A aplicação de aços de alta resistência está fortemente difundida na indústria mecânica, principalmente em aplicações onde a redução de peso é importante, como por exemplo, a indústria de implementos rodoviários e maquinários agrícolas. Esta dissertação visa analisar a influência de diferentes aportes térmicos no comportamento microestrutural e mecânico de juntas soldadas através do processo MAG de modo a obter juntas com propriedades otimizadas. Para este estudo foram utilizadas chapas metálicas com espessura de 3 mm do aço de alta resistência e baixa liga USI LNE700. Os parâmetros nominais de energia de soldagem foram variados de acordo com os valores descritos pelo fornecedor SSAB. O processo de soldagem foi realizado com o auxílio de um sistema robotizado para manter a homogeneidade ao longo da junta, distância e posicionamento correto no comprimento total da junta soldada. Os ensaios para verificação do comportamento microestrutural e mecânico foram realizados com auxílio de microscopia ótica, perfis de microdureza e ensaios de tração. Buscaram-se utilizar aportes térmicos reduzidos para minimizar os efeitos de revenimento da martensita presente no metal de base, um dos principais responsáveis pela redução das propriedades mecânicas da junta soldada. Os resultados não mostraram significativa variações na microestrutura e propriedades de tração do material, porém o preenchimento da junta soldada formada apresenta um comportamento diretamente proporcional à energia de soldagem. / The application of high strength steels is strongly diffused in the engineering industry, especially in applications where weight reduction is important, such as the industry of agricultural machines and trailers industry. This investigation aims to analyze the influence of different heat inputs on microstructural and mechanical behavior of joint welded by GMAW in order to obtain joints with optimized properties. Sheet metal with a thickness of 3 mm high strength low alloy steel LNE700 (supplier Usiminas) were used. The welding energy was varied around the nominal value informed by the steel supplier SSAB for this study. The welding process was made using robotic system to maintain homogeneity along the joint, right distance and position during the total weld joint length. The microstructural and mechanical behaviors were performed with the optical microscope, microhardness profile and traction test. We attempted to use lower heat inputs to minimize the effects of tempering of martensite present in the base metal, a major contributor to the reduction of the mechanical properties of the welded joint. The results did not show significant microestructural and tensile properties variation, however, when the welding energy is increased, the welded joint penetration formed was increased as well.

Friction stir spot welding (FSSW) is quickly becoming a method of interest for welding of high strength steel (HSS) and ultra high strength steel (UHSS). FSSW has been shown to produce high quality welds in these materials, without the drawbacks associated with fusion welding. Tool grade for polycrystalline cubic boron nitride (PCBN) tools has a significant impact on wear resistance, weld quality, and tool failure in FSSW of DP 980 steel sheet. More specifically, for a nominal composition of 90% CBN, the grain size has a significant impact on the wear resistance of the tool. A-type tools performed the best, of the three grades that were tested in this work, because the grain size of this grade was the finest, measuring from 3-6 microns. The effect of fine grain size was less adhesion of DP 980 on the tool surface over time, less abrasive wear, and better lap shear fracture loads of the welds that were produced, compared to the other grades. This is explained by less exposure of the binder phase to wear by both adhesion and abrasion during welding of DP 980. A-type tools were the most consistent in both the number of welds per tool, and the number of welds that reached acceptable lap shear fracture loads. B-type tools, with a bimodal grain size distribution (grain size of 4 – 40 microns) did a little bit better than C-type tools (grain size of 12-15 microns) in terms of wear, but neither of them were able to achieve consistent acceptable lap shear fracture load values after the first 200 welds. In fact only one out of five C-type tools was able to produce acceptable lap shear fracture loads after the first 100 welds.

The current US fleet of nuclear reactors has been in service for three decades. Over this period, existing welds in stainless steel (SS) shrouds have sustained stress corrosion cracking (SCC) and are in need of repair. Additionally, helium has formed interstitially as a byproduct of proton bombardment. Current repair technology, such as TIG welding, puts extreme amounts of heat into the material and allows for interstitial helium atoms to aggregate and form bubbles/voids at grain boundaries. This significantly weakens the material, proving to be a very counterproductive and ineffective repair technique. Much study has been done on friction stir processing (FSP), but none has explored it as an enabling repair technology for use in nuclear applications. Because of its relatively low energy input as a solid state joining technology, it is proposed that FSP could effectively heal SCCs in these existing welds without the negative side effect of helium bubble formation. A spread of speeds and feeds were initially tested using a PCBN-W-Re tool on 304L SS. Six of these parameter sets were selected as representations of high, medium, and low temperature-per-power outputs for this research: 2 IPM-80 RPM, 2 IPM-150 RPM, 4 IPM-150 RPM, 4 IPM-250 RPM, 6 IPM-125 RPM, and 6 IPM-175 RPM. These varied parameter sets were tested for their tensile, micro-hardness, and corrosion resistant properties. In general, the lower IPM and RPM values resulted in higher ultimate tensile strengths (UTS). Higher IPM and RPM values resulted in tunnel, pin hole, and surface void defects. These defects caused premature failure in tensile tests and could often be identified through microscopy. Micro-hardness testing demonstrated a strong correlation per the Hall-Petch relationship – finer grain sizes resulted in higher yield strength (hardness values) of the material. The tool temperature during FSP was a good indicator of the expected hardness – lower temperatures resulted in higher hardness values. Corrosion testing was performed with a 1000-hour alternate immersion test in a room temperature 3.5% NaCl solution. With these testing parameters, the results demonstrated that FSP had no effect on the corrosion resistance of 304L SS under these conditions.

Continuing an investigation on using FSP to heal stress corrosion cracks (SCC) in welds on nuclear reactors, this study seeks to use AM in addition to FSP to aid crack repair. Previous studies address that current repair technology on nuclear reactors involves the use of TIG welding which can allow helium atoms to aggregate and form voids at the grain boundaries. This weakens the material and renders the repair ineffective. Another previous study evaluated the effectiveness of FSP alone in repairing SCC which did have defects depending on the parameters used during FSP. This study evaluated the use of AM in addition to FSP. Literature is available on FSP and AM separately and literature is available on technologies that used both them together. However, the current processes that are available that use both AM and FSP can be expensive and may be impractical for some purposes. This study shows a new process that is both less expensive and more practical in SCC repair. Initial proof of concept trials was performed on 1018 mild steel using both wire fed additive and insert additive technologies. A slot would be removed and filled in with an additive process and processed using FSP. Because of poor repeatability, substantial distortion, and voids present this study went forward using insert technologies in further experiments rather than wire wed additive technologies. In addition, the depth and width of the insert or area where the added material would be placed was varied in initial trails. Tensile testing was performed on initial steel trials and the stainless steel experiments and it demonstrated a correlation between depth of the added material and the tensile strength. Micro-hardness mapping performed on initial steel trials also showed hardening in the FSP stir zone. Three-point bend tests were performed to show that an existing crack underneath the FSP zone would not propagate through the nugget. All evaluations supported a substantial increase in yield strength increased after FSP.

In this study, microstructural, micro hardness evaluation and residual stress distribution, of low carbon steel after single pass gas metal arc welding technique (GMAW) were investigated. The goal of this investigation were to reveal the microstructures, micro hardness, residual stress distribution and tensile strength of welded joints by using welding current as varying parameter. In order to realize this objective, welded plate of low carbon steel with thickness of 2.5mm and 250mm long by 200mm wide were welded together with different welding current of 70A, 100A through MIG process. Four different parts of samples were tried. The first part of samples was annealed in a furnace to a temperature of 750 and allowed to cool in air before welding. While the second was not heated, third and fourth trials were heated to a temperature of 200˚C and 580˚C respectively after the welding and allowed cooling in air. Nikon optic microscope and CSM micro hardness testing instrument were used to determine the microstructure of the weld bead and HAZ of the samples, and hardness tests were carried out at different zones of welded joint. Micro hardness behavior was observed by using CSM instrument using 20N load for indentation, which reveals the correlation between hardness, elasticity and plasticity on the heat affected zone (HAZ) and weld bead of the welded plates. The samples were subjected to tensile strength and the distribution of residual stress of the weld. Tensile strength test... [to full text] / Šiame darbe aprašomi mikrostruktūros, mikrokietumo nustatymo bei liekamųjų įtempimų pasiskirstymo tyrimai mažo anglingumo plienuose po lankinio suvirinimo. Tyrimo tiksla - nustatyti suvirintos jungties mikrostuktūros ir mikrokietųmo priklausomybę nuo suvirinimo srovės, kaip kintamo dydžio. Remiantis užduotimi buvo suvirintos 2.5 mm storio, 250 mm ilgio ir 200 mm pločio mažaanglio plieno plokštės, naudojant skirting dydžio (70A ir 100A) suvirininant apsauginių dujų aplinkoje (MIG) srovę. Buvo paruoštos keturios partijos bandinių. Pirmoji partija, proies suvirinant, buvo atkaitinta 750°C temperatųroje, ir ataušintas ore. Tuo tarpu antroji partija nebuvo apdorojama, o trečioji ir ketvirtoji atleista 200 C° ir 580°C temperatūroje ir atvėsinta ore. Suvirinimo vonelės ir erminio poveikio zonos mikrostruktūrai tirti bei mikrokietumui nustatyti buvo naudotas Nicon optinis mikroskopas bei CSM mikrokietumo bandymų įrenginys. Matuojant CSM įrenginiu, 20N įspaudimo apkrova, buvo pastebėtas įdomus kietuvo būvis, kuris atskleidė ryšį tarp kietumo, elastingumo ir plastiškumo esantį suvirintų plokštelių terminio poveikio zonoje bei suvirinimo vonelėje. Buvo matuojamas suvirintų bandinių stiprumas tempiant ir liekamųjų įtempimų pasiskirstymas. Tempimo stiprumo bandymų duomenys parodė ducharakteringus suirimo atvejus – plastiio-elastinio bei trapaus tipo. Liekamųjų įtempimų bandymų rezultati neparodė rėikšmingos liekamųjų įtempimų įtakos pasirinktomis sąlygomis suvirintuose bandiniuose.

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2011Bitstream added on 2014-06-13T19:35:03Z : No. of bitstreams: 1 munekata_rm_me_ilha.pdf: 4705141 bytes, checksum: 56254cadfa4c90cb796f3b90671140ee (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho estudou a influência da energia do pulso de soldagem, no caso processo laser de Nd:YAG operando no modo pulsado, na soldagem de duas lâminas finas com 100 μm de Hastelloy C-276, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química petroquímica e alimentícia. Utilizou-se energia de pulso de 1,0 Joule a 2,25 Joules, com incremento de 0,25 Joules com a velocidade de soldagem de (ν) taxa de repetição (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio. Foram realizadas análises macrográficas e micrográficas das juntas soldadas, através de secções transversais das mesmas e ensaios de microdureza Vickers e ensaio de tração. Os resultados obtidos mostraram que o controle da energia do pulso, em processo de soldagem por laser de lâminas finas é de fundamental importância para a geração de juntas soldadas livres de descontinuidades. Os parâmetros geométricos da junta soldada, tais como largura do cordão, largura de união e profundidade do cordão, aumentaram em função do aumento da energia do pulso. O processo mostrou-se muito sensível à formação de porosidade e à presença de gap entre as lâminas / This work measured experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser welding to examine the influence of the pulse energy in two thin foil welding with 100 μm thickness, employed to cover sensors that work in corrosive environment of the sugar and alcohol industry,chemical petrochemistry and nourishing. The pulse energy was varied from 1,0 to 2,25 J at an increment of 0.25 J and an increment of 0.25 Joules with a welding speed and(ν) repetition rate (Rr) fixed 525mm/min and 39Hz respectively and 4 ms pulse duration. The specimens were laser-welded in an argon atmosphere. The welds were analyzed by macroscopic and microscopic observations using optical microscopy and micro hardness and tensile test. The results indicated that pulse energy control, in laser welding of thin foils, is of considerable importance for weld quality since it can generate discontinuities free weld joints. The geometric parameters of the welded joints like bead width, connection width and bead depth increased with the pulse energy increasing. The process showed very sensitive to porosity formation and gap between couple

Made available in DSpace on 2016-06-02T19:12:21Z (GMT). No. of bitstreams: 1 4512.pdf: 12085865 bytes, checksum: 9c98b7edb2a0238a143b2c8e9469a515 (MD5) Previous issue date: 2012-03-06 / Ion nitriding is a process of thermo-physical-chemical treatment that provides a surface hardening, originated by interstitial diffusion of nitrogen on the ferrous and nonferrous alloys surfaces. Understanding and controlling the formation of the nitrided layer have considerable industrial interest due to the improvements regarding wear, corrosion and fatigue resistances on the metals and their alloys. In this work, it was performed the surface modification in sintered iron samples by ion nitriding process, with a gaseous mixture of 80% vol H2 and 20% vol N2, during times of 3 and 5 hours, using ion nitriding temperature of 500°C, 540°C and 580°C. The samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, and wear and micro-hardness tests, comparing the results with sintered and steam treatment samples. The results showed that both nitride thickness and wear resistance increased with higher nitriding time and temperature, where the temperature was the variable that most influenced the aforementioned characteristics. The XRD analysis indicated that the nitrided layer near to the surface, for all samples, consisted in a mixture of y-Fe4N and e-Fe3N phases. / A nitretação iônica é um processo de tratamento termo-físico-químico que consiste em um endurecimento superficial, provocado pela difusão intersticial de nitrogênio atômico na superfície de ligas ferrosas e não ferrosas. O entendimento e o controle da formação da camada nitretada apresentam considerável interesse industrial devido às melhorias alcançadas nas resistências ao desgaste, corrosão e à fadiga dos metais e suas ligas. Neste trabalho, promoveu-se a modificação superficial de amostras de ferro sinterizado por meio do processo de nitretação a plasma, com uma mistura gasosa de 80% vol H2 e 20% vol N2, nos tempos de 3 e 5 horas, e temperaturas de nitretação de 500°C, 540°C e 580°C. As amostras foram caracterizadas por meios de análise de microscopia eletrônica de varredura (MEV) e difração de raios X (DRX), e quantificadas quanto aos níveis de desgaste e microdureza, em comparação com amostras sinterizada e ferroxidada. Os resultados mostraram que tanto as espessuras das camadas de nitretos como as resistências ao desgaste das amostras aumentaram com o tempo e temperatura de nitretação, sendo a temperatura a variável que mais influenciou nas características mencionadas. A análise de DRX indicou que a camada nitretada próxima a superfície, para todas as amostras, consiste de uma mistura de fases de  -Fe4N e -Fe3N.

The doctoral thesis is divided into two parts - Thermal analysis in physics education on high school and Material research of Al-Zn-Mg(-Cu-Sc-Zr) alloys. Within the first part, the areas of crystallization and/or melting of selected foods were determined using differential scanning calorimetry. A practical lesson for high school physics has been created and tested. The study text focused mainly on differential scanning calorimetry and its use was made. In the second part of the doctoral thesis, there was analysed thermal evolution of the phase transformation in the Al- Zn-Mg(-Cu) alloys with Sc and Zr addition. The effect of (cold and hot) deformation on the decomposition sequences was studied. The hardening effect after annealing above 300 řC in the Sc and Zr alloys is caused by the precipitation of the secondary Al3Sc,Zr) particles. These particles were observed by transmission electron microscopy after annealing up to 360 řC in all studied AlZnMg(Cu)ScZr alloys. In the AlZnMgCu alloy the partial recrystallization was observed after annealing at 350 řC/10 hours and after annealing at 450 řC/10 hours the grain size was 50-200 m (depending on the treatment of the alloy). The addition of Sc, Zr in the AlZnMgCuScZr stabilizes grains and there is no recrystallization in the AlZnMgCuScZr alloy at temperature...

Made available in DSpace on 2015-05-08T14:59:48Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3074686 bytes, checksum: ed7a06179e3d3259d7c106457864da4c (MD5) Previous issue date: 2013-03-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / With the recent discovery of the existence of oil deposits in Brazil. Those responsible for the exploitation are becoming increasingly aware of the development of technologies for the extraction of oil and natural gas in deep waters. In this scholarly work, one of these developed technologies, the base metal steel SAE 8630 modified by the addition of metal buttery INCONEL 625 (AWS ER NiCrMo 3) through the MIG welding process, was investigated. To minimize the formation of martensite thermal cycles of annealing 873oC in a period of one hour and two thermal cycles strain relief (before and after buttering), both at temperatures of 677oC in a range of two hours. After these processes it was possible to verify the presence of diffusion processes of chemical elements and formation of possible precipitates. These trials were conducted by optical microscopy and scanning electron microscopy coupled with EDS while changes in hardness and toughness were observed before and after heat treatment for stress relief of the metal. These are the metallurgical and mechanical results from analysis of the areas close to regions of the MB, HAZ, ZL and MB. / Com as recentes revelações da existência de jazidas de petróleo no território brasileiro. Fez se que os responsáveis pela exploração destas regiões, se demonstrem apreensivos quanto ao desenvolvimento de tecnologias para a extração de petróleo e de gás natural em águas profundas. Neste trabalho acadêmico, com o uso de uma dessas tecnologias em desenvolvimento, foi abordado o uso do metal de base o aço SAE 8630 modificado, amanteigado pelo metal de adição INCONEL 625 (AWS E NiCrMo 3) através do processo de soldagem MIG. Para minimizar a constituição da martensita, foram aplicados ciclos térmicos de têmpera de 873oC em um intervalo de uma hora e mais dois ciclos térmicos de alívio de tensões (antes e após o amanteigamento), ambos em temperaturas de 677oC em um intervalo de duas horas. Verificou se a presença de processos de difusão de elementos químicos e formação de possíveis precipitados. Estes foram caracterizados pelos ensaios de microscopia ótica e microscopia eletrônica de varredura juntamente com o EDS e alterações quanto a microdureza e dureza foram observadas antes e após o tratamento térmico de alívio de tensões. Sendo estes resultados metalúrgicos e mecânicos analisados em áreas próximas das regiões do MB, ZTA, ZL e MB.

The master thesis is focussed on evaluation of mechanical properties and fracture behaviour of basic materials and weld joints of a water turbine supply pipe. The results of tensile tests, fracture toughness tests, hardness and micro-hardness tests and further chemical and metallography analysis are used for operating degradation level evaluation of the construction material and also for a residual operating recognition of the second, identical specimen of supply pipe.