Validation of Tornio AP3 model based furnace control and grain size calculation

Abstract. Automation for annealing and pickling -line 3 was renewed in 2016, but the model-based control wasn’t good enough that production could rely on it, so doing modifications to the model was necessary. The goal was to get the model working so that automation could control furnaces mostly without input from line operators. Phenomena concerning grain size calculation in the automation system was studied theoretically to acquire sufficient information. The solving of problem was done by inspecting source code for programming errors, examining calculation log files and tables used by automation and finally measuring accuracy of the calculation both statistically and comparing calculated results with measured grain size from production trials. The accuracy was improved by modifying both grain size calculation and set-point calculation. Many changes were suggested for general parameters, grain specific grain growth parameters and source code. After these changes maximum grain size calculation error improved to 0,45 ASTM, but because of poor control of zone temperatures high accuracy in annealing can’t be done. The fixing of automations system is started, and it continues even when this thesis project is finished.Tiivistelmä. Hehkutus- ja peittauslinja 3:n automaatio uusittiin vuonna 2016, mutta uunien mallipohjainen ohjaus ei ollut riittävän hyvällä tasolla, jotta tuotannossa voitaisiin luottaa siihen. Tämän vuoksi mallin validointi oli tarpeellista. Tavoitteena oli saada malli toimimaan siten, että uuneja voitaisiin ohjata pääasiassa pelkästään automaatiolla ilman operaattoreiden panosta. Raekokolaskennan taustalla olevia ilmiöitä ja automaatiota tarkasteltiin kirjallisuuden pohjalta tietopohjan luomiseksi. Ongelmaa lähestyttiin tarkastelemalla lähdekoodia ohjelmointivirheiden osalta, seuraamalla laskennan lokitietoja, tarkastelemalla automaation käyttämiä taulukoita, hyödyntämällä tilastollista tietoa, sekä vertaamalla laskennan tuloksia tuotantokokeiden tuottamaan raekokoon. Laskennan tarkkuutta on mahdollista parantaa modifioimalla sekä raekoko-, että vyöhykkeiden asetusarvojen laskentaa. Laskentaan ehdotettiin useita parannuksia yleisiin parametreihin, laatukohtaisiin rakeenkasvuparametreihin ja lähdekoodiin. Näiden parannusten perusteella laskennan suurin virhe on 0,45 ASTM yksikköä. Tuotantolinjan heikon vyöhykelämpötilan hallinnan takia näidenkään muutosten jälkeen tarkkuutta vaativia hehkutuksia ei voida suorittaa. Automaation korjaus on aloitettu, mutta sitä ei ehditty viemään loppuun tämän projektin puitteissa

Heat balance analysis of annealing and galvanneal furnace in continuous galvanizing lines

Galvanizing facilities are highly energy intensive operation with electrical and fuel energy representing a significant share of their total energy usage. Furnaces are extensively used in galvanizing process. Production process expertise along with the energy conservation practices can play a significant role in proper usage of energy at galvanizing facilities. Therefore, benchmarking galvanizing energy consumption and understanding the specific energy consumption by various elements are critical. E-GEPDSS (Enhanced Galvanizing Energy Profiler Decision Support System) was built to identify this specific energy consumption by using heat balance analysis. The use of E-GEPDSS does not hinder the production process and the user may run the model for different set of operating conditions and observe the results. The results obtained from the analysis will help the user to make energy enhancing decisions.;This research involved the analysis of galvanizing operations focusing on the furnace side of energy consumption. The furnace heat balance was built and applied using the data collected from a host company during the plant visit. Sensitivity analysis were done to study the impact of changing process and product parameters on the total heat loss from the system.;From the energy analysis conducted for the furnace equipment at the host facility, it was found that the useful heat absorbed by the product is only 50% of the heat supplied to the furnace and rest of heat dissipates as losses. Heat losses from surfaces, walls, water cooling and stack are significant. Heat loss due to opening and phase change heat loss seem not to be significant. Emissivity, dimensions of the furnace, temperature of the zones, thermal conductivity of insulation materials and the strip temperature at the entry and exit of each zone have significant impact on the total heat loss. In the future, the model will be applied extensively to more galvanizing lines in order to help the galvanizers to have a better understanding about the energy consumption while producing their product

CFD Modeling and Validation of Blast Furnace Gas/Natural Gas Mixture Combustion in an Experimental Industrial Furnace

The use of residual gases from steel production processes as fuel for steel treatment furnaces has attracted great interest as a method for reducing fossil fuel consumption and the steel footprint. However, these gases often have a low calorific value, and a direct substitution can lead to low temperatures or combustion instability issues. CFD simulations of the combustion of these gases can help steel producers forecast the results of the substitution before real testing and implementation. In this study, a CFD model of an industrial experimental furnace in the steel sector is developed and validated. The results are calculated using the combustion, radiation, and heat transfer models included in the software Ansys Fluent. The validation of the simulated results is performed with data acquired from experimental tests under the same simulated conditions at three air-to-fuel equivalence ratios, which vary from an excess of 0% to an excess of 5% oxygen at the outlet. The model is adjusted to the results, capturing the trends of the measured physical variables and pollutant concentrations. In the case of the combustion temperature, the differences between the simulated and measured values vary from 0.03% to 6.9. Based on the simulation results, the use of blast furnace gas as fuel produces temperatures inside the chamber between 1004 °C and 1075 °C and high stream velocities because of the high flow needed to keep the power constant. Flames exhibit straight movements since the high flows absorb the effect of the swirling flames. The addition of natural gases increases the combustion temperature up to 1211 °C and reduces the flow and length of the flames. Finally, temperatures up to 1298 °C and shorter flames are reached with natural gas enriched with a stream of oxygen, but in this case, NOx emissions need to be controlled

Heat Transfer, Hardenability and Steel Phase Transformations during Gas Quenching

Quenching is the rapid cooling process from an elevated temperature. Compared to water and oil quench medium, high pressure and velocity gas is preferred to quench medium and high hardenability steel, with the potential to reduce distortion, stress and cracks. Currently, no standard test exists to characterize the gas quench steel hardenability and measure the performance of industrial gas quench furnaces. In this thesis, the fundamental difference between the liquid and gas quenching, heat transfer coefficient, was emphasized. It has been proven that gas quenching with constant HTC cannot generate the similar cooling curves compared to liquid quenching. Limitations on current gas quench steel hardenability tests were reviewed. Critical HTC, a concept like critical diameter, was successfully proved to describe the gas quench hardenability of steel. An attempt to use critical HTC test bar and measure the HTC distribution of gas quench furnace was made. Gas quenching, usually with slow cooling rate, may reduce hardness and Charpy impact toughness, compared to water and oil quenching. Lattice parameter and c/a ratio of as-quenched martensite in steel was measured using high resolution X-ray diffraction and Rietveld refinement. For AISI 4140, Charpy impact toughness decreases when the cooling rate decreases after quenching and tempering. Austenite percentage and carbon content in austenite is proposed as the dominated mechanism

Fundamentals of materials modelling for hot stamping of UHSS panels with graded properties

The aim of this study is to develop the fundamentals of materials modelling to enable effective process control of hot stamping for forming UHSS panels with graded properties for optimised functional performance. A selective heating and press hardening strategy is adopted to grade the microstructural distribution of a press hardened component through differential heat treatment of the blank prior to forming. Comprehensive material models, to enable prediction of austenite formation and deformation behaviours of boron steel under hot forming conditions, as well as the dynamic response of a press hardened part with tailored properties in collision situations, have been developed based on experimental investigations and mechanism studies. The research work is concerned with four aspects: feasibility of the selective heating and press hardening strategy, austenite formation in boron steel during selective heating, thermo-mechanical properties of boron steel under hot stamping, and mechanical properties of boron steel with various microstructures at room temperature. Feasibility studies for the selective heating and press hardening strategy were carried out through a designed experimental programme. A lab-scale demonstrator part was designed and relevant manufacturing and property-assessment processes were defined. A heating technique and selective-heating rigs were designed to enable certain microstructural distributions in blanks to be obtained. A hot stamping tool set was designed for forming and quenching the parts. Test pieces were formed under various heating conditions to obtain demonstrator parts having variously graded microstructures. Microstructural distributions in the as-formed parts were determined through hardness testing and microstructural observation. Ultimately, the structural performance of the parts was evaluated through bending tests. Heat treatment tests were performed to study the formation of austenite in boron steel during selective heating. Characterisation of the effects of heating rate and temperature on transformation behavior was conducted based on the test results. A unified austenite formation model, capable of predicting full or partial austenite formation under both isothermal and non-isothermal conditions, was developed, and determined from the heat treatment test results. Hot tensile tests were performed to study the thermo-mechanical properties of the austenite and initial phase (ferrite and pearlite) of boron steel. The viscoplastic deformation behaviours of the both phase states were analysed in terms of strain rate and temperature dependence based on the test results. A viscoplastic-damage constitutive model, capable of describing the thermo-mechanical response of boron steel in a state corresponding to hot stamping after selective heating, was proposed. Values of constants in the model for both the austenite and initial phase were calibrated from the hot tensile test results. Dynamic and quasi-static tensile testes combined with hardness testing and microstructural observation were carried out to study the mechanical properties of press hardened boron steel with various microstructures at room temperature. Based on the results, the strain rate sensitivity of the martensite and initial phase of boron steel was characterised; the relationships between mechanical properties (true ultimate tensile strength, 0.2% proof stress, elongation, and hardness) and phase composition (volume fraction of martensite), for boron steel with various microstructures, were rationalised. Finally, a viscoplastic-damage constitutive model, capable of predicting the mechanical response of a press hardened boron steel part with graded properties being subjected to crash situations in automobiles, were developed, and determined from the test results.Open Acces

Examination of the factors affecting quality on continuous annealing processing lines.

The Continuous Annealing Processing Line (CAPL) of the Corus Strip Products UK integrated works in South Wales, United Kingdom, is one of the most modern lines of its type in the world. It produces thin and wide carbon strip steels of the highest quality in terms of metallurgical consistency, surface quality and dimensional tolerances. Tensioned strip can travel at a velocity of up to 600m/min at temperatures in excess of 750°C. The yield point of the strip is naturally reduced at these annealing temperatures; therefore the contact interaction that develops between the transport roll and the strip steel it is transporting is critical. The primary focus of research is on maintaining the elasticity of the strip steel as it passes through the furnace section of the continuous annealing processing line. In particular focusing on the heating and adjacent soaking sections of the CAPL, where the temperatures are at their highest. The thesis is concerned with the roll-strip interaction and its many different parameters - roll geometry, strip dimensions, strip tension and strip temperature. Research concentrated on the initial contact plane, where the strip first comes into contact with the transport roll. Results indicate that the strip's elastic stress- state is most affected by the fillet that circumnavigates the transport roll, especially where the fillet intersects the initial contact plane. The parameters chosen took into consideration the future operational commitments of the CAPL, because continual demand is always increasing the threshold. To perform the task assigned the author made use of extensive computational finite element method models. A second aspect of the research was to consider acceptable temperature differentials between the transport roll and the strip steel at initial contact. The strip has a low yield stress at its annealing temperature, thus an excessively high temperature differential will create a buckle risk. Therefore, an experimental programme was developed in conjunction with industrial partners Stein Heurtey to investigate acceptable temperature differentials for initial contact conditions

Study of Abnormal Grain Growth in Beta Annealed Ti-6al-4v Forgings

Beta annealed Ti-6Al-4V has been used extensively in current aerospace platforms due to properties such as high strength to weight ratio. Recent inspections during aircraft production have revealed regions of excessive grain sizes, resulting in quarantined parts and excessive time spent on root cause analysis and risk mitigation efforts. Uncertainty surrounding these parts has led to increased costs and may cause future aircraft production delays. Part manufacturers have intermittently reported problems with abnormal grain growth in these alloys for years, but to date no supplier has been able to determine the source of this microstructural phenomenon. Leveraging common Finite Element Method (FEM) software, sidepressing and upsetting forging processes are simulated to predict internal strain and temperature results for use in identifying regions of localizations effecting grain development. Results were used to guide forging tests in an attempt to reproduce abnormal grain growth in the material. Microscopy and image analysis were used to quantify effects of forging parameters on successful development of coarse grains in sidepressing and upsetting forgings. This work seeks to directly support Air Force Research Laboratory (AFRL)’s Materials and Manufacturing Directorate in determining cause of this ongoing issue

Developing a Thermometallurgical Model and Furnace Optimization for Austenitization of Al-Si Coated 22MnB5 Steel in a Roller Hearth Furnace

Lightweighting of vehicles while preserving crash-worthiness, in order to satisfy stringent restrictions imposed by the government on the automotive industry, has become a sought after solution which can be realized via hot-forming die quenching (HFDQ). HFDQ is a process where boron-manganese steel blanks, a grade of ultra-high strength steels with a thin eutectic Al-Si coating, are heated beyond TAc3 to achieve a fully austenitic microstructure, a precursor for martensite. Heat treatment is performed using 30 to 40 meter long roller hearth furnaces, comprised of multiple heating zones, with two key objectives: (1) ensure complete austenitization of blanks and (2) transformation of the Al-Si coating into a protective Al-Si-Fe intermetallic coating. Blank heating rates are controlled by the roller speed and zone set-point temperatures, which are currently set by trial-and-error procedures. Therefore, a thorough understanding of the furnace parameters and the industrial objectives are essential. Patched blanks, with spatially varying thickness, leads to inhomogenous heating, making this relationship elusive. Previous furnace-based energy models only focused on simulating the sensible energy of the load with no explicit information about the latent energy associated with austenitization. Consequentially, the latent term had been incorporated into the sensible energy term thereby defining an effective specific heat. In order to realize how blank heating rate influences microstructural and Al-Si layer evolution, a model coupling heating and austenite kinetics is necessary. This integrated model serves as means for optimizing the heating process. In this work a thermometallurgical model is developed, combining a heat transfer submodel with two austenite kinetic submodels, an empirical first-order kinetics model and a constitutive kinetics model, via the latent heat of austenitization. The models simultaneously predict the heating and austenitization curves, for unpatched/patched blanks heated within a roller hearth furnace. Validation studies showed that the first-order kinetics model reliably estimated heating and transformation kinetics compared to the constitutive model. The validated models are then used to optimize the zone set-point temperatures, roller speed, and cycle length for a 12-zone roller hearth furnace whilst minimizing the cycle time in a deterministic setting. A gradient-based interior point method and hybrid scheme were used to assess the constrained multivariate minimization problem with two alternative austenitization constraints imposed: a soak-time based and explicitly modeled requirement. In both cases, the most savings in cycle time were achieved using the explicitly modeled phase fraction austenite constraint, with reductions of approximately 2 to 3 times from the nominal settings