The cleanliness of high strength low alloy (HSLA) steel was assessed qualitatively and quantitatively. The determination of inclusion type and inclusion morphology were carried out using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED) method allowing in-situ examination of inclusion morphology by analytical techniques such as SEM/EDS. Inclusion size analysis mainly involved a combination of an analytical technique to provide images of the sample surface and an image analysis system to accurately measure the inclusion size. Four analytical methods were compared in order to evaluate their suitability for subsequent quantitative analysis. It was found that images taken with backscattered electron imaging mode from the scanning electron microscope provides the most accurate representation of inclusion distribution. The various techniques were used to evaluate HSLA steel grades of similar chemistry produced with and without gas shrouding. The results confirmed that with reoxidation minimized by gas shrouding between ladle and tundish, the steel cleanliness was significantly improved.

The cleanliness of high strength low alloy (HSLA) steel was assessed qualitatively and quantitatively. The determination of inclusion type and inclusion morphology were carried out using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED) method allowing in-situ examination of inclusion morphology by analytical techniques such as SEM/EDS. Inclusion size analysis mainly involved a combination of an analytical technique to provide images of the sample surface and an image analysis system to accurately measure the inclusion size. Four analytical methods were compared in order to evaluate their suitability for subsequent quantitative analysis. It was found that images taken with backscattered electron imaging mode from the scanning electron microscope provides the most accurate representation of inclusion distribution. The various techniques were used to evaluate HSLA steel grades of similar chemistry produced with and without gas shrouding. The results confirmed that with reoxidation minimized by gas shrouding between ladle and tundish, the steel cleanliness was significantly improved.

Thèse de doctorat : Géosciences : Nancy 1 : 2008. / Titre provenant de l'écran-titre.

No description available.

A fabricação de aços com elevada qualidade interna está diretamente relacionada ao entendimento de como inclusões não-metálicas se comportam ao longo de cada etapa do processo. Aços com maior limpeza inclusionária são cada vez mais solicitados à medida que aplicações mais nobres e específicas são exploradas, a exemplo das novas gerações de wheel hub. O aço SAE 52100, utilizado na fabricação de rolamentos, é um dos casos em que o controle para a quantidade, distribuição, tamanho e morfologia das inclusões deve ser rígido, para que atenda à aplicação a que se destina. A compreensão dos fenômenos que estão envolvidos na formação e os possíveis métodos para evitar ou tornar menos deletérias inclusões não-metálicas são de suma importância. Neste estudo, amostras de aço e escórias foram retiradas em várias etapas do processo de fabricação do aço em aciaria elétrica. As amostras de aço foram analisadas em MEV/EDS ASPEX (microscopia eletrônica de varredura acoplada à espectrometria de energia dispersiva automático) e de escórias via XRF (fluorescência de raios X). Aliado a isso, dados obtidos via simulação termodinâmica (software comercial FactSage) possibilitaram compreender melhor a interação entre escória-banho e de que forma parâmetros das escórias, por exemplo, influenciam na formação, modificação e remoção de inclusões não-metálicas em aços para rolamentos. A correlação entre os dados de processo e as análises realizadas permitiram mapear como cada operação adotada em refino secundário influencia na limpeza do aço ao final do processo. O objetivo deste estudo é estabelecer de forma clara como as inclusões no aça SAE 52100 com processo de produção específico se comportam ao longo do processamento em Aciaria Elétrica. Além disso, visa estudar de forma mais clara como as interações escória/banho influenciam na modificação da composição química das inclusões e na sua remoção ao final do processo. / The manufacture of steel with high internal quality is directly related to the understanding of how non-metallic inclusions behave along each step of the process. Steels with higher inclusions cleanliness are increasingly requested as more noble and specific applications are explored, as the new generation of wheel hub. The SAE 52100 steel, used in the manufacture of bearings, is one case that the control for the amount, distribution, size and morphology of the inclusions must be hard to meet the application for that it is intended. The understanding of the phenomena involved in the formation and the possible methods to prevent or to turn less harmful non-metallic inclusions are too important. In this study, steel and slag samples were taken at various stages of the meltshop process. The steel samples were analyzed by SEM / EDS ASPEX (automatic scanning electron microscopy coupled to energy dispersive spectrometry) and slag via XRF (X-ray fluorescence). Allied to this, data via thermodynamic simulation (commercial software FactSage) allowed better understanding of the interaction between slag-bath and how parameters of slag, for example, influence the formation, modification and removal of non-metallic inclusions in bearings steel. The correlation between the process data and the analyzes, allow map how each operation adopted in secondary metallurgy influence on steel cleanliness at the end of the process. The objective of this study is to establish clearly how the inclusions in the SAE 52100 steel with specific production process behave throughout Meltshop process. In addition, it aims to study more clearly how the slag / bath interactions influence the modification of the chemical composition of the inclusions and their removal at the end of the process.

A fabricação de aços com elevada qualidade interna está diretamente relacionada ao entendimento de como inclusões não-metálicas se comportam ao longo de cada etapa do processo. Aços com maior limpeza inclusionária são cada vez mais solicitados à medida que aplicações mais nobres e específicas são exploradas, a exemplo das novas gerações de wheel hub. O aço SAE 52100, utilizado na fabricação de rolamentos, é um dos casos em que o controle para a quantidade, distribuição, tamanho e morfologia das inclusões deve ser rígido, para que atenda à aplicação a que se destina. A compreensão dos fenômenos que estão envolvidos na formação e os possíveis métodos para evitar ou tornar menos deletérias inclusões não-metálicas são de suma importância. Neste estudo, amostras de aço e escórias foram retiradas em várias etapas do processo de fabricação do aço em aciaria elétrica. As amostras de aço foram analisadas em MEV/EDS ASPEX (microscopia eletrônica de varredura acoplada à espectrometria de energia dispersiva automático) e de escórias via XRF (fluorescência de raios X). Aliado a isso, dados obtidos via simulação termodinâmica (software comercial FactSage) possibilitaram compreender melhor a interação entre escória-banho e de que forma parâmetros das escórias, por exemplo, influenciam na formação, modificação e remoção de inclusões não-metálicas em aços para rolamentos. A correlação entre os dados de processo e as análises realizadas permitiram mapear como cada operação adotada em refino secundário influencia na limpeza do aço ao final do processo. O objetivo deste estudo é estabelecer de forma clara como as inclusões no aça SAE 52100 com processo de produção específico se comportam ao longo do processamento em Aciaria Elétrica. Além disso, visa estudar de forma mais clara como as interações escória/banho influenciam na modificação da composição química das inclusões e na sua remoção ao final do processo. / The manufacture of steel with high internal quality is directly related to the understanding of how non-metallic inclusions behave along each step of the process. Steels with higher inclusions cleanliness are increasingly requested as more noble and specific applications are explored, as the new generation of wheel hub. The SAE 52100 steel, used in the manufacture of bearings, is one case that the control for the amount, distribution, size and morphology of the inclusions must be hard to meet the application for that it is intended. The understanding of the phenomena involved in the formation and the possible methods to prevent or to turn less harmful non-metallic inclusions are too important. In this study, steel and slag samples were taken at various stages of the meltshop process. The steel samples were analyzed by SEM / EDS ASPEX (automatic scanning electron microscopy coupled to energy dispersive spectrometry) and slag via XRF (X-ray fluorescence). Allied to this, data via thermodynamic simulation (commercial software FactSage) allowed better understanding of the interaction between slag-bath and how parameters of slag, for example, influence the formation, modification and removal of non-metallic inclusions in bearings steel. The correlation between the process data and the analyzes, allow map how each operation adopted in secondary metallurgy influence on steel cleanliness at the end of the process. The objective of this study is to establish clearly how the inclusions in the SAE 52100 steel with specific production process behave throughout Meltshop process. In addition, it aims to study more clearly how the slag / bath interactions influence the modification of the chemical composition of the inclusions and their removal at the end of the process.

No description available.

Aluminum alloy castings are becoming commonplace for critical applications in the automotive and aerospace industries where materials failure is not an option. In order to meet such property demands, tight control over the cleanliness of the melt (mitigation of solid particle inclusions) and microstructure must be achieved. In order to control cleanliness, it must first be well defined and measured. Very few techniques exist in industry that can quantitatively measure inclusion levels in-situ. Laser-induced breakdown spectroscopy (LIBS) is presented as a promising technique to quantify solid particles, desired or undesired, in aluminum melts. By performing LIBS with subsequent statistical analysis on liquid aluminum with varying concentrations of Al2O3, AlB2, TiB2, and SiC particles, calibration curves relating particle concentration and elemental intensity were drawn. Through metallography and automated electron microscopy, it was found that inclusions less than 10 um in size could be detected with LIBS. Concentrations down to at least one part-per-million could be detected and accurately measured, allowing for LIBS to be use as a tool for complete, real-time melt cognition.

The unique Selukwe Subchamber of the Great Dyke is bounded by the Shurugwi greenstone belt (SGB) on the west side for approximately 25 km and granitoids on the east side, as compared to other subchambers of the Great Dyke that are bounded on both sides by granitoids. It is also the narrowest section of the entire Great Dyke. The extensive xenolith suite is found on the western flank and the central zone of the subchamber. This study focuses on the PAR 11 borehole and the surface xenoliths in the Selukwe Subchamber (SSC). The PAR 11 core was drilled into an anomalous sequence of ultramafic rocks situated in the Mafic Succession of the SSC. There are basically two rock types in the PAR 11 borehole: peridotites and pyroxenites. Comparison of the major and trace element geochemistry of the PAR 11 body with the MR 92 data of Coghill (1994) for the SSC reveals that they are similar but less evolved. The mineral assemblages and proportions of phases in the PAR 11 borehole samples are indicative of essentially the same composition as that which formed the layered sequence of the Great Dyke. Therefore, on the basis of the rock types and chemical compositions, the PAR 11 body and the Great Dyke cumulates appear to be petrologically and chemically similar and had the same petrogenesis. There are three rock types in the xenolith suite that have been observed in the mafic succession of the Unki area: peridotites, pyroxenites and gabbros. Major and trace elements show a wide range of compositions that have CaO/Al2O3 ~ 1, which are dissimilar to both PAR 11 and MR 92 borehole data. REE patterns show depletion of LREE, with flat HREEs indicating a different magma to that which gave rise to the Great Dyke. Such flat patterns are typical of a primitive mantle source similar to that of komatiite magma. Stowe, (1974) describes dunite and chromite in the SGB and does not describe pyroxenites and gabbros. Therefore, it is not clear in the first instance that the xenoliths were derived from the SGB. It also does not necessarily mean that these rock types did not occur in the SGB and, if they did, maybe they were derived from an intrusion within the SGB that is at depth and never been seen iv before. The xenoliths do not have mineral compositions that are similar to the Great Dyke and therefore precludes them as having been derived from the Great Dyke Marginal Facies, a possible source of such rocks. Therefore, it is concluded from this study that they were inherited from another source which also does not appear to be the SGB because there is no report of such rock types (other than peridotite) in the SGB. They are also not mantle derived. The metasedimentary rocks that occur as xenoliths are banded iron formation and quartzites and are all clearly derived from the different formations of the SGB. The quartzites are from the Mont d’Or Formation and Wanderer Formation. The BIFs are from the Upper Greenstone and Wanderer Formation. The Shurugwi Greenstones were stripped off from the western flank whereas the Archean granitoids to the eastern flank of the Great Dyke remained. The conclusion from this study is that the Shurugwi greenstones and Archean granitoids of the Selukwe area were intruded by the large volume of new magma that was the parental magma to the Great Dyke. The hot parental magma carried up with it xenoliths from outside the Great Dyke and large blocks from within the Great Dyke to the uppermost rocks of the level of the P1 pyroxenite layer and mafic unit.

Neste trabalho foram estudadas 10 corridas em duas usinas siderúrgicas semi-integradas, de aço baixa liga para uso em construção mecânica. Em cada uma das corridas foram retiradas 9 amostras, cada uma ao final de uma etapa do processo de produção: após a remoção de escória na panela, antes da desgaseificação a vácuo, após a desgaseificação a vácuo, após a adição de arame de Al, após a adição de arame de CaSi, após a adição de arame de S, após o fim da turbulência no distribuidor no lingotamento contínuo, 30 minutos após o fim da turbulência no distribuidor no lingotamento contínuo, e 60 minutos após o fim da turbulência no distribuidor no lingotamento contínuo. As amostras foram preparadas metalograficamente e analisadas ao microscópio eletrônico de varredura (MEV) com espectrometria de dispersão de energia (EDS), a fim de se identificar as inclusões presentes no aço em cada etapa do processo. Com isto pode-se fazer a caracterização das inclusões encontradas em cada etapa do processo e a sua classificação segundo a composição química e morfologia. Através da comparação da composição química das inclusões encontradas ao final do refino e no lingotamento contínuo foi possível verificar uma tendência de formação de inclusões de espinélio, e através da composição química das inclusões encontradas no lingotamento contínuo foi possível identificar em quais das corridas estudadas houve a presença de inclusões de aluminatos de cálcio formados no estado líquido. / In the present work it was studied 10 heats in two steelworks, of low alloyed steel for use in mechanical construction. From each heat were taken 9 samples, each one of them at end of one production stage: after deslagging in the ladle; before vacuum degassing; after vacuum degassing; after Al wire addiction; after CaSi wire addiction; after S wire addiction; after the end of tundish turbulence at continuously casting; 30 minutes after the end of tundish turbulence at continuously casting; and 60 minutes after the end of tundish turbulence at continuously casting. Samples were metallographic prepared and analyzed by scanning electronic microscopic (SEM) with energy dispersive X-ray spectroscopy (EDX), in order to identify the inclusions present in steel in each process stage. This allowed the founded inclusions in each process stage to be characterized and classified according to chemical composition and morphology. By comparing founded inclusions chemical composition at end of refining and continuous casting was possible to observe a tendency of formation of spinel inclusions, and by founded inclusions chemical composition in continuous casting was possible to identify in which studied heats there were presence calcium aluminates inclusions formed in the liquid state.