Water Capacity Model of Al2O3‐CaO‐MgO‐SiO2 Quaternary Slag System

The focus of the present work was to develop a water capacity model for the quaternary slag system Al₂O₃‐CaO‐MgO‐SiO₂. In the model, a silicate melt was considered to consist of two ion groupings, viz. cation grouping and oxygen ion. The water capacity of a melt is supposed to depend on the interactions between the cations in the presence of oxygen ions. These interactions were determined on the basis of the experimentally measured water solubility data. Only binary interactions were employed in the model. For the system CaO‐SiO₂, disagreement in the literature data was found. Since the interaction between Ca²⁺ and Si⁴⁺ would play an important role, experiments were carried out to determine the water capacities of some CaO‐SiO₂ slags. For this purpose a thermogravimetric method was employed. Iso‐lines of water capacities at constant MgO contents were predicted by the model and compared with the experimental data from literature. The model calculations agreed well with the experimental results.     

Influence of SiO2 Addition on the Properties of Al2O3‐CaO‐CaF2 Slag

The Al₂O₃‐CaO‐CaF₂ slag system is used in making special quality steels by the electro‐slag re‐melting process (ESR). The purpose of our investigation was to analyse ESR slag that contained SiO₂. The slag samples with different SiO₂ fractions (0 ‐ 20 mass %) were examined by chemical analysis, differential thermal analysis, simultaneous thermal analysis, X‐ray diffraction, electron microscopy and wetting angle measurement. With addition of SiO₂ the polymerization of slags was increased due to the formation of new silicate complex compounds that influenced their melting points and wetting angles.     

Composition Control of CaO‐MgO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel ‐ a Thermodynamic Analysis

The effect of oxide component content on the low melting point zone (LMP) in the CaO‐MgO‐Al₂O₃‐SiO₂ system has been analysed using FactSage software. The contents of dissolved elements [Si], [Mg], [O] and [Al] in liquid steel in equilibrium with the LMP inclusions in the CaO‐MgO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MgO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the MgO content is 10%. The LMP zone becomes wide with the increase in CaO content (within the range of 0~30 mass%) and the decrease in SiO₂ (from 25 to 5 mass%). To obtain the LMP (below 1400°C) inclusions, the [Mg], [Al] and [O] contents must be controlled within the range of 0.2~2 ppm, 1.0~2.0 ppm and 60~100 ppm, respectively.     

Thermodynamics of Composition Control of CaO‐MnO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel

The effect of oxide component content on the low melting point zone (simplified as LMP) in the CaO‐MnO‐Al₂O₃‐SiO₂ system has been analysed by FactSage. The contents of [Si], [Mn], [O] and [Al] in liquid steel which are in equilibrium with the LMP inclusions in the CaO‐MnO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MnO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the CaO content is 15%, and that the LMP zone becomes wider with increase in SiO₂ and MnO contents (within the range of 0~25%). To obtain LMP inclusions (below 1400°C), [Si] and [Mn] can be controlled within a wide range, but [Al] and [O] must be controlled within the range of 0.5~5 ppm and 50~120 ppm, respectively.     

Thermodynamic assessment of CaO‐SiO2‐Al2O3‐MgO‐Cr2O3‐MnO‐FetO slags for refining chromium‐containing steels

The slag system of CaO‐SiO₂‐Al₂O₃‐MgO‐Cr₂O₃‐MnO‐Fe_tO relevant to refining chromium‐containing steels such as bearing steel is thermodynamically assessed at 1873 K. The activity coefficient of Fe_tO shows an initially rapid increment followed by a gradual reduction according to Cr₂O₃ content at a constant basicity, and decreases with increasing slag basicity. γ_MnO is decreased abruptly by increasing Cr₂O₃ content and thereafter, maintains a nearly constant level. From the standpoint of inclusion control, the Cr₂O₃ presence in ladle refining slags is thermodynamically harmful in that it minimizes the inclusion level by inducing the increment of γ_FetO even though Cr₂O₃ exists in extremely small amounts. However, it is beneficial in that it diminishes AI reoxidation by decreasing γ_MnO. The presence of carbon in slag decreases γ_FetO and γ_MnO, which turns out to be favourable for the reduction of Al reoxidation. The thermodynamic equilibria of chromium and manganese are quantified in terms of Fe_tO and Cr₂O₃ content as well as slag basicity by using multiple regression analysis. L_Cr and L_Mn are increased by the presence of Cr₂O₃, indicating a low recovery efficiency of Cr and Mn in the treatment of ferroalloy addition. In determining L_S values, Cr₂O₃ is not so important as the basicity of slags.     

Influence of Manganese and Nickel on the α´ Martensite Transformation Temperatures of High Alloyed Cr‐Mn‐Ni Steels

The martensite start temperature (M_s), the martensite austenite re‐transformation start temperature (A_s) and the re‐transformation finish temperature (A_f) of six high alloyed Cr‐Mn‐Ni steels with varying Ni and Mn contents in the wrought and as‐cast state were studied. The aim of this investigation is the development of the relationships between the M_s, A_s, A_f, T₀ temperatures and the chemical composition of a new type of Cr‐Mn‐Ni steels. The investigations show that the M_s, A_s and A_f temperatures decrease with increasing nickel and manganese contents. The A_f temperature depends on the amount of martensite. Regression equations for the transformation temperatures are given. The experimental results are based on dilatometer tests and microstructure investigations.     

Solubility of nitrogen in liquid nickel and Ni‐Cr alloys under elevated pressure

The present work focuses on the experimental evaluation of the solubility of nitrogen during the melting process in nickel and binary Ni‐Cr alloys under elevated nitrogen partial pressure at 1550°C. In order to estimate the attainable nitrogen concentrations, the solubility of nitrogen in dependence of melt temperature and nitrogen partial pressure has been calculated by using Thermo‐Calc. Thermo‐Calc supported predictions of the achievable nitrogen contents referring to the investigated alloys show good agreement with the experimental data only up to nitrogen partial pressures of 0.1 MPa. The applicability of Sieverts law has been examined for nitrogen partial pressures up to 6 MPa and Ni‐Cr alloys with chromium mass contents of 15, 20, 30, 40 and 50 %. A deviation from Sieverts law was observed for the alloys with chromium mass contents higher than 20 % and a nitrogen partial pressure above 0.1 MPa. The effect of chromium and the nitrogen partial pressure on the solubility of nitrogen is described in terms of the Wagner's first and second order interaction parameters.     

Galvannealing of (High‐)Manganese‐Alloyed TRIP‐ and X‐IP®‐Steel

In this study the influence of Mn on galvannealed coatings of 1.7% Mn‐1.5% Al TRIP‐ and 23% Mn X‐IP®‐steels was investigated. It is shown that the external selective oxides like Mn, Al and Si of the TRIP steel which occur after annealing at 800 °C for 60 s at a dew point (DP) of ‐25 °C (5% H₂) hamper the Fe/Zn‐reaction during subsequent galvannealing. Preoxidation was beneficially utilized to increase the surface‐reactivity of the TRIP steel under the same dew point conditions. The influence of Mn on the steel alloy was investigated by using a 23% Mn containing X‐IP®‐steel which was bright annealed at 1100 °C for 60 s at DP ‐50 °C (5% H₂) to obtain a mainly oxide free surface prior to hot dip galvanizing (hdg) and subsequent galvannealing. As well known from the literature Mn alloyed to the liquid zinc melt stabilizes δ‐phase at lower temperatures by participating in the Fe‐Zn‐phase reactions, it was expected that the metallic Mn of the X‐IP®‐steel increases the Fe/Zn‐reactivity in the same manner. The approximation of the effective diffusion coefficient (D_eff(Fe)) during galvannealing was found to be higher than compared to a low alloyed steel reference. Contrary to the expectation no increased Fe/Zn‐reaction was found by microscopic investigations. Residual η‐ and ζ‐phase fractions prove a hampered Fe/Zn‐reaction. As explanation for the observed hampered Fe/Zn‐reaction the lower Fe‐content of the high‐Mn‐alloyed X‐IP®‐steel was suggested as the dominating factor for galvannealing.     

Control and Engineering of Non‐metallic Inclusions belonging to xSiO2‐yCaO‐zAl2O3 System in Ca‐treated Al‐killed and Al‐Si‐killed Steel

A model based on the fundamental principles of thermodynamics has been applied to forecast and control the precipitation of non‐metallic inclusions in Ca‐treated Al‐killed or Al‐Si‐killed steels. The engineering of the non‐metallic inclusions takes place during the period just after the tapping from the electric arc furnace until the beginning of the casting period. The construction of the model and its validation have been accomplished through a precise monitoring of the treatment of several steel grades characterized by different oxygen contents after tapping. The oxygen killing of the steel melt with an oxygen content between 750‐1200 ppm is performed by the addition of Si and Al, which produces the formation of pure Al₂O₃ but not always the formation of pure SiO₂. This is a fundamental hypothesis of the model confirmed by experimental observations. The other fundamental aspect is related to the determination of the oxygen activity in the steel bath, which is defined from experimental measurements by an electrochemical concentration cell and through the computation of the equilibrium between the steel bath and the ladle slag. The comparison between the experimental data and the non‐metallic evolution forecast by the model on the basis of the minimization of the oxygen potentials has shown very interesting performances, which makes the model a suitable and very stable tool for industrial application.     

Some Thermophysical Properties of Liquid Cr‐Mn‐Ni‐Steels

In the last years new Cr‐Mn‐Ni‐TRIP/TWIP steels have been developed at the Institute of Iron and Steel Technology, Freiberg University of Mining and Technology. Within the Collaborative Research Center SFB 799, the ZrO₂‐ceramic‐TRIP‐steel composite materials are produced using the infiltration of open foam ceramics with liquid steel and using powder metallurgy with small additions of ceramic powder before sintering. The thermophysical properties of liquid steel play an important role in both production routes. They affect the infiltration efficiency in one process and the produced powder size in the other, and therefore finally determine the composite properties. In this work some of these properties were estimated, as they are not available in literature. The investigated steels contain approximately 16% chrome, 7% manganese and 3% to 9% nickel. The surface tension was estimated using two methods: the drop weight method and the maximum bubble pressure method. In the drop weight method similar conditions at the gas/metal interface exist as during the atomization or the infiltration process, where liquid metal is exposed to high volume of inert gas. In all these cases the evaporation of manganese affects the surface tension. For comparison of results and for estimation of the liquid steel density the maximum bubble pressure method was used where the evaporation of manganese is limited. The wettability on partially MgO‐stabilized ZrO₂ ceramic substrates and its change with contact time was determined using the sessile drop method.     

Relationship between Work Hardening Behaviour and Deformation Structure in Ni‐free High Nitrogen Austenitic Stainless Steels

The work hardening behaviour of high nitrogen austenitic steel (HNS) depends not only on the nitrogen content but also on the addition of substitutional alloying elements such as Mn and Ni, although the effect of nitrogen content has been considered to be a main factor controlling the work hardening rate in HNS. In this study, two kinds of high nitrogen austenitic steels containing nearly 1 mass‐% of nitrogen with and without Mn (Fe‐25%Cr‐1.1%N and Fe‐21%Cr‐0.9%N‐23%Mn alloys) were tensile‐tested and their work hardening behaviour was investigated for the purpose of clarifying the effect of Mn on the work hardening behaviour. Then the results were related to the change in deformation substructure. In the Fe‐25Cr‐1.1N alloy, the work hardening rate kept high until fracture occurred, while in the Fe‐21Cr‐0.9N‐23Mn alloy it tended to decrease gradually with tensile deformation in the high strain region. It was concluded that the difference in work hardening behaviour between both alloys is attributed to the change in dislocation substructure from planar dislocation array to dislocation cell by the addition of Mn.     

Effect of alloying by transitional refractory metals on the microstructure and thermal stability of Al–5Zn–3Mg alloys

Abstract

The effect of additions of transitional refractory metals on the structure and properties of Al–Zn–Mg alloys, made by ingot and PM routes, was investigated. The strength of the ingot alloys especially is increased by scandium and zirconium. The modifying action of scandium inhibits recrystallisation and precipitation of the fine-grained coherent Al₃(Sc_1–xZr_x) phase. The effect is weaker in PM alloys where the ultra-high cooling rate during high pressure water atomisation produces the fine-grained structure. PM semi-products of the base composition Al–5Zn–3Mg and alloys without scandium are not recrystallised during heating to 500°C, whereas cast alloys of similar composition recrystallised on the hot extrusion stage at 400–450°C. Of the Sc alloys, Al–5Zn–3Mg–0·5Mn–0·7Zr–0·3Sc showed the highest strength (UTS?=?651 MPa, YS?=?596 MPa), whereas of the PM alloys without scandium Al–5Zn–3Mg–0·85Zr–0·22Cr–0·17Ni–0·15Ti alloy showed UTS?=?618 MPa and YS?=?553 MPa. At melt cooling rates of 10⁵–10⁶ K s^–1 the total content of transitional refractory metals must not exceed 1·5–1·7 wt-% and total content (Zn+Mg) should be <8 wt-% at a Zn/Mg ratio of 5:3.     

Thermodynamic behaviours of manganese and phosphorus between CaO‐MgOsat‐SiO2‐Al2O3‐FetO‐MnO‐P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iron and CaO‐MgO_Sat‐SiO₂‐Fe_tO‐MnO‐P₂O₅‐Al₂O₃ (0–33%) ladle slag have been investigated at 1873 K from the viewpoint of Mn and P yields for the production of high‐strength steels. The equilibrium distribution ratios of Mn and P were found to increase with increasing Fe_tO content; however, these ratios vary with basicity, but they do this the other way round. The addition of alumina into slag at a fixed basicity and Fe_tO content decreases both the equilibrium manganese and phosphorus distributions. The equilibrium distribution ratios were discussed in terms of the variation of activity coefficients of Fe_tO, MnO and PO_2.5, according to the slag basicity and Al₂O₃ content. The quantitative contributions of basicity and (%Fe_tO + %MnO) on L_Mn and L_P were empirically determined and their usefulness was discussed with the aid of plant data: To improve Mn and P yields in the practical RH operation, it is strongly recommended that Fe‐Mn and Fe‐P alloys be added after Al deoxidation treatment inducing relatively high Al₂O₃ in slag and maintaining low Fe_tO content. In addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.     

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.     

Hot Workability of as‐Cast High Manganese‐High Carbon Steels

In order to produce new high Mn‐high C austenitic steels (R_m>700 MPa), different tests and methods were used to determine a suitable window of process parameters. In‐situ melting hot tensile tests and hot compression tests were carried out to investigate the hot ductility, fracture characteristics and flow behaviour during continuous casting and hot deformation of 3 steels with Mn and C contents between 9‐23% and 0.6‐0.9%, respectively. The results show that these steels are susceptible to interdendritic fracture at high temperatures. Decreasing Mn content improves the reduction of area at high temperatures to 60% or more. Hot deformation loads for processing the investigated steels are not higher in comparison to the stainless steel 1.4301.     

Deformation Behaviour of Iron‐Rich Iron‐Aluminium Alloys with Ternary Transition Metal Additions

The hardness and yield stress at room temperature and the brittle‐to‐ductile transition temperature of Fe‐Al alloys with 16 at.% Al, which is in the range of the so‐called K‐state with possible short‐range ordering reactions, and ternary additions of 0.5 and 4 at.% of the transition metals Cr, Mo, Mn, V, Ti and Ni were studied with respect to possible hardening effects of the ternary additions. The addition of Cr, Mo and Mn to the Fe‐Al alloys produce solid‐solution hardening which corresponds to the hardening effect of Al. Only Ti, V and Ni produce extra hardening effects which cannot be related to solid‐solution hardening. This extra hardening is attributed to possible fine NiAl precipitates in the Fe‐Al‐Ni case and to possible enhanced short‐range ordering and/or fine carbide precipitates in the cases of Fe‐Al‐V and Fe‐Al‐Ti.     

A Review of the Relationship between Viscosity and the Structure of Calcium‐Silicate‐Based Slags in Ironmaking

This review focuses on elucidating the viscosity of ironmaking slags and the effect of various components in the multi‐component calcium‐silicate‐based slag system on the viscosity. Using various widely used spectroscopic techniques including Fourier transform infrared (FTIR), Raman, X‐ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR), the viscous behavior and the slag structure of this system were correlated. In particular, the review begins with an introduction to the viscous behavior of binary silicate systems and an identification of the intricate details of the slag structure. Using the binary system as a basis, the compounded effect of typical ironmaking slag components such as Al₂O₃, MgO, alkali oxides, and TiO₂ on the viscosity is introduced through expansion to a quinary slag system. Using a combination of the aforementioned spectroscopic methods, the meticulous details of the slag structure were ascertained, and the depolymerization or polymerization mechanisms of the silicate and alumino‐silicate structures were subsequently identified. This review also compares well‐known viscosity prediction models with experimentally measured values and identifies potential fields of research in the ironmaking industry associated with slag viscosities.     

Viscosities of the Quaternary Al2O3‐CaO‐MgO‐SiO2 Slags

Viscosities of some quaternary slags in the Al₂O₃‐CaO‐MgO‐SiO₂ system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub‐systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso‐viscosity contours in the Al₂O₃‐CaO‐MgO‐SiO₂ system relevant to ladle slags were calculated at 1823 K and 1873 K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.     

MgO Saturation in Secondary Metallurgical Lime‐aluminate and Lime‐silicate Slags

This paper provides an informative basis on MgO saturation in secondary metallurgical slags by conducting thermo‐chemical calculations in the ternary base system Al₂O₃‐CaO‐SiO₂ at 1600 °C, 1650 °C and 1700 °C using FactSage^TM6.0. The results for lime‐aluminate and lime‐silicate slag are displayed in a straightforward and illustrative manner. In addition, approximate equations describe the temperature dependencies: a temperature rise of 50 °C increases the MgO saturation limit by about 1 wt. %.     

A Study in the Thermodynamic Behavior of Nickel in the MgO‐SiO2‐FeO Slag System

The dissolution behavior of nickel in the MgO‐SiO₂‐FeO slag system was investigated by using the thermodynamic equilibrium technique. Nickel distribution ratio between molten MgO‐SiO₂‐FeO slag and molten Fe‐Ni alloy at 1773 K and 1873 K was measured to understand the dissolution mechanism of nickel into the slags. In particular, the effect of oxygen potential and basicity on the distribution of nickel was investigated. Nickel distribution between slag and Fe‐Ni alloy increased with higher oxygen potential showing a slope of 1/2. For basic slag systems near the olivine saturated composition, the nickel distribution ratio increased with higher basicity and for acidic slag systems near the cristobalite saturated composition, the nickel distribution ratio decreased with higher basicity. Thus, the nickel dissolution into the MgO‐SiO₂‐FeO slag system showed two independent mechanisms similar to that found in the CaO‐SiO₂‐CaF₂ system. The contour of the iso distribution ratio was represented in the MgO‐SiO₂‐FeO ternary phase diagram. From the results, an optimum slag composition was determined to be near the olivine saturated with approximately $X_{MgO} /X_{SiO_{2} } $ of 0.8 at 1773 K and 1.0 at 1873 K.