<p>Recrystallisation annealing, a repeated heat treatment between different stages of cold rolling of martensitic chromium steel strip, is successful when neither high rolling forces nor wear of the working rolls occur during the subsequent cold rolling. Mechanical properties as tensile strength, yield, elongation or hardness have been, by tradition, the criteria that described the quality of the annealing process. In recent years, the development of the measurement equipment in the rolling mills and of the instruments for material investigations has accentuated more and more the role played by the microstructural properties in the evaluation of the heat treatment. Two microstructural characteristics of the degree of annealing are, firstly and most important, the recrystallisation degree, and, secondly, the secondary carbide density.</p><p>The sample manufacturing and heat treatment, modelling and microstructure investigations by light optical- (LOM) and scanning electron microscopy (SEM) described in this article were carried out at Sandvik Materials Technology’s R&D Department and Bell Furnace Line in Sandviken, Sweden, while microstructure investigations and evaluation by scanning electron microscopy with field emission gun (FEG-SEM) and electron back scatter diffraction (EBSD) were done at the Corrosion and Metals Research Institute (KIMAB) in Stockholm, Sweden.</p><p>The first part of this work shows that, in contrast to the traditional methods LOM and SEM, that use chemical etching for the preparation of the samples, EBSD can successfully characterise recrystallised structures in annealed martensitic chromium steels. Unlike conventional microscopy with LOM and SEM, EBSD is able to reveal the grain geometry, as well as to separate and identify the different phases in this kind of steels (ferrite, M23-, M6-carbides). Important parameters such as grain size, particle size and recrystallised fraction can be measured with high accuracy. This information can be used to understand, evaluate, control and even predict the recrystallisation annealing of martensitic chromium steel.</p><p>The second part of this work presents how the results from microstructure description by EBSD can be directly used in relatively simple empirical models for determination of recrystallisation degree as function of the annealing parameters and the deformation history. EBSD was applied to evaluate the degree of recrystallisation in a series of annealing tests, with the purpose to model recrystallisation temperature in two types of martensitic chromium steel strip, a traditional one and one alloyed with molybdenum, cold rolled with different amounts of reduction and annealed with different temperatures, soaking times and heating rates. The empirical quadratic models were built with Umetrics’ software for experimental design, MODDEÒ 8.0 and they defined the recrystallisation degree (limits for LAGB and HAGB were set to 1.5° and 7.5° for the first grade and 2.5° and 10° for second one) and the secondary carbides density as functions of annealing temperature, soaking time and cold reduction (the factor heating rate was removed as nonsignificant). To be observed that these empirical models were fit much better for the recrystallisation degree than for the secondary carbides density.</p><p>The modelling work described above, together with the implementation of online physical temperature models in the bell annealers may lead to an increased productivity in the production plant by shortening the annealing cycle and minimising scrap and thus to an economical gain of ca 1,5 MSEK per year at Sandvik Materials Technology.</p><p> </p>

Recrystallisation annealing, a repeated heat treatment between different stages of cold rolling of martensitic chromium steel strip, is successful when neither high rolling forces nor wear of the working rolls occur during the subsequent cold rolling. Mechanical properties as tensile strength, yield, elongation or hardness have been, by tradition, the criteria that described the quality of the annealing process. In recent years, the development of the measurement equipment in the rolling mills and of the instruments for material investigations has accentuated more and more the role played by the microstructural properties in the evaluation of the heat treatment. Two microstructural characteristics of the degree of annealing are, firstly and most important, the recrystallisation degree, and, secondly, the secondary carbide density. The sample manufacturing and heat treatment, modelling and microstructure investigations by light optical- (LOM) and scanning electron microscopy (SEM) described in this article were carried out at Sandvik Materials Technology’s R&amp;D Department and Bell Furnace Line in Sandviken, Sweden, while microstructure investigations and evaluation by scanning electron microscopy with field emission gun (FEG-SEM) and electron back scatter diffraction (EBSD) were done at the Corrosion and Metals Research Institute (KIMAB) in Stockholm, Sweden. The first part of this work shows that, in contrast to the traditional methods LOM and SEM, that use chemical etching for the preparation of the samples, EBSD can successfully characterise recrystallised structures in annealed martensitic chromium steels. Unlike conventional microscopy with LOM and SEM, EBSD is able to reveal the grain geometry, as well as to separate and identify the different phases in this kind of steels (ferrite, M23-, M6-carbides). Important parameters such as grain size, particle size and recrystallised fraction can be measured with high accuracy. This information can be used to understand, evaluate, control and even predict the recrystallisation annealing of martensitic chromium steel. The second part of this work presents how the results from microstructure description by EBSD can be directly used in relatively simple empirical models for determination of recrystallisation degree as function of the annealing parameters and the deformation history. EBSD was applied to evaluate the degree of recrystallisation in a series of annealing tests, with the purpose to model recrystallisation temperature in two types of martensitic chromium steel strip, a traditional one and one alloyed with molybdenum, cold rolled with different amounts of reduction and annealed with different temperatures, soaking times and heating rates. The empirical quadratic models were built with Umetrics’ software for experimental design, MODDEÒ 8.0 and they defined the recrystallisation degree (limits for LAGB and HAGB were set to 1.5° and 7.5° for the first grade and 2.5° and 10° for second one) and the secondary carbides density as functions of annealing temperature, soaking time and cold reduction (the factor heating rate was removed as nonsignificant). To be observed that these empirical models were fit much better for the recrystallisation degree than for the secondary carbides density. The modelling work described above, together with the implementation of online physical temperature models in the bell annealers may lead to an increased productivity in the production plant by shortening the annealing cycle and minimising scrap and thus to an economical gain of ca 1,5 MSEK per year at Sandvik Materials Technology.

No description available.

The purpose with this thesis was to examine the cold rolling mill located at Högskolan Dalarna and to stabilize the rolling process, to achieve steady state. Experiments with cold rolling of an aluminium strip have given results for rolling force, friction, reduction, strip tension and strain hardening. Results show that steady state has been found for the experiments with roll force and strain hardening, and not been found for the experiments with friction and reduction. Results show that increased strip tension gives lower roll forces. The roll force equation of Stone shows comparable results with reality for dry contact with reductions up to 30 %, but starts being incomparable with higher reductions. The roll force equation of Stone shows a bit higher roll forces than reality gave, but was comparable within reductions from 13 to 50 %. Experiments have shown that the aluminium strip has gone through strain hardening. Experiments show how the set roll gap did not yield the desired thickness reduction, there for the elastic spring constant for the rolling mill was examined and determined to be 417 N / mm for the specific alloy band. The influence of tension strip for roll force was examined and Results confirm the theory about how the roll force is decreased by increasing tension strip. The work rolls started to slip against the alumina strip as high tension strip; 70 N/mm2, gave low roll force; < 15kN.

Introduction 100Mo target design is key to commercially viable large scale cyclotron production of 99mTc. The target back plate supporting the 100Mo must be chemically inert to the target dissolution conditions but ideally it should also be able to dissipate the high thermal loads of irradiation, not contaminate target substrate with radionuclidic by-products, and be adequately inexpensive to allow for single use. Aluminum was selected as our target support as it satisfies these requirements. Our process entails rolling 100Mo powder into a foil of desired thickness, and then diffusion bonding [1] the foil onto an aluminum back plate. The 100Mo targets were designed to be 20×80×0.1 mm to match our TR24 cyclotron’s proton beam profile and energy. Efforts are currently underway to scale up the process to allow for simultaneous production of multiple targets at once. Material and Methods The crude enriched 100Mo foil (99.815% enrichment) was made from 100Mo powder using a horizontally mounted rolling mill and an aluminum hopper. The crude foil was rolled repeated-ly, and the space between the rollers gradually reduced until the thickness of the foil was changed from an initial thickness of 0.3 mm to a thickness of 0.1 mm. The rolled 100Mo foil was annealed under reducing atmosphere and then bonded to the aluminum target plate support under inert atmosphere in a heated press at 500 °C. Results and Conclusion By rolling 100Mo foils from powder we were able to produce uniform foils with an average density of > 98 % compared to the maximum theoretical density of 100Mo (n = 5) and thicknesses of roughly 0.1 mm. All foils produced were the desired 20 mm width (i.e. limited by the width of the opening of the hopper) and trimmed to the desired 80 mm length. The annealing process was necessary due to the brittleness of the un-annealed rolled foil and the difference in the thermal expansion coefficients of molybdenum and aluminum which caused un-annealed foils in previous experiments to crack and break off during pressing (n = 10). Surface preparation of the aluminum support plate was also found to play a critical step in the efficiency of the bond, and continuing effort to scale the above de-scribed procedure to mass produce 100Mo tar-gets is ongoing. Targets have undergone preliminary testing to 250 μA.

No description available.

Multilayers provide an ideal tool to study thermodynamics of heterogeneous systems far from equilibrium. In this study, synthesis, characterization, thermal stability and phase equilibrium of multilayers are investigated based on Au-Pt system. Au-50%Pt multilayers were first formed by repeated rolling and folding. The microstructure was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These methods revealed that the process reduced layer thicknesses to below 30nm. However, delaminating and non-uniform spacings were also observed in some regions. To get well- welded and regular multilayers, the experiment was redesigned. The improved approach, involving repeated cutting, stacking, annealing and cold rolling, has yielded uniform multilayers with interlamellar spacings as low as 6nm. XRD demonstrated the formation of a homogeneous solid solution during cold rolling at room temperature. TEM suggested that the multilayers were discontinuously homogenized via steady state motion of boundaries. The reason for the solid solution formation is that the stored interface energy is higher than the energy barrier for solid solution formation. The solid solution is unstable. It decomposes into Au and Pt after heating to 500°C at 50°C/min by differential scanning calorimetry (DSC). The phase diagram is strongly modified in the nanometer range when we take into account of interface energy. The grain size dependent phase diagram model of Au-Pt system shows that the melting points of Au and Pt can be lowered more than 300K if the average grain size is reduced to 10nm. The melting temperature of Au/Pt multilayers has been studied with theoretical and experimental approaches. High speed laser heating was used to minimize any modification of the multilayer structure prior to melting. The qualitative experimental results are shown to be in agreement with expectations. / Thesis / Master of Applied Science (MASc)

Particulate reinforced Al alloy composites (AlMCs) are recognized as important structural materials due to their lightweight, high modulus and strength and high wear resistance. In order to understand the effect of matrix, reinforcement and secondary processing techniques on the microstructure development and mechanical properties of AlMCs produced by powder metallurgy routes, Al alloy composites reinforced with three types of reinforcements by different secondary processing techniques have been produced and examined. Fabrication of Al or 6061Al alloy based composites reinforced with nano-sized SiC particles (~500nm), micro-sized (<25µm) quasicrystalline alloy particles (hereinafter referred to as “NQX”) and micro-sized Nb particles (~130µm) has been carried out by powder metallurgy routes followed by extrusion or cold rolling. After extrusion, a homogeneous distribution of secondary particles has been obtained with rare interfacial reaction products. The 6061Al/SiC composites exhibit superior mechanical properties than either monolithic alloys or composites reinforced with micro-sized particles with retained ductility while the 6061Al/NQX and 6061Al/Nb composites show limited improvement in tensile strength mainly due to their reinforcement size and poor interfacial bonding. After cold rolling, the evolution in microstructure, texture and strength has been analysed. A typical near β fibre texture with highest intensities near Copper and Brass orientations has been developed for 6061Al/NQX and 6061Al/Nb composites. For 6061Al/SiC composites, a randomized texture with very small grains has achieved due to the presence of the non-deformable SiC particles. Mechanical property tests including microhardness, three-point bending tests and tensile tests have been carried out on cold rolled samples and the results exhibit some level of improvement when compared with as-extruded samples due to work hardening. Finally, the work moves on to the general discussion based on the previous result chapters. The microstructural development related to reinforcement, matrix and interfacial areas during extrusion and cold rolling has been summarised and the correlation between microstructure and mechanical properties has been discussed. The thesis provides a thorough understanding of AlMCs produced by powder metallurgy routes in terms of matrix, reinforcement and processing techniques. It can provide reference to the future development of AlMCs for high strength applications.

Les matériaux ODS (Oxide Dispersion Strengthened), mis au point par métallurgie des poudres, sont la solution de référence pour le gainage du combustible nucléaire des nouveaux réacteurs de génération IV à fort taux de combustion. Ils présentent une résistance au gonflement sous irradiation augmentée par rapport aux aciers austénitiques et une grande stabilité dimensionnelle en fluage induite par une dispersion homogène de nano-particules stables à haute température. Après co-broyage de la poudre d'alliage maître avec une poudre d'oxydes d'yttrium, le matériau est consolidé par filage à chaud, puis mis en forme à froid par laminage à pas de pèlerin. Les matériaux ODS sont caractérisés par une faible ductilité et une dureté élevée à température ambiante. Les passes de laminage doivent être entrecoupées par des traitements thermiques intermédiaires afin de restaurer le tube et éviter tout endommagement pendant la gamme de transformation.Cette étude vise à identifier les points clés pour la maîtrise de la gamme de transformation à froid de deux nuances ODS : une nuance ferritique Fe-14Cr-1W et une nuance martensitique Fe-9Cr-1W. Les relations entre les traitements thermomécaniques et la microstructure sont étudiées à partir de caractérisations multi-échelles. La compréhension des mécanismes d'évolution de la microstructure permet de proposer, pour chaque nuance, une gamme de transformation à froid robuste. Pour la nuance ferritique Fe-14Cr-1W, la déformabilité est assurée par une croissance des grains à haute température suivant un mécanisme de type Strain Induced Boundary Migration (SIBM). Des optimisations s'appuyant sur une recristallisation primaire sont envisagées. Pour la nuance martensitique Fe-9Cr-1W, la gamme mise en œuvre permet d'obtenir un matériau dont la déformabilité et les caractéristiques mécaniques à chaud sont équivalentes voire meilleures que celles des nuances de la littérature. Des évolutions des gammes et de la composition chimique sont proposées pour améliorer la résistance à la corrosion et au fluage. / Oxide dispersion strengthened steels, elaborated by powder metallurgy, are considered as reference materials for high burn up cladding tubes for future Sodium Cooled Fast reactors. They present superior radiation resistance compared with austenitic steels and high creep strength due to reinforcement by the homogeneous dispersion of hard nano-sized particles. After mechanical alloying of the matrix powder and the yttrium oxides, ODS steels are consolidated by hot extrusion and manufactured by using cold pilgerin process. ODS steels are usually characterized by a low ductility and a high hardness at room temperature. The cold-rolling passes have to be punctuated by intermediate heat treatments in order to soften the raw tube and avoid any damage in the course of manufacturing.The aim of this study is to identify the key points for the control of the manufacturing of two grades: a Fe-14Cr-1W ferritic grade and a Fe-9Cr-1W martensitic grade. The relationship between thermomechanical treatments and microstructure is studied by multi-scale characterizations. The understanding of the microstructure evolution permits the determination of robust fabrication routes for both grades. The deformability of the ODS Fe-14Cr-1W ferritic grade is ensured by grain growth at high temperature following a Strain Induced Boundary Migration (SIBM) mechanism. Optimizations through primary recrystallization are proposed. Fabrication route of ODS Fe-9Cr-1W martensitic grade permits to obtain a material characterized by deformability and high temperature mechanical properties similar or even better than those of literature grades. Fabrication routes evolutions and chemical composition optimization are proposed to improve the corrosion and thermal creep resistance.

L'industrie sidérurgique rencontre depuis des années un développement important. Les caractéristiques des produits destinés aux différents secteurs industriels deviennent de plus en plus exigeantes. Actuellement des régulateurs avancés de type PID sont utilisés avec une structure multi-boucles locales. Afin de traiter les cahiers des charges de plus en plus contraints, il devient intéressant de revoir cette stratégie de contrôle. Ce sujet de thèse CIFRE entre ArcelorMittal et le CRAN a pour objectif de proposer de nouvelles stratégies de contrôle avancé pour le laminage à froid des bandes d'acier de type tôle fine, notamment des stratégies centralisées de contrôle remplaçant des boucles de régulation locales et indépendantes, afin d'élargir le champ des matériaux traitables, d'augmenter et d'optimiser la productivité et les capabilités du procédé ainsi que de minimiser les coûts de production. Dans une première partie, une étude bibliographique sera effectuée afin de mieux cerner les différents modèles métallurgiques et dynamiques du système à piloter. Dans une seconde partie, le cahier des charges sera traduit en termes d'un problème d'optimisation dont la solution est un contrôleur de type retour d'état. Enfin dans une troisième et dernière partie, une synthèse de retour de sortie dynamique sera proposée pour résoudre le problème des mesures manquantes / The steel industry has been developing for years. The characteristics of the products intended for the various industrial sectors are becoming more and more demanded. Currently advanced PID controllers are used with a local multi-loop structure. In order to deal with the increasingly constrained specifications, it is interesting to review this control strategy. This CIFRE PhD thesis between ArcelorMittal and CRAN aims to propose new advanced control strategies for the cold rolling of thin sheet steel strips, including centralized control strategies replacing local and independent control loops, to broaden the scope of treatable materials, increase and optimize process productivity and capabilities, and minimize production costs. In a first part, a bibliographic study will be carried out in order to better define the various metallurgical and dynamic models of the system to be controlled. In a second part, the specifications will be translated in terms of an optimization problem whose solution is the state feedback controller. Finally, in a third and final part, a dynamic output feedback synthesis will be proposed to solve the problem of missing measurements