Orientador: Célia Marina de Alvarenga Freire / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-22T11:43:34Z (GMT). No. of bitstreams: 1 Costa_GiselleBarata_D.pdf: 6195639 bytes, checksum: 7b424607db5a3372771d157f6bac717c (MD5) Previous issue date: 2013 / Resumo: O hidrogênio é reconhecido como sendo um elemento residual sempre prejudicial ao aço. Proveniente de reações químicas e eletroquímicas, tais como, corrosão, proteção catódica e reações de processo, é absorvido pelo aço e retido nos defeitos da rede cristalina podendo causar a fragilização do aço e a propagação de trincas e fraturas. O presente trabalho visa analisar a influência do hidrogênio na estrutura cristalina e no comportamento magnético do aço AISI 4340 obtido pelas normas AMS 6414K e 6415S, nas condições como recebido, temperado e revenido. Para tanto corpos-de-prova foram retirados da posição transversal dos lingotes, temperados a 845°C e revenidos a três diferentes temperaturas (350°C, 400°C e 500°C). Para a caracterização do material foram feitas micrografias, ensaios de dureza, difração de raios-X, voltametria cíclica e análise de difusão. As propriedades magnéticas foram obtidas utilizando-se um magnetômetro de amostra vibrante (VSM) onde a magnetização de saturação foi obtida e foram analisadas amostras antes da hidrogenação e após hidrogenação. O carregamento de hidrogênio foi feito em solução de H2SO4 a 0,05 M em temperatura ambiente. Os resultados obtidos nos ensaios de voltametria cíclica e difusão foram correlacionados às difrações de raios-x e magnetização de saturação em função da contaminação por hidrogênio e as diferentes condições de tratamento térmico. A comparação das curvas antes e após hidrogenação para as difrações de raios-X mostraram que a hidrogenação provoca uma diminuição das curvas em todas as condições de tratamento térmico para os dois tipos de aço. As curvas de difusão mostraram que os coeficientes de difusão da amostra como recebida é menor que as tratadas com revenimento para o aço AISI 4340 AMS 6415S e maior para o aço AISI6414K. A magnetização de saturação mostrou que os aços AISI 6414K e 6415S antes da hidrogenação apresentaram magnetização de saturação maior que após hidrogenação / Abstract: Hydrogen is recognized as a residual element always harmful to steel. From chemical and electrochemical reactions, such as corrosion, cathodic protection and reaction process, the steel is absorbed and retained in the crystal lattice defects may cause embrittlement of steel and propagation of cracks and fractures. This study aims to analyze the influence of hydrogen in the crystal structure and magnetic behavior of AISI 4340 obtained by the rules AMS 6414K 6415S and the conditions as received, quenched and tempered. For this purpose the test piece bodies were removed from the transverse position of the ingots, quenched to 845 ° C and tempered at three different temperatures (350 ° C, 400 ° C and 500 ° C). For the characterization of the micrographs were taken, hardness tests, X-ray diffraction, cyclic voltammetry analysis and dissemination. The magnetic properties were obtained using a vibrating sample magnetometer (VSM), where the saturation magnetization was obtained and analyzed samples before hydrogenation and after hydrogenation. The hydrogen loading was done in a solution of 0.05M H2SO4 at room temperature. The results obtained in the test and cyclic voltammetry were correlated to diffusion x-ray diffraction and saturation magnetization due to hydrogen contamination and different heat treatment conditions. A comparison of the curves before and after hydrogenation for X-ray diffraction showed that the hydrogenation causes a decrease of the curves in all heat treatment conditions for both types of steel. The curves show that the diffusion coefficient of diffusion of the sample as received is lower than those treated with tempering for the steel AISI 6415S AMS 4340 steel and higher for AISI6414K. The saturation magnetization showed that AISI 6415S 6414K and exhibited before the hydrogenation higher than saturation magnetization after hydrogenation / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica

Abstract This thesis studies controlling factors that govern transverse hydrogen cracking in high-strength multipass weld metal (WM). The experiments were concerned with heavy-restraint Y- and U-Groove multipass cracking tests of shielded-metal arc (SMAW) and submerged-arc (SAW) weld metals. Results of tensile tests, hardness surveys, weld residual stress measurements and microstructural investigations are discussed. The analytical phase comprised numerical calculations for analysing the interactions between crack-controlling factors. The objectives were: (i) the assessment of WM hydrogen cracking risk by defining the Crack-No Crack boundary conditions in terms of 'safe line' description giving the desired lower-bound estimates, and (ii) to derive predictive equations capable of giving reliable estimates of the required preheat/interpass temperature T0/Ti for the avoidance of cracking. Hydrogen cracking occurred predominantly in high strength weld metals of Rp0.2 ≈ 580-900 MPa. At intermediate strengths of Rp0.2 ≈ 500-550 MPa, cracking took place in the cases where the holding time from welding to NDT inspection was prolonged to 7 days. Low strength WMs of Rp0.2 ≤ 480 MPa did not exhibit cracking under any conditions examined. Cracking occurrence was, above all, governed by WM tensile strength, weld diffusible hydrogen and weld residual stresses amounting to the yield strength. The appearance of cracking vanished when transferring from 40 to 6 mm thick welds. The implications of the holding time were more significant than anticipated previously. A period of 16 hrs in accordance with SFS-EN 1011 appeared much too short for thick multipass welds. Interpass time and heat input showed no measurable effect on cracking sensitivity, hence being of secondary importance. Equations were derived to assess the weld critical hydrogen content Hcr corresponding to the Crack-No Crack conditions as a function of either weld metal Pcm, yield strength Rp0.2 or weld metal maximum hardness HV5(max). For the calculation of safe T0/Ti estimates, a formula incorporating: (i) WM strength as a linear function of either weld carbon equivalent CET or weld HV5(max), (ii) weld build-up thickness aw in the form of tanh expression and (iii) weld diffusible hydrogen HD in terms of a combined [ln / power law] expression was found descriptive.

No description available.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17154号 / 工博第3644号 / 新制||工||1553(附属図書館) / 29893 / 京都大学大学院工学研究科建築学専攻 / (主査）教授 中島 正愛, 教授 吹田 啓一郎, 教授 金子 佳生 / 学位規則第4条第1項該当

S960 and S700 are two types of high strength low alloy steels (minimum yield strengths at 960 MPa and 700 MPa, respectively) developed recently by Tata Steel. These steels are typically used in heavy lifting equipment. This research examines the feasibility and characteristics of single pass autogenous laser welding (ALW), multi-pass ultra-narrow gap laser welding (NGLW) of 8 mm thick S960 and 13 mm thick S700 high strength low alloy (HSLA) steels and compared the characteristics of the welds with those of gas metal arc welding (GMAW). The work aims to understand the development of welding induced residual stresses, microstructures, microhardness, tensile properties, bending properties and Charpy impact toughness at different temperatures as produced by different welding techniques (ALW, NGLW and GMAW).Design of experiments and statistical modelling were used to predict and optimise laser welding parameters of S960 and S700 HSLA steels. The contour method was used to measure the 2D distribution of residual stresses of the welded specimens. X-ray diffraction was carried out to measure the surface residual stresses of the welded specimens. The main novel contributions include:(1) Development of welding procedures for ultra-NGLW of HSLA steels. The ultra-NGLW process was successfully applied to the welding of 8 mm thick S960 and 13 mm thick S700 HSLA steels with a very narrow groove (1.2-1.4 mm wide) using a moderate laser power (2-3 kW).(2) Resolving the melt sagging problem for single pass autogenous laser welding of thick section materials. Horizontal (2G) welding position was applied to successfully resolve the melt sagging problem when single pass flat (1G) position ALW was applied to welding a 13 mm thick S700 steel plate. Computational fluid dynamic (CFD) modelling was carried out to understand the dynamic force interactions in the weld pool and the factors affecting the formation of the weld bead profile.(3) Understanding the effects of heat input on the microstructures evolution and mechanical properties of the welded high strength steel joints. The much lower heat input for ALW of 8 mm thick S960 steel and ultra-NGLW of both 8 mm thick S960 and 13 mm thick S700 steels results in the generation of hard martensite in the narrow fusion zone (FZ) and heat affected zone (HAZ), which strengthened the welded joints but deteriorated the toughness of the welded joints. The strengthened narrow FZ and HAZ for both the ALW and ultra-NGLW of 8 mm thick S960 steels demonstrated almost the same tensile strength and elongation as the base material. A relatively high heat input for the ALW of 13 mm thick S700 steel results in the generation of bainite in the FZ, which has almost the same microstructure and hardness as the base material.(4) Understanding the effect of solid-state phase transformation on the residual stresses of the welded specimens. It was demonstrated that the solid-state phase transformation from austenite to ferrite, bainite and martensite changes the magnitude of residual stress in the fusion zone for the welded S700 steel plates. In addition, it also changes the yield strength of the FZ, which also has a significant effect on the welding residual stress. In summary, this work has resulted in a significantly enhanced understanding of the way in which the choice of welding process affects the properties of welded joints in high strength steels. Laser welding was found to offer strengthened welded joints. However, the laser welded joints presented low impact toughness. If the toughness of the laser welded joints can be improved, laser welding will be a promising technique for joining high strength steels.

Malgré les avantages multiples du béton à hautes performances, il reste relativement peu étudiédans les structures en béton armé. Notamment, la servicibilité du matériau et son comportementvis-à-vis de la fissuration nécessitent une investigation profonde. En effet, dans les structures enbéton armé, c’est souvent la servicibilité du matériau qui se détériore et écourte la durée de vied’une construction. Dans le même contexte, le comportement à l’effort tranchant du béton àhautes performances (BHP) reste insuffisamment étudié comparativement à la littératureabondante sur le béton ordinaire (BO). Le principe de l’effort tranchant en béton armé n’estd’ailleurs toujours pas suffisamment explicité avec rationalité et l’on continue à utiliser desméthodes empiriques pour se prémunir contre les effets désastreux de cette sollicitation sur lesstructures en béton armé. Ce manque de compréhension est illustré par des approches de calculdifférentes et parfois contradictoires utilisées dans les principaux règlements de calcul en bétonarmé. L’applicabilité de ces approches de calcul réglementaires au béton à hautesperformances nécessite une evaluation profonde. Cet aspect fait partie des objectifs de laprésente étude. L’utilisation des fibres d’acier comme renforcement en béton en général et enbéton à hautes performances en particulier semble améliorer le comportement structural de cematériau en effort tranchant. Sur ces aspects de comportement structural, un total de 70 poutresen béton armé, ordinaire et de hautes performances, avec et sans fibres d’acier, ont été testéesen flexion quatre-points. Les fibres d’acier ont été utilisées en différentes quantités /f et différentsélancements lf/df. Les essais réalisés dans ce travail ont montré que les fibres d’aciers couturentefficacement les fissures et ainsi permettent aux éléments de structures d’être servicibles à desniveaux de chargement élevés. Cette efficacité se distingue particulièrement dans le matériauBHP qui développe une adhérence relativement meilleure avec l’acier par comparaison au BO.Ces effets de coutures efficaces ne sont, cependant, pas reflétés dans les modèles de calculsutilisés dans les règlements universels. / Despite de multiple advantages of high performances, it is still relatively unknown. It is thusimportant to study this material from all the aspects in the aim of understanding its structuralbehavior and using it as a building material in composition with steel and hence beneficiate fullyfrom its higher compressive strength and denser compactness. In this sense, the serviceability ofthe material, particularly its behaviour towards cracking which affects its integrity, necessitates adeeper investigation. In the same context, the shear behavior of high performances concrete(HPC) is still insufficiently investigated by comparison to the abundant literature for that of ordinaryconcrete (OC). On the aspect of shear behaviour, it is worth noting that such a solicitation inreinforced concrete is a topic which continues to arouse a lot of interest despite the abundanceof the existing literature. The applicability of the different design approaches to high performancesconcrete requires further investigations. This aspect is a part of the objectives of the presentexperimental study. The use of steel fibers as reinforcement for concrete in general and for highperformances concrete in particular seems to improve the structural behavior of this concretematerial, particularly for shearing. On these aspects of structural behaviour, a total of 70 reinforcedconcrete beams, from ordinary concrete and high performances concrete, with and withoutsteel fibers, have been tested in four-point flexural bending. The steel fibers were used in differentquantities /f and different aspect ratios lf/df. The test carried out in this investigation have shownthat fibers stitch up effectively the two faces of a crack and thus enable structural elements to beserviceable at higher loading levels. This efficiency is particularly distinguishable for highperformances concrete (HPC) which develops a relatively better bond with the reinforcement bycomparison to ordinary concrete (OC). These stitching effects are however not reflected in thedesign models presented in the different universal design codes.

Sulfide Stress Cracking (SSC) resistance of the newly developed API-X100 High Strength Low Alloy (HSLA) steel was investigated in the NACE TM0177 "A" solution. The NACE TM0177 "A" solution is a hydrogen sulfide (H2S) saturated solution containing 5.0 wt.% sodium chloride (NaC1) and 0.5 wt.% acetic acid (CH3COOH). The aim of this thesis was to study the effect of microstructure, non-metallic inclusions and alloying elements of the X100 on H2S corrosion and SSC susceptibility. The study was conducted by means of electrochemical polarization techniques and constant load (proof ring) testing. Microstructural analysis and electrochemical polarization results for X100were compared with those for X80, an older generation HSLA steel. Uniaxial constant load SSC testing was conducted using X100 samples and the results were compared with those reported for older generation HSLA steels. Addition of H2S to the NACE TM0177 "A" solution increased the corrosion rate of X100from 51.6 to 96.7 mpy. The effect of H2S on the corrosion rate was similar for X80. The corrosion rate for X80 increased from 45.2 to 80.2 mpy when H2S was added to the test solution. Addition of H2S enhanced the anodic kinetics by forming a catalyst (FeHSads) on the metal surface and as a result, shifted the anodic polarization curve to more current densities. Moreover, the cathodic half cell potential increased due to the decrease in pH, from 2.9 to 2.7, which shifted the cathodic polarization curve to more current densities. The increase in both the anodic and cathodic currents, after H2S addition, caused the rise in the corrosion current density. In H2S saturated NACE TM-0177 "A" solution, the X100 steel corrosion rate was higher than the X80 steel by 20%. Longer phase boundaries and larger nonmetallic inclusions in the X100 microstructure generated more areas with dissimilar corrosion potentials and therefore, a stronger driving force for corrosion. Higher density of second phase regions and larger nonmetallic inclusions acted as an increased cathode area on the X100 surface which increased the cathodic current density and consequently, increased the corrosion current density. Proof ring tests on the X100 gave a threshold stress value, C5th, of 46% YS, 343.1 MPa(49.7 ksi). The main failure was caused by SSC cracking. SSC nucleated at corrosion pits on the metal surface and microcracks in the metal body and propagated perpendicular to the applied stress. Hydrogen Induced Cracking (HIC) was observed in the X100. HIC cracks nucleated at banded martensite-ferrite interfaces and propagated along the rolling direction parallel to the applied tensile stress through the softer ferrite phase. When compared to older HSLA grades, the X100 tested in this study had a high SSC susceptibility and therefore, is not be recommended for H2S service applications. The high X100 SSC susceptibility was caused by the material high corrosion rates in H2Smedia which formed corrosion pits that acted as crack initiation sites on the metal surface and provided more hydrogen that migrated into the steel. In addition, the X100 inhomogeneous microstructure provided a high density of hydrogen traps in front of the main crack tip which promoted SSC microcrack formation inside the metal. Microcracks in the metal body connected with the main crack tip that originated from corrosion pits which assisted SSC propagation. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

This diploma thesis deals with weldability of Domex 460 MC material. There are two welding methods and three other welded materials in heterogenous connection which will be researched in this diploma thesis. The welding methods are fiber solid-state laser and a new method of hybrid welding called laser – TIG. The other materials are Domex 700 MC, S355J2 and DC01. Domex 460 MC is a high-strenght steel with fine-grained structure. During the welding process the imput heat decreases mechanical properties of the materials. This effect is caused by material seeds growing. From these samples (which were produced by welding) were created metallographic cuts. These metallographic cuts were analysed focusing on their makrostructure, microstructure, mikrohardnest and Mn arrangement in welded heterogenous samples using electron microscope and EDX analysis.

In South Africa, as much as 33 million tons of ash, a waste product of burning coal, are produced per year. Of the total ash produced, just over 8% is sold for utilisation, the remainder of which is disposed of in landfills or ash lagoons. Countries like the UK, USA, Germany, Poland and Russia are producing Lightweight Aggregates (LWAs) commercially by using fly ash and clay, however, this technology is not available in many developing countries. The opportunity to utilise the fly ash produced in South Africa for the production of coarse LWA for use in structural concrete has therefore been identified and investigated in this dissertation. This dissertation consists of two phases, firstly to determine a suitable method for the manufacture of a high quality LWA, and secondly to determine the manufactured aggregate’s performance and potential for use in structural concrete. In the first phase, different LWA batches were produced using fly ash as the main constituent and kaolin clay, in contents of 0%, 10%, 20% and 30% by mass, as a binder. Green aggregate particles were produced in a disc granulator and then hardened using sintering at 1200°C for one hour. It was found that the LWA batch containing 20% kaolin produced LWA with the most suitable mechanical properties for use in concrete, and was therefore mass produced for further aggregate testing and for the production of concrete specimens for concrete testing. The final LWA produced was found to have an apparent density of 1600 kg/m3 and 24 hour water absorption of 12% by mass. The produced LWA was also found to have an Aggregate Crushing Value (ACV) and 10% FACT of 24.4% and 185 kN, respectively, which indicated that it would be suitable for use in High Strength Concrete (HSC). The sintering process was found to induce liquid phase sintering and the formation of new phases, mainly mullite, which contributed to the relatively high strengths of the aggregates. In the second phase of this dissertation, the manufactured LWA was then used to produce HSC and Normal Strength Concrete (NSC) specimens for concrete testing, which were compared to control mixes made with normal weight dolomite aggregate. In the HSC testing, concrete with a density of 2300 kg/m3 and compressive strength of 90 MPa was produced with the LWA. In HSC, it was found that internal curing was improved when up to 50% of the normal weight coarse aggregate was replaced by saturated LWA for this specific concrete mix. By using different stiffness relationship models between the concrete constituents, it was found that the manufactured LWA modulus of elasticity was between 8-23 GPa, and had a compressive strength of between 49-60 MPa. The Interface Transition Zone (ITZ) in concrete produced with the LWA was found to be stronger than the LWA as a result of the impregnation of the cement paste within the aggregate, and that the LWA was reactive in an alkaline environment. This resulted in an improved early age strength development, as well as caused the concrete failure surface to occur through the LWA particles rather than at the ITZ. Finally, Lightweight Concrete (LWC), having a dry density below 2000 kg/m3, was produced with the manufactured LWA. The LWC, produced with a water-to-cement ratio of 0.75, 28 day compressive strength of 24 MPa, modulus of elasticity of 21 GPa and dry density of 1800 kg/m3, was found to be suitable for use as structural concrete when assessed in terms of EN 1992-1-1 (2004). / Dissertation (MEng (Structural Engineering))--University of Pretoria, 2020. / Civil Engineering / MEng (Structural Engineering) / Restricted