Das Promotionsthema war die numerische Untersuchung des Einflusses der mechanisch induzierten martensitischen Phasenumwandlung auf das Bruchverhalten hochlegierter TRIP-Stähle. Die Analyse der Spannungsfelder vor einer abstumpfenden Rissspitze hat ergeben, dass die Phasenumwandlung zu höheren rissöffnenden Spannungen führt. Außerdem wurden charakteristische Spannungsverläufe mit Wendepunkten beobachtet. Für duktiles Versagen wurde ein positiver Einfluss der Phasenumwandlung geschlussfolgert, da die umwandlungsinduzierte Verfestigung das Porenwachstum in der Bruchprozesszone erschwert. Dies wurde an Hand mikromechanischer Simulationen der duktilen Rissausbreitung demonstriert. Im Rahmen der Theorie materieller Kräfte konnte eine abschirmende Wirkung des TRIP-Effekts auf die Rissspitze nachgewiesen werden. Durch Phasenumwandlung wird Arbeit dissipiert, die nicht mehr für Rissfortschritt verfügbar ist. Die energetische Triebkraft für Risswachstum wird demzufolge reduziert. Die Rissausbreitung im TRIP-Stahl wurde mit einer Kohäsivzone modelliert. Die Parameter des Kohäsivzonenmodells charakterisieren den Bruchprozess und konnten unter Verwendung experimenteller Daten identifiziert werden. Um zukünftig die Rolle der Phasenumwandlung bei Ermüdungsrisswachstum untersuchen zu können, wurde ein Materialmodell für TRIP-Stähle unter zyklischer Beanspruchung entwickelt. Die erforderlichen Materialparameter wurden mit Hilfe der Daten aus Wechselverformungsversuchen bestimmt. / This thesis is focused on the numerical investigation of the fracture behavior of high alloy austenitic TRIP-steels and especially on the effect of mechanically induced martensitic phase transformation. The analysis of stress fields in front of a blunting crack tip has shown that phase transformation leads to higher crack opening stresses. Additionally, characteristic courses of the stress components with inflection points were observed. A positive influence of phase transformation on ductile fracture was concluded, because transformation induced hardening retards void growth in the fracture process zone. This was demonstrated by micromechanical simulations of ductile crack extension. In order to investigate the shielding effect of phase transformation on the crack tip, the theory of material forces was applied. Mechanical work is dissipated due to the TRIP-effect, which is no longer available for crack growth. Hence, the energetic driving force for fracture is reduced. Furthermore, crack extension is modeled with a cohesive zone. The parameters of the cohesive zone model, which characterize the fracture process, are identified based on experimental data. In future work the role of phase transformation during fatigue crack growth should by studied. Therefore, a material model for TRIP-steels under cyclic loading was developed. The associated material parameters were estimated based on the results of cyclic deformation experiments.

Modeling the interaction of a silicon (Si) surface with a pointed asperity is a crucial step towards the understanding of several phenomena related to machining of this important semiconductor. If subjected to pressure or contact loading, Si undergoes a series of stress-driven phase transitions accompanied by large volume changes. We developed a finite deformation constitutive model that captures the semiconductor-to-metal (cd-Si ➙ β-Si) and metal-to-amorphous (β-Si ➙ a-Si) transitions within the framework of thermodynamics with internal variables. The model was implemented as a user material subroutine for the finite element code Abaqus/Std. in analogy to pressure sensitive, rate independent, non-associated, non-smooth multisurface plasticity. Material parameters were identified from indentation load-displacement curves in (111)-Si using a Berkovich indenter tip. The constitutive model was verified by successfully predicting the load-displacement curves for different indenters, the residual surface profile, as well as the size and shape of the transformation zone under the indenter tip as compared to TEM results.

Ti-Nb alloys are characterized by a diverse metallurgy which allows obtaining a wide palette of microstructural configurations and physical properties via careful selection of chemical composition, heat treatment and mechanical processing routes. The present work aims to expand the current state of knowledge about martensite forming Ti-Nb alloys by studying 15 binary Ti-c_{Nb}Nb (9wt.% ≤ c_{Nb} ≤ 44.5wt.%) alloy formulations in terms of their structural and mechanical properties, as well as their thermal stability. The crystal structures of the martensitic phases, α´ and α´´, and the influence of the Nb content on the lattice (Bain) strain and on the volume change related to the β → α´/α´´ martensitic transformations are analyzed on the basis of Rietveld-refinements. The magnitude of the shuffle component of the β → α´/α´´ martensitic transformations is quantified in relation to the chemical composition. The largest transformation lattice strains are operative in Nb-lean alloys. Depending on the composition, both a volume dilatation and contraction are encountered and the volume change may influence whether hexagonal martensite α´ or orthorhombic martensite α´´ forms from β upon quenching. The mechanical properties and the deformation behavior of martensitic Ti-Nb alloys are studied by complementary methods including monotonic and cyclic uniaxial compression, nanoindentation, microhardness and impulse excitation technique. The results show that the Nb content strongly influences the mechanical properties of martensitic Ti-Nb alloys. The elastic moduli, hardness and strength are minimal in the vicinity of the limiting compositions bounding the interval in which orthorhombic martensite α´´ forms by quenching. Uniaxial cyclic compressive testing demonstrates that the elastic properties of strained samples are different than those of unstrained ones. Also, experimental evidence indicates a deformation-induced martensite to austenite (α´´ → β) conversion. The influence of Nb content on the thermal stability and on the occurrence of decomposition reactions in martensitic Ti-Nb alloys is examined by isochronal differential scanning calorimetry, dilatometry and in-situ synchrotron X-ray diffraction complemented by transmission electron microscopy. The thermal decomposition and transformation behavior exhibits various phase transformation sequences during heating into the β-phase field in dependence of composition. Eventually, the transformation temperatures, interval, hysteresis and heat of the β ↔ α´´ martensitic transformation are investigated in relation to the Nb content. The results obtained in this study are useful for the development and optimization of β-stabilized Ti-based alloys for structural, Ni-free shape memory and/or superelastic, as well as for biomedical applications. / Ti-Nb Legierungen zeichnen sich durch eine vielfältige Metallurgie aus, die es nach sorgfältiger Auswahl der chemischen Zusammensetzung sowie der thermischen und mechanischen Prozessierungsroute ermöglicht eine große Bandbreite mikrostruktureller Konfigurationen und physikalischer Eigenschaften zu erhalten. Das Ziel der vorliegenden Arbeit ist es den gegenwärtigen Wissensstand über martensitbildende Ti-Nb Legierungen zu erweitern. Zu diesem Zweck werden 15 binäre Ti-c_{Nb} Nb (9 Gew.% ≤ c_{Nb} ≤ 44.5 Gew.%) Legierungen hinsichtlich ihrer strukturellen und mechanischen Eigenschaften sowie ihrer thermischen Stabilität untersucht. Die Kristallstrukturen der martensitischen Phasen, α´ und α´´, sowie der Einfluss des Nb-Gehalts auf die Gitterverzerrung (Bain-Verzerrung), auf die Verschiebungswellenkomponente (Shuffle-Komponente) und auf die Volumenänderung der martensitischen β → α´/α´´ Transformationen werden anhand von Rietveld-Verfeinerungen analysiert. In Abhängigkeit des Nb-Gehalts tritt entweder eine Volumendilatation oder -kontraktion auf, die bestimmen könnte ob hexagonaler Martensit α´ oder orthorhombischer Martensit α´´ aus β bei Abkühlung gebildet wird. Die mechanischen Eigenschaften und das Verformungsverhalten martensitischer Ti-Nb Legierungen werden mit einer Reihe komplementärer Methoden (monotone und zyklische einachsige Druckversuche, Nanoindentation, Mikrohärte, Impulserregungstechnik) untersucht. Die Ergebnisse zeigen durchgehend, dass die mechanischen Eigenschaften martensitischer Ti-Nb Legierungen stark vom Nb-Gehalt beeinflusst werden. Die mechanischen Kennwerte sind minimal in der Nähe der Zusammensetzungen, innerhalb derer β → α´´ bei Abkühlung auftritt. Aus Druckversuchen geht hervor, dass die elastischen Eigenschaften verformter Proben verschieden zu denen unverformter sind. Die experimentellen Ergebnisse weisen außerdem auf eine verformungsinduzierte Umwandlung von Martensit in Austenit (α´´ → β) hin. Der Einfluss des Nb-Gehalts auf die thermische Stabilität und das Auftreten von Zerfallsreaktionen in martensitischen Ti-Nb Legierungen wird anhand von dynamischer Differenzkalorimetrie, Dilatometrie, und in-situ Synchrotronröntgenbeugung in Kombination mit Transmissionselektronenmikroskopie untersucht. Das thermische Zerfalls- und Umwandlungsverhalten ist durch das Auftreten einer Vielzahl von in Abhängigkeit des Nb-Gehalts unterschiedlichen Phasentransformationssequenzen gekennzeichnet. Abschließend werden die Transformationstemperaturen und -wärmen, das Transformationsinterval und die thermische Hysterese der martensitischen β ↔ α´´ Umwandlung untersucht. Die Ergebnisse dieser Arbeit sind für die Entwicklung und Optimierung β-stabilisierter Ti-Legierungen für strukturelle und biomedizinische Anwendungen sowie Ni-freier Komponenten, die Formgedächtniseffekt und/oder Superelastizität aufweisen, von Nutzen.

>Magister Scientiae - MSc / Hydrogen has high energy density and it is regarded as the future energy carrier. Hydrogen can be stored as a gas in high-pressure cylinders, as a liquid in cryogenic tanks and as a solid in metal hydrides. The storage of hydrogen in gas and liquid form has many limitations. Light metal hydrides show high energy density and are a promising and more practical mode of hydrogen storage. In particular, titanium and its alloys are promising metal hydrides for hydrogen storage due to their high affinity to hydrogen. The aim of this study is to investigate the effect of thermal annealing on hydrogen storage capacity of Ti-Pd multilayer systems. Ti-Pd multilayer films were prepared on CP-Ti (commercial pure Ti) and Ti6Al4V substrates using an electron beam evaporator equipped with a thickness monitor. The sequential deposition of layers Pd(50nm)/Ti(25nm)/Pd(50nm) was done at a constant deposition rate of 0.6 Å/s. The first batch of samples were thermally annealed at 550 °C in vacuum for two hours, the second batch of samples were annealed at 550 oC under H2(15%)/Ar(85%) gas mixture for two hours and the third series of samples was annealed under pure H2 gas at 550 oC for one hour. SEM showed relatively homogeneous and smooth topography of surfaces in as-deposited samples, while a rough textured surface was observed in both samples annealed under vacuum and under H2/Ar gas mixture. The samples annealed under pure H2 gas did not show any sign of crystallites grow but instead a relatively smooth surface with sign of etching. XRD revealed structural transformation as evidenced by the presence of PdTi2 phase in samples annealed under vacuum; in samples annealed under the gas mixture Pd2Ti was noted in addition to TiH2 and TiO2. While the TiH2 phase is an indication of hydrogen absorption, the TiPd2 phase suggests intermixing of the deposited layers and the presence of TiO2 is evidence of oxidation. The samples annealed under pure H2 gas showed only TiH2 with no trace of structural transformation. RBS confirmed the intermixing of layers in the samples annealed under vacuum and H2(15%)/Ar(85%) gas mixture, while samples annealed under pure H2 gas did not show any intermixing of layers. ERDA revealed an average H content of ~ 3.5 at.% in CP-Ti and ~6.2 at.% in Ti6Al4V for samples annealed under H2(15%)/Ar(85%) gas mixture. We recorded an hydrogen content of ~19.5 at.% in CP-Ti annealed under pure H2 while ~25.5 at.% was found in Ti6Al4V annealed under the same conditions. When the thickness of the Pd catalyst layers was increased to 100 nm (i.e. Pd (100 nm)/Ti (25 nm)/Pd (100 nm)), only ~ 12.5 at.% and 11.2 at. % hydrogen content was recorded in samples prepared on CP-Ti and Ti6Al4V alloy respectively, both annealed under pure hydrogen for one hour as above.

Dans ce travail, nous nous intéressons à l’étude des propriétés structurales et magnétiques de films déposés sur des substrats de silicium et de verre, qui sont : Fe85Pd15, Fe80Pd20, Fe64Pd36 et Fe56Pd44, ainsi qu’aux corrélations qui peuvent être déduites de ces propriétés. Ces films minces sont élaborés par la technique d’évaporation thermique par effet Joule. Par ailleurs, ces films ont été analysés par plusieurs techniques, à savoir: la diffraction des rayons X (DRX), la microscopie électronique à balayage (MBE), la microscopie à force atomique (AFM), la spectrométrie Mössbauer, la magnétométrie SQUID, la magnétométrie à gradient de champ alternatif (AGFM) et la microscopie à force magnétique (MFM). L’analyse de DRX a révélé que les échantillons Fe80Pd20, Fe64Pd36 sont bi-phasiques et constitués d’une phase (Fe,Pd)-α cubique centrée (cc) et d’une phase FePd cubique à faces centrées (cfc). Par ailleurs, les échantillons Fe85Pd15 et Fe56Pd44 se sont avérés monophasiques et formés de la phase (Fe, Pd)-α, et de la phase FePd respectivement. Concernant les alliages, Fe85Pd15, Fe80Pd20et Fe64Pd36, nous avons trouvé, que la phase (Fe, Pd)-α se saturait à 20 % de Pd; et la phase ‘FePd’ apparaissait à ce même pourcentage. Ensuite, l’alliage Fe56Pd44 déposé sur le silicium a subit un recuit isotherme, à 550°C à différents temps de maintien, dans le but d’induire une transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. La variation, en fonction du temps, de la fraction transformée de la phase ordonnée, révélée par la DRX et le SQUID, s’est avérée obéir à la loi d’Avrami. Concernant les propriétés magnétiques, nous avons trouvé que l’alliage Fe64Pd36, était également le siège de la transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. Cette transformation est marquée par l’existence d’un couplage d’échange entre la phase douce (Fe, Pd)-α et la phase dure L10FePd. Ce phénomène a été mis en évidence par plusieurs techniques révélant, par exemple, la forme du cycle d’hystérésis caractérisée par un champ coercitif élevé et une aimantation à saturation élevée. / In this work, we are interested in the study of the structural and magnetic properties of thin films deposited on silicon and glass substrates which are: Fe85Pd15, Fe80Pd20, Fe64Pd36 and Fe56Pd44, as well as in the correlations which can be deduced from these properties. These thin films are prepared using the thermal evaporation technique by Joule effect. Moreover, these films have been analyzed by several techniques, namely: X-rays diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Mössbauer spectrometry, SQUID magnetometer, alternating field gradient magnetometer (AFGM) and magnetic force microscopy (MFM). The XRD analysis revealed that the Fe80Pd20 and Fe64Pd36 samples are biphasic, and present a body centered cubic (bcc) α-(Fe, Pd) and a face centered cubic (fcc) FePd structure respectively. Furthermore, the samples Fe85Pd15 and Fe56Pd44 were observed to be monophasic and formed of a body centered cubic α-(Fe, Pd) phase and a face centered cubic FePd phase respectively. Concerning the Fe85Pd15, Fe80Pd20 and Fe64Pd36 alloys, we found that the α-(Fe, Pd) phase saturated at 20% of Pd and that the FePd phase appeared at this same concentration. Then, the Fe56Pd44 alloy deposited on silicon substrates was subjected to isothermal annealing, at 550 ° C for different holding times, in order to induce a transformation of the disordered FePd phase into the ordered L10FePd phase. The variation, as a function of time, of the transformed fraction of the ordered phase, revealed by XRD and SQUID, was found to obey to Avrami's law. Concerning the magnetic properties, we have found that the Fe64Pd36 alloy was also observed to present a transformation of the disordered FePd phase into the ordered L10FePd phase. This transformation is marked by the existence of an exchange coupling between the soft α-(Fe, Pd) phase and the hard L10FePd phase. This phenomenon has been confirmed by several techniques revealing, for instance, the shape of the hysteresis cycle characterized by a high coercive field and a high saturation magnetization.

Zincor, a refinery in South Africa, uses the conventional roast-leachelectrowinning process to produce zinc metal. The roasting process of ZnS concentrate makes use of four Lurgi fluidized bed roasters to produce calcine (contains ZnO and ZnFe2O4 as zinc products) and SO2 gas. The roasting plant consists of two 18 m2 and two 35 m2 cross sectional area roasters. Prior to 1996, Zincor utilized air as the only oxidant and fluidizing medium in its roasters. The maximum dry feed rates that the roasters could process were 6.5 t/d.m2. In an attempt to increase production, oxygen enrichment was first trialled and then introduced into the fluidizing air. The ability of oxygen enrichment to increase the rate of the ZnS oxidation reaction allowed higher feed rates to the roasters. This was successful and oxygen enrichment was permanently implemented. That enabled dry feed rates to be maintained at 7.0 t/d.m2 and 7.3 t/d.m2 for the small and big roasters respectively. Oxygen enrichment up to 26% in the fluidizing air is utilized. Due to the highly competitive nature of the zinc industry, innovative processing techniques are necessary to be competitive. The aim of this study is to determine whether oxygen enriched air can be reduced by introducing micro-pelletized concentrate into the roaster feed blend, whilst maintaining current roaster feed rates and calcine quality. This study was executed in four parts. Firstly, the role entrainment played in influencing average particle residence time. Secondly, a study of production methods for stable micro-pellets. Thirdly, a study of the influence of oxygen enrichment and particle size on the roasting of micropellets. The fourth part of the study was introduction of micro-pellets into the Zincor roasters to determine whether oxygen enrichment could be reduced. The particle size distribution of a blend of feed concentrate to the roasters is 50% passing approximately 48 μm. This leads to entrainment values between 87% and 91%. The micro-pelletization process reduces the –500 μm fraction from 87% to 10%, which degrades to 30% during roasting. This requires that approximately 48% of the concentrate needs to be micro-pelletized to restore the 70% designed entrainment target. It was determined that entrained particles spend on average 0.46 hr to 2.44 hr in the bed compared to particles in the overflow that have residence times between 3.93 and 4.00 hr. The calculated times for entrainable particles are somewhat higher and for the bed overflow lower compared to the values measured by Spira, 1970. The required reaction time for micropellets was found to be far below their residence time inside a Zincor roaster. With a load of 20% micro-pellets introduced into the feed concentrate, the oxygen enrichment could be reduced by 60%. The quality of the calcine produced was maintained above the target of 98.8% ZnS to ZnO conversion. The results of this study have shown that the use of micro-pelletization of concentrate at Zincor reduces entrainment of particles successfully. Manipulation of entrainment through micro-pelletization can be used successfully to reduce oxygen enrichment, whilst improving production and maintaining quality at Zincor. Copyright / Dissertation (MEng)--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted

Indiana University-Purdue University Indianapolis (IUPUI) / Statement of problem: Yttria-partially stabilized tetragonal zirconia polycrystal (Y-TZP) all-ceramic restorations have been reported to suffer from chipping or cracking of the veneering porcelain (VP) as the most common complication. There is little information in the literature regarding the influence of surface treatment on VP shear bond strength to Y-TZP after cyclic loading. Purpose of this study: The goals of this study were (1) to investigate the influence of zirconia surface treatments on veneering porcelain shear bond strength and (2) to investigate the influence of cyclic loading on the shear bond strength between VP and Y-TZP. Materials and Methods: 48 cylinder–shaped specimens (6mm in diameter and 4mm in height) were divided into 4 groups containing 12 specimens each according to the surface treatment. As a control group (C), no further treatment was applied to the specimens after grinding. Group H was heat-treated as a pretreatment according to the manufacturer’s recommendations. Group S was airborne-particle abraded with 50 µm alumina (Al2O3) particles under a pressure of 0.4 MPa for 10 seconds. In the group SH, the heat-treatment was performed after the airborne-particle abrasion. A VP cylinder (2.4 mm in diameter and 2 mm in height) was applied and fired on the prepared Y-TZP specimens. The shear bond strength was tested using a universal testing machine. Six specimens from each group were subjected to fatigue (10,000cycles, 1.5Hz, 10N load) before testing. Results: The 3-way ANOVA showed no statistically significant effect of surface treatment and cyclic loading on shear bond strength. The highest mean shear bond strength was recorded for the air-particle abrasion group without cyclic loading (34.1 + 10 MPa). The lowest mean shear bond strength was the air-particle abrasion group with cyclic loading (10.7 ± 15.4 MPa). Sidak multiple comparisons procedure demonstrated cyclic loading specimens had significantly lower shear bond strength than non-cyclic loading specimens after air-particle abrasion without heat treatment (p=0.0126) Conclusion: Within the limitations of this study, (1) Shear bond strength between Y-TZP and VP is not affected statistically by surface treatment using heat treatment, airborne-particle abrasion, and heat treatment after airborne-particle abrasion. (2) There is significant difference in shear bond strength with air-particle abrasion between with and without cyclic loading groups. This difference suggested that air-particle abrasion should be avoided in clinical situations as a surface treatment without heat treatment.

No description available.

The press hardening belongs to state-of-the-art technology at sheet metal forming to gain high strength and crash resistant parts in automotive industry. This process could establish due to its cost- and esourceefficiency. According to ongoing developments on direct press hardening processes it is necessary to describe and understand the thermo-mechanical treatment of 22MnB5. Therefore the flow behavior and phase transformation during cooling with simultaneous forming is investigated. The experimental process considers industrial parameters in order to get industry-oriented results. In deep drawing processes the sheet metal is roped into the draw die and bended around the die edge. Thereby sheets perform different stages of compressive and tensile strain at the die oriented side and the punch oriented side of the sheet. There are different stages and values of stress and strain according to several layers of the sheet over its cross-section. The values of stress, strain and forming rate were FEcalculated for industry-relevant bending radii and sheet thicknesses of manganese-boron steel 22MnB5. According to the calculations different cooling and forming strategies were performed by dilatometric tests. The forming behavior is described by the microstructural development with regard to the cooling rate and temperature. Beside the influence of austenite forming on the phase transformation and mechanical properties is considered. A prospective view is given to illustrate ongoing examinations under compressive and combined tensional and compressive forces.

[pt] A demanda por veículos mais seguros e com baixo consumo de combustível vem levando a indústria automotiva a buscar novos materiais. A indústria do aço, ameaçada pela competitividade da indústria do alumínio, reagiu com uma série de novos aços de alta resistência. Dentre estes aços, os Aços Avançados de Alta Resistencia (AHSS) podem ser destacados. Esses aços podem ser divididos em 3 gerações, cada uma delas com suas vantagens e desafios. A primeira geração tem os aços mais baratos, geralmente com microestrutura ferritica/martensitica. A segunda geração possui os aços inoxidáveis austeníticos/ferríticos, com composição mais cara devido ao maior teor de liga, muitos deles apresentando efeito de plasticidade induzida por maclagem (TWIP). Entre essas duas gerações, uma terceira vem se sobressaindo, baseada em aços de composição mais barata, porém com processamento mais complexo, como os aços de tempera e partição (Quenching and Partitioning - Q and P). Como não existe apenas um único caminho para o sucesso, todas as três gerações vêm recebendo bastante atenção e pesquisa. Buscando atender parte da demanda do setor, a Companhia Siderúrgica Nacional (CSN), vem aprimorando seu portfólio de aços AHSS de primeira geração. Entre os aços de primeira geração, os mais utilizados hoje são os Dual-Phase (DP). No entanto, os aços DP apresentam alguns problemas, como a nucleação de vazios durante a deformação, o que é um fator limitante para suas propriedades mecânicas. Sua substituição por aços Complex-Phase (CP), com maiores quantidades de bainita e menos propensos a nucleação de vazio, vem sendo proposta. O processamento de aços de fase complexa envolve uma sequência de etapas de laminação a quente e a frio, seguidas de um tratamento térmico. Na presente tese, foi estudada a produção de um aço CP1200 em uma linha industrial de galvanização por imersão a quente. O ponto de partida foi um aço CP1100. Amostras deste aço laminado a frio foram analisadas por dilatometria de forma a se obter a curva CCT. Utilizando os dados dilatométricos, um novo tratamento térmico foi proposto e realizado nas instalações da CSN, produzindo com sucesso um aço CP 1200. Ensaios de tração, dureza, dobramento e expansão de buraco foram realizados para medir as propriedades mecânicas do novo aço. A caracterização microestrutural foi realizada por meio de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), microscopia de força atômica (MFA), difração de elétrons retroespalhados (EBSD) e microscopia eletrônica de transmissão (MET); a quantificação das micrografias foi realizada usando processamento digital de imagem e redes neurais. O aumento da propriedade mecânica foi atribuído ao aumento na fração de bainita, bem como de interfaces bainita-ferrita e bainita-martensita, que são menos suscetíveis a nucleação de vazios. / [en] The demand for safer and fuel-efficient vehicles leads the automotive industry to seek new and stronger materials. The steel industry, threatened by the aluminum competition, reacted with new and higher strength steels. Among the possible steels, the Advanced High Strength Steels (AHSS) can be highlighted. These steels can be divided into 3 generations, each one possessing advantages and challenges. The first generation includes more economical alloying and processing strategies, usually with a ferritic/martensitic microstructure. The second generation contains the more expensive, higher alloyed ferritic/austenitic stainless steels, using TWinning Induced Plasticity (TWIP). Between these two classes, a third generation is growing, based on more inexpensive compositions but with more complex processing, such as Quenching and Partitioning (Q and P). There is not only a single path to success, because of that, all three generations receive their fair amount of attention and research. Trying to fulfill part of the industry demand, the Companhia Siderúrgica Nacional (CSN) is conducting research on the first generation of AHSS steels. Among the first generation steels, Dual-Phase (DP) are the most used. However, DP steels present some problems, such as void nucleation during deformation, which is a limiting factor on their mechanical properties. Therefore, their replacement by Complex-Phase (CP) steels, with higher bainite amounts, and less prone to void nucleation, is welcome. The complex phase steels processing involves a sequence of hot-rolling and cold rolling steps, followed by a heat treatment. In the present thesis, the production of a CP1200 steel in an industrial hot dip galvanizing line was studied. The starting point was an industrial CP1100 steel. Samples of this cold rolled steel were analyzed by quenching dilatometry to obtain the CCT curve. Using the dilatometric data, a new heat treatment was proposed and done at CSN facilities, successfully producing a CP 1200 steel. Tension, hardness, bending and hole expansion tests were performed to measure the mechanical properties of the new steel. The microstructural characterization was done using light optical microscopy (LOM), scanning electron microscopy (SEM), atomic force microscopy (AFM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM); neural networks and digital image processing were used to quantify the obtained micrographs. The increase in tension and yielding strengths was explained based on the higher amounts of bainite as well as of bainite-ferrite and bainite-martensite interfaces, found to be less prone to void nucleation.