F. Vode, J. Burja, F. Tehovnik, B. Arh, Institute of Metals and Technology, Ljubljana, Slovenia A... more F. Vode, J. Burja, F. Tehovnik, B. Arh, Institute of Metals and Technology, Ljubljana, Slovenia A novel method for description of stress-strain relationship for hot deformability of steels is presented. Laplacian transformation of stress-strain data obtained on cylindrical hot compression tests offer simple description of dynamical input/output relationship between strain (input) and stress (output). In this paper, strain/stress relationship is described using transfer function of the third order. Parameters of transfer function are determined by numerical optimization for temperatures 1 000, 1 100 and 1 200 °C and logarithmic strain rates 10, 5 and 1 s-1. Obtained relative model error is around 1 % for logarithmic deformations in the range 0,1 < < 0,8.
F. Tehovnik (e-mail: [email protected]), J. Burja, S. Malej, F. Vode, B. Podgornik, B. Arh, B... more F. Tehovnik (e-mail: [email protected]), J. Burja, S. Malej, F. Vode, B. Podgornik, B. Arh, B. Šetina Batič, Institute of Metals and Technology, Ljubljana, Slovenia Hot compressions tests of Inconel 625 superalloy were conducted using a deformation dilatometer to the strain level of 0,7 at 1 050 °C, with a different strain rate. Optical microscope and electron backscatter diffraction technique were used to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. Microstructural evolution of Inconel 625, deformed to the strain level of 0,7 at 1 050 °C, reveals that the size of the dynamic recrystallization (DRX) grains and the fraction of DRX increase with the decrease in strain rate. At the strain rate 10 s-1, the grain sizes are mainly located in the size below 20 μm, indicating that nucleation of DRX was dominant due to the combined effects of high stored energy and short deformation time for grain growth at high strain rate.
B. Arh, F. Tehovnik, F. Vode, S. Malej, B. Podgornik,, Institute of Metals and Technology, Ljublj... more B. Arh, F. Tehovnik, F. Vode, S. Malej, B. Podgornik,, Institute of Metals and Technology, Ljubljana, Slovenia Austenitic stainless steel solidify under non-equilibrium conditions, and form two-phase microstructure of austenite and δ-ferrite. Workability of steels in hot are better in the primary crystallization of δ-ferrite. The influence of chemical composition on solid-state formation of delta ferrite phase during hot deformation was investigated. The laboratory prepared austenitic stainless SS2343 steel with the Creq/Nieq index – 1,62 were chosen for this research. The transformation of δ-ferrite during annealing in range 1 050 – 1 250 °C was analyzed. Hot bending test was selected for the evaluation of the initial plasticity of “as cast” SS2343 steel. Bending test of as cast steel plates with volume fraction 12,5 % of δ-ferrite have shown, that cracks do not form.
Hot-tensile tests in the temperature range from 800 °C to 1200 °C were carried out on selected au... more Hot-tensile tests in the temperature range from 800 °C to 1200 °C were carried out on selected austenitic stainless steels containing mass fractions 0.6 % to 2.83 % of Mo with the aim being to study the effect of molybdenum on the mechanical properties. The tensile strength of the investigated steels decreased rapidly in the temperature range from 800 °C to 950 °C and slowly at the testing temperatures from 1000 °C to 1200 °C. In addition, the steel with the highest Mo content had a sharper decrease in the tensile strength. The temperature at which the maximum elongation was measured decreased with an increasing Mo content. It was found that molybdenum has a negative influence on the hot-ductility of austenitic stainless steels. In the steel with 2.83 % of Mo, the transformation from -ferrite to -phase started at 1000 °C.
The 2101 lean duplex stainless steel (LDX) was designed mainly for lightweight constructions and ... more The 2101 lean duplex stainless steel (LDX) was designed mainly for lightweight constructions and as a more economical substitute for the dominating stainless-steel grades. Compared with other duplex stainless steels, the corrosion resistance and costs of processing the 2101 duplex stainless steel are usually worse, as the Ni and Mo contents are lower; it is compensated by higher N and Mn contents to stabilize the austenite. At lower test temperatures the precipitation of different phases was observed, so different annealing experiments were conducted to further investigate the occurrence of precipitation. As the composition of lean duplex stainless steel differs from that of conventional duplex stainless steels, a different aging behaviour is expected. The embrittlement of 2101 lean duplex stainless steel occurs at approximately 700°C to 750°C, because of the precipitation of the deleterious Cr2N and M23C6 at the d/g and d/ d interfaces, which begins after a few minutes of aging. These temperatures of the nitride precipitations are crucial to the cracking during the end of hot-working operations, which should stop at higher temperatures. The purpose of the research was to qualitatively analyse the phases in lean duplex stainless steel after thermal aging. Optical microscopy (OM), scanning electron microscopy (SEM) and electron-backscatter diffraction (EBSD) were used to investigate the structural stability and the chemical compositions of the phases.
Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of h... more Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of hot-rolled steel plates were characterized. Based on automated metallographic analyses of representative microstructures, a quality characterization in terms of cleanliness of the hot-rolled steel plates was performed. Elevated contents of impurities, especially Pb, Bi, and oxygen, which affect the hot workability of stainless steels, were detected. The recycled FeTi-cored wire was the main source of the elevated levels of impurities detected in the hot-rolled, Ti-stabilized, stainless-steel plates. Related to this, elevated levels of nonmetallic inclusions (NMIs) and segregations were formed. The three charges were classified based on calculations of the Mahalanobis distance (MD) between the inclusions. The charge with the smallest number of nonmetallic inclusions was set as the reference class. The selection of outlier inclusions based on their MDs and their back-representation into ter...
The main aim of the work was to measure transient response characteristics of interface between p... more The main aim of the work was to measure transient response characteristics of interface between platinum stimulating electrodes and isolated swinish left cervical vagus nerve (segment), when electrical stimulating pulses are applied to preselected locations along the segment and elicited neural signals, also described as compound action potentials (CAPs), are recorded from particular compartments of the nerve. The stimulating system was manufactured as a silicone self-coiling spiral cuff (cuff) with embedded matrix of ninety-nine rectangular electrodes (0.5 mm in width and 2mm in length), made of 45 μm thick annealed platinum ribbon (99.99 % purity), and a geometric surface of 1 mm 2 . For electrical stimulation, a current quasitrapezoidal, asymmetric and biphasic pulses with frequency of 1 Hz, were used. To test an influence of stimulating pulses having different parameters and waveforms on elicited CAPs, various degree of imbalance between an electric charge (charge) injected in c...
This research provides an overview of the structural changes that occur during the hot rolling of... more This research provides an overview of the structural changes that occur during the hot rolling of the nickel superalloy Inconel 625. It is well known that microstructure control is of paramount importance concerning the mechanical properties of a material. The microstructure also plays an important role in processing materials at elevated temperature. In this work the hot-rolling behaviour of the Inconel 625 superalloy has been investigated. The specimens were hot rolled at a temperature of 1200°C using different numbers of passes. During the hot rolling the loads were measured and recorded. A light microscope and an electron microscope, employing the electron-backscatter-diffraction (EBSD) technique, were employed to investigate the microstructure evolution, revealing a necklace dynamic-recrystallization mechanism.
The role of a protective coating is to diminish the steel surface scaling during the reheating fo... more The role of a protective coating is to diminish the steel surface scaling during the reheating for hot rolling. The protective coating consists of several components, and the effect of the coating is based on the formation of the modification of Al2O3, amorphous SiO2 and FeO×Al2O3, which all exhibit low permeability to oxygen at temperature up to 1200 °C. The silica sand powder from the cyclone is a waste product in the separation of silica sand. Tests confirmed that waste cyclone powder could replace the silica flour as one of the ingredients in the protective coating. The results of the efficiency of the protective coating after the advanced application of waste cyclone powder on AISI 1059 and AISI 6150 steels are presented. The application of the coating decreased the oxidation and decarburisation of the steel surface during the reheating for hot rolling.
In forced-convection furnaces for reheating Al-alloys, convective heat transfer mechanism dominat... more In forced-convection furnaces for reheating Al-alloys, convective heat transfer mechanism dominates. Al-body temperature prediction model uses measured furnace temperature as boundary condition. To calibrate such model, a convective heat transfer coefficient h is to be determined. Optimization technique is used here to determine h for every measured temperature sample so that measured temperatures match calculated, supposing radiative heat transfer coefficient constant and neglecting conductive heat transfer. Obtained h stably converges during normal reheating conditions. The obtained model is 4-fold cross-validated and obtained Root Mean Square Error of whole reheating profiles are [7,7; 20,4; 10,4; 12,5] °C.
We present the implementation of an online mathematical model for billet reheating in the OFU wal... more We present the implementation of an online mathematical model for billet reheating in the OFU walking-beam furnace at the [tore Steel d.o.o. steelworks in Slovenia. For the real-time operation of the simulation model the data about furnace charging and real-time measurements in the furnace are needed. The simulation model is connected to the existing information system of the OFU furnace, which can ensure the required data. The simulation is performed for all the billets (up to 125) that are currently charged in the furnace. The modeling of the reheating process in a gas-fired walking-beam furnace consists of descriptions of complex partial mechanisms. For the validation of the model, measurements of the billet reheating in the OFU furnace were made. These measurements involved a test billet and five trailing thermocouples. The comparison of the measurements and the simulation results, which are stored in a local database, shows good agreement across the whole temperature range of t...
This paper presents the implementation of a mathematical model for an Al-coil’s temperature evolu... more This paper presents the implementation of a mathematical model for an Al-coil’s temperature evolution during heat treatment in a forced-circulation furnace. The coil’s spatial-temperature evolution is calculated using the finite-difference method in the axial and radial directions, i.e., 2 dimensional. The model is verified by measuring the coil’s temperature during reheating using 10 pre-installed thermocouples arranged in two lines of 5 thermocouples, each at a different coil radius. The sensitivities of the furnace-air temperature and the initial-coil temperature on the time to switch are determined, i.e., –52.5 s/°C and –55.5 s/°C, respectively. The mathematical model proved to be a multipurpose tool for different simulation-based reheating studies, while its industrial real-time application offers an even wider range of uses and capabilities: automatic coil-temperature control and observing reheating conditions on an industrial level.
For Inconel 625, where the γ” and δ phases precipitate, the influence of prior hot rolling on the... more For Inconel 625, where the γ” and δ phases precipitate, the influence of prior hot rolling on the process is not well covered. The influence of segregation bands and prior hot rolling on the precipitation of secondary phases during aging at 750 °C for different times was investigated. Prior hot-rolling was conducted on a hot rolling mill at 1050 °C and 1150 °C with three different deformation levels. The hot rolled samples were aged at 750 °C for 1, 5, 25 and 125 h. The γ″ precipitated in both the deformed and recrystallized grains in the segregation bands containing a high concentration of niobium and molybdenum and a lower concentration of nickel, chromium and iron. The opposite was observed between the segregation bands where no γ″ precipitate was found. There was a smooth transition in the density and the size of the γ″ particles in the deformed grains at the border of the segregation bands, while a more complex transition occurred in the recrystallized grains. This occurred in ...
The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the... more The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the volume fraction of δ-ferrite in the as-cast state and its transformation after subsequent annealing were investigated. Monitoring of morphological transformations of δ-ferrite in the microstructure show the progress of δ-ferrite dissolution. Annealing tests were conducted at 1050 °C, 1150 °C and 1250 °C with soaking times of 5 and 40 min. The thermodynamic prediction and metallographic identification of δ-ferrite are presented. The ferrite fractions were measured using a magnetic method and determined to be in the range between 10.7% and 14.6%. The volume share of δ-ferrite decreased with an increase in temperature and the time of annealing. About 50–55% the δ-ferrite was effectively transformed. The δ-ferrite phase, originally present in a dendritic morphology, tends to break up and spheroidize. The morphology varies from vermicular, lacy and acicular shapes to globular for higher temp...
The production of hot-rolling strips of known dimensions requires planning of the slab dimensions... more The production of hot-rolling strips of known dimensions requires planning of the slab dimensions and the dimension-change traction of slabs along the production line. A combination of an edger-roll gap measurement and the deformational energy consumed to achieve the desired slab width on the edger enable a rough estimation of the slab widths during rolling. The paper is focused on an automatic calculation of the deformational energy consumed for slab-width rolling on the basis of existing edger measurements. For the calculation of the deformational energy consumed for slab-width rolling a mathematical model of an unloaded edger was built. The edger roller was treated as a stiff, rotary-driven body. The model calculates the consumed power for the velocity changes of the unloaded edger using the velocity input signal. The constructed model has enabled an estimation of the power consumed for the slab-width rolling only. The integration of the power over every pass through the edger yi...
V okviru elaborata narejeni so temperaturni profili segrevanja odkovkov klescnica Shark v peci Br... more V okviru elaborata narejeni so temperaturni profili segrevanja odkovkov klescnica Shark v peci Brettman ki omoguca kaljenje v zascitni atmosferi endoplina. Narejene su premerjave in analiza peci, mikrostrukture in mehanskih lasnosti klescnica Shark z klescima Knipex
In this paper the implementation of an online mathematical model of slab reheating in a pusher-ty... more In this paper the implementation of an online mathematical model of slab reheating in a pusher-type furnace at the Acroni, d. o. o., steelworks in Slovenia is presented. The simulation model is connected to the existing information system of a hot-rolling plant that can ensure the required data for the simulation model online. The simulation is performed for all the slabs that are currently charged in the furnace. In order to validate the model, measurements of the slab reheating in the pusher-type furnace were made. The measurements were performed on a test slab using trail thermocouples. The comparison of the measurements and the simulation results shows good agreement across the whole temperature range of the reheating process. For a user-friendly presentation of the simulation model results a graphical user interface (GUI) was developed. The GUI allows the selection of a particular slab from the figure of currently charged slabs. The temperature field and the history of the rehe...
The role of a protective coating is to diminish the steel surface scaling during the reheating fo... more The role of a protective coating is to diminish the steel surface scaling during the reheating for hot rolling. The protective coating consists of several components, and the effect of the coating is based on the formation of the modification of Al2O3, amorphous SiO2 and FeO×Al2O3, which all exhibit low permeability to oxygen at temperature up to 1200 °C. The silica sand powder from the cyclone is a waste product in the separation of silica sand. Tests confirmed that waste cyclone powder could replace the silica flour as one of the ingredients in the protective coating. The results of the efficiency of the protective coating after the advanced application of waste cyclone powder on AISI 1059 and AISI 6150 steels are presented. The application of the coating decreased the oxidation and decarburisation of the steel surface during the reheating for hot rolling.
Mathematical descriptions of true stress/true strain curves, experimentally obtained on cylindric... more Mathematical descriptions of true stress/true strain curves, experimentally obtained on cylindrical specimens under hot compressive conditions, are of great importance and are widely investigated. An additional black-box modelling approach using transfer functions (TF) is tested. For tested 51CrV4 steel, a TF of third order is employed for description of true stress (output) depending on the strain rate (input). Sets of TF coefficients are determined using numerical optimization techniques for each testing temperature and strain rate. To avoid scattering of TF parameters, time in Laplacian transformation is replaced with strain, while TF input is the strain rate. Obtained models cover deformations starting practically from zero to 0.7. Average absolute relative error for models based on TF of the third order and of the second order are 0.93% and 3.64%.
F. Vode, J. Burja, F. Tehovnik, B. Arh, Institute of Metals and Technology, Ljubljana, Slovenia A... more F. Vode, J. Burja, F. Tehovnik, B. Arh, Institute of Metals and Technology, Ljubljana, Slovenia A novel method for description of stress-strain relationship for hot deformability of steels is presented. Laplacian transformation of stress-strain data obtained on cylindrical hot compression tests offer simple description of dynamical input/output relationship between strain (input) and stress (output). In this paper, strain/stress relationship is described using transfer function of the third order. Parameters of transfer function are determined by numerical optimization for temperatures 1 000, 1 100 and 1 200 °C and logarithmic strain rates 10, 5 and 1 s-1. Obtained relative model error is around 1 % for logarithmic deformations in the range 0,1 < < 0,8.
F. Tehovnik (e-mail: [email protected]), J. Burja, S. Malej, F. Vode, B. Podgornik, B. Arh, B... more F. Tehovnik (e-mail: [email protected]), J. Burja, S. Malej, F. Vode, B. Podgornik, B. Arh, B. Šetina Batič, Institute of Metals and Technology, Ljubljana, Slovenia Hot compressions tests of Inconel 625 superalloy were conducted using a deformation dilatometer to the strain level of 0,7 at 1 050 °C, with a different strain rate. Optical microscope and electron backscatter diffraction technique were used to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. Microstructural evolution of Inconel 625, deformed to the strain level of 0,7 at 1 050 °C, reveals that the size of the dynamic recrystallization (DRX) grains and the fraction of DRX increase with the decrease in strain rate. At the strain rate 10 s-1, the grain sizes are mainly located in the size below 20 μm, indicating that nucleation of DRX was dominant due to the combined effects of high stored energy and short deformation time for grain growth at high strain rate.
B. Arh, F. Tehovnik, F. Vode, S. Malej, B. Podgornik,, Institute of Metals and Technology, Ljublj... more B. Arh, F. Tehovnik, F. Vode, S. Malej, B. Podgornik,, Institute of Metals and Technology, Ljubljana, Slovenia Austenitic stainless steel solidify under non-equilibrium conditions, and form two-phase microstructure of austenite and δ-ferrite. Workability of steels in hot are better in the primary crystallization of δ-ferrite. The influence of chemical composition on solid-state formation of delta ferrite phase during hot deformation was investigated. The laboratory prepared austenitic stainless SS2343 steel with the Creq/Nieq index – 1,62 were chosen for this research. The transformation of δ-ferrite during annealing in range 1 050 – 1 250 °C was analyzed. Hot bending test was selected for the evaluation of the initial plasticity of “as cast” SS2343 steel. Bending test of as cast steel plates with volume fraction 12,5 % of δ-ferrite have shown, that cracks do not form.
Hot-tensile tests in the temperature range from 800 °C to 1200 °C were carried out on selected au... more Hot-tensile tests in the temperature range from 800 °C to 1200 °C were carried out on selected austenitic stainless steels containing mass fractions 0.6 % to 2.83 % of Mo with the aim being to study the effect of molybdenum on the mechanical properties. The tensile strength of the investigated steels decreased rapidly in the temperature range from 800 °C to 950 °C and slowly at the testing temperatures from 1000 °C to 1200 °C. In addition, the steel with the highest Mo content had a sharper decrease in the tensile strength. The temperature at which the maximum elongation was measured decreased with an increasing Mo content. It was found that molybdenum has a negative influence on the hot-ductility of austenitic stainless steels. In the steel with 2.83 % of Mo, the transformation from -ferrite to -phase started at 1000 °C.
The 2101 lean duplex stainless steel (LDX) was designed mainly for lightweight constructions and ... more The 2101 lean duplex stainless steel (LDX) was designed mainly for lightweight constructions and as a more economical substitute for the dominating stainless-steel grades. Compared with other duplex stainless steels, the corrosion resistance and costs of processing the 2101 duplex stainless steel are usually worse, as the Ni and Mo contents are lower; it is compensated by higher N and Mn contents to stabilize the austenite. At lower test temperatures the precipitation of different phases was observed, so different annealing experiments were conducted to further investigate the occurrence of precipitation. As the composition of lean duplex stainless steel differs from that of conventional duplex stainless steels, a different aging behaviour is expected. The embrittlement of 2101 lean duplex stainless steel occurs at approximately 700°C to 750°C, because of the precipitation of the deleterious Cr2N and M23C6 at the d/g and d/ d interfaces, which begins after a few minutes of aging. These temperatures of the nitride precipitations are crucial to the cracking during the end of hot-working operations, which should stop at higher temperatures. The purpose of the research was to qualitatively analyse the phases in lean duplex stainless steel after thermal aging. Optical microscopy (OM), scanning electron microscopy (SEM) and electron-backscatter diffraction (EBSD) were used to investigate the structural stability and the chemical compositions of the phases.
Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of h... more Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of hot-rolled steel plates were characterized. Based on automated metallographic analyses of representative microstructures, a quality characterization in terms of cleanliness of the hot-rolled steel plates was performed. Elevated contents of impurities, especially Pb, Bi, and oxygen, which affect the hot workability of stainless steels, were detected. The recycled FeTi-cored wire was the main source of the elevated levels of impurities detected in the hot-rolled, Ti-stabilized, stainless-steel plates. Related to this, elevated levels of nonmetallic inclusions (NMIs) and segregations were formed. The three charges were classified based on calculations of the Mahalanobis distance (MD) between the inclusions. The charge with the smallest number of nonmetallic inclusions was set as the reference class. The selection of outlier inclusions based on their MDs and their back-representation into ter...
The main aim of the work was to measure transient response characteristics of interface between p... more The main aim of the work was to measure transient response characteristics of interface between platinum stimulating electrodes and isolated swinish left cervical vagus nerve (segment), when electrical stimulating pulses are applied to preselected locations along the segment and elicited neural signals, also described as compound action potentials (CAPs), are recorded from particular compartments of the nerve. The stimulating system was manufactured as a silicone self-coiling spiral cuff (cuff) with embedded matrix of ninety-nine rectangular electrodes (0.5 mm in width and 2mm in length), made of 45 μm thick annealed platinum ribbon (99.99 % purity), and a geometric surface of 1 mm 2 . For electrical stimulation, a current quasitrapezoidal, asymmetric and biphasic pulses with frequency of 1 Hz, were used. To test an influence of stimulating pulses having different parameters and waveforms on elicited CAPs, various degree of imbalance between an electric charge (charge) injected in c...
This research provides an overview of the structural changes that occur during the hot rolling of... more This research provides an overview of the structural changes that occur during the hot rolling of the nickel superalloy Inconel 625. It is well known that microstructure control is of paramount importance concerning the mechanical properties of a material. The microstructure also plays an important role in processing materials at elevated temperature. In this work the hot-rolling behaviour of the Inconel 625 superalloy has been investigated. The specimens were hot rolled at a temperature of 1200°C using different numbers of passes. During the hot rolling the loads were measured and recorded. A light microscope and an electron microscope, employing the electron-backscatter-diffraction (EBSD) technique, were employed to investigate the microstructure evolution, revealing a necklace dynamic-recrystallization mechanism.
The role of a protective coating is to diminish the steel surface scaling during the reheating fo... more The role of a protective coating is to diminish the steel surface scaling during the reheating for hot rolling. The protective coating consists of several components, and the effect of the coating is based on the formation of the modification of Al2O3, amorphous SiO2 and FeO×Al2O3, which all exhibit low permeability to oxygen at temperature up to 1200 °C. The silica sand powder from the cyclone is a waste product in the separation of silica sand. Tests confirmed that waste cyclone powder could replace the silica flour as one of the ingredients in the protective coating. The results of the efficiency of the protective coating after the advanced application of waste cyclone powder on AISI 1059 and AISI 6150 steels are presented. The application of the coating decreased the oxidation and decarburisation of the steel surface during the reheating for hot rolling.
In forced-convection furnaces for reheating Al-alloys, convective heat transfer mechanism dominat... more In forced-convection furnaces for reheating Al-alloys, convective heat transfer mechanism dominates. Al-body temperature prediction model uses measured furnace temperature as boundary condition. To calibrate such model, a convective heat transfer coefficient h is to be determined. Optimization technique is used here to determine h for every measured temperature sample so that measured temperatures match calculated, supposing radiative heat transfer coefficient constant and neglecting conductive heat transfer. Obtained h stably converges during normal reheating conditions. The obtained model is 4-fold cross-validated and obtained Root Mean Square Error of whole reheating profiles are [7,7; 20,4; 10,4; 12,5] °C.
We present the implementation of an online mathematical model for billet reheating in the OFU wal... more We present the implementation of an online mathematical model for billet reheating in the OFU walking-beam furnace at the [tore Steel d.o.o. steelworks in Slovenia. For the real-time operation of the simulation model the data about furnace charging and real-time measurements in the furnace are needed. The simulation model is connected to the existing information system of the OFU furnace, which can ensure the required data. The simulation is performed for all the billets (up to 125) that are currently charged in the furnace. The modeling of the reheating process in a gas-fired walking-beam furnace consists of descriptions of complex partial mechanisms. For the validation of the model, measurements of the billet reheating in the OFU furnace were made. These measurements involved a test billet and five trailing thermocouples. The comparison of the measurements and the simulation results, which are stored in a local database, shows good agreement across the whole temperature range of t...
This paper presents the implementation of a mathematical model for an Al-coil’s temperature evolu... more This paper presents the implementation of a mathematical model for an Al-coil’s temperature evolution during heat treatment in a forced-circulation furnace. The coil’s spatial-temperature evolution is calculated using the finite-difference method in the axial and radial directions, i.e., 2 dimensional. The model is verified by measuring the coil’s temperature during reheating using 10 pre-installed thermocouples arranged in two lines of 5 thermocouples, each at a different coil radius. The sensitivities of the furnace-air temperature and the initial-coil temperature on the time to switch are determined, i.e., –52.5 s/°C and –55.5 s/°C, respectively. The mathematical model proved to be a multipurpose tool for different simulation-based reheating studies, while its industrial real-time application offers an even wider range of uses and capabilities: automatic coil-temperature control and observing reheating conditions on an industrial level.
For Inconel 625, where the γ” and δ phases precipitate, the influence of prior hot rolling on the... more For Inconel 625, where the γ” and δ phases precipitate, the influence of prior hot rolling on the process is not well covered. The influence of segregation bands and prior hot rolling on the precipitation of secondary phases during aging at 750 °C for different times was investigated. Prior hot-rolling was conducted on a hot rolling mill at 1050 °C and 1150 °C with three different deformation levels. The hot rolled samples were aged at 750 °C for 1, 5, 25 and 125 h. The γ″ precipitated in both the deformed and recrystallized grains in the segregation bands containing a high concentration of niobium and molybdenum and a lower concentration of nickel, chromium and iron. The opposite was observed between the segregation bands where no γ″ precipitate was found. There was a smooth transition in the density and the size of the γ″ particles in the deformed grains at the border of the segregation bands, while a more complex transition occurred in the recrystallized grains. This occurred in ...
The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the... more The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the volume fraction of δ-ferrite in the as-cast state and its transformation after subsequent annealing were investigated. Monitoring of morphological transformations of δ-ferrite in the microstructure show the progress of δ-ferrite dissolution. Annealing tests were conducted at 1050 °C, 1150 °C and 1250 °C with soaking times of 5 and 40 min. The thermodynamic prediction and metallographic identification of δ-ferrite are presented. The ferrite fractions were measured using a magnetic method and determined to be in the range between 10.7% and 14.6%. The volume share of δ-ferrite decreased with an increase in temperature and the time of annealing. About 50–55% the δ-ferrite was effectively transformed. The δ-ferrite phase, originally present in a dendritic morphology, tends to break up and spheroidize. The morphology varies from vermicular, lacy and acicular shapes to globular for higher temp...
The production of hot-rolling strips of known dimensions requires planning of the slab dimensions... more The production of hot-rolling strips of known dimensions requires planning of the slab dimensions and the dimension-change traction of slabs along the production line. A combination of an edger-roll gap measurement and the deformational energy consumed to achieve the desired slab width on the edger enable a rough estimation of the slab widths during rolling. The paper is focused on an automatic calculation of the deformational energy consumed for slab-width rolling on the basis of existing edger measurements. For the calculation of the deformational energy consumed for slab-width rolling a mathematical model of an unloaded edger was built. The edger roller was treated as a stiff, rotary-driven body. The model calculates the consumed power for the velocity changes of the unloaded edger using the velocity input signal. The constructed model has enabled an estimation of the power consumed for the slab-width rolling only. The integration of the power over every pass through the edger yi...
V okviru elaborata narejeni so temperaturni profili segrevanja odkovkov klescnica Shark v peci Br... more V okviru elaborata narejeni so temperaturni profili segrevanja odkovkov klescnica Shark v peci Brettman ki omoguca kaljenje v zascitni atmosferi endoplina. Narejene su premerjave in analiza peci, mikrostrukture in mehanskih lasnosti klescnica Shark z klescima Knipex
In this paper the implementation of an online mathematical model of slab reheating in a pusher-ty... more In this paper the implementation of an online mathematical model of slab reheating in a pusher-type furnace at the Acroni, d. o. o., steelworks in Slovenia is presented. The simulation model is connected to the existing information system of a hot-rolling plant that can ensure the required data for the simulation model online. The simulation is performed for all the slabs that are currently charged in the furnace. In order to validate the model, measurements of the slab reheating in the pusher-type furnace were made. The measurements were performed on a test slab using trail thermocouples. The comparison of the measurements and the simulation results shows good agreement across the whole temperature range of the reheating process. For a user-friendly presentation of the simulation model results a graphical user interface (GUI) was developed. The GUI allows the selection of a particular slab from the figure of currently charged slabs. The temperature field and the history of the rehe...
The role of a protective coating is to diminish the steel surface scaling during the reheating fo... more The role of a protective coating is to diminish the steel surface scaling during the reheating for hot rolling. The protective coating consists of several components, and the effect of the coating is based on the formation of the modification of Al2O3, amorphous SiO2 and FeO×Al2O3, which all exhibit low permeability to oxygen at temperature up to 1200 °C. The silica sand powder from the cyclone is a waste product in the separation of silica sand. Tests confirmed that waste cyclone powder could replace the silica flour as one of the ingredients in the protective coating. The results of the efficiency of the protective coating after the advanced application of waste cyclone powder on AISI 1059 and AISI 6150 steels are presented. The application of the coating decreased the oxidation and decarburisation of the steel surface during the reheating for hot rolling.
Mathematical descriptions of true stress/true strain curves, experimentally obtained on cylindric... more Mathematical descriptions of true stress/true strain curves, experimentally obtained on cylindrical specimens under hot compressive conditions, are of great importance and are widely investigated. An additional black-box modelling approach using transfer functions (TF) is tested. For tested 51CrV4 steel, a TF of third order is employed for description of true stress (output) depending on the strain rate (input). Sets of TF coefficients are determined using numerical optimization techniques for each testing temperature and strain rate. To avoid scattering of TF parameters, time in Laplacian transformation is replaced with strain, while TF input is the strain rate. Obtained models cover deformations starting practically from zero to 0.7. Average absolute relative error for models based on TF of the third order and of the second order are 0.93% and 3.64%.
Uploads
Papers by Franci Vode