Showing papers in "Steel Research in 1999"

The tensile failure of mild steel oxides under hot rolling conditions

Abstract: The failure of oxide scales formed on mild steel (mass contents of 0.17% C, 0.13% Si, 0.72% Mn) was investigated using a high-temperature tensile test technique over the temperature range 830 - 1150°C. Strain and strain rates used were 1.5 - 20% and 0.02 - 4.0 s -1 , respectively. The scales were 10 - 300 μm thick. The variations of these test parameters were chosen to approximate the tensile loading of the oxidised surface layer at the slab faces just before roll contact at the upper or lower surfaces. Oxide scales formed cannot be assumed either to be perfectly adhering during tensile loading, in the sense of slipping, or to be fully brittle. Two limit modes leading to oxide spallation have been observed which are strongly influenced by the temperature, strain rate and strain. For the first mode initial through-scale cracking occurs followed by initiation and propagation of a crack along the oxide-metal interface between adjacent cracks. The second mode corresponds to the slipping of the oxide scale relative to the metal surface before spallation. The delamination and following slipping of the oxide raft can take place along the interface within the non-homogeneous oxide scale.

Experimental determination of the stability of retained austenite in low alloy TRIP steels

Abstract: The stability of retained austenite is the most important parameter controlling the transformation plasticity effects in multiphase low alloy TRIP steels. In this work the thermodynamic stability of the retained austenite has been determined experimentally by measuring the M s σ temperature as a function of bainite isothermal transformation (BIT) temperature and time in two low alloy TRIP steels. A single-specimen temperature-variable tension test technique (SS-TV-TT) has been employed, which allowed to link the appearance of yield points in the stress-strain curve with the mechanically-induced martensitic transformation of the retained austenite. The results indicated that the M s σ temperature varies with BIT temperature and time. Higher austenite stability is associated with a BIT temperature of 400°C rather than 375°C. In addition, the chemical stabilization of the retained austenite associated with carbon enrichment from the growing bainite is lowered at short BIT times. This stability drop is due to carbide precipitation and comes earlier in the Nb-containing steel. At longer BIT times the retained austenite dispersion becomes finer and its stability rises due to size stabilization. The experimental results are in good agreement with model predictions within the range of anticipated carbon enrichment of the retained austenite and measured austenite particle size.

TRIP steel with reduced silicon content

Abstract: At present high strength thin sheet steel grades are gaining considerable market shares due to the intensified application in the automotive industry. Although several new high strength steels for cold forming have been developed and continuously improved for some decades there is still a necessity to increase the formability at a given high strength level. TRIP steels are a consistent further step to meet these requirements. Most of the published work concentrates on compositions with high C, Mn and Si contents which causes problems during production. Therefore in this work TRIP steels with reduced C and Si contents were produced and the influence of the annealing parameters on the microstructure and mechanical properties was investigated in detail for production via continuous annealing lines. Based on these investigations optimized heat cycles were proposed.

Activity of chromium oxide and phase relations for the CaO-SiO2-CrOX system at 1873 K under moderately reducing conditions

Abstract: In order to optimize the slag composition operated in the decarburization process of stainless steel production, activity of chromium oxide, aC r O x , and phase relations for the CaO-SiO 2 -CrO x system have been investigated under moderately reducing conditions, P O2 = 7.04○10 - 6 Pa at 1873 K. Activity coefficients of chromium oxides show strong dependencies on X CaO /X SiO2 , an index of basicity, and chromium content of the slag. Solubility of chromium oxide in the slag system drastically decreases with increasing X CaO /X SiO2 . which is consistent with increase in activity coefficients of chromium oxides. The optimal CaO-SiO 2 -CrO x slag for a practical decarburization process has been recommended to be doubly saturated with CrO 1.5 and CaCr 2 O 4 , namely X CaO /X SiO2 = 1.47 at 1873 K, which may not be significantly affected by operating temperatures.

New thermomechanical strategies for the production of high strength low alloyed multiphase steel showing a transformation induced plasticity (TRIP) effect

Abstract: In the last years a lot of research was done in the development of TRIP-assisted multiphase steels. Two principal ways were proposed: - controlled cooling during the hot-rolling process to obtain hot-rolled TRIP-assisted multiphase steels and - the combination of intercritical annealing and isothermal holding at bainite formation temperatures during continuous annealing resulting in cold-rolled TRIP-assisted steel products. Unfortunately both proposed thermomechanical methods require a high silicon level to inhibit cementite precipitation in order to avoid a loss of stability for the metastable retained austenite. In addition, due to high silicon levels, red scale surface defects and a moderate hot dip galvanizability appear. In this article, new thermomechanical strategies for the production of high strength low alloyed TRIP-assisted multiphase steels with good hot-dip galvanizability and without red scale defects will be presented. Regarding the thermomechanical path, the stabilization of the retained austenite in the final microstructure can be optimized by the application of the additional step of batch annealing between hot rolling and cold rolling. This additional thermomechanical step activates manganese diffusion in the ferrite matrix and manganese enrichment processes of the cementite. During the step of continuous annealing, the manganese enriched cementite is transformed into stabilization-optimized retained austenite. Regarding the final microstructure, a fine grained ferrite matrix of about 3 μm grain size containing small islands of intragranular and intergranular stabilzation-optimized retained austenite can be obtained.

The sulphide capacity of CaO‐SiO2‐Al2O3‐MgO(‐FeO) smelting reduction slags

Abstract: The effects of MgO and FeO contents on the sulphide capacity of Corex slags were investigated at 1773 K using gas/slag equilibrium technique as a fundamental study for stabilising Corex operational conditions. The gradual substitution of MgO for CaO at a fixed basicity [B = {(%CaO)+(%MgO)}/(%SiO 2 ) decreased the sulphide capacities of CaO-SiO 2 -Al 2 O 3 -MgO slags. The addition of FeO into the CaO-SiO 2 -Al 2 O 3 -MgO slags at the fixed (%CaO)/(%SiO 2 ) ratio, MgO and Al 2 O 3 contents significantly increased the sulphide capacities. The sulphide capacity decreased according to the increasing Al 2 O 3 content at the fixed (%CaO)/(%SiO 2 ) ratio, MgO and FeO content. Based on the previously reported and present values of sulphide capacities, the sulphide capacity as a function of slag composition on the mole fraction base at 1773 K was expressed by the formula of log C S = X CaO - 3.89 X SiO2 - 3.18 X Al2O3 - 0.55 X MgO + 2.43 X FeO - 2.61. In addition, the relationship between the sulphide capacity and optical basicity could be represented as the formula of log Cs = 12.51 Λ -12.24 and the theoretical optical basicity of FeO was found be 0.94 from the correlation. The effect of FeO on the sulphur distribution ratio was estimated using the present sulphide capacity values and the oxygen activity in liquid iron, which could be determined with the help of Fe/FeO equilibrium. FeO activity in slag was well described by the quadratic formalism based on the regular solution model. The sulphur distribution ratio according to FeO content varies in an opposite way, compared with that of the sulphide capacity.

Mechanical properties and crack susceptibility of steel during solidification

Abstract: The determination of high temperature mechanical properties is a necessity for the better understanding of defect formation during continuous casting of steel. Although a lot of studies have been performed on this topic, some aspects like the influence of cast structure on crack susceptibility are still unclear. The present paper focuses on the effect of carbon on high temperature strength and crack susceptibility. Tensile tests have been performed on steel shells with different carbon content during solidification. The results indicate an impor tant influence of the orientation of the inhomogeneous cast structure towards main stress axis. The initial shell with a thickness of only a few millimetres is more sensitive to defect formation than commonly believed. The critical limits of straining range from about 0.15 to 0.4 %. With increasing shell thickness, the critical strain ascends up to 1.6 %. The detected segregated internal cracks form within the critical temperature range. The strength near solidus temperature is lower than in comparable hot tensile tests, which can also be attributed to the detrimental effect of the inhomogeneous structure. The strength at solidus temperature amounts to 2.5 MPa for higher carbon steels and about 1 MPa for low carbon steels.

Evolution of dislocation structure in martensitic steels : the subgrain size as a sensor for creep strain and residual creep life

Abstract: The results on the evolution of the dislocation structure in martensitic CrMoV-steels published by two research groups are shown to be consistent: The steady state dislocation spacings vary in inverse proportion to shear modulus normalized stress, the subgrains grow with strain at a rate which is determined by the initial subgrain size W 0 , the steedy state subgrain size w∞ and the strain rate, independent of the composition of the material. At constant stress and temperature the strain e and the subgrain size w are uniquely related by e = e w In[log(w 0 / w∞) / log(w / w∞)] with e w = 0.12. Thus w can be used as a sensor for strain and, if the relation between strain and time is known, for the residual creep life.

Mixing enthalpy measurements of liquid Ti-Zr, Fe-Ti-Zr and Fe-Ni-Zr alloys

Abstract: The mixing enthalpies of liquid Ti-Zr, Fe-Ti-Zr and Fe-Ni-Zr alloys were measured by levitation alloying calorimetry. The mixing enthalpy of Ti-Zr alloys is slightly exothermic and symmetric with an extreme value of -5.2 kJ mol -1 , It can be described according to the regular solution model. Experimental investigations of the mixing enthalpies of the strongly non-ideal binary systems Fe-Ti, Fe-Zr and Ni-Zr had already been subject of earlier works. Based on experimental data temperature dependent descriptions of the mixing enthalpies were calculated with a regular associate model. From the model parameters of the binary subsystems the mixing enthalpy of the respective ternary system can be predicted. Model calculations of the mixing enthalpies of liquid Fe-Ti-Zr and Fe-Ni-Zr alloys were performed along different concentration sections and compared with experimental data, respectively. A good accordance was observed. The mixing enthalpies of liquid Fe-Ti-Zr and Fe-Ni-Zr alloys are given at T = 2152 K and T = 1892 K in form of isoenthalpy diagrams, respectively. Moreover, with help of the temperature dependence of the mixing enthalpy the excess heat capacities of the alloys were calculated.

Investigations of the solidification structure of continuously cast slabs

Abstract: A study of solidification phenomena performed under industrial conditions is presented. The solidification structure of high carbon, medium carbon and microalloyed steel grades was observed and correlated to casting parameters such as superheat and secondary cooling. Experimental data of dendrite morphology are related to calculated solidification variables. The calculation is based on the solution of the enthalpy balance equation. An expression for the dependence of secondary dendrite arm spacing on solidification variables is proposed for columnar growth. The results are compared to the findings of other authors. The effect of chemical composition on secondary dendrite arm spacing was observed. Therefore the developed relationships are extended to carbon content on the basis of the presented experimental data.

Solidification structure and micro‐segregation of unidirectionally solidified steels

Abstract: Two linepipe steels with carbon mass contents of 0.09 and 0.15% were subjected to steady state unidirectional solidification in a special apparatus. The specimens were positioned in alumina tubes of 15 mm internal diameter, and were pulled downwards at a constant rate, R, from the high temperature furnace. The temperature gradient, G, at the solidification boundary was varied between 5 and 136 K/cm. The dendrite arm spacings measured were quantitatively assessed using the relationship λ = cRG. The exponents m and n for the primary arm spacing, λ 1 , are in agreement with theoretical predictions, at m = -1/4 and n = -1/2, Comparison with other steels containing 0.59 % C and 1.48 % C showed that λ 1 increases with increasing carbon content. The exponents m and n for secondary arm spacing are nearly the same, at -0.4 to -0.5. Correlations with local solidification time, θ f , show that λ 2 decreases as the carbon content increases. In the δ-phase regime, coarsening of the secondary arms is possible through remelting. Interdendritic segregation peaks are more quickly reduced in the δ-phase regime. This is confirmed by the results of electron beam microprobe analyses for segregation. Reduction of the carbon content of linepipe steels reduces the susceptibility to centreline segregation in the continuously cast slabs.

Inclusions in continuously cast steel slabs - numerical model and validation

Abstract: A numerical model for liquid steel flow and inclusion transport and separation in continuous casting moulds is presented, which covers several features simultaneously. The free surface at the meniscus is computed; the submerged entry nozzle is discretised in detail to resolve the outlet geometry; gas injection through the SEN and its effect on liquid steel flow are considered; capture of inclusions within gas bubbles is covered in a simplified approach; the solidifying shell and the process of inclusion entrapment by the growing shell are simulated. Computed flow profiles are compared to experimental results on water and to measurements on liquid steel in a slab caster. Predicted inclusion profiles in solid slabs are compared to empirical findings from literature. Results of the model for various cases will be presented in a subsequent publication.

Study of heat transfer through layers of casting flux: experiments with a laboratory set‐up simulating the conditions in continuous casting

Abstract: The heat transfer through layers,of casting flux has been studied with a laboratory set-up which consists of a water-cooled heat flux probe made of copper and an electrically heated steel plate with a trough to hold the flux sample. The measured heat flux density values were converted to system conductivities k sys which contain the radiation/conduction conductivity in the flux layer and the contact resistance at the probe side. It was found that k sys is almost independent from the layer thickness. Ten commercial casting fluxes were investigated and the data for k sys are given as functions of composition and strand surface temperature.

Estimation of escape rate of volatile components from slags containing CaF2 during viscosity measurement

Abstract: In continuous casting process, the viscosity of the mould powder/flux has direct impact on the size of the gap between the mould wall and the solidified shell, which in turn affect the heat transfer characteristics between the metal and the mould. Numerous experiments have been conducted to determine the viscosity of various mould powders using rotation cylinder method. The pre-melting of the mould powder as well as the viscosity measurement are carried out in a cylindrical crucible placed in a tubular furnace with constant argon flow to maintain inert atmosphere. One of the main difficulties encountered during viscosity measurement is the liberation of volatile fluorides, which in turn changes the flux composition, and consequently the viscosity of the flux. Thermodynamic calculations have shown that SiF4 and HF are major constituents of the volatile matter. Present study aims to estimate the liberation rate of SiF 4 and HF from flux samples during viscosity measurement by computing the detailed gas flow pattern inside the tubular furnace. The gas flow pattern is computed by solving momentum and continuity of equations. Further, the effect of argon gas flow rate and slag level in the crucible on liberation rate has been studied to arrive at proper experimental conditions during viscosity measurement.

Grain boundary segregation of antimony in iron base alloys and its effect on toughness

Abstract: The equilibrium grain boundary segregation of antimony was investigated in iron base alloys (Fe-Sb, Fe-C-Sb, Fe-Ni-Sb) after annealing at temperatures between 550 and 750°C. Utilizing Auger electron spectroscopy (AES) the concentration of antimony at intergranular fracture faces was determined as a function of bulk concentration and equilibration temperature. The segregation of antimony in Fe-Sb alloys with mass contents of between 0.012 and 0.094 % Sb was described by the Langmuir-McLean equation. The evaluation leads to the free enthalpy of segregation ΔG segr = -19 kJ/mol - T 28 J/mol K. The relatively low value for the segregation enthalpy AH = -19 kJ/mol indicates a rather small tendency for grain boundary segregation of Sb. However, its embrittling effect is strong, scanning electron micrographs (SEM) of fractured samples show that the percentage of intergranular fracture strongly increases with an increasing coverage of antimony at the grain boundaries. The data for Fe-0.93% Sb and Fe.1.91% Sb (mass contents) do not fit in the thermodynamic evaluation obviously due to formation of antimonide precipitates in the grain boundaries. The addition of carbon to Fe-Sb alloys results in a higher grain boundary cohesion which is caused by two effects of carbon, displacement of antimony from the grain boundaries by carbon and enhanced grain boundary cohesion. In the Fe-Ni-Sb alloys additional segregation of nickel was found at the grain boundaries but no enhanced antimony segregation, as expected from previous models of other authors, assuming Ni-Sb cosegregation.

Mathematical modelling of alloy melting in steel melts

Abstract: This paper deals with a mathematical model for melting of ferro-manganese particles in liquid iron in a ladle. With the assumption that the resistance of heat transport in the iron shell that initially freezes at the particle surface is zero, the particle melting time can be calculated analytically. To describe the total melting rate of alloy particles added into the ladle, a melting distribution function is introduced. It includes the melting time of the individual particles, the particle size distribution, and the addition function of the particles. The factors influencing the melting behaviour of the addition are investigated. The melting behaviour is greatly affected by the particle size distribution, the temperature of the melt, and the particle-melt slip velocity. The addition time and the addition function have only a small influence on the melting behaviour.

Investigation into rheological characteristic and foaming behaviour of molten slags

Abstract: The rheological characteristic and foaming behaviour of molten slags have been investigated at different temperatures and with different additives, such as coke, coal and CaO. In the experiment of rheological characteristic, a modified rotational viscometer with variable revolution's speed was applied. Therefore, constitutive equations and rheological parameters of molten slags have been established. The tolerance-analysis method is applied to judge whether a molten slag belongs to Newtonian fluid or not. The results of foaming behaviour in the blowing gas show that addition of coarse grain coke and coal decreases the foam height. However, the carbonaceous materials of fine grain and CaO powder can cause the increase in foam height. It has also been found from the experimental results that the foam index Σ is only available for slag of Newtonian fluid in blowing gas. The reason may be well explained with the rheological characteristic of molten slags.

Kinetics of inclusion precipitation during steel solidification

Abstract: The precipitation of non-metallic inclusions (complex oxides, sulphides, nitrides ...) during steel solidification is analysed using the multiphase equilibrium code CEQCS and a nucleation and growth model. The CEQCSI code is based in part on the Irsid slag model, and it provides an evaluation of the composition of inclusions formed at equilibrium, as well as guidelines for industrial treatments in order to reach desirable compositions in semi-killed steel grades. The nucleation and growth model can be applied to the formation, during steel solidification, of stoichiometric compounds or liquid oxide inclusions. Two particularities of this kinetic model are that nucleation and growth are treated simultaneously, and they compete in consuming the supersaturation at each moment, and that a mixed controlled growth model transport/interfacial kinetics at the precipitate/liquid steel interface is considered. The predicted size distribution of TiN precipitates formed in two steel grades is in good agreement with the results of laboratory experiments. In the case of liquid oxide precipitation, the lirst calculations indicate that the composition of inclusions can be significantly different from that of inclusions assumed to precipitate under equilibrium conditions.

An inverse analysis of the hot uniaxial compression test by means of the finite element method

Abstract: A computer simulation using the finite element method is carried out in the present work to model a hot compression test. Real constitutive equations of the hot flow behaviour of a medium carbon microalloyed steel, experimentally determined, are implemented in a commercial computer code and an inverse analysis is performed to determine under which conditions the experimental test can be considered as valid. In other words, the degree of strain and strain rate heterogeneity as well as the isothermatility of the test, for the given material, are verified. The effect of the friction coefficient is also included in the current analysis.

Simulation of transverse crack formation on continuously cast peritectic medium carbon steel slabs

Abstract: Reliable data are limited to the critical strain for the formation of transverse cracks on the slabs, owing to experimental difficulty to simulate temperature gradient in solidified shell in continuous casting mold. The present study is to determine the critical strain, e c , for the formation of transverse cracks on continuously cast slabs. A convenient and simple hot tensile test using rectangular test pieces with either V-notch or semi-circle notch or oscillation marks has been developed by placing the specimen under similar temperature gradient to that in solidified shell in the mold. The e c has been determined at a better accuracy and reproducibility, and the e c at a strain rate of 5.10 -4 s -1 is found to be a high 35% for test pieces without notch. It sharply decreases, however, to 10% for those with V- and semi-circle-notches, slightly decreases with increasing notch depth, and further decreases for those with oscillation marks that accompany solute segregation. Reduction of the oscillation mark depth is shown to be important measure to prevent the occurrence of transverse cracking of continuously cast slabs.

Sheet metal forming behaviour and mechanical properties of TRIP steels

Abstract: Recently various kinds of high-strength sheet steels have been developed to meet the requirements of the automotive industry such as passive safety, weight reduction and saving energy. Usually the main problem of high-strength steels is their inferior ductility. Multiphase steels however show a very good combination of strength and formability so that the applicable region of high-strength steels has been widely enlarged. Multiphase steels have been developed for various purposes because of their ability to tailor properties by adjusting the type, the amount, and the distribution of different phases. Especially new developed triple-phase steels which make use of the TRIP effect (transformation Induced plasticity) can further improve formability as well as strength due to the transformation of retained austenite to martensite during the deformation. In this work the transformation behaviour and the mechanical properties of low alloyed TRIP steels were investigated. The influence of the annealing parameters on transformation behaviour and on the amount of retained austenite were determined. In addition the temperature dependence of the mechanical properties and the effect of testing speed on the formability were studied. The investigation was carried out on seven different TRIP steels with different chemical compositions, especially the influence of the microalloying element niobium was considered. For reasons of comparison various mild and high-strength steels were tested parallel to the TRIP steels. It was found that the investigated TRIP steels offer very attractive combinations of elongation and strength values. An interesting temperature dependence of the mechanical properties can be observed, in such a way that the elongation values of the TRIP steels possess a maximum between +50 and +100°C. Due to its effect on grain size and on precipitation behaviour the addition of niobium leads to higher strength values without a strong decrease in ductility. In general, the mechanical properties are strongly affected by the type and the distribution of the different phases. The most important parameters, however, to influence the mechanical behaviour are the amount and the stability of the retained austenite, which are mainly controlled by the heat treatment and the chemical composition.

Cold model investigations of fluid flows and mixing within top and combined blowing in metallurgical processes

Abstract: Cold model investigations were performed during top and combined blowing in metallurgical processes. The investigations include 2- and 3-phase systems with gas, water and oil phase. The results of top blowing tests can be used to arrange and optimise the fluid flow. Further, conclusions can be drawn for the spraying and emulsification process, if the slag thickness is known. Under combined blowing conditions a small amount of stirring gas injected from the bottom has a great influence on mixing. According to the slag thickness, in combination with the power of the top blowing momentum, the fluid flow is dominated by top or bottom blowing. If bottom blowing is added as a stirring mechanism, a better mixing can not be guaranteed by this means. The bottom blowing conditions have to be adapted to the top blowing conditions and to the reactor geometry.

The determination of formability for cold and hot forming conditions

Abstract: This paper discusses current developments to determine the formability of a material during a crack-endangering production process. The presentation of the theoretical background is followed by a description of the technology developed at the IBF to investigate the material failure. Characteristic formability limit curves have been plotted from FEM simulations of the basic tests which were performed parallel to the experimental tests. These curves enable the forecast of material failure to be transferred to an industrial process. It is shown that this test technology is valid for both cold and hot forming conditions.

Laboratory study of heat transfer through thin layers of casting slag : minimization of the slag/probe contact resistance

Abstract: The heat flux densities through thin layers of casting slag have been measured with a soft cooling heat flux probe which made smooth probe/slag interfaces. Thus the contact resistance was avoided. The evaluated effective thermal conductivities were applied, together with the data on the contact resistance, to compute the system conductivities existing in the continuous casting system water cooled copper/slag/strand. The refractive index and absorption spectrum were measured and used to deduce functions for the radiative and conductive (phonon) conductivities. Although precise values could not be obtained, due to the many assumptions involved, the data indicate that the conductive conductivity does not change drastically at high temperatures and on melting.

Mixing phenomena inside the ladle during RH decarburization of steel melts

Abstract: The RH (Rheinstahl-Heraeus) process is in widespread use to produce ultra-low carbon steel by vacuum treatment. Among other factors, the decarburization rate is effected by mixing phenomena inside the ladle. Thus, supervisory control of the RH treatment requires an adequate and precise representation of the mixing conditions. In this work, mixing is characterised by concepts of chemical reaction engineering. Different sizes and geometries of RH installations are taken into account using similarity criteria. A simple model is derived from the experimental results and detailed numerical flow computations. For this model, a mathematical function of mixing is developed which can be incorporated into supervisory control systems.

Oxygen and nitrogen reactions in Fe-X and Fe-Cr-Ni-X melts

Abstract: A modified e formalism is developed to perform thermodynamic analysis for metallic solutions. The model calculation is successfully applied to describe oxygen and nitrogen equilibria in both liquid iron and alloyed steel melts. Relations between oxygen activities or contents and composition of Fe-O-X (X = Si, Cr, Ti and Al) melts are given quantitatively. The results are widely supported by the available experimental results. Nitrogen solubilities in Fe-Cr and Fe-Cr-Ni melts predicted by the present model calculation feature good agreement with experimental results.

Surface and interfacial properties of Fe-30%Cr-S alloys in contact with alumina

Abstract: The surface tension of liquid iron-30% chromium alloys at 1823 K was determined as a function of sulfur content using the sessile drop technique. The surface tension of iron-30% chromium alloys decreases with increasing sulfur content and the results can be described by the following equation for sulfur mass contents of greater than 21 ppm: γ: 1592 - 1781n(1 + 145a S )mN/m. The contact angle between the droplet and an alumina substrate was also measured and found to decrease from 142° at 21 ppm sulfur activity to 80° at a sulfur activity of 0.53 (related to the standard state with a mass content of 1%). From these measurements the interfacial energy between liquid iron-30% chromium alloys and alumina was calculated using Young's equation. The interfacial tension can be described by the following equation: γ = 2026-5191n(1 + 29a S )mN/m.

The effect of carbon content on the rate of reduction of FeO in slag relevant to iron smelting

Abstract: In the iron smelting, or bath smelting, process the tapped metal contains high amounts of sulfur and the slag contains high amounts of FeO, relative to blast furnace slag. After tapping, the FeO can be further reduced by carbon in the metal, which will also lead to better desulfurization. Although there have been many studies of the reaction of carbon in iron with FeO in slag, discrepancies exist with regards to the effect of carbon in iron on the rate of FeO reduction in slag, which is the subject of this study. Experiments were conducted at 1723 K, using a slag with basicity close to one with an FeO mass content of 5 %. The rate of reduction was measured using a pressure increase technique. For moderate and high sulfur contents, as in the case of iron smelting, the rate is primarily controlled by the dissociation of CO 2 on the surface of the molten iron. Furthermore, if the effect of carbon on sulfur is taken into account, for the range of carbon mass contents of 2 to 4.5 %, there is no effect of the carbon level on the rate of FeO reduction. At low sulfur contents it was found that there is considerable slag foaming, which inhibits mass transfer of FeO in the slag, and significantly reduces the rate. Even when there is no slag foaming at low sulfur contents, mass transfer of FeO in the slag can influence the rate of FeO reduction.

Investigation of solidification and microsegregation of near‐net‐shape cast carbon steel

Abstract: Different near-net-shape casting techniques are investigated in terms of solidification parameters, microstructure, and microsegregation of manganese in carbon steels based on experimental simulation methods: ingot casting of thick and thin slab samples, strip samples, and thin strip. The as-cast thicknesses were between 1.9 and 150 mm. By calculations and measurements data have been determined which lead to the solidification structure like solidification- and cooling-rate, secondary dendrite arm spacings, and the concentrations of microsegregations. Finally, some literature data of material properties of steel strip produced by the investigated methods are given.

Effect of vanadium on grain boundary segregation of phosphorus in low alloy steels

Abstract: The phosphorus grain boundary segregation at 853 K was investigated in three low alloy steels with different vanadium content. Kinetic dependence of the phosphorus grain boundary concentration was determined experimentally by means of AES and described theoretically, as well. To assess the influence of the individual alloying elements on the phosphorus segregation, the metal composition of carbide phases at 853 K was predicted by means of thermodynamic calculations and confirmed by experimental measurements (TEM + EDX). The vanadium was found to enhance the phosphorus grain boundary segregation by reducing the amount of dissolved and segregated carbon. Thereby, the equilibrium of mutual displacement C (segregated) ⇔ P (segregated) was shifted to more phosphorus segregation. The results achieved indicate that vanadium indirectly increases sensitivity of low alloy steels to intergranular embrittlement.