Showing papers in "Steel Research in 1994"
TL;DR: In this paper, the surface tension of liquid Fe-Al, Fe-Co and Fe-Cr-Ni ternary alloys has been calculated from thermodynamic data in a database constructed by Kaufman.
Abstract: Thermodynamic models based on Butler's equation for surface tension of liquid alloys has been discussed. In alloys, in which activities of components deviate largely from Raoult's law, the calculated surface tensions are found to be affected by the selection of the ratio of the coordination number in the surface phase to that in the bulk phase. Then, the surface tension of liquid Fe-Al, Fe-Co, Fe-Cr, Fe-Mn, Fe-Mo, Fe-Ni, Fe-Si, Fe-Ti and Fe-W binary alloys and liquid Fe-Cr-Ni ternary alloys have been calculated from thermodynamic data in a database constructed by Kaufman. The calculated results reproduce the concentration dependence of the surface tension in those alloys reported so far, but their absolute values are dependent upon the selection of surface tension values for pure elements
110 citations
70 citations
TL;DR: In this paper, two specific examples for the application of adaptive neural nets (ANN) in steel industry are described, and the results of the trained ANN model for a completely new set of input test data compare well with the actual values obtained on the shop floor.
Abstract: Neural nets can be adapted to complex patterns of interrelated input and output variables in a process even if the data sets contain a lot of noise. In this work two specific examples for the application of adaptive neural nets (ANN) in steel industry are described. First, the sulphur content of hot-metal, obtained at the end of calcium carbide powder injection into 400 t torpedo ladles is predicted as a function of hot-metal weight, treatment time, initial sulphur content, gas flow rate and powder injection rate. The values predicted by the trained ANN model for a completely new set of input test data compare well with the actual values obtained on the shop floor. In the second example, the sulphur content of steel, obtained at the end of blow is predicted as a function of liquid-metal weight, total amount of oxy of oxygen injected, amount of iron ore added, and the temperature, contents of carbon, manganese, phosphorus and sulphur determined by in-blow sampling in a 300 t converter
31 citations
TL;DR: In this article, the effect of thermomechanical treatment on the γ-α-transformation in steel has been reviewed and it has been shown that the thermo-mechanically conditioned austenite significantly influences the kinetics of transformation due to the differences in the formation of product phases.
Abstract: The effect of thermomechanical treatment on the γ – α-transformation in steel has been reviewed. It has been shown that the thermo-mechanically conditioned austenite significantly influences the kinetics of transformation due to the differences in the formation of product phases. An enhanced nucleation during the diffusion controlled transformation, as a result of austenite grain refinement and/or austenite strengthening, leads to a substantial refinement of the microstructure (ferrite grains, pearlite nodules). The deformation substructure of austenite may strongly affect the shear mechanism of the diffusionless transformation, which leads to finely fragmented martensite crystals. Such differences in the transformation characteristics result in different formation temperatures of transformation products and so to the changes in CCT diagrams.
29 citations
TL;DR: In this article, a two-dimensional model for the analysis of the temperature and solidification behavior in the substrate and deposit for the spray forming process of metals has been developed, where the influence of process parameters, i.e., thermal conditions of the metal spray at impact, heat transfer coefficient at the surface of the deposit and geometrical parameters, are qualitatively and quantitatively discussed.
Abstract: A mathematical, two-dimensional model for the analysis of the temperature and solidification behaviour in the substrate and deposit for the spray forming process of metals has been developed. Due to the irregular shape of the growing deposit, which changes with spraying time, a grid transformation method was successfully developed for the calculation of the temperature distribution and solidification front in the growing deposit. The influence of process parameters, i.e. thermal conditions of the metal spray at impact, heat transfer coefficient at the surface of the deposit and geometrical parameters, are qualitatively and quantitatively discussed
28 citations
TL;DR: In this article, a mathematical model is developed to predict the thermal behavior of steel strips cooled by an array of round jets, which is one of the best ways to achieve both high cooling efficiency and desirable product qualities.
Abstract: Starting from slabs of known dimensions and chemical composition in a hot strip mill, homogeneous strips of predetermined geometry and mechanical properties may be produced. While the geometry and the surface quality are influenced by the deformation process, mechanical properties depend on the cooling process applied immediately after the last stand. Accelerated cooling of steel strips is one of the best ways to achieve both high cooling efficiency and desirable product qualities. A mathematical model is developed to predict the thermal behaviour of steel strips cooled by an array of round jets
25 citations
TL;DR: In this article, the main mechanism of slag carry-over during drainage of metallurgical vessel is studied in a physical model, where vortex and drain sink formation are found to be the main mechanisms of carryover of slags to the underlying vessel.
Abstract: Mechanism of slag carry-over during drainage of metallurgical vessel is studied in a physical model. Vortex and drain sink formation are found to be the main mechanism of carry-over of slag to the underlying vessel. Empirical equations are obtained to determine vortex and drain sink height under a wide range of draining conditions. Macroscopic mass and energy balance are used to determine vortex time. The vortex time is discussed in relation to the synchronization of the ladle change-over time during sequence casting
22 citations
22 citations
TL;DR: In this article, the distribution of gas fraction and the flow field of gas-stirred liquid metal in steel ladles at eccentric injection of the stirring gas through the bottom of the vessel were measured in melts of 437 kg liquid Wood's metal.
Abstract: The distribution of gas fraction and the flow field of gas-stirred liquid metal in steel ladles at eccentric injection of the stirring gas through the bottom of the vessel were measured in melts of 437 kg liquid Wood's metal. The melts had a temperature of 100° C. The bath height was 37 cm and the vessel diameter 40 cm. The blowing nozzle was positioned at half of the vessel radius. Gas flow rates were between 100 and 800 cm 3 (STP)/s. The gas fractions were measured by electrical resistance probes. The flow velocity of the liquid metal was determined by magnet-probes. The gas fraction and the velocity distribution in the plume were found to have a Gaussian shape. The cross-section of the plume is ellipsoid, as the plume width in the direction of the radius was a little smaller than the width in the direction perpendicular to it
21 citations
TL;DR: In this paper, the development of residual stresses and distortions of SAE 4140 steel cylinders with a diameter of 30 mm and a length of 90 mm was modelled using a special device which allows martensitic transformation under constant external loads.
Abstract: Residual stresses and distortions developing during martensitic hardening of steel can be quantitatively determined by finite element calculations, if the underlying processes are adequately modelled and the materials and process data necessary are known. In this context also transformation plasticity effects have to be taken into account. Model calculations for SAE 4140 steel cylinders demonstrate the influence of these effects on the developing residual stresses. Using a special device which allows martensitic transformation under constant external loads, for SAE 4140 the transformation plasticity constant K = 4.2 . 10 −5 mm 2 /N is determined. With this constant and assuming realistic heat transfer conditions, the development of residual stresses and distortions of SAE 4140 cylinders with a diameter of 30 mm and a length of 90 mm is modelled
19 citations
TL;DR: Genetic adaptive search (GAS) techniques, based on the mechanics of natural genetics, are used in this article to find an optimal model of desulphurization process of iron-melt by powder infection.
Abstract: Genetic adaptive search (GAS) techniques, based on the mechanics of natural genetics, are used in this paper to find an optimal model of desulphurization process of iron-melt by powder infection. Industrial data on 400 t torpedo are used to evaluate contributions of transitory and permanent contact reactions to the overall desulphurization process during calcium carbide powder injection. The results obtained with GAS agree more closely with the plant data than the theoretical model. GAS solutions are also found to be better than regression models. These results suggest immediate application of GAS in similar metallurgical problems.
TL;DR: In this article, the phase transformation of steel is investigated using a continuous annealing simulator and an in-situ thermal analysis method (ISTA), which can be applied to any cooling curve, enabling to draw conclusions as to the transformation behaviour of the steel.
Abstract: In the study of the phase transformation of steel several methods can be used to obtain information about the behaviour of steel during heating and cooling. In this research several conventional methods, e.g. dilatometry, were studied together with an in-situ thermal analysis method (ISTA). This method, which can be applied to any cooling curve, enables us to draw conclusions as to the transformation behaviour of the steel. Using a continuous annealing simulator (Casim) a range of cooling rates can be investigated with the resulting mechanical properties. It will be demonstrated that ISTA can be performed on the results of a variety of experimental techniques and therefore under very different experimental conditions. It is possible to investigate transformation behaviour and mechanical properties on a single test piece
TL;DR: In this paper, the influence of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficients on the development of residual stresses are discussed.
Abstract: In this paper results of systematic FE-calculations about the influence of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficient on the development of residual stresses are discussed. The numerical investigations were carried out for SAE 1045 and 4140 steel cylinders with 10 and 20 mm O quenched in water and oil, respectively. In this work experimentally determined h, T-curves are linearly approximated in the successive stages of heat transfer. Changes of the Leidenfrost-temperature do not influence the middle plane residual stresses of the cylinders investigated
TL;DR: Genetic adaptive search (GAS) method is used to optimize the mathematical model for desulphurization and when the input data are preprocessed with this optimized model and fed into an artificial neural net, the generalization ability of the net becomes even better.
Abstract: Adaptive neural net (ANN) model of hot metal desulphurization is first optimized by various search methods including the golden section search and Davies-Swann-Campey methods. Logarithmic preprocessing of input data leads to a further improvement in generalizaton ability of the net. Genetic adaptive search (GAS) method is used to optimize the mathematical model for desulphurization and when the input data are preprocessed with this optimized model and fed into an artificial neural net, the generalization ability of the net becomes even better. Best results are obtained when using GAS to optimize the interconnection weights during the training phase, while training data are proprocessed through a mathematical model already optimized by GAS.
TL;DR: In this article, modified plug-type sensors and new combined tube plug type sensors with optimized cell design are presented to reduce the flux of ionic oxygen across the solid electrolyte and thereby minimize polarisation effects over extended periods.
Abstract: Oxygen sensors are helpful tools to control and monitor continuous operations in steelmaking processes, e.g. in ladle refining and in the tundish of a continuous casting system. Up to the present no suitable oxygen probes for on-line measurements have been developed. In search of new sensors much work has been done to investigate and discuss possible error sources which impede the use of the conventional one-reading probes for continuous measurements. In the present study modified plug-type sensors and new combined tube plug-type sensors with optimized cell design are presented. Furthermore, new solid oxide electrolytes combined with new reference materials are used to reduce the flux of ionic oxygen across the solid electrolyte and thereby minimize polarisation effects over extended periods
TL;DR: In this paper, an evaluation of the influence of welding on the uniaxial creep rupture behavior of some ferritic, martensitic and austenitic creep resistant materials is presented.
Abstract: An evaluation is presented of the influence of welding on the uniaxial creep rupture behaviour of some ferritic, martensitic and austenitic creep resistant materials. After a description of evaluation the most reliable figures for the effect of welding will be presented in the form of two parameters. One is the strength reduction factor (SRF) for design conditions. The other is the lifetime reduction factor (LRF) for judging the lifetime of welded components at normal design stresses. Two criteria will be introduced to ludge whether the introduction of a stress reduction factor for design of welded components is advisable. The needs for further research in this field are indicated
TL;DR: In this paper, the authors describe measurements of the kinetics of iron oxidation in CO 2 -CO mixtures of various compositions in the temperature range of 1300 to 1450°C.
Abstract: The paper describes measurements of the kinetics of iron oxidation in CO 2 -CO mixtures of various compositions in the temperature range of 1300 to 1450°C. The reaction product is solid wustite below and liquid iron saturated iron-oxygen melt above 1377°C, the incongruent melting temperature of iron saturated wustite. The experiments were carried out by measuring the weight increase during the oxidation of an iron specimen connected to a thermo-balance with a platinum wire. The specimen had the shape of a flat plate, and the oxidising gas flowed past this plate with a defined velocity. Among the experiments the flow velocities were varied. The rate law is linear in the beginning of the single experiment and later becomes parabolic. The linear law was interpreted as caused by two resistances connected in series: the transport of the oxidising gas through the adjacent gas boundary layer, and the phase boundary reaction at the oxide interface
TL;DR: In this prosthesis the weld joint between two sections was found to be weak and hence its capacity to withstand the load bearing forces are not completely balanced and evenly distributed.
Abstract: Failure investigation was carried out on a failed orthopaedic total knee prosthesis removed from a patient. In this prosthesis the weld joint between two sections was found to be weak and hence its capacity to withstand the load bearing forces are not completely balanced and evenly distributed. As a result bending and torsional stresses due to dynamic and cyclic loading had been concentrated on the welded section of the prosthesis. Moreover, the welded construction contained deficiencies such as delta ferrite, heat affected zone and macro cavities. However, the grain size, inclusion content and chemical composition of the prosthesis were within the limits recommended by ASTM standard. Therefore, the failure of the total knee prosthesis was a result of improper welding at the critical site
TL;DR: In this article, a thermodynamic model is presented enabling calculation of the composition of the carbonitride embryo as well as the chemical driving force for nucleation in the austenite region of a multicomponent microalloyed steel.
Abstract: The extent and degree of dispersion of carbonitrides in high strength low alloy (HSLA) steels is controlled by nucleation and growth processes. A thermodynamic model is presented enabling calculation of the composition of the carbonitride embryo as well as the chemical driving force for nucleation (CDF) in the austenite region of a multicomponent microalloyed steel. The analysis made for a Nb-Ti HSLA steel indicates that the critical carbonitride nucleus is richer in N and Ti than the bulk precipitate at equilibrium at a given temperature and the difference increases when the holding temperature decreases. The results also show that the Ti addition has an optimum value defined by the maximum in the ratio of bound Ti and Nb to their total content
TL;DR: In this paper, the authors made an examination as to whether these mechanisms also play a part in the use of CaB 6, and the results confirm the pattern of chemical behaviour in MgO-C materials with boron-containing antioxidants recorded in previous tests.
Abstract: The oxidation-inhibiting action of B 4 C as an antioxidant is to be attributed to two possible mechanisms. The first describes the formation of reactive gases (Mg vapour and B 2 O 2 ) that react with oxygen reducing its partial pressure in pores of the material. The second mechanism results in the formation of a borate layer which includes carbon between the oxide grains and thus protects it from further oxidation. The present study made an examination as to whether these mechanisms also play a part in the use of CaB 6 . The results confirm the pattern of chemical behaviour in MgO-C materials with boron-containing antioxidants recorded in previous tests. However, the temperature at which the protective effect begins lies in this case at about 200 °C lower when compared to B 4 C
TL;DR: In this paper, a set of flat nozzles from a starting temperature of 615 °C were used to check the cooling properties of a steel plate by means of flat lets and provide us with a comparison of the flat and the full cone jets.
Abstract: The paper summarizes results obtained by carrying out a large set of experiments that studied cooling of rolls. The experiments are based on the cooling of a steel plate by a set of flat nozzles from a starting temperature of 615 °C. The temperature histories measured in 39 points of the test plate are the inputs to the evaluation procedure. The sensor distribution covers a surface of a size of 450 × 110 mm. Classical Beck's inverse task was extended for the 3-dimensional area. The inverse task computes the surface distribution of heat transfer coefficient history, heat flux history and surface temperature. The results have pointed out a non-homogeneity in cooling by means of flat lets and provide us with a comparison of the flat and the full cone jets
TL;DR: In this paper, the authors evaluated the behavior of laser-beam weldments under cyclic loading and found that the fatigue properties of the welded joints are considerably better than those of weld seams produced by other methods.
Abstract: The intention of this investigation is to evaluate the behaviour of laser-beam weldments under cyclic loading. The materials tested are several high-strength steel plates with thicknesses of 7-8 mm differing in chemical composition, delivery state and strength level. A number of S-N curves was established not only for the as-welded condition but also for the stress relieved and dressed state. It was found that the fatigue properties of laser-beam welded joints are considerably better than those of weld seams produced by other methods. The increase in fatigue strength amounts to approximately 50%, neither depending on the material used nor on an additional stress-relief annealing. By using the R1MS notch stress model, the good behaviour of the weld seams can be entirely attributed to the favourable weld geometry. (orig.)
TL;DR: The microstructures of three steels with metastable austenite with mass contents of 10-14 % Cr, 10-15 % Mn and 0.1-0.35 % C were optimized by a simulation of the cavitation load as discussed by the authors.
Abstract: The microstructures of three steels with metastable austenite with mass contents of 10-14 % Cr, 10-15 % Mn and 0.1-0.35 % C were optimized by a simulation of the cavitation load. Results of cavitation tests show that the microstructure should be fine grained, to avoid the arise of cracks in the early stages. The materials were pretreated by a thermomechanical treatment. Criteria for a selection were the mechanical properties and the microstructure. According to the results a steel with mass contents of 13 % Cr, 10 % Mn and 0.35 % C (X 35 CrMn 1310) should have the best cavitation resistance. In this steel a deformation of 400 °C produces a dislocation network that forces a transformation of austenite to very fine martensite plates during cavitation and gives a smooth abrasion
TL;DR: An automatic facility for rapid determination of the activities of FeO in metallurgical slags has been developed, by employing an electrochemical technique incorporating stabilized zirconia as solid electrolyte, a mixture of Mo + MoO 2 as reference electrode and an Mo rod as an electrical contact.
Abstract: An automatic facility for rapid determination of the activities of FeO in metallurgical slags has been developed, by employing an electrochemical technique incorporating stabilized zirconia as solid electrolyte, a mixture of Mo + MoO 2 as reference electrode and an Mo rod as an electrical contact. With this equipment, one datum is obtainable within 5 minutes. In the present article, discussions were held on potential applications of this system to steelmaking process control. A particular emphasis is given to the control of FeO levels in slags used for secondary steelmaking and chromium levels in stainless steelmaking slags