Дисертації з теми "Grain-Oriented electrical steels"

Localised magnetic flux density, magnetising field and power loss are believed to distribute non-uniformly in grain oriented electrical steel. Understanding of the causes of their variation can help reduce the overall power loss of the material. In this investigation, magnetic domain observation was often used in the study of domain configuration and crystal orientation of the test specimens. Methods of domain observation have been studied and compared in order to select the appropriate method for different parts of the investigation and to improve the understanding of the image observed. A less destructive local loss measurement sensor has been built for the measurement of localised flux density, magnetising field and power loss. The sensor was tested and evaluated specifically for the measurement of localised magnetic power loss of the high permeability grain oriented electrical steel. The results obtained from local loss scanning measurements indicated that localised flux density and magnetising field can vary substantially in grain oriented electrical steel under AC magnetisation of 50 Hz. The variation of localised flux density has been found mainly resulted by grain misorientation and local grain arrangement. The transverse component of flux density was detected and has been found increases with increasing grain misorientation. The variation of localised magnetising field has been found mainly influenced by the localised demagnetising field due to formation of free magnetic poles at grain boundaries. It has been proved that both flux density and magnetising field have strong influence on the distribution of localised power loss. The study of the effect of domain refinement on distribution of localised flux density showed that domain refinement by means of ball scribing on one surface of grain oriented electrical steel can improve the uniformity of distribution of flux density. However, results also inferred that excessive scribing in a confined area can cause obvious uneven distribution of flux density in the direction of the specimen’s thickness.

Récemment, les gestionnaires de réseau et de système de transmission, comme le Réseau européen des gestionnaires de réseau de transport d'électricité (ENTSO-E), mettent en place des réglementations pour étendre la plage de fonctionnement des équipements connectés au réseau électrique. Les principaux objectifs de ces modifications sont : d'augmenter la flexibilité du réseau en le rendant capable de supporter des variations de fréquence et de tension (dues aux modifications de l'équilibre des puissances active et réactive) et de faciliter l'intégration et la production d'énergie renouvelable. Cependant, de nombreux équipements installés et raccordés au réseau n'ont pas été conçus pour être exploités dans ces plages de fonctionnement et leur utilisation dans ces conditions peut avoir un impact négatif sur le cycle de vie des équipements, en particulier dans les turbo-alternateurs.Les grands turbo-alternateurs, utilisés pour la production d'électricité dans les centrales nucléaires et hydroélectriques, sont impactés par ces nouvelles réglementations. Cet impact est particulièrement observé aux extrémités de ces machines électriques où les pertes fer sont susceptibles d'augmenter significativement. Ces pertes peuvent entraîner des échauffements, notamment des points chauds, qui peuvent conduire à la fusion de l’isolation entre les tôles du noyau du stator, provoquant ainsi des courts-circuits et des dommages irréversibles à l'équipement. Afin de pouvoir analyser et limiter l'impact des mécanismes physiques mis en jeu, la société EDF s’appuie sur des simulations numériques tridimensionnelles de la machine électrique pour calculer les pertes pour différents régimes de fonctionnement.Une partie de ce travail a déjà été réalisée au laboratoire L2EP, où le logiciel d'analyse par éléments finis code_Carmel a été adapté pour le calcul des pertes dans le noyau du stator et des pertes joule dans les modèles tridimensionnels. Cependant, la complexité physique des propriétés des circuits magnétiques aux extrémités des turbo-alternateurs doit être prise en compte pour obtenir des résultats fiables. En effet, compte tenu du schéma tridimensionnel du chemin du flux magnétique et des propriétés fortement anisotropes du circuit magnétique en acier électrique à grains orientés (GO), la description des pertes fer nécessite des modèles de matériaux magnétiques anisotropes précis combinés à une modélisation numérique efficace.Dans le cadre de ce travail de thèse, des modèles anisotropes dédiés aux aciers GO, notamment pour décrire la loi de comportement et les pertes fer, ont été étudiés puis implémentés dans un environnement de simulation par éléments finis (FEM) au sein du logiciel code_Carmel. La mise en œuvre a été validée par rapport à des données expérimentales obtenues sur un acier GO de qualité industrielle conventionnelle généralement utilisée dans les turbo-alternateurs. De plus, un démonstrateur expérimental a été développé pour étudier plus finement le comportement magnétique d'un empilement de tôles GO soumis à des excitations de flux magnétique 3D non conventionnelles. Un modèle numérique du démonstrateur expérimental a été développé et étudié, incluant les modèles de matériaux anisotropes, en comparant le comportement global du matériau GO ainsi que les pertes de fer dans l'échantillon d'intérêt.Les résultats montrent que, dans des configurations d'attaque de flux magnétique non conventionnelles, en particulier avec une attaque de flux magnétique normale au plan de laminage, les caractéristiques anisotropes de l’acier GO peuvent influencer la distribution du flux magnétique dans l'empilement de tôles étudié ainsi que les pertes de fer associées. Notamment, et comme attendu, les pertes par courants de Foucault classiques constituent la contribution majeure aux pertes fer dans l’empilement de tôles étudiées
Recently, network and transmission system operators like the European Network of Transmission System Operators of Electricity (ENTSO-E) have started to create regulations to extend the range of operation of the equipment connected to the electrical grid. The main purposes of these changes are: to increase the flexibility of the grid by making it able to withstand variations of frequency and voltage (due to alterations in the active and reactive power balance), and to ease the integration of renewable energy generation. However, many of the installed equipment connected to the grid have not been conceived to be exploited in these operating ranges and their use under these conditions will have a negative impact, especially on the turbo-generators life cycle.Large turbo-generators, used for the generation of electricity in nuclear and hydroelectric power plants, are affected by these new regulations. This impact is especially evident at end-regions of these electrical machines, where the iron losses are likely to increase significantly. These losses can lead to overheating, in particular hot points which can lead to the melting of the insulation layers between the lamination of the stator core, causing short-circuits and irreversible damage to the equipment. To be able to analyze and limit the impact of the involved physical mechanisms, the EDF Company works with tridimensional numerical simulations of the electrical machine to calculate the losses under different regimes of operation.Part of this work has already been realized in the L2EP laboratory, where the finite element analysis software code_Carmel have been adapted for the calculation of core losses and joule losses in tridimensional models. However, the physical complexity of the magnetic circuit properties at the end-regions of turbo-generators must be accounted for, in order to have reliable results. Indeed, considering the tridimensional pattern of the magnetic flux path and the strongly anisotropic properties of the magnetic circuit made from grain oriented electrical steel (GOES), the description of the iron losses requires accurate anisotropic magnetic material models combined with an efficient numerical modelling.In the framework of this PhD work, anisotropic GOES models, related to the behavior law and iron losses, have been studied and successfully implemented in a finite element method (FEM) simulation environment within the software code_Carmel. The implementation has been validated against experimental data achieved on an industrial conventional GO grade typically used in turbogenerators. Also, an experimental demonstrator has been developed to investigate more closely the magnetic behavior of a lamination stack made of GOES under non-conventional 3D magnetic flux excitations. A numerical model of the experimental demonstrator has been developed and studied with the implemented material models by comparing the global behavior of GOES as well as the iron losses in the sample of interest.The results show that under non-conventional magnetic flux attack configurations, especially with a magnetic flux attack normal to the lamination plane, the anisotropic characteristics of the GOES can influence the magnetic flux distribution within the lamination stack and the associated iron losses. In particular, the classical eddy current losses constitute, as expected, the most significant contribution of the total iron losses in the GOES laminations

Direct, real time domain observations in electrical steel during its magnetisation at 50 Hz and 75 Hz was limited due to low the limited sensitivity and frame sampling rate of the camera systems available. In this work, a high efficiency Kerr magneto-optic microscope was coupled to a recent commercially available high speed intensified camera. The superior efficiency of the developed system enabled domain dynamics measurement to be made at magnetisation frequencies up to 100 Hz in the real time mode and up to 1.8 kHz in stroboscopic mode. The application of the system was focussed on the study of grain-oriented electrical steel. Observations in this work revealed that the behaviour of the domain walls under sinusoidal excitation is far from being ideal sinusoidal motion. The deviations from the ideal behaviour can be summarised as non-sinusoidal, non uniform and non-repetitive domain wall motion. The dependence of the non- uniformity of wall motion and cycle-to-cycle non-repeatability on magnetisation conditions studied by direct real-time observation revealed that under certain conditions the non-uniformity and non-repeatability is much higher. Recommendations have been made on how to reduce losses by adjusting the magnetisation conditions and "magnetic history" of the steel core. The observations confirmed previous researchers' suggestions that the perfection of grain-to-grain orientation and grain size uniformity would improve wall motion uniformity, hence reducing power loss in the material. In addition to Kerr-microscopy observations, the application of a magnetic indicator imaging technique was demonstrated. Moving domains under the insulating, opaque coating on commercial grain-oriented electrical steel were observed using this method. The influence of surface roughness and the effect of coating tension on the domain structure and distortion of bar domains under dynamic magnetisation was observed. New experimental techniques and image processing programs have been developed such as the first attempt of automatic domain wall recognition and analysis by computer vision methods. It was demonstrated that the system and software tools were flexible for use with other materials such as steel, NiFe and CoFe alloys, amorphous ribbons and wires, ferrites and magnetic films.

Fully processed, grain oriented electrical steel possesses a forsterite glass film and a phosphate-based insulation coating on both of its surfaces. The composition, quality and thickness of these layers, in addition to a preceding decarburisation oxide layer, are known to have a significant effect on the properties of the material on which the final product is assessed. This includes physical properties, such as appearance, as well as the magnetic properties upon which the electrical steel is routinely graded. Due to their importance, methods of rapidly and accurately assessing these surface layers would provide great benefits as the characteristics could be monitored to ensure the optimum processing conditions are achieved. Unfortunately, it has previously been found that the complexity of the layers has made their analysis problematical, particularly in terms of accuracy and the time required for testing. A number of experimental techniques have been investigated to establish their potential for the analysis of the aforementioned surface layers, including Fourier Transform Infrared (FTIR), Electrochemical Potential (ECP), X-ray Photoelectron Spectroscopy (XPS) and Sputtered Neutral Mass Spectrometry (SNMS). Further methods were also used to determine characteristics of the coated material such as magnetostriction and magnetic loss, which provided an insight into the stressing capability of the material. As a result of these investigations: Combining a number of techniques resulted in a correlation between ECP profiles and the composition and / or morphology of the decarburisation oxide layer. A link has been established between the transmittance levels of the FTIR spectra and the thickness of the forsterite glass film layer. FTIR absorption bands have been linked to the constituents of the insulation coating. Further to the study into the feasibility of these methods, a number of the techniques were used to analyse material during the development of an alternative, chrome-free insulation coating, which has subsequently been adopted as the standard production coating for the grain oriented electrical steel produced at Orb Works.

Deformation mechanism and dislocation dynamics in grain oriented electrical steel (GOES) is not well established during the continuous flattening anneal process. This work deals with the study of deformation mechanisms during the process and the effect of lattice defects created during the process on the final magnetic properties of GOES. A heat transfer model of the continuous flattening anneal furnace was developed to calculate the temperature profile of the strip throughout the process. The heat transfer model showed the stability of peak strip temperature at 850oC when the line speed was varied from 60-90m/min. A deformation mechanism map was constructed for two varieties of GOES. The main implication of this model is the knowledge of the effect of process parameters like stress, temperature and strain rate on the formation of dislocation structure in GOES during continuous flattening anneal process. LAFFAS (Lab Annealing Furnace for Flattening Anneal Simulation) was constructed to simulate the continuous flattening anneal process and produce samples for dislocation study and magnetic testing. The high temperature mechanical behaviour of Conventional Grain Oriented+ ® (CGO+ - new GOES product) and its effect on magnetic properties were also analysed. Polygonization in GOES and the factors affecting polygonization were studied in detail. Initial orientation of the grains was determined to be a rate controlling factor for degree of polygonization along with temperature and annealing time. The degree of polygonization was shown to be an important parameter affecting the change in domain width. A localised decrease in specific total loss was observed at 1.5T and 50Hz in grains where polygonization was complete. An increase in specific total loss of about 10-35% at 1.5T and 50Hz in bulk polycrystalline material was observed due to the sensitivity of polygonization to initial texture resulting in incomplete polygonization in a high percentage of grains.

Le transformateur est aujourd’hui l’un des convertisseurs statiques les plus utilisé notamment dans la distribution électrique. Les tôles magnétiques servant à la construction de leurs circuits magnétiques sont devenues de plus en plus performantes permettant une réduction des pertes produites. Néanmoins, les tests normalisés permettant de caractériser les tôles magnétiques ne reflètent pas totalement le comportement énergétique du transformateur. De plus, une autre problématique a gagné en importance durant ces dernières années : le bruit acoustique émis. Malheureusement, il n’y pas encore de lien entre la qualité de la tôle à grains orientés choisie pour construire le circuit magnétique et le bruit acoustiques que va produire celui-ci. L’objectif de cette thèse est de répondre à cette double problématique à partir de tests simplifiés. En effet, de nombreux dispositifs expérimentaux et méthodologies ont été développés tels que la méthode des trois cadres, permettant d’étudier la répartition des pertes fer dans le transformateur, les circuits magnétiques décalés, permettant d’étudier les phénomènes à l’origine des bruit acoustique, et des modèles de transformateurs monophasés et triphasés. De plus, des simulations numériques ont été effectuées afin d’approfondir nos analyses des résultats expérimentaux. L’étude des dispositifs ont permis de mettre en évidence trois paramètres relatifs à la qualité des tôles magnétiques, entrainant des différences de répartition d’induction set donc des différences de répartition de pertes fer, d’une part, et de bruit acoustique dans les transformateurs, d’autre part
The transformer is now a static converter most notably used in electrical distribution. The electrical steel sheet used in the construction of their magnetic circuits have become more efficient to reduce losses occurred. However, standardized tests to characterize the electromagnetic steel do not fully reflect the energy behavior of the transformer. In addition, another issue has gained importance in recent years: the acoustic noise. Unfortunately, there is no link between the quality of grain oriented steel selected to construct the magnetic circuit and acoustic noise that will produce it. The objective of this thesis is to answer this dual problem from simplified test. Indeed, many experimental devices and methodologies have been developed such as the method of three frames, to study the distribution of core losses in the transformer, the magnetic circuits shifted, to study phenomena at the origin of acoustic noise, and models of single and three phase transformers. In addition, numerical simulations were performed to deepen our analysis of the experimental results. The study of the devices have allowed to identify three parameters relating to the quality of grain oriented electrical steel, resulting from differences in the distribution of the flux density and therefore, first, the differences in distribution of core loss and, hand, acoustic noise in transformers

Les bobinages des machines électriques tournantes actuelles sont, pour la plupart, isolés avec des matériaux issus de la chimie organique. La limite en température des bobinages actuels se situe au-dessous de 240°C. L’augmentation significative de la température de fonctionnement d’une machine permettrait d’envisager, indirectement, une augmentation de la densité de courant dans les conducteurs actifs. Dans ces conditions, ces nouvelles machines peuvent présenter une puissance, tant massique que volumétrique, supérieures à celles exploitées actuellement. De plus, les matériaux magnétiques permettent vraisemblablement de fonctionner jusqu’à 800°C. La limite technologique actuelle pour les machines est clairement l’isolant des conducteurs électriques. Ce sujet de thèse propose de définir une approche théorique couplée à des validations expérimentales pour définir les matériaux les mieux adaptés aux machines hautes températures en termes de mise en œuvre et de performances électriques. La conception, repensée autour du bobinage, sera concrétisée par le calcul d’une machine asynchrone à haute température (400°C au cœur du bobinage). Le bobinage devra être placé au cœur de la démarche de conception des machines en adaptant les formes et les propriétés des circuits magnétiques aux caractéristiques des nouvelles bobines
The windings that are currently used in electrical machines are mostly insulated based on organic insulation. The temperature limit of these windings is up to 240°C. Increasing the working temperature of electrical motors means, indirectly the increasing of current density on the main conductors. Therefore these new motors may provide a higher mass and volume power as classical machines. Furthermore, the magnetic materials can work up to 800 °C. Indeed, in reality technical limit today is the wire insulation. The objective of thesis is to define a theoretical approach combined with experimental validations for identify the appropriate electrical materials used on high-temperature electrical machines. Design is fixed around the winding, that will implemented by calculating a high-temperature asynchronous machine (400°C of windings). The windings are placed as the base of machine design and will determine the geometrical shape and properties of magnetic core

碩士
國立雲林科技大學
機械工程技術研究所
87
Grain oriented electrical steel is an important core material of transformers. Its magnetic properties significantly affect the energy efficiency of electrical apparatus. Inclusions are used as inhibitors to impede the normal grain growth of grain oriented electrical steel during the primary recrystallization. But, abnormal grain growth occurs to develop the preferred Goss texture during secondary recrystallization. Secondary recrystallization behaviors are influenced by its inclusion inhibitors. In this study, we systematically investigate the effect of reheating temperature and time on the size and distribution of inclusions of four extra low carbon silicon steels with various sulfur, maganese and aluminum contents. The experimental results from chemical analysis could be fitted with a singleline represented by an equation applicable to MnS. Log[Mn(wt%)*S(wt%)]=-2683/T-0.8197 where T is in kelvins. As same as, the solubility products of aluminum nitride could be fitted with a single line represented by an equation. Log[Al(wt%)*N(wt%)]=-4809/T-1.4165 The solubility products of inclusion increase with the get long time. Inclusion sizes are decreased with elevate reheating temperature. At high temperature, activation energy of inclusion elevates the diffusion coefficient , So, the dissolved rate increase with the elevated reheating temperature. As the time of inclusion dissolved increase, any size inclusion is decrease with time keep reheating temperature. In compnnent of inclusion, the count and distribution of inclusion is elevated by increased sulfur and aluminium contents.

碩士
雲林科技大學
機械工程系碩士班
98
Grain oriented electrical steel is used to make transformer core. Its magnetic properties affect the energy efficiency of electrical machines. The size and volume of precipitates inhibit the primary grain growth and develop favorite Goss texture during secondary recrystallization. This study investigated the effect of MgO coating on the secondary recrystallization behaviors of grain oriented electrical steels by acquired inhibitor process. It is found that abnormal grain growth didn’t occur in the steels with aluminum less than 0.013 wt% due to insufficient precipitate amounts. On the other hand, abnormal grain growth occurred in the steels with aluminum higher than 0.035 wt%. Coated specimens had less deviation degree from Goss texture and better magnetic properties. The reason was insulator layer can prevent the dissociation of precipitates in the specimen and let abnormal grain growth developed completely. After secondary recrystallization, impurities such as nitrogen, sulfur and manganese diffused to the glassy layer and improve the magnetic properties. The phase formed in the insulator layer was Mg2Al4Si5O18 in the specimens decarburized below 700oC due to less SiO2. Dense Mg2SiO4 layer formed in the specimens decarburized higher than 750oC due to more SiO2 layer. Na2B4O7 is a catalyst to decrease the glassy forming temperature of Mg2SiO4. Therefore, add Na2B4O7 into MgO powder film can get dense glassy phase and good abnormal grain growth in the steels. TiO2 can improve the glassy film more dense.

碩士
國立雲林科技大學
機械工程系碩士班
97
Grain oriented electrical steel is an important function magnetic material. It has excellent permeability during magnetization.Grain oriented electrical steel is usually used to make the transformer cores. The normal grain growth during primary annealing and let the preferred Goss grain grow during secondary recrystallization.The purpose was studied the effects of copper content at different hot band annealing temperature and cold rolling thickness of slab on the secondary recrystallization. Copper impeded the normal grain growth during primary annealing and let the preferred Goss grain grow during secondary recrystallization. Hot-rolling were not recrystallization in slab reheating at 1200℃. Hot rolling aneealing the grain size increases with increasing temperature. Carbon content will affect the content of nitrogen , however , the content of nitrogen will also affect the formation of precipitates. The highest induction(B8) was obtained when the nitrogen content in the steel sheet was 400ppm. After nitride treatment﹐the precipitates of CuS2、Si3N4 and AlN、MnS of the substrate, these precipitates will inhibit grain growth. Stable secondary recrystallization and the best magnetic properties are obtained for the specimens in hot band annealing at 1150℃.

博士
雲林科技大學
工程科技研究所博士班
99
Electrical steels are representative soft magnetic materials which can effectively convert electricity into magnetic energy. Electrical steels are classified into grain oriented electrical steel and non-oriented electrical steel. Grain oriented electrical steel is an important functional material used as lamination cores in various transformers. Its magnetic properties affect the energy efficiency of transformers and are closely related to the sharpness of (110)<001> texture. If (110)<001> texture is strongly developed after secondary recrystallization annealing, superior magnetic properties, such as high magnetic flux density and low core loss are obtained. In this study, the effect of nitriding process to the secondary recrystallization behaviors and magnetic properties of grain oriented electrical steel was investigated. The grain oriented electrical steels were produced by the single-stage cold rolling process and the acquired inhibitor method. The precipitates, Si3N4 and MnSiN2, were formed by nitriding treatment after primary recrystallization, which retarded primary grain growth effectively. However, the volume fraction of precipitates and the average diameter of precipitates are important factors to influence the secondary recrystallized development. In our experiment, there is a suitable nitriding condition to develop the complete secondary recrystallizaiton and best achieve the magnetic properties. The nitrogen content injected into the grain oriented electrical steel by acquired inhibitor process to get the best magnetic properties is 150 ppm. Influence of Sn, range from 0 - 0.31wt%, on the recrystallization behavior and texture of grain oriented electrical was also discussed in the present thesis. It was found that nitrogen content in the steels decreases with increasing Sn content after nitriding. It is postulated that Sn segregates to grain boundary and retards the diffusion of nitrogen atom into the steels. The pinning effect of Sn is very strong for secondary recrystallization. The specimens containing less than 0.05wt% Sn finish secondary recrystallization after SRT (secondary recrystallization temperature) at 1000oC. The secondary recrystallization grain growth became difficult as the Sn content is above 0.10wt%. Both EBSD and XRD results show that the intensities of (111)<uvw> textures in the specimens with or without nitriding decrease with increasing Sn content and reaches a minimum value at 0.31 wt% Sn. Sn restrains the grain growth during secondary recrystallization. Finally, the effect of Sn content from 0 to 0.31wt% on the primary and secondary recrystallization behaviors of grain oriented electrical steel has also been studied. There has a maximum value of frequency of middle misorientation angle (20°<ω<45°) in the specimen without Sn content after primary recrystallization annealing. Then, the frequency of middle misorientation angle decreased with increasing Sn content. After secondary recrystallization annealing, the specimen containing 0.31wt% Sn has the largest area percentage of abnormal grain. Furthermore, the area percentage increases with increasing annealing time. However, abnormal grain growth can’t occur that is due to many precipitates in the specimen without Sn as soaking less than 3 hours. In the specimen containing 0.05 wt% Sn, the area percentage abruptly increases after soaking 3 hours. The (100) pole figures of onset abnormal grains measured by EBSD. It is found that abnormal grains have sharp Goss orientation in the specimen without Sn. However, there is a large abnormal grain in the specimen containing 0.05wt% Sn. But, the deviation angle from ideal Goss texture is more than 15°. The deviation angle from idea Goss texture was broad in the Sn added specimens after secondary recrystallization.

碩士
國立雲林科技大學
機械工程系碩士班
89
Grain oriented electrical steel is an important function materials used as laminated cores of transformers. Its magnetic properties influence the efficiency of transformers. This study investigates the effects of carbon content and various process variables on the magnetic properties of oriented electrical steels added with MnS inhibitor. The carbon content in the steels is 0.0021wt% and 0.032wt% respectively. The process variables studied are slab reheating temperature, hot band annealing temperature, cold-roll stages, intermediate annealing temperature, heating rate and secondary recrystalliz-ation temperature. Meanwhile, the microstructure, inclusion, texture and magnetic properties at various stages are studied. It is found that the intensity of (110)<001> component at the surface is stronger than that at quarter thickness during hot rolling and is weak after the stages of hot band annealing and intermediate annealing in both electrical steels. If the low carbon electrical steel reheated to 1300℃, Goss Texture at the quarter thickness is stronger than that at surface and half thickness. However, strong Goss texture develops after secondary recrystallization annealing in certain process conditions. It is better to get lower core loss, higher flux density and permeability for the specimens reheated to 1100℃ than 1300℃ in the extra-low carbon electrical steel. Specimens with 1℃/min heating rate gets better magnetic properties than that with 5℃/min. But in the low carbon electrical steel it gets better magnetic properties for the specimens reheated to 1300℃ than 1100℃. The hot band annealing temperature, intermediate annealing temperature, cold-roll stages, secondary recrystallization temperature interact with each other. It exists an optimum conditions for the flux density, core loss and permeability. It is found that the optimum conditions are as follows: reheating temperature at 1100℃ in extra-low carbon electrical steel, but reheating temperature at 1300℃ in low carbon electrical steel, the hot band annealing temperature at 1100℃, two stages cold-roll, 1℃/min heating rate in extra-low carbon electrical steel and the secondary recrystallization temperature is between 1200℃ and 1250℃.

碩士
國立雲林科技大學
機械工程系碩士班
94
Grain oriented electrical steel is an important function magnetic material. It has excellent permeability after magnetization. Grain oriented electrical steel is usually used to make the transformers core. It’s magnetic properties affect the energy efficiency of electric machinery. Proper size and distribution of inclusions can impede the the normal grain growth during primary annealing and let the preferred Goss grain grow during secondary recrystallization. After hot rolled band nitriding at different time; from 30 min to 4 hours , it was found that the amount of nitrogen in hot rolled band increased with increasing nitriding time. Furthermore, the nitriding depth also increased with increasing nitriding time. The amount of nitride decreased from the surface download to the center. After hot rolled band annealing , the volume fraction of recrystallized grain increases with increasing annealing temperature and time. Moreover, texture component of (001) <100> orientation increases from the surface download to the center. On the other band, texture component of (110) <001> decreases from the surface download to the center. It slows that the texture gradient exists in the hot rolled band. It also found that nitrogen content in the steel sheet decreased after primary annealing. After primary annealing , α-Si3N4 precipitates gradually decomposed and new stabled (Al , Si)N formed as the inhibitor for the secondary recrystallization annealing , Furthermore, heating rate also affect the abnormal grain growth during secondary recrystallization.

碩士
國立雲林科技大學
機械工程系
103
Grain-oriented electrical steel is an important core material of transformer. It has strong Goss texture after secondary recrystallization. The percentage of Goss grain size would directly affect its magnetic properties. Therefore, both secondary recrystallization behavior and Goss texture development were important subject for grain-oriented electrical steel. This study investigated the effect of low primary recrystallization annealing temperature, various ammonia flow rate, secondary recrystallization temperature on the microstructure, size and volume fraction of precipitates, secondary recrystallization behavior, area percentage of Goss grain, and magnetic properties. During decarburized annealing at 650 ° C, with dew point setting at 45 ° C, the calculated effluent gas partial pressure ratio was 0.316. Then the carbon content can be controlled to less than 30 ppm. The injection nitrogen into steel sheet increased with increasing ammonia flows rate. The optimum conditions to obtain the best abnormal grain growth and magnetic properties for the two-stage hot band annealing grain oriented electrical steels was primary annealed at 650 °C for 5 minutes. Then nitriding was conducted at 700 °C for 30 seconds, with 1.6L/min. Finally, secondary recrystallization was performed at 950 ° C for 12 hours. The flux density, B8, reached 1.81 Tesla and the core loss, W15/50, was 1.08 watt / kg. Keywords: grain-oriented electrical steel steel, core loss, magnetic flux density.

碩士
國立雲林科技大學
機械工程系碩士班
92
The grain structure, size and distribution of precipitates and texture in the primary recrystallized matrix affect the secondary recrystallization behaviors of grain-oriented electrical steel. But, the primary recrystallization microstructure was influenced by manufacture process variables. In this thesis, the first part studied the effect of cold rolling on microstructure and texture in the primary recrystallized matrix and high temperature annealing behavior. The second part studied the effect of non-equilibrium nitriding condition on microstructure, size and distribution of precipitates and texture in the primary recrystallized matrix, and the secondary recrystallization behavior. In the first part, it was found that specimens conducted by one stage cold rolling have strong (111) texture after primary annealing. However, specimens conducted by two stage cold rolling have strong (110)<001> texture after primary annealing. After primary recryatallization annealing, specimens annealed in nitrogen and hydrogen mixed atmosphere at the high annealing can’t form enough AlN precipitate to impede normal grain growth. And the abnormal grain growth did not occur in the specimens. Therefore, the specimens after high temperature annealing have similar texture as in the primary recryatallization annealing. In the secondary part, the nitriding temperature and time do not affect the phases of precipitates in the primary recrystallized matrix. Most of the precipitates were Si3N4 and (Mn , Si)N nitrides. During high temperature incubation annealing, another composite nitride, such as (Al, Si, Mn) N and fine AlN came out. Non-equilibrium nitriding condition strongly affects the development of texture after the primary recrystallization annealing. During secondary recryatallization annealing , slow heating rate is favorable for the abnormal grain growth and development of Goss texture. And the proper nucleation temperature of precipitate is favorable for the occurrence of secondary recryatallization.

碩士
國立雲林科技大學
機械工程系碩士班
91
Grain oriented electrical steel is an important function magnetic material. It has no magnetism but has excellent permeability after magnetization. Grain oriented electrical steel is usually used to be the core of transformers and it’s magnetic properties affect the energy efficiency of electric machinery. Proper size and distribution of inclusions can impede the normal grain growth during primary annealing and let the preferred Goss grain grow during secondary recrystallization. This study will investigate the effect of inclusion on texture , microstructure and secondary recrystallization behaviors of grain oriented electrical steels added with MnS and AlN inclusions at various temperature. It is found that when the steels were reheated to 1200℃, low sulfur sample has AlN inclusions because many of MnS had dissolved. And high sulfur sample has both MnS and AlN inclusions. Those steels reheated to 1200℃ occurred abnormal grain growth after secondary annealing. Hot band annealing at 900℃ can get optimum distribution and size of inclusions and let secondary recrystallization occur. Intermediate annealing at 900℃ can also get proper amount and size of inclusions that are suitable for development of secondary recrystallization. For low sulfur sample reheated to 1200℃ and hot band annealing at 900℃, there are many fine inclusions precipitated and impede normal grain growth. That will maintain matrix grain size to be small and let abnormal grain growth occur. For high sulfur sample reheated to 1200℃ and hot band annealing at 900℃ and 1000℃, because of matrix grain be impeded well that there are more secondary recrystallization grains to grow. After decarburized five minutes at 800℃, the carbon level of low carbon electrical steels added with MnS and AlN reduced to less than 16 ppm. It meets the demand of industry. It is found that when the steels are annealing at 100% nitrogen atmosphere, the better secondary recrystallization grains and magnetic properties will occur. For different rate of raising temperature, it is found that better secondary recrystallization grains and magnetic properties will appear at the rate of 1℃/min.

碩士
雲林科技大學
材料科技研究所
98
Grain oriented electrical steel is an important function material. It is used as transformer lamination cores. Its magnetic properties will affect the energy efficiency of electrical equipments. Furthermore, Goss texture is benefit to its magnetic properties after secondary recrystallizarion. This study investigated the effect of aluminum content, slab reheating temperature, primary annealing temperature on the inhibitor distribution and secondary annealing and magnetic properties of grain oriented electrical steels by acquired process. After primary annealing, grain size of steels that were reheated to 1300oC was smaller than that were reheated to 1200oC. The reason is that more fine precipitates existed in the steel that was reheated to 1300 oC. Furthermore, grain size increased with increasing aluminum content and reached a maximum at 0.035 wt% aluminum. And then, it declined. It is attributed to the size and volume fraction of precipitates formed during nitriding. After secondary recrystallization, abnormal grain growth occurred in the steel containing aluminum more than 0.035wt%. Zener parameter, ZH, was able to predict the occurrence of abnormal grain growth. The best magnetic properties was found in the steel with 0.035wt% aluminum, and conducted at slab reheating temperature1300 oC, primary annealing temperature 875 oC. The volume fraction of Goss grain within deviation angle less than 20o reached 99%.

碩士
雲林科技大學
機械工程系碩士班
98
Grain-oriented electrical steel is a soft magnetic material. It has coarse grain microstructure and strong {110}&lt;001> texture after secondary recrystallization. The relationships among secondary recrystallization behavior and the Goss texture development and magnetic properties are very important. This study investigated the influence of aluminum content and slab reheating temperature and secondary recrystallization temperature on the recrystallization behavior and magnetic properties of grain oriented electrical steels by Acquired inhibitor method. In the hot band annealing，it was found that AlN, MnS, TiN, Si3N4 existed in the matrix. It wad also found cementite and pearlite along the rolling direction in the the hot band. After primary recrystallization, the main inhibitor was (Al、Si) N with size less than 100nm. It affects the abnormal grain growth and texture development of grain oriented electrical steels during secondary recrystallization. The onset secondary recrystallization temperature was influenced by the size and distribution of precipitates and primary grain size. Therefore, aluminum content and slab reheating temperature affected inhibitor retarding force and onset secondary recrystallization temperature. Precipitate could be enlarged by increasing the aluminum content. The optimum condition to have best magnetic properties and Goss texture in the steel with 0.035wt% of aluminum. Its slab reheating temperature was 1100℃ for 2hours and hot-rolled finished at 770℃. Then, hot band was annealed at 1100℃for 5 seconds. After that , steel was decarburized at 875℃for 5 minutes. The secondary recrystallization was conducted at 995℃for 12 hours and then soaking at 1200℃ for 12 hours to purify the impureties.The magnetic property of this steel has 1.92 Tesla at B8 and 95.23% Goss grains.

碩士
雲林科技大學
機械工程系碩士班
98
This study investigated the effect of decarburization annealing process on the secondary recrystallization behaviors in MgO coated grain oriented electrical steels. It was found that microstructure changed from cold rolled structure to full recrystalization structure with increasing decarburization annealing temperature and the holding time. Specimen with a short time preheating before the decarburization annealing was able to decrease carbon content than the specimen without preheating. During nitriding, injection quantity of nitrogen into steel was influenced by the carbon content in steel specimen. Nitrogen quantity into steel increased with decreasing carbon content. After decarburization annealing, the steel sheets were coated with MgO powder to form insulation oxide film during secondary recrystallization. The quality of insulator film was influenced by decarbirizarion temperature. Porous film was formed in the specimen decarburized at low temperature. The reason is that a little SiO2 layer on the specimen surface and not enough to react with MgO to form dense insulator film. The structure of the oxide film is spinel MgAl2O4. On the contrary, dense insulator film was formed in the specimen decarburized at high temperature. The structure of the oxide film is forsterite (Mg2SiO4) and spinel (MgAl2O4). After secondary recrystallization, specimen with preheating and decarburized at 850oC in the primary annealing occurred complete abnormal grain growth and had the best magnetic property.

碩士
國立雲林科技大學
機械工程系碩士班
100
This study mainly investigated that using hot band decarburization annealled time process of 2mins& 5mins to observe the microstructure and texture differences to check the differences of the grain size after primary recrystallization annealing. With the decarbonization process and nitriding process to explore the variation in thickness of the oxide precipitates size and distribution,and to view its follow-up processes. Secondary recrystallization annealing macroscopic organization and the theory of grain growth situation as compared to identify a suitable grain size and permeability of nitrogen. Using the above analysis methods and annealing processes to deal with different hot band annealing process .the nitriding process to explore the secondary recrystallization behaviors and the effect of the magnetic properties. By observating hot band decarburization annealing at different times, I found that the lamellar structure of the hot band and the average distance between time recrystallization annealing temperature for primary recrystallization grain size have a great impact. Furthermore, the primary recrystallization annealing of decarbonization time changes in the different view of the variation in thickness of the oxide layer and its follow-up process , after which the precipitate size and distribution of different nitriding processes observed and found to 540ppm the infiltration nitrogen for the final magnetic propertieshave a great impact with the core loss. Finally, in this study the best experimental condition, hot-band decarburization annealed 5 minutes after the primary recrystallization decarburization annealing 750℃、5 minutes,the nitridation 750℃、20 seconds、1.7(L/min),annealing recrystallization front by the second temperature 995℃,holding temperature for 12 hours to achieve the best experimental value of flux density and iron loss.

碩士
國立雲林科技大學
機械工程系碩士班
97
Grain-oriented electrical steel is an important function material used as lamination core in various transformers. Its magnetic properties affect the energy efficiency of electrical machines. Therefore, based on academic interest and industrial application, it is worthwhile to study grain oriented electrical steels. This study investigated the effect of aluminum content on grain oriented electrical steel by acquired inhibitor method. There are two parts in this thesis. The first part is effect of hot band annealing temperature and cold-rolled reduction on the magnetic properties of grain oriented electrical steels. The second part is effect of decarburization temperature on the magnetic properties of grain oriented electrical steels. In the first part, it was found primary recrystallization grain size decreased with increasing cold-rolled reduction ratio. Furthermore, primary recrystallization grain size increased with increasing hot band annealing temperature. Secondary recrystallization grain size increased with decreasing hot band annealing temperature. Abnormal grain growth didn’t occur in the specimens with heavy cold rolled reduction. Therefore, the specimens with 0.35mm thickness and hot band annealing at 1050℃,had complete abnormal grain growth and got the best magnetic properties. In the second part, it was found that abnormal grain growth and magnetic properties were improved by nitriding treatment. Primary recrystallization grain size increased with increasing decarburization temperature. Decarburization at 700℃ could obtain the best magnetic properties after secondary recrystallization. After primary recrystallization annealing, main texture concentrated in γfiber (111) , and the strongest intensity was in (111) <1-21>. However, the best magnetic properties are obtained in the steel with 0.035wt% aluminum. The precipitates were identified as coarse Si3N4 and fine MnSiN2, AlN and Mn6N2.58 after nitriding treatment and primary recrystallization annealing.

碩士
國立雲林科技大學
機械工程系碩士班
95
Grain oriented electrical steel is an important function magnetic material. It has excellent permeability during magnetization. Grain oriented electrical steel is usually used to make the transformer cores. It’s magnetic properties affecting the energy efficiency of electric machinery. Proper size and distribution of inclusions can impede the normal grain growth during primary annealing and let the preferred Goss grain grow during secondary recrystallization. After hot band annealing, it was found that the volume fraction of recrystallized grain increases with increasing annealing temperature. It was also found Si3N4 and V2C precipitates existed in the matrix. Nitrogen content in the steel sheet increases with increasing annealing temperature and decarburization influence it, too. The best induction(B8) was obtained when the nitrogen content in the steel sheet was 200-320ppm. After primary recrystallization annealing and nitriding, AlN and vanadium carbide was found. The grain growth was inhibited by these precipitates. Different materials and inhibitors affect the Goss texture development during secondary recrystallization. Stable secondary recrystallization and the best magnetic properties are obtained for the specimens annealing at 1150℃ in hot band stage.

碩士
雲林科技大學
機械工程系碩士班
98
Grain oriented electrical steels are used to make transformer cores. Its magnetic properties will directly affect the energy efficiency of electrical machinery. Therefore, this study investigated the heating rate in primary recrystallization annealing on the magnetic properties of grain oriented electrical steels. It was found that both residual carbon content and injection nitrogen into steel after primary annealing was affected by the decarbonization temperature and heating rate. The reason was that the thickness of SiO2 oxidation layer was influenced by decarbonization temperature and heating rate. When the heating rate was slow or decarburization temperature was high, the oxide layer became thick. On the contrary, if the heating rate was fast or decarburization temperature was low, the oxide layer became thin. If the oxide layer was thick, it hinder the diffusion of carbon atom to the surface to react with water gas. It also prevented the infiltration of ammonia to inject into steel sheet. In order to effectively control the grain size after primary annealing to drive abnormal grain growth occurred during secondary recrystallization. An appropriate primary recrystallization grain size was among 24μm to 27μm. When the (110) &lt;001> Goss texture intensity was strong, it had better magnetic properties. Dense Mg2SiO4 and MgAl2O4 insulation layer formed in slow heating rate during decarburization annealing due to more silica to react with MgO. The optimum condition to obtain the best magnetic properties was kept the heating rate of 300 ℃ / sec and decarbonized at 850 ℃. Its flux density was 1.915Tesla and its grain focused in (110) &lt;001> direction.

碩士
國立雲林科技大學
機械工程系碩士班
100
The effect of coating powder composition on the secondary recrystallization behavior of grain oriented electrical steel was studied. Three hot rolled bands that were annealed in different methods were cold rolled to 0.285mm. Then the specimens were decarburized at 750, 800, and 850oC and injected with nitrogen. After secondary recrystallization annealed at 960, 980, 995 and 1010oC, the macrostructure, texture and magnetic properties were measured. It was found that oxide layer thickness increased with increasing decarburization temperature. Conversely, the nitrogen content in steels decreased with increasing decarburization temperature. Furthermore, the optimum condition to obtain best magnetic properties was that specimen decarburized at 750oC with grain size in 12-14μm, and ammonia flow rate at 0.5 liter per minute with nitrogen content in 420-580 ppm. After secondary recrystallization, the predominant phase in coating film was Mg2SiO4 in the specimens coated with MgO + TiO2+Na2B4O7, MgO+V2O3+CrN, and MgO+MgSO4+FeSO4+Na2B4O7. On the other hand, the predominant phase in coating film was Mg2Al4Si5O18 in the specimens coated with MgO + TiO2+Sb2(SO4)3. The mechanism was that melting temperature of coating flux affected the film porosity and dissociation of aluminum nitride in steels. The specimen that coated with MgO + TiO2+Na2B4O7 and secondary recrystallization annealed at 995oC had the best magnetic properties. Its flux density reached 1.92 T and core loss was 0.98 watt/Kg. EBSD also showed its Goss texture were more concentration.

碩士
國立雲林科技大學
機械工程系碩士班
92
This thesis studied the effect of cold rolling process and nitriding condition on the primary annealing microstructure, size and distribution of precipitates, texture, secondary recrystallization behaviors and magnetic properties of aluminum and manganese sulfide added grain oriented electrical steels. It was found that there were little difference in the primary recrystallization grain size between the specimens conducted by 85 % one stage cold reduction and 50 % two stage cold reduction respectively. It was also found that specimens nitriding in hydrogen and nitrogen mixed atmosphere could not formed enough aluminum nitride precipitates to impede the normal grain growth. But specimens conducted by one stage cold roll reduction had more strongerγ-fiber(111) texture than specimens conducted by two stage cold roll reduction. On the contrary, specimens conducted by two stage cold roll reduction had more stronger (110)<001> texture than specimens conducted by one stage cold roll reduction. Both specimens occurred partial secondary recrystallization after annealed at 1100℃. After high temperature annealing, the magnetic properties of two stage cold reduction specimen were better than one stage cold roll reduction specimens. It was found that nitriding in cracked ammonia atmosphere increase the nitrogen content in the specimens. Furthermore, there exits a nitrogen gradient from the surface to the center of the specimens. EDS shows that most of the precipitates are composite type. There are composite of Si2ON2 and MnS. The nitrogen content and the quantities of precipitates in the specimens also increased with increasing nitriding time. After high temperature annealing, only part of the specimens occurred abnormal grain growth. Therefore, the magnetic properties of the specimens were poor. Before final high temperature annealing, specimens holded at 900℃ to let precipitate come out had little improvement in the development of secondary recrystallization. However, slow heating rate in the final high temperature have positive improvement in the development of secondary recrystallization.

碩士
國立雲林科技大學
機械工程系碩士班
99
Grain-oriented electrical steels are used to make transformer cores. In the rolling direction of steels has excellent magnetic,and magnetic will directly affect the efficiency of mechanical energy ,magnetic influence of the main precipitation inhibitor, primary recrystallization grain size and txture to play final evolution of the three magnetic role. This research aims to explore the different hot-band annealing process in the texture organization changes, and primary recrystallization precipitation size and distribution and the texture changes, and to explore the theory of grain growth behavior, followed by secondary recrystallization annealing at different annealing temperatures to explore the secondary abnormal grain growth temperature, and heat treatment process by the above analysis to explore the different hot-band annealing process on magnetic properties of the final value of the relationship with the iron loss. First explore the hot-band annealing conditions and different annealing time, the hot-band rolling direction the microstructure of the organization,lamellar spacing was found for the primary recrystallization grain size have a significant impact, follow-up of the surface of hot-band annealing to the center, texture changes, found that when the annealing time increases center Goss{110}&lt;001> texture on the increases, then annealing of hot-band surface to 1/4 in Goss orientation content changes. For the primary recrystallization annealing of precipitate size and distribution of precipitation inhibitor found strength and primary recrystallization grain size is closely related to the driving force, between the two need to get a balance to facilitate follow-up to the secondary recrystallization annealing abnormal grain growth has occurred complete. In the secondary recrystallization annealing, must choose the appropriate initial temperature of secondary recrystallization, the purpose is to produce the abnormal grain growth complete, so that Grain-oriented electrical steels can get best value of flux density and iron loss. In this study the best experimental condition, hot-band decarburization annealed 5 minutes after the primary recrystallization decarburization annealing 730℃、5 minutes,the nitridation 750℃、20 seconds,annealing recrystallization front by the second temperature 995℃,holding temperature for 12 hours to achieve the best experimental value of flux density and iron loss.

碩士
國立雲林科技大學
機械工程系碩士班
100
To coat glassy film on the steel sheet surface is an important process in the production of grain oriented electrical steel. It could provide insulation, antirust and improve the magnetic properties. This study investigated the effect of coating film composition on the secondary recrystallization behaviors. It was divided into two parts. Part 1 was designed to find the optimum condition of the hot band annealing and primary annealing to obtain the abnormal grain growth. And part 2 investigated the effect of coating film composition on the secondary recrystallization behavior and magnetic properties.It was found that the residual carbon content increased and injection nitrogen content decreased with increasing decarburization temperature. The reason was that the oxidation layer thickness increased with increasing decarburization temperature. It hindered the diffusion of carbon atom to the surface to react with water gas. It also prevented the infiltration of nitrogen atom into steel sheet. In addition, when the decarburization temperature was higher, the grain size also became coarser. And the driving energy became littlefor occurrence of secondary recrystallization. It caused incomplete abnormal grain growth. The appropriate primary grain size was among 15μm to 16μm. The optimum condition to obtain the best magnetic properties was two-stage hot band annealing and decarburized at 730 ℃ and secondary recrystallization at 995 ℃. After coated with four film compositions, secondary recrystallization was conducted at 965℃～1025℃. It was found that specimens coated with MgO + TiO2 + Na2B4O7 and MgO + V2O5 + CrN obtained the better magnetic properties after secondary recrystallization annealed at 995℃. Its the flux density was 1.918 Tesla and 1.901Tesla, and W15/50 was 0.98 Watt/Kg and 0.96 Watt/Kg respectively.

碩士
國立雲林科技大學
機械工程系碩士班
93
This thesis studied the effect of the parameter of acquired inhibitor method by injection nitrogen into the hot-rolled bands on the amount, size and distribution of precipitates in to grain oriented electrical steels. After hot band annealing and cold rolling, the effects of nitriding conditions on the behaviors of primary annealing and secondary annealing were also studied. It was found that both nitrogen content and nitriding thickness increased with increasing nitriding time. The precipitates were identified as alpha-Si3N4 and their amounts quickly decreased with thickness. The intensity of{100}〈001〉in the annealed hot band increased from the surface to the center. On the contrary, the intensity of {110}〈001〉gradually decreased from the surface to the center. Furthermore, nitriding specimen has more strong {110}〈001〉texture than that without nitriding. After primary annealing, the nitrogen content in the specimen decreased. Alpha- Si3N4 precipitates existed near the surface and (Al,Si)N precipitates existed in the central portion. It shows that alpha-Si3N4 transform to AlN during high temperature annealing. After secondary recrystallization, coarse Goss grains converged within 10-20 degree were measured by EBSD technique. Since Goss grain converged in 10-20 degree, the magnetic properties don’t meet the industrial standard.

碩士
國立雲林科技大學
機械工程技術研究所
88
Grain oriented electrical steel is an important function materials used as laminated cores of transformers. Its magnetic properties influence the efficiency of transformers. This study investigate the effects of carbon contents and various process variables on the magnetic properties of oriented electrical steels added with MnS and AlN inhibitors. The carbon content in the steels is 0.034 and 0.004wt% respectively. The process variables studied are slab reheating temperature, hot band annealing temperature, intermediate annealing temperature, heating rate and secondary recrystallization temperature. Meanwhile, the microstructure, inclusion, texture and magnetic properties at various stages are studied. It is found that the intensity of (110)<001> component exists at the surface and quarter thickness and is weak at the center during the stages of hot rolling, hot band annealing and intermediate cold-roll annealing in the electrical steel containing 0.004wt% carbon. However, strong Goss texture develop after secondary recrystallization annealing in certain process conditions. It is better to get lower core loss for the specimens reheated to 1100℃ than 1300℃. Core loss decreases with increasing secondary recrystallization temperature. Low slab reheating temperature is also benefit to magnetic flux density and permeability. Maximum magnetic flux density and permeability exists at certain optimum process condition. Slab reheating temperature affects the solubility of MnS and AlN inclusions in steels. At 1300℃, MnS and AlN almost dissolve in the steel matrix. After hot band annealing, fine inclusion comes out uniformly and impedes the primary recrystallization. It also increases the start temperature of secondary recrystallization. Therefore, specimen that reheated to 1300℃ has less completely secondary recrystallization and develop weak Goss texture. On the other hand, specimens that reheated to 1100℃ has coarse inclusion and lower secondary recrystallization start temperature. After secondary recrystallization, it develops strong Goss texture and gets better magnetic properties.

碩士
國立雲林科技大學
機械工程系碩士班
100
This study investigated the effect of primary recrystallization temperature, from 725 to 800 °C, partial pressure ratio of water to hydrogen, ammonia flow rate, and secondary recrystallization temperature on the microstructure, size and volume of precipitates, thickness of the oxide layer, secondary recrystallization behavior, magnetic properties of two-stage hot band annealing grain-oriented electrical steel During annealing at 750 °C, and dew point setting at 42 °C, the calculated effluent gas partial pressure ratio was 0.267. Then the carbon content could decrease to 45 (ppm). Moreover, the primary grain size was 18.5 μm and the thickness of the oxide layer is 1.45 μm. The injection nitrogen into steel sheet increased with increasing ammonia flows rate and nitriding time. The optimum conditions to obtain the best abnormal grain growth and magnetic properties for the two-stage hot band annealing grain oriented electrical steels was primary annealed at 750 °C for 5 minutes. Then nitriding was conducted at 750 °C for 30 seconds. Finally, secondary recrystallization was performed at 995 ° C for 12 hours. The flux density, B8, reached 1.926 Tesla and the iron loss, W15/50, was 1.04 watt / kg. Keywords: grain-oriented electrical steel steel, iron loss, magnetic flux density.

碩士
國立雲林科技大學
機械工程系碩士班
91
Grain oriented electrical steel is an important function material used as lamination cores of transformers, and it’s magnetic property directly affects the efficiency of electric machinery equipment. Traditional process needs high temperature to dissolve larger inclusion, but there are metallurgical problems of controlling secondary recrystallization and the disadvantage of consuming energy in high temperature. Therefore, this investigation discuss the effect of using acquired inhibitor method for microstructure and precipitate of oriented electrical steel in secondary recrystallization. High Aluminum specimen can’t obtain secondary recrystallization after final annealing, because reheating temperature needs up to 1350℃ that MnS and AlN are able to dissolve in the steel matrix. So this result can’t provide suitable precipitate before secondary recrystallization. In addition, nitriding reaction didn’t occur to form AlN. Therefore, it can’t prevent normal grain growth during final annealing. Low aluminum specimen cause local grain development due to inhomogeneous precipitate distribution. When slow heating rate(0.2℃/min) and injecting pure nitrogen gas by final annealing favor grain growth of low aluminum specimen. It’s grain is more coarse. We can obtain better core loss and permeability. For the change of heating rate and nitrogen gas ratio on the high aluminum sample can’t get good magnetic property because it’s abnormal grain growth didn’t occur during final annealing.

碩士
國立雲林科技大學
機械工程系
103
The effect of as hot rolled and two stage annealing hot band and low primary annealing temperature and nitriding process on the microstructure, texture, carbon and nitrogen content, size and volume fraction of precipitates and magnetic properties were studied. It was found that inter lamellar distance of as hot rolled specimen was shorter than two stage annealing specimen. The intensity of η fiber and (011)<100> texture in as hot rolled band decreased from surface to central. However, the intensity of (001)<100> texture increased from surface to central. Furthermore, the intensity of α fiber texture was strong at surface and subsurface. After two stages annealing, there were more recrystallized grain at the surface layer of hot band. The intensity of η fiber and (011)<100> texture at subsurface were stronger than surface. The intensity of (001)<100> was almost the same. Moreover, the intensity of α fiber and γ fiber texture was similar to that in the as hot rolled specimen. After primary annealing, it was found that specimen decarburized at 650oC had the optimum grain size and nitrogen content. There were several precipitates, such as AlN, Si3N4, TiN, and MnS existed in the specimen. The optimum nitrogen content for magnetic properties was 210ppm. The optimum process parameters in this study were hot band annealed 1120oC for 10 seconds, cooled down to 920oC kept 2 minutes. Then, cold rolled steel sheet was decarburized at 650oC for 5 minutes and heated up to 700oC nitriding 30 seconds with NH3 flow at 1.8 L/min. During secondary recrystallization annealing, the specimen was heated up to 935oC soaking for 12 hours and purified at 1200oC for 12 hours.