Showing papers in "Isij International in 2002"
TL;DR: In this article, the decomposition of austenite in austenitic stainless steels is reviewed in detail including nucleation sites and orientation relationships and the influence of several factors such as composition, previous deformation and solution annealing temperature.
Abstract: Austenitic stainless steels are probably the most important class of corrosion resistant metallic materials. In order to attain their good corrosion properties they rely essentially on two factors: a high chromium content that is responsible for the protective oxide film layer and a high nickel content that is responsible for the steel to remain austenitic. Thus the base composition is normally a Fe-Cr-Ni alloy. In practice the situation is much more complex with several other elements being present, such as, Mo, Mn, C, N among others. In such a complex situation one almost never has a single austenite phase but other phases invariably form. Those phases are, with few exceptions, undesirable and they can be detrimental to the corrosion and mechanical properties. It is therefore of considerable importance to study the formation of such phases. In this work the decomposition of austenite in austenitic stainless steels is reviewed in detail. First the binary equilibrium diagrams relevant to the system Fe-Cr-Ni are briefly presented as well as other diagrams, such as the Schaeffler diagram, that traditionally have been used to predict the phases present in these steels as a function of composition. Secondly the precipitation of carbides and intermetallic phases is presented in detail including nucleation sites and orientation relationships and the influence of several factors such as composition, previous deformation and solution annealing temperature. Next, the occurrence of other constituents such as nitrides, sulfides and borides is discussed. TTT diagrams are also briefly presented. Finally the formation of martensite in these steels is discussed.
378 citations
TL;DR: In this paper, the authors investigated theoretically the contribution of transformation plasticity to the total elongation of TRIP-assisted steels, and they concluded that the observed high uniform elongation is a consequence of the martensitic transformation of the retained austenite under the influence of an applied stress or strain.
Abstract: The weight of an automobile can be reduced by using high-strength steels as long as they have the ductility essential in metal-forming operations. One class of suitable alloys is known as the “TRIP-assisted steels”, in which the microstructure is a mixture of allotriomorphic ferrite and bainite; the term TRIP stands for transformation-induced plasticity. The typical chemical composition is Fe–0.15C– 1.5Si–1.5Mn wt%; the high silicon concentration ensures that cementite is not precipitated during the growth of upper bainite. The carbon that is partitioned from bainitic ferrite stabilises the residual austenite, enabling it to be retained at ambient temperature. The final microstructure typically contains 20% bainitic ferrite, 10% retained austenite with the remainder being allotriomorphic ferrite. There have been many publications on the microstructure and property relationships of TRIP-assisted steels. Most of these studies highlight the presence of the retained austenite and many imply that the observed high uniform elongation is a consequence of the martensitic transformation of the retained austenite under the influence of an applied stress or strain. The purpose of the present work was to investigate theoretically, the magnitude of the contribution that transformation plasticity can make to the total elongation.
179 citations
TL;DR: This work outlines the use of an artificial neural network to model the calculation of Ms temperature in engineering steels from their chemical composition, and a physical interpretation of the results is presented.
Abstract: The knowledge of the martensite start (Ms) temperature of steels is sometimes important during parts and structures fabrication, and it can not be always properly estimated using conventional empirical methods. The additions in newly developed steels of alloying elements not considered in the empirical relationships, or with compositions out of the bounds used to formulate the equations, are common problems to be solved by experimental trial and error. If the trial process was minimised, cost and time might be saved. This work outlines the use of an artificial neural network to model the calculation of Ms temperature in engineering steels from their chemical composition. Moreover, a physical interpretation of the results is presented.
178 citations
TL;DR: In this paper, the effects of microstructural features on the yield ratio and toughness of high strength linepipe steels have been investigated, and the optimum microstructure for a better combination of strength, toughness and yield ratio is suggested to be the one having second phase of polygonal ferrite in an acicular ferrite or bainite matrix.
Abstract: The present study aims at elucidating the effects of microstructural features on the yield ratio and toughness of high strength linepipe steels. The main emphasis has been placed on understanding the effects of constituents on the properties. Several alloy systems with different constituents, i.e. ferrite-pearlite steels, ferrite steels with acicular ferrite as second phase, acicular ferrite steels with ferrite as second phase, and bainite steels, have been investigated. Experimental results show that while the refinement of ferrite grain size improves both yield strength and low temperature toughness of ferrite-base steels, it increases the yield ratio. Modification of matrix from ferrite to acicular ferrite or bainite results in improvements in both yield strength and yield ratio. However, bainite steels have worse low temperature toughness (i.e., higher DBTT) than the other types of steels. It has been shown that the low temperature toughness of acicular ferrite steels can be improved by the introduction of polygonal ferrite as a second phase. This is mainly due to the refinement of effective grain size by the introduction of second phases. The relationship between the yield ratio and work hardening exponent has also been established using the Swift equation. Based on the results, the optimum microstructure for a better combination of strength, toughness and yield ratio is suggested to be the one having second phase of polygonal ferrite in an acicular ferrite or bainite matrix.
163 citations
TL;DR: In this paper, the FT-IR spectra of the CaO-SiO2 and CaO SiO2-CaF2 slags were measured to understand the structural aspects of (fluoro-) silicate systems.
Abstract: The FT-IR spectra of the CaO-SiO2 and CaO-SiO2-CaF2 slags were measured to understand the structural aspects of (fluoro-) silicate systems. The relative intensity of Si-O rocking band is very strong at SiO2 saturation condition and this band disappears in the composition greater than 44.1 (mol%) CaO in the CaO-SiO2 binary system. The bands for [SiO4]-tetrahedra at about 1 150-760 cm-1 split up with increasing content of CaO greater than 44.1 mol%. The IR bands in this wavenumber range are divided into four groups, that is about 1090, 990, 920, and 870 cm-1, which have been assigned to NBO/Si=1, 2, 3, and 4, respectively. In the CaO-SiO2 -CaF2 (2CaO · SiO2-Satd.) system, the center of gravity of the bands at about 1170-710 cm-1 shifts from about 980 to 850 cm-1 by increasing the ratio XCaF2/XSiO2 from 0.22 to 0.64. The bands for [SiO4]-tetrahedra are observed from about 1 070 to 730 cm-1 in the CaO-17.6(mol%)SiO2-CaF2 system, while these bands are observed from about 1120 to 720 cm-1 in the CaO-40.0(mol%)SiO2-CaF2 system. The effect of substitution of CaF2 for CaO on the depolymerization of silicate network is observed to significantly depend on the SiO2 content in the slags. The bands for [SiO4]-tetrahedra are observed from about 1110 to 720 cm-1 in the CaO-SiO2 -14.1(mol%)CaF2 system and the center of gravity of these bands shifts from about 990 to 850 cm-1 with increasing CaO/SiO2 ratio. The fraction of the relatively depolymerized units continuously increases from about 0.5 to 0.8 as the composition of slags changes from 2CaO · SiO2 to CaO saturation condition.
122 citations
TL;DR: In this article, the effect of improved heat treatment on creep strength and distribution of B in precipitates is investigated to effectively utilize and decrease added B. The authors have revealed in the previous report that the addition of 139ppm B significantly improves creep strength of the steels, whereas most of added B forms unidentified borides, which are deemed almost ineffective to creep strength.
Abstract: For the construction of ultra super critical (USC) power plant, 9Cr-3W base ferritic heat-resistant steels with relatively high B and no N have been investigated. Authors have been revealed in the previous report that the addition of 139ppm B significantly improves creep strength of the steels, whereas most of added B forms unidentified borides, which are deemed almost ineffective to creep strength. The effect of improved heat treatment on creep strength and distribution of B in precipitates is investigated to effectively utilize and decrease added B. As a result of the analysis of the extracted residue and characterization of precipitates using field emission Auger electron spectroscopy (FE-AES), most of added B still forms borides in the 92ppm B added steel. These composites are almost dissolved and the B content in M 23 C 6 carbides is significantly increased by normalizing at 1423K. It is also found by FE-AES analysis that B content in M 23 C 6 carbides near prior-austenite grain boundaries is relatively higher than that inside grains. Creep strength at 923K for the 92ppm B added steel normalized at 1423K is not improved at short times, but it is remarkably improved to almost the same level as the 139ppm B added steel at long times. This excellent creep strength is achieved resulting in improving microstructural stability through the effective utilization of added B by high-temperature normalizing.
111 citations
TL;DR: In this article, the FT-IR spectra of the CaO-Al 2 O 3 -CaF 2 slags were measured to understand the structural aspects of (fluoro-) aluminate slags.
Abstract: The FT-IR spectra of the CaO-Al 2 O 3 and CaO-Al 2 O 3 -CaF 2 slags were measured to understand the structural aspects of (fluoro-) aluminate slags. The infrared spectra of the CaO-Al 2 O 3 slag was interpreted based on the relationship between bond length and force constant of Al-O bond. Thereafter, the role of F - ions in the depolymerization of aluminate network was discussed. The wavenumbers of [AlO 4 ]-tetrahedra higher than that of [AlO 6 ]-octahedra would be originated from the Al-O bond length in tetrahedra shorter than that in octahedra. In the CaO satd -Al 2 O 3 -CaF 2 system, the IR-transmitting bands of [AlO n F 4-n ]-complexes are observed through the entire composition of the fluoroaluminate system, while the bands of [AlO 4 ]-tetrahedra, [AlO 6 ]- and [AlF 6 ]-octahedra appear in the composition less than 24.0 (mol%) CaF 2 . In the 26.2 (mol%) Al 2 O 3 -containing system, the bands of interlinked [AlO 4 ]-tetrahedra are shown at only 2-liquids boundary, while these bands are shown in the whole composition region in the 41.5 (mol%) Al 2 O 3 -containing system. In the 41.7 and 51.0(mol%)CaO-Al 2 O 3 -CaF 2 systems, the transmitting bands of [AlO n F 4-n ]-complexes are observed through the entire composition, while those of [AlO 4 ]-tetrahedra are shown in the composition of X CaF2 /X Al2O3 ≤1.0. Also, the relative intensity of the bands indicating [AlO 4 ]-tetrahedra in the 51.0 (mol%) CaO-containing slag is much less than that in the 41.7 (mol%) CaO-containing system.
110 citations
TL;DR: In this article, a high-strength low-alloy TRIP-aided sheet steels with annealed martensite matrix was developed for automotive applications, which exhibited a superior large elongation and reduction of area.
Abstract: Formable high-strength low-alloy TRIP-aided sheet steels with annealed martensite matrix or "TRIP-aided annealed martensitic steel" were developed for automotive applications. The steels possessed a large amount of plate-like retained austenite along annealed martensite lath boundary, whose stability against the strain-induced transformation was higher than that of the conventional "TRIP-aided dual-phase steel" with polygonal ferrite matrix. In a tensile strength range between 600 and 1000 MPa, the TRIP-aided annealed martensite steels exhibited a superior large elongation and reduction of area. In addition, they possessed the same excellent stretch-flangeability and bendability as "TRIP-aided bainitic steel" with bainitic ferrite matrix. These properties were discussed by matrix structure, a strength ratio of second phase to matrix, retained austenite stability, internal stress and so on.
104 citations
TL;DR: In this article, a short survey of nitrogen influence on stainless steel welds is given, which covers: the levels of nitrogen in weld metal, the influence of nitrogen on weld metal characteristics such as weld defects, corrosion resistance and mechanical properties.
Abstract: The purpose of this paper is to give a short survey of nitrogen influence on stainless steel welds. The review are covers: the levels of nitrogen in weld metal, the influence of nitrogen on stainless steel weld metal characteristics such as weld defects, corrosion resistance and mechanical properties. High nitrogen steel welding must consider the risk of nitrogen escape from the weld pool. Avoiding nitrogen losses may be accomplished by controlling shielding gas, welding parameters and compositions of filler metal. The increase of nitrogen in the weld metal decreases in the δ ferrite content. The reduction of δ ferrite in austenitic weld metals will result in an increase in the solidification cracking susceptibility. However, the role of nitrogen in affecting the solidification cracking susceptibility of fully austenitic weld metals is unclear. Nitrogen addition increases the pitting corrosion resistance in weld metals whereas decreases resistance to stress corrosion cracking because of δ ferrite reduction. Nitrogen also improves mechanical properties in weld metals. However, the presence of nitrides may be detrimental to the mechanical properties in stainless steel welds.
98 citations
TL;DR: In this article, a three-dimensional multiphase mathematical model of the blast furnace is presented, where all phases behave like fluids and conservation equations for mass, momentum, energy and chemical species for all phases are solved based on the finite volume method.
Abstract: The blast furnace process is a multi-phase chemical reactor whose main purpose is to reduce iron oxides producing hot metal. In the actual blast furnace operation several phases simultaneously interact with one another exchanging momentum, mass and energy. In this paper a three-dimensional multiphase mathematical model of the blast furnace is presented. This model treats the blast furnace process as a multiphase reactor in which all phases behave like fluids. Five phases are treated by this model, namely, gas, lump solids (iron ore, sinter, pellets and coke), pig iron, molten slag and pulverized coal. Conservation equations for mass, momentum, energy and chemical species for all phases are solved based on the finite volume method. In the discretized momentum equations, the covariant velocity projections are used, which is expected to give the best coupling between the velocity and pressure fields and improve the convergence of the calculations. This is a new feature of the present model regarding to the numerical procedures applied to the blast furnace modeling, which emphasizes its originality. In addition, gas and solid phases are treated as continuous phases possessing a pressure field and the SIMPLE algorithm is applied to extract the pressure field and ensure mass conservation. Hot metal, slag and pulverized coal are treated as discontinuous phases consisting of unconnected droplets. For such phases, momentum conservation is used to calculate the fields of velocity while the continuity equations are used to calculate the phase volume fractions. This model was applied to predict the three-dimensional blast furnace operation and predicted temperature distributions and operational parameters like productivity, coke rate and slag rate presented close agreement with the actual measured ones in the blast furnace process.
96 citations
TL;DR: In this paper, the authors proposed a kinetic model for the overall transformation of austenite into bainite including both nucleation and growth of the new phase, which is considered in the general framework of the classical nucleation theory.
Abstract: The present article proposes a kinetic model for the overall transformation of austenite into bainite including both nucleation and growth of the new phase. Nucleation of bainitic ferrite laths is considered in the general framework of the classical nucleation theory. Analysis of experimental data in a low alloyed 0.5% C steel suggests that austenite grain boundary diffusion of carbon is the limiting step in the formation of ferrite nuclei. Growth of bainitic laths is controlled by volume diffusion of carbon in austenite. Nucleation and growth equations are included in a Kolmogorov-Johnson-Mehl-Avrami analysis to provide a simple relationship for the bainite fraction as a function of time and temperature which contains only two semi-empirical parameters. This model is fitted to isothermal kinetics and extrapolated to continuous cooling conditions without changing the two parameters. Comparison between predictions and experimental kinetics in two different 0.5% C steels gives a very good agreement.
TL;DR: In this article, the effect of trace boron in steels, especially the influence of BORON on microstructure and properties of low carbon bainitic steels were summarized.
Abstract: The effect of trace boron in steels, especially the influence of boron on microstructure and properties of low carbon bainitic steels were summarized. It was pointed out that the hardenability of boron steels is determined by non-equilibrium boron segregation on grain boundaries. The synergistic effect of boron with other elements can enhance the boron effect. The abnormal boron segregation on the moving new grain boundaries is the basic reason of the boron retarding the recrystallization of deformed austenite, the addition of copper and niobium will increase this effect. The addition of boron accelerates the strain induced niobium carbonitride precipitation, and trace boron can refine the microstructure and improve the mechanical properties of HAZ. The mechanisms of boron effect were also expounded preliminarily in this paper.
TL;DR: In this paper, the effect of the strain, the strain rate and the deformation temperature on the dynamic recrystallization of Type 304 austenitic stainless steel is investigated.
Abstract: Ultrafine grain structure in the Type 304 austenitic stainless steel are pursed through dynamic recrystallization. The recrystallization behaviors are studied at various combinations of deformation temperatures and strain rates accompanying the higher strain under a plain strain compression. The effects of the strain, the strain rate and the deformation temperature are investigated, and the relationship between the deformation conditions and the dynamic recrystallized grain size is analyzed. The critical strain needed for the initiation of recrystallization increases with the Z-H parameter. Empirical equations concerning the critical strain and the dynamic recrystallized grain size are discussed, and processing parameter maps are proposed for the complete dynamic recrystallization.
TL;DR: In this article, the effect of the film thickness on the strength of capsules was experimentally examined and the obtained PCM had enough strength by increasing the thickness and showed an excellent catalytic property for reforming reaction from methane to hydrogen.
Abstract: For efficient heat-recovery of high temperature waste gas such as LDG in the form of latent heat, the utilization technology of phase change material, PCM, was experimentally studied. Copper balls as the PCM were encapsulated by nickel film with/without an insertion of carbon or ruthenium as an inhibition layer, based on an electro-plating method. Then, the effect of the film thickness on the strength of capsules was experimentally examined. As a result, the obtained PCM had enough strength by increasing the film thickness and showed an excellent catalytic property for reforming reaction from methane to hydrogen. In conclusion, the copper PCM with the thick film of nickel and an inactive layer between nickel and copper was available for producing hydrogen by recovering high-temperature waste heat efficiently.
TL;DR: In this paper, the effect of C-Ti added steel on hardenability was investigated and it was shown that hardness increases with increasing B content up to the optimum B content without effect of Mo.
Abstract: The hardenability change by an addition of B to 0.15%C-Ti added steel was investigated considering the effect of Mo in order to understand one of the peculiar characteristics that austenitizing at higher temperatures reduces the hardenability effect of B. Hardenability monotonically increases with increasing B content up to the optimum B content without the effect of Mo. The optimum B content increases with increasing Mo; 6 ppm, 9 ppm, 13 ppm for 0 % Mo, 0.25 % Mo, 0.50 % Mo. The addition of Mo retards the precipitation of M 23 (CB) 6 and thus more B in solution that contributes to hardenability can exist along grain boundaries by Mo. The optimum B content is reduced with increasing temperatures because much more B concentrates along grain boundaries through non-equilibrium segregation mechanism during cooling from an elevated temperature and thus precipitation of M 23 (CB) 6 easily occurs.
TL;DR: In this paper, a large number of new ferritic-martensitic compositions, which have been designed on the basis of the positive outcomes attained in previous studies as well as on the results obtained with advanced thermodynamic calculation tools, are under investigation in the new COST 522 programme.
Abstract: Advanced Steam Power Plant is one of three working groups within the frame of European COST 522 with the aim of developing and evaluating ferritic steels for steam conditions up to 650°C. Today's state-of-the-art large fossil-fired steam turbines comprise live steam conditions of up to 610°C/ 300 bar and re-heat temperatures of up to 630°C. These ultra super critical steam parameters significantly increase plant efficiency and reduce fuel consumption and emissions of CO 2 . Ferritic materials should be used for thick-walled components to maintain high operational flexibility of such large plants. Rotors, casings, bolts, tubes/pipes and waterwalls are the critical components under current investigation. The class of the 9-12 % Cr steels offers the highest potential to meet the required property level for critical components. Therefore a significant effort to increase the application temperature of these steels was the focus of study within the European COST 501 programme and has led to improved materials for 600°C application of forged and cast components and for pipework. These 600°C materials are already being successfully utilised in a number of advanced European power plants. Further potential for improvement in creep strength seems possible after taking into account the oxidation resistance for T> 600°C. A large number of new ferritic-martensitic compositions, which have been designed on the basis of the positive outcomes attained in previous studies as well as on the results obtained with advanced thermodynamic calculation tools are under investigation in the new COST 522 programme. Full-size cast and forged components have been manufactured from the most promising compositions and now are being evaluated by intensive mechanical testing.
TL;DR: In this paper, the dissolution rate of Al 2 O 3 into the CaO-SiO 2 -Al 2 O3 slag system at 1 873 K was investigated by employing a novel experimental method which involved continual measurement of torque variation on a rotating alumina rod dipped into a molten slag.
Abstract: The dissolution rate of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system was investigated at 1 873 K by employing a novel experimental method which involved continual measurement of the torque variation on a rotating alumina rod dipped into a molten slag. Measured torque variation was successfully related to the dissolution rate of the rod. The dissolution rate of alumina was found affected by a number of factors: the rate increased with increasing temperature, the rotating speed of the rod, the CaO content in the slag, and the Al 2 O 3 content in the slag for a fixed CaO content. It was found that the dissolution rate was highly dependent on the viscosity and the diffusivity of slags. The activation energy obtained from an Arrhenius type analysis was in the range of 84 kJ mol -1 . It was concluded that the dissolution of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system was controlled by the mass transfer in the slag phase. An iso-dissolution rate diagram was constructed for the dissolution of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system at 1 873 K.
TL;DR: In this paper, the authors investigated the stretch-flangeability of low-alloy TRIP type bainitic sheet steels with different silicon and manganese contents for automotive applications.
Abstract: Retained austenite characteristics and stretch-flangeability in low alloy TRIP type bainitic sheet steels with different silicon and manganese contents were investigated for automotive applications. As increasing silicon and manganese contents, an initial volume fraction of retained austenite film along bainitic ferrite lath boundary was increased in accompany with a decrease in the carbon concentration. An excellent stretch-flangeability was completed in the steels containing a small amount of stable retained austenites (i.e., volume fraction of 2-4 vol% and carbon concentration of more than 1.0 mass%). This was caused by small surface damage on hole-punching and effective strain-induced transformation plasticity of untransformed retained austenite on hole-expanding. When austempered at temperatures less than M s of the steel after intercritical annealing, further superior stretch-flangeability was achieved due to absence of initial blocky martensite, resulting from developments of long shear section and severe plastic flow and difficult void-initiation on hole-punching.
TL;DR: In this paper, both thermal and mechanical stability of retained austenite is investigated by thermo-magnetic as well as in situ conventional X-ray diffraction and micro synchrotron radiation diffraction measurements.
Abstract: Stability of retained austenite is the key issue to understand transformation-induced plasticity (TRIP) effect. In this work, both thermal stability and mechanical stability are investigated by thermo-magnetic as well as in situ conventional X-ray diffraction and micro synchrotron radiation diffraction measurements. The thermal stability in a 0.20C-1.52Mn-0.25Si-0.96Al (wt%) TRIP steel is studied in the temperature range between 5 and 300 K under a constant magnetic field of 5T. It is found that almost all austenite transforms thermally to martensite upon cooling to 5 K and M S and M f temperatures are analyzed to be 355 and 115 K. Transformation kinetics on the fraction versus temperature relation are well described by a model based on thermodynamics. From the in situ conventional X-ray and synchrotron diffraction measurements in a 0.17C-1.46Mn-0.26Si-1.81Al (wt%) steel, the volume fraction of retained austenite is found to decrease as the strain increases according to Ludwigson and Berger relation. The diffraction measurements also show that the mechanical stability depends on the orientation of the grain with respect to the direction of the applied stress, and the austenite grains at an angle of 45° or 60° were found to be more stable than those at lower or higher angles. Both thermal and diffraction experiments show an increase in the average carbon concentration of the remaining austenite with lowering temperature or increasing stress. Thermal and mechanical stability of retained austenite is therefore attributed to the carbon distribution over different austenite grains.
TL;DR: In this article, the effect of fluorine addition on the degree of polymerization of silicate network was investigated for the CaO-SiO 2 -CaF 2 and CaO -SiO2 -CAF 2 -FeO x glasses using X-ray photoelectron spectroscopy (XPS) and Mossbauer spectra.
Abstract: The chemical state of fluorine and the effect of fluorine addition on the degree of polymerization of silicate network have been investigated for the CaO-SiO 2 -CaF 2 and CaO-SiO 2 -CaF 2 -FeO x glasses using the X-ray photoelectron spectroscopy (XPS) and Mossbauer spectroscopy measurements. The F1 s XPS spectra indicate that the fluorine is dominantly coordinated with calcium rather than silicon. The O1 s XPS spectra for the CaO-SiO 2 -CaF 2 glasses and the values of Fe 2+ /Fe 3+ obtained by Mossbauer spectra for the CaO-SiO 2 -CaF 2 -FeO x glasses indicate that CaF 2 addition does not depolymerize the silicate network for both systems.
TL;DR: In this paper, a coupled mathematical model of microsegregation and inclusion precipitation during solidification is established, which can be used to calculate the kind of precipitated inclusion, the amount of inclusion precipitation and the growth of inclusion during the solidification process.
Abstract: A coupled mathematical model of microsegregation and inclusion precipitation during solidification is established. The model can be used to calculate the kind of precipitated inclusion, the amount of inclusion precipitation and the growth of inclusion during solidification. The calculation by this model shows that the segregation degree of solute elements is suppressed greatly due to the precipitation of inclusions during solidification. A non-coupled model will overestimate the segregation degree and the amount of inclusion precipitation and even give a wrong prediction for the kind of the inclusions. In this paper, the effects of cooling rate on the precipitation and growth of oxides are also discussed.
TL;DR: In this article, a mathematical model of mould flux infiltration and heat transfer through the flux film has been developed, considering the effect of static pressure of molten steel, temperature dependency of flux viscosity and determination of liquid flux thickness with pressure gradient.
Abstract: A mathematical model of mould flux infiltration and heat transfer through the flux film has been developed. The model considers the effect of static pressure of molten steel, temperature dependency of flux viscosity and determination of liquid flux thickness with pressure gradient. Present model gives the results that agree well with actual plant data such as mould flux consumption, mould friction and the heat transfer. The results of the model give remarkable effect of static pressure of molten steel as follows: decrease of the static pressure causes increase of liquid and total flux film thickness, reduction of heat flux and decrease of friction force on solidified shell.
TL;DR: In this article, the strengthening mechanism due to copper (Cu) particles was discussed in terms of the interaction between dislocation and Cu particles in aged Fe-Cu alloys, and the precipitation strengthening due to Cu particles was expressed as a function of mean particle spacing (λ) and the θ c (π/2) gave Orowan stress.
Abstract: The strengthening mechanism due to copper (Cu) particles was discussed in terms of the interaction between dislocation and Cu particles in aged Fe-Cu alloys. Since Cu particles are softer than the iron matrix, its interaction with dislocation is different from that with the Orowan mechanism. The moving dislocations can cut the soft Cu particles and pass through them when the bowing angle reaches some critical value (θ c ), and the precipitation strengthening due to Cu particles is expressed as a function of mean particle spacing (λ) and the θ c (π/2 gives Orowan stress). The θ c increased with increasing the size of Cu particles and reached π/2 when the Cu particle size became 70 nm. This means that the precipitation strengthening due to Cu particles is dependent on not only λ but also the Cu particle size, and 70 nm is the minimum Cu particle size for obtaining the Orowan stress.
TL;DR: In this article, two high strength transformation-induced plasticity (TRIP) sheet steels with 0.10wt% and 0.14wt% carbon were produced with retained austenite volume fractions varying from less than 3 % up to 16 %.
Abstract: Two high strength transformation-induced plasticity (TRIP) sheet steels with 0.10wt% and 0.14wt% carbon were produced with retained austenite volume fractions varying from less than 3 % up to 16 %. These TRIP steels were tensile tested at strain rates ranging from 10 -3 to 2.5×10 2 s -1 to determine the effects of strain rate and retained austenite volume fraction on tensile properties. Increasing the retained austenite volume fraction increases UTS, total elongation, uniform strain and total absorbed energy, but decreases yield strength and absorbed energy below 10% engineering strain. Increasing strain rate increases yield strength and UTS, and creates a better-defined yield point, but has little effect on strain hardening behavior for TRIP steels with 11 % or less retained austenite. The TRIP steel with 16% retained austenite shows increasing strain hardening rate with strain rate at low strains.
TL;DR: In this article, a 3D modified cellular automata model (3-D MCA) was developed to simulate the evolution of microstructures in solidification of alloys.
Abstract: A three dimensional modified cellular automaton model (3-D MCA) was developed in order to simulate the evolution of microstructures in solidification of alloys. Different from the classical cellular automata in which only the temperature field was calculated, this model included the solute redistribution both in liquid and solid during solidification. The relationship between the growth velocity of a dendrite tip and the local undercooling, which consists of thermal, constitutional and curvature undercooling terms, was calculated according to the KGT (Kurz-Giovanola-Trivedi) and LKT (Lipton-Kurz-Trivedi) models. The finite volume method, which was coupled with the cellular automaton model, was used to calculate the temperature and solute fields in the calculation domain. The present 3-D MCA model was applied to predict the microstructures, such as the free dendritic growth from an undercooled melt, the competitive dendritic growth in practical casting solidification. Some of the simulated results were compared with those obtained experimentally.
TL;DR: In this article, aluminum-deoxidized iron at 1 873 K was solidified at three different cooling speed; (1) the ultra-rapid cooling of iron using twin rollers, (2) the quenching of iron into copper mold, and (3) the queuing of the iron bearing crucible in a water bath; the most rapid cooling rate achieved with (1), which was probably about 10 5 K/s.
Abstract: Aluminum-deoxidized iron at 1 873 K was solidified at 3 different cooling speed; (1) the ultra-rapid cooling of iron using twin rollers, (2) the quenching of iron into copper mold, and (3) the quenching of the iron-bearing crucible in a water bath; the most rapid cooling rate achieved with (1), which was probably about 10 5 K/s, followed (2) and (3). Dendritic, maple-like, polygonal, network-like, coral-like and spherical inclusions were observed in the samples. The dendritic, maple-like and polygonal inclusions varied in size from several tens to a few pm and were classified as primary inclusions since their sizes were independent of cooling speed. However, the network-like and coral-like inclusions (in the sample cooled ultra-rapidly and quenched into copper mold), and spherical inclusions were classified as secondary inclusions since they decreased in size with increased cooling speed. A few large spherical inclusions, which would be primary inclusions, were also present. The analysis of the electronic diffraction of the inclusions established that the a, y, δ-alumina were present as secondary inclusions. An amorphous silica spherical inclusion was also observed.
TL;DR: In this paper, the authors report on the chemical compatibility of a number of potential refractory materials: Al 2 O 3, ZrO 2, Al O 3 -carbon, SiO 2 and MgO with liquid steel, an amount of simulated inclusions and synthetic slag.
Abstract: Al 2 O 3 -carbon composite submerged entry nozzles (SEN) are used for continuous casting of steels. Although this material has excellent mechanical and thermal properties, it frequently leads to clogging. The purpose of our research is to find a suitable refractory material that can be used to coat SENs. This paper reports on the chemical compatibility of a number of potential refractory materials: Al 2 O 3 , ZrO 2 , Al 2 O 3 -carbon, SiO 2 and MgO with liquid steel, an amount of simulated inclusions and synthetic slag. For this purpose, an experimental laboratory procedure was optimised to simulate the nozzle behaviour during continuous casting. Al 2 O 3 was found to give satisfactory results, and therefore a Al 2 O 3 plasma coated Al 2 O 3 -carbon material was also tested in the laboratory with good results.
TL;DR: The viscosities of CaO-FeO-SiO2-CaF2 slags with various amounts of alumina addition were measured using a rotating-cylinder method in the temperature range 1714-1757 K as discussed by the authors.
Abstract: The viscosities of CaO-FeO-SiO2-CaF2 slags with various amounts of alumina addition were measured using a rotating-cylinder method in the temperature range 1714-1757 K. The first part of the experi ...
TL;DR: In this article, an overview of research performed at Oak Ridge National Laboratory on inclusion-formation, weld-solidification, and solid-state transformations in low-alloy steel welds is presented.
Abstract: The paper presents an overview of research performed at Oak Ridge National Laboratory on inclusion-formation, weld-solidification, and solid-state transformations in low-alloy steel welds. The competition between oxide and nitride formation in Fe-C-Al-Mn self-shielded flux-cored arc steel welds was predicted using computational thermodynamics. Nonequilibrium austenite phase selection was monitored in a Fe-C-Al-Mn weld using an in situ time-resolved X-ray diffraction technique. The competition between acicular ferrite and bainite formation from austenite was evaluated in Fe-C-Mn steel welds containing small amounts of titanium.
TL;DR: In this article, the evolution of microstructure and texture in two ferritic stainless steels was investigated in order to identify the existence of grain colonies associated with ridging and their origin.
Abstract: The evolution of microstructure and texture in two ferritic stainless steels was investigated in order to identify the existence of grain colonies associated with ridging and their origin. Special attentions were placed upon examining how the columnar crystals with an initial [001]//ND orientation in continuously-cast slabs can affect the formation of the grain colonies or band structures in the cold-rolled sheet specimens. The rolling and recrystallization textures at each process stage were examined by the orientation distribution function (ODF). Micro-texture measurements using an electron back-scattered diffraction (EBSD) technique were carried out on the ND, RD, and TD section, respectively. The existence of grain colonies having both {001} and {112} orientations at the central region of the sheets was clearly identified. These orientations were caused by both the crystal rotation toward a-fibre texture, which is stable orientation during rolling and the suppressed recrystallization. The relation between the presence of grain colonies and ridging phenomena was discussed.