to 1 MPa in the 7M phase, while in the T phase only the level 6 MPa was reached, even at elevated temperatures. The magneto-mechanical tests confirmed that the magnetically induced stress (Δσmag) in the 7M structure is 1.5 MPa and in the T structure approximately 1 MPa. By applying the criteria of Δσmag ≥ σtw for the magnetic shape memory effect (MSME), it is obvious that MSME is possible in the 7M structure, but it can not be obtained in the T structure.
  • On hearth phenomena and hot metal carbon content in blast furnace
    (2003-11-14) Raipala, Kalevi
     Doctoral dissertation (monograph)
    The objective of this work was to investigate the hearth operation and the factors influencing the total quality of hot metal, especially its carbon and sulphur contents. Regarding the hot metal quality there are many sources of disturbances starting from raw materials, continuing through the blast furnace process and ending the hot metal casting. The carbon content of hot metal is an important part of the total quality of hot metal. Nearly 80 % of the total reaction energy in the BOF process comes from the oxidation of carbon in hot metal. Therefore, a high and stable carbon content of hot metal is most beneficial. Sulphur in hot metal is known to retard the carbonisation of hot metal. The sulphur content in hot metal is controlled by the sulphur load in the coke and other fuels as well as the slag basicity and low level of unreduced iron oxides. Both carbonisation and desulphurisation are strongly dependent on the hearth operation. To secure a proper hearth operation the hearth coke, the deadman should neither be clogged nor get inactive. Good hearth operation prolongs the campaign life of the hearth lining improving thus the total economy. In this work the factors influencing the hot metal carbon content have been investigated. The carbonisation of solid iron starts in the shaft by CO gas and also by coke carbon when the metal melts down. Hot metal does not get saturated with carbon. The difference between the saturation and actual carbon contents was observed to be around 0.7 % in average and it increases with increasing sulphur content. The carbon content of hot metal can be maintained on a high level by keeping the sulphur content of hot metal below 0.05 % which can be attained with a sufficient slag basicity, e.g. CaO / SiO = 1.2. A progressive vicious circle in blast furnace operation was observed. Problems may start with some disturbance in the hearth operation gradually resulting in low permeability or total clogging of the deadman. The raceways become shorter which leads to a hanging cohesive zone. A hanging cohesive zone transfers insufficiently reduced iron oxides into the slag. Desulphurisation of hot metal weakens due to a higher FeO content in the slag. A high sulphur content in hot metal promotes the precipitation of calcium sulphide. Calcium sulphide together with other compounds with high melting point may clog the hearth further. There are several factors which strengthen vicious circle like a low heat level, an overfilled hearth, too acid slag etc. Different factors influencing the hearth phenomena and start up of the vicious circle including CaS precipitation were observed and analysed in this work. Early warning symptoms of a clogged hearth and methods to identify an inactive deadman were collected. Measures to cure an inactive deadman were developed and practised as well.
  • Pneumatic servo-controlled material testing device capable of operating at high temperature water and irradiation conditions
    (2004-06-21) Moilanen, Pekka
     Doctoral dissertation (monograph)
    Special requirements set for the constructional materials used in energy production have strongly influenced the challenges in the component design work. Many material parameters such as corrosion, fracture mechanics, fatigue and oxide films are needed as input data for such work. The generation of reliable data calls also for more sophisticated testing systems. The newly developed pneumatic loading technology (patented in Finland and international patents pending) provides important potential benefits and has already been successfully applied to testing many kinds of materials in different test environments. As the moving parts that penetrate the pressure boundary are not needed, the friction force at the sealing element location is avoided. Therefore the load control with pneumatic loading unit is more accurate than with the conventional servo-hydraulic devices. This enables testing of small size samples which is an advantage e.g. when testing irradiated materials or testing materials inside the reactor core of a nuclear power plant and especially in determining environmentally assisted crack growth rates of structural materials. Furthermore, the new design enables simultaneous testing of several samples, which helps produce more reliable statistical data in a more economical way. This thesis summarizes my work done at the Technical Research Centre of Finland over the past 9 years to increase the knowledge of factors affecting material testing devices and material properties in gas and aqueous coolants at high temperatures. The developed pneumatic servo-controlled material testing device has been used to perform crack growth rate tests as a function of stress intensity factor K for AISI 316 stainless steel and Inconel 182 weld metal in Boiling Water Reactor (BWR) coolant by using small size (10x10x55 mm) three point bending specimens. The load and displacement were controlled during these tests by the pneumatic servo-controlled fracture measuring device (PSCFM device) and based on test results crack growth rates for Inconel weld metal and AISI 316 have been calculated. During the tests, accuracy with very slow constant displacement rates of 1.2 10-5 mm/min and 1.2 10-6 mm/min and long term stability of the pneumatic material testing system under high temperature water environment, has been verified. Furthermore, the crack growth rate for Inconel 182 weld metal as a function of sulphate content (10, 20, 30 ppb) of BWR coolant has been determined. These results shows that the crack growth rate of Inconel 182 weld material is strongly affected by the sulphate content of BWR coolant. Furthermore, prototypes of pneumatically powered fatigue (PSCFAT-device), controlled distance electrode (PSCCDE-device) and tensile (PSCINCORE-device) devices have been designed and tested. The units, which were based on proven technology, operated well and gave reliable test results for the material design parameters. The PSCFAT device was tested at room temperature and the degree of specimen bending and general system performance were measured. A strain controlled axial fatigue test in a 12 MPa autoclave at 100°C was also performed. The test material was AISI 316 stainless steel and the specimen failed in its midsection due to fatigue after 15600 cycles. The preliminary tests with pneumatically powered controlled distance electrode arrangement equipment (PSCCDE) is presented. The equipment was tested in air at room temperature and in typical BWR environments. The test material was pure nickel and its oxide film properties were tested in BWR environment as a function of potential. The design work for the pneumatic tensile testing device which is capable of working in a real reactor core is introduced. Prototype design, load calibrations, load frame for thin specimen tensile testing, and reactor installation with 30 m gas lines is presented. Furthermore, the PSCINCORE device was used to determine stress and strain curves for pure Cu specimen in the BR-2 reactor at Mol in Belgium. Reactor pool water temperature was 90°C, neutron flux ∼0.3∗1014 n cm-2s-1s (E>1 MeV) and damage rate ∼2∗10-4 h-1. The test type was constant displacement rate test with strain rate ∼10-7 1/s. Some of the results gained in this work are unique, whenever possible however, the test results have been verified by comparison to earlier results with alternative techniques. Invariably, the comparisons prove applicability of the pneumatically powered technology developed in this work.
  • Quality characteristics of fine aggregates and controlling their effects on concrete
    (2001-05-11) Järvenpää, Hanna
     Doctoral dissertation (monograph)
    For the aggregate producer, the concrete aggregates are end products, while, for the concrete manufacturer, the aggregates are raw materials to be used for mix designs and successful concrete production. The aim of this study was to identify which fine aggregate characteristics are important, and additionally to relate the extent of the effect that the aggregate has on the concrete as compared against the effect of the changes in mix design. The testing programme contained six different mix designs in which 21 fine aggregate products were studied in 215 castings. The mix designs consisted of two cement amounts (300 or 350 kg/m3) corresponding to low and high paste volumes, with three admixture possibilities: no admixture, superplasticizer or air-entraining agent. The results of the experiments show that the effect of the fine aggregate characteristics on the flow value was greater than the effect of the cement amount. Furthermore, the entrained and entrapped air amounts correlated strongly with the flow value of the concrete. The compressive strength for the same mix design differed according to the fine aggregate characteristics, and the difference ranged between 8.4...18.8 MPa on the six mix designs. The superplasticizer enhanced the quality differences of the aggregate products. The effect of the porosity of the fine aggregate on the drying shrinkage exceeded twice the effect of the mix design changes, i.e. amount of paste and/or the admixtures. A program for predicting the interaction between the fine aggregate and concrete was developed. The Bayesian method was used for statistical processing, and non-parametric non-linear Gaussian process models were applied for the interaction models. The program includes four concrete properties; flow value, air %, bleeding and compressive strength. The most important fine aggregate characteristics in the models are: shape and particle porosity related semi-coarse fraction parameters (flow value and air %), flakiness and Los Angeles value of the semi-coarse fraction (compressive strength) and particle porosity of the semi-coarse and surface area of the fines fractions (bleeding). As an example of the model predictions, six different fine aggregate combinations were modelled; two gravel products representing past and future gravel types and four crushed rock products representing different strength qualities and shape characteristics.
  • A study on the erosion and erosion-oxidation of metal matrix composites
    (2003-10-31) Liu, Xuwen
     Doctoral dissertation (monograph)
    The potential of metal matrix composites (MMCs) as new generation erosion and erosioncorrosion resistant materials is investigated. As a type of wear attack, erosion involves destructive impact of free-moving particles on a solid. The high-strain-rate and hence adiabatic deformation conditions that the target surface experiences during erosion are often the reasons behind the poor correlation of erosion rate with static mechanical properties of the targets, imparting difficuties on erosion study. On the other hand, a good correlation exists between erosion rate and the thermophysical properties of the target. This, however, suggests limited possibilities of enhancing erosion resistance on a monolithic alloy. A literature study at the beginning elaborates the complex of erosion as a physical phenomenon, and lies the theoretical base for the experiment. In the experiment, nickel-chromium superalloy- and heat resistant steel-based composites are manufactured through a powder metallurgy route. Ceramic particles are added at different volume fractions as the reinforcements. Efforts are made to optimise the powder mixing and powder consolidation procedures to ensure a homogeneous microstructure and full densification of the final composites. Two types of erosion tester are used in the study: a centrifugal erosion tester is for the erosion tests at room temperature, and a gas-blast erosion tester is for the erosion-oxidation tests at high temperature. With the gas-blast tester, both the temperature and oxygen concentration is controlled to simulate real application situations. The discussion is focused on the tests under a 60° angle of impact. Optical and SEM (scanning electron microscopy) observations are carried out on the eroded surfaces to assess the damage pattern and general behaviour of the studying composites. Meanwhile, on cross-sectioned specimens the bonding and material dissolution at the matrix/reinforcement interfacial regions and the deformation situation at the sub-surfaces are examined by EDS (energy dispersion spectroscopy) and microhardness measurements to reveal the erosion mechanisms of the composites. The experimental results suggest that the strain localisation mode is valid in describing erosion process of a ductile metal, but may need modifications when applying to MMCs. The erosion response of a MMC system is determined by not only the internal parameters of the composites, but also external factors involving all parameters of erosion. In addition, this study provides useful guidelines to the selection of composite systems having high erosion resistance for industrial applications and to the future study as well.
  • Sulphation of cuprous and cupric oxide dusts and heterogeneous copper matte particles in simulated flash smelting heat recovery boiler conditions
    (2004-04-28) Ranki-Kilpinen, Tiina
     Doctoral dissertation (monograph)
    Copper smelting with the Outokumpu flash smelting process generates significant amounts of SO2-rich off-gas and flue dust. From the smelting unit, gases with a dust load are directed into a heat recovery boiler (also known as a waste heat boiler). In the radiation section temperature decreases, sulphates become thermodynamically stable, and the sulphation of oxidic dust particles commences. Releasing heat may lead to an increase in particle temperatures, softening of the sulphated particles, and the formation of dust accretions on the heat transfer surfaces. Decreased heat transfer efficiency and blockages of the gas flow paths may cause severe operational problems. To maintain stable boiler operation, sulphation behaviour has to be well understood, but only scant published data concerning dust sulphation reactions is available. The objective of this work was to gain basic knowledge of the sulphation behaviour of dust components to ascertain that boiler design and operation can be carried out so that sulphate formation takes place in a controlled manner. The reactions of synthetic Cu2O and CuO (mainly 37-53 µm) and a partially oxidised copper matte were studied experimentally with the aim of arriving at a better understanding of dust sulphation in industrial heat recovery boilers. The parameters in the laboratory-scale experiments were gas composition (20-60 vol-% SO2, 2.5-10 vol-% O2), temperature (560-660 °C), reaction time, and particle size. Standard chemical analysis and scanning electron microscopy with EDS were utilised when examining the samples. Sulphate formation was found to be sensitive to gas composition and temperature. Also particle size and surface morphology have significant effects on the sulphation rate. On the basis of the experimental results the temperature range for effective sulphation of pure cuprous oxide is narrow; the optimal sulphate formation temperature lies between 580-640 °C, depending on the gas composition. An increase in oxygen concentration expands the favourable temperature range and lowers the most optimal sulphate formation temperature; on the contrary an increase in sulphur dioxide concentration raises the favourable sulphation temperature. On the basis of the present experiments pure cupric oxide behaves like cuprous oxide, but the conversion degrees are slightly lower and there is not such a clear enhance in the sulphation rate at a certain temperature. Fine, heterogeneous partially oxidised matte reacts significantly faster compared to synthetic oxides. The reason for more effective sulphation is suggested to be the smaller particle size and more detailed morphology (larger specific surface area). In the heat recovery boiler dust particles must have a sufficient residence time in the gas phase at a correct temperature range to allow the dust particles to reach complete conversion in the radiation section before they enter the boiler convection section and come into contact with the convection tube banks. Enough oxygen has to be supplied to the appropriate zone to ensure effective sulphation at the right place. Also, mixing of the oxygen must be efficient.
  • A thermodynamic analysis of the system Fe-Cr-Ni-C-O
    (2002-12-05) Luoma, Rauno
     Doctoral dissertation (monograph)
    A thermodynamic database for the system Fe-Cr-Ni-C-O has been built using previously assessed binary and ternary systems. Six ternary systems, Fe-Cr-O, Fe-C-O, Fe-Ni-O, Cr-Ni-O, Cr-C-O, and Ni-C-O, have been assessed. Quaternary and quinary systems were calculated using only interpolation models. This method of building a database is known as the Calphad method and it is widely used in modern thermodynamics. An associated solution model with a non-ideally interacting species, namely 'Fe', 'Cr', 'Ni', 'C', 'FeO', 'FeO1.5', 'Cr2/3O', and 'NiO' was used for the liquid phase. The solid metallic phases were described using the sublattice model with carbon and oxygen on the second sublattice, and solid oxide phases were described using the compound energy model. The carbide phases were treated as stoichiometric or semistoichiometric phases. The optimisation was performed using the Parrot module included in the Thermo-Calc program. The model parameters for the liquid phase in metal-oxygen systems were transformed from the parameters optimised with the ionic liquid model by other authors. Because of the new assessments of the binary systems, all the ternary systems including oxygen were optimised. Only in the Ni-C-O system could the parameters not reproduce the experimental data. The calculated quaternary systems are in good agreement with the experimental data without using any quaternary parameters. The model parameters assessed in this work describe the system Fe-Cr-Ni-C-O well according to the experimental information from its sub systems. The complete Gibbs energy expressions for the alloy phases were presented, allowing the calculation of the phase diagrams and thermodynamic mixing properties of the mixture phases.