Made available in DSpace on 2014-06-12T17:38:03Z (GMT). No. of bitstreams: 2 arquivo3823_1.pdf: 1925092 bytes, checksum: c28739759fef3b35a51684329d53f339 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Petróleo Brasileiro S.A. / As transformações de fase de um aço estrutural foram estudadas a partir do resfriamento contínuo num substrato metálico capaz de simular as transformações microestruturais de diferentes pontos de uma ZTA (Zona Termicamente Afetada). O Material estudado foi o Aço API 5L Grau X-70, muito utilizado em tubulações nas Industriais Petroquímicas pela sua elevada resistência mecânica e baixo peso, constituindo-se num dos chamados aços ARBL (Alta Resistência e Baixa Liga). Neste contexto, o estudo térmico realizado simula as transformações microestruturais no metal de base nos processos de soldagem SMAW (Shield Metal Arc Welding) ou Eletrodo Revestido e GTAW (Gas Tungsten Arc Welding) ou TIG (Tungstem Insert Gas), assumindo por isso uma grande importância para levantamento das propriedades físicas e mecânicas de diferentes pontos da zona termicamente afetada. O Simulador Térmico de Soldas desenvolvido e aqui denominado de Gleeble mostrou-se capaz de reproduzir as diferentes condições termodinâmicas de pontos de uma ZTA, possibilitando o levantamento de curvas do ciclo térmico em função das condições impostas. Para o aquecimento dos corpos de prova foram utilizados dois fornos de resistência elétrica de alta potência para realização de aquecimento rápido e durante o resfriamento dos corpos de prova no Gleeble a temperatura era registrada por meio de termopar com registrador de temperatura digital gerando as curvas de resfriamento em microcomputador. Assim sendo, foram levantadas curvas de resfriamento para corpos de prova resfriados em Gleeble a partir de diferentes temperaturas utilizando-se Software (aplicativo) comercial para aquisição dos dados. Os resultados obtidos no Gleeble foram comparados aos resultados simulados num outro aplicativo comercial (SOLDASOFT) capaz de reproduzir ciclos térmicos e repartições térmicas em função dos parâmetros de soldagem, fornecidos como dados de entrada. Para comparação das microestruturas resultantes do Gleeble foram feitas soldas reais realizadas pelos processos ER (Eletrodo Revestido) e TIG. A caracterização microestrutural foi feita por microscopia ótica

Nickel super alloy Inconel 718 was tested and compared to Haynes 230 using Gleeble and Varestraint mechanical test methods. Hot cracking susceptibility was examined in either alloy using a sub-scale Varestraint test method at 5 augmented strain levels: 0.25%, 05.%, 1%, 2%, and 4%. Maximum crack length, total crack length, and number of cracks were measured for each strain level. Gleeble hot ductility on-heating and on-cooling tests were performed on both alloys. Inconel 718 was tested on-heating at target temperatures of 1600˚F, 2000˚F, 2100˚F, 2200˚F, and on cooling at 1600˚F, 1700˚F, 1800˚F, 1900˚F, and 2100˚F. Haynes 230 was tested on-heating at target temperatures of 2050 ˚F, 2200 ˚F, 2240 ˚F, 2330 ˚F, and on-cooling at 1800 ˚F, 1900 ˚F, 1990 ˚F, 2040 ˚F, 2090 ˚F, 2100 ˚F, 2140 ˚F, and 2190 ˚F. Ductility in Gleeble samples was measured in a reduction of surface area. A nil-strength temperature was established for either alloy. The nil-strength temperature was 2251˚F and 2411˚F, for Inconel 718 and Haynes 230, respectively. The nil ductility temperature <5% R/A) was 2188˚F for Inconel 718 and 2341˚F for Haynes 230. Ductility recovery temperature occurred at 1924˚F for Inconel 718 and 2147˚F for Haynes 230. The brittle temperature range was determined to be 326˚F for Inconel 718 and 228˚F for Haynes 230. Varestraint testing revealed that Inconel 718 had a lower threshold strain for crack initiation than Haynes 230 (0.5% vs 1%), and a higher number of cracks, as well as a larger maximum crack length, at every strain level. These results show a greater tendency for liquation cracks to form in Inconel 718 than in Haynes 230.

At temperatures above 0.5 Tm and in aggressive atmospheres predicting alloy performance is particularly challenging. Nickel alloys used in regimes where microstructure and properties are altered dynamically present unique requirements. Exposure may alter properties with unexpected early failure. The Gleeble is a valuable tool for investigation and simulation of thermo-mechanical properties of an alloy in various regimes up to the threshold of melting. In this study, four regimes of temperature and strain rate were simulated in an argon atmosphere to both investigate and document normal and abnormal failure modes. Commercial Inconel 601 was tested in selected regimes and in two treatments (as received and strain aged). Next two exposed conditions (TEOS and Hydride) were tested. Slow strain-rate and high temperature produced brittle intergranular fracture. Exposure at elevated temperature to process gases reduced both strength and ductility in both TEOS and Hydride. TEOS exposure reduced reduction in area in the alloy significantly more than the Hydride exposure.

No description available.

Dual-phase (DP) advanced high-strength steels (AHSSs) are widely used in the automotive industry due to their excellent combination of strength, ductility, and work hardening properties. However, defects occurring during processing make these ferrous alloys expensive. Toward this ends, high-temperature tensile tests using a Gleeble thermomechanical simulator have been conducted to determine the stress/strain behaviour at temperatures between 1250 to 1480 C in order to quantify the tensile strength and ductility. The results of both as-cast and transfer-bar material will be presented as well as three different sample geometries in order to better understand the effects of starting microstructure, thermal gradient, and tress/strain distribution on the reproducibility of high temperature properties. Optical and scanning electron microscopy are then performed to further elucidate the structure/property relationships. The results show that the presence of preexisted prorosities in the as-cast structure decreases the high-temperature strength of the material, while the transfer-bar samples show lower ductility at ultra-high temperatures, (T 1450 C), due to their severe susceptibility to melting. In terms of the two mentioned thermomechanical characteristics, voids nucleation, growth, and coalescence initiated with porosity clustering are the main mechanisms behind the lower strength of the as-cast samples, whilst tearing apart of the melt plays an important role to drastically drop the ductility of transfer-bars at mentioned temperature interval. Moreover, the long-gauge-length (LGL) geometry proposes better reproducibility of data compared with the other geometries. This is attributed to a suitable combination between low stress localization and high thermal gradient during the Gleeble testing that provides a condition in which the samples experience sharp localized necking right on the hot-spot zone. The obtained data can be used as part of multi-physics process and microstructure continuous casting models. / Thesis / Master of Applied Science (MASc)

[pt] Os aços inoxidáveis duplex (AID) possuem uma estrutura mista de Delta-ferrita e Gamma-austenita em frações de volume aproximadamente iguais e combinam muitas das propriedades benéficas das duas fases, a ferrita fornece alta resistência mecânica e resistência à corrosão, enquanto que a austenita aumenta a ductilidade e a resistência à corrosão uniforme. Uma vantagem dos AID é a resistência à trincas de solidificação, que está associado à soldagem. Pela combinação de propriedades, esses aços são amplamente utilizados na indústria de equipamentos químicos, petróleo e gás, plantas de dessalinização, controle de poluição, usinas elétricas e, mais recentemente, em aplicações off-shore como na extração de petróleo em águas profundas. No entanto, a exposição destes aços a temperaturas elevadas entre 600 graus celsius e 1000 graus celsius, que ocorre durante a soldagem por fusão resulta na precipitação de diferentes compostos, sendo os mais frequentemente encontrados a fase sigma, a fase x, os nitretos de cromo e os carbonetos que reduzem tanto a resistência mecânica quanto a resistência a corrosão. Este trabalho teve como objetivo simular fisicamente as microestruturas da zona termicamente afetada (ZTA) dos AIDs UNS S32304, S32205 e S32750. De modo a obter diferentes ZTAs foi utilizado o simulador termo-mecânico Gleeble, por meio deste simulador foram aplicados vários aportes de calor que permitiram avaliar a evolução microestrutural e as propriedades mecânicas destas zonas. As temperaturas utilizadas nas simulações físicas foram determinadas por meio do software Thermo-Calc assegurando assim as faixas de transformações microestruturais. A temperatura de pico utilizada foi de 1350 graus celsius por 2 segundos; seguida de resfriamento em acordo com o modelo Rykalin-2D, onde um grupo de amostras sofreu resfriamento até alcançar a temperatura de 500 graus celsius seguido de uma têmpera em água e um outro grupo até 250 graus celsius seguido de uma têmpera. Este procedimento foi adotado de modo a identificar a influência dos aportes de calor e as taxas de resfriamento na frações volumétricas das fases obtidas. Foi observado um aumento da fração volumétrica da austenita, assim como um aumento do tamanho de grão da ferrita e um crescimento nos grãos da austenita, em função do aumento do aporte de calor durante as simulações físicas das ZTAs. Estas variações microestruturais ocasionaram o decréscimo da resistência mecânica nos três AID avaliados quando comparados ao respectivo metal de base. / [en] The duplex stainless steels (DSS) have a structure that consist of approximately equivalent amounts of delta-austenita and gamma-ferrite, exhibit excellent properties combinations of both phases. DSS combine the high strength and resistance to stress corrosion cracking come from ferrite, whereas the austenite phase influences ductility and uniform corrosion resistance. The advantage of DSS is solidification cracking resistance; it is associated to welding processes. The application of DSS have being increasingly used as structural material in various industrial sectors, such as chemical, petrochemical, pulp and paper, power generation, desalination, oil and gas, for the constructions in marine and chemical industries and most recently for manufacturing components used in off-shore oil platforms for oil extraction in deep water. However, the exposure of these steels to high temperatures between 600 celsius degrees and 1000 celsius degrees, which occurs during fusion welding results in different compounds precipitation, the most frequently encountered being the sigma phase, the X phase, the chromium nitrides and carbides which reduce both mechanical strength and corrosion resistance. The aim of this work was to simulate physically the Heat Affected Zone (HAZ) microstructures in DSS UNS S32304, S32205 and S32750. In order to obtain different HAZ the Gleeble system was used. Several heat inputs were applied through this simulator, which allowed evaluate the microstructural evolution and the mechanical properties of these zones. The temperatures used in physical simulations were determined by Thermo-Calc Software, this supplied the microstructural transformations temperature ranges. The peak temperature used was 1350 celsius degrees for 2 seconds; followed by cooling in accordance with the Rykalin-2D model; one sample set was cooled to 500 celsius degrees followed by water quenching, and the second sample set was cooled to 250 celsius degrees followed by quenching. This procedure was adopted in order to identify the effect of the final temperature on the phases volume fraction obtained. An increase in the austenite volume fraction, as well as an increase in the ferrite grain size and a widening in the austenite grains, due to the increase of the heat input during the physical simulations of the ZTAs was observed. These microstructural variations caused the tensile strength and Yield strength decreasing in HAZ of DSS evaluated when these zones were compared to the respective base metal.

The third-generation advanced high strength steels, AHSS, represent an opportunity for today’s steel development, where lighter materials with maintained strength and toughness are in demand. The unique properties of these materials often stem from a tailored microstructure. In the continued development of these steels, without relying on expensive alloying methods, process design in the form of precise heat treatments plays an increasingly important role. This work focuses on Medium Mn AHSS with the aim of investigating one of these heat treatments, intercritical annealing, which is essential for achieving the desired material properties. Experimental testing of annealing effects is acknowledged to be a challenging process, and this study aims to present a novel approach for these types of tests. During experimental testing of intercritical annealing, the thermomechanical testing system Gleeble 3800 is a recognized tool. The mounting technique employed in the Gleeble results in an inhomogeneous heat distribution in the samples, generating a thermal gradient. This report aims to utilize this gradient as an opportunity to test the effect of several intercritical annealing temperatures on one sample, thereby increasing the efficiency of experimental work. The method is based on data retrieved from thermocouples attached to the specimen during Gleeble trials with the intent to identify the thermal gradient. This data is combined with x-ray diffraction measurements where the retained austenite fraction is measured. Thermodynamic calculations of expected retained austenite fraction following intercritical annealing are performed parallel to experimental work. The results of this work show that it is possible to utilize the thermal gradient to retrieve extensive data regarding the effect of intercritical annealing using only one sample. The results show a distinct thermal gradient and a corresponding gradient of retained austenite fraction along the specimen. The results for retained austenite fraction at room temperature can be rationalized on the basis of computational predictions. These variations potentially arise due to the material not reaching equilibrium within the annealing timeframe. This conclusion is supported by other computational results concerning austenite composition. In summary, the present work illustrates a new approach streamlining experimental work that, with some refinements, has the potential to benefit the broader scienitific community, in addition to providing a powerful new tool for rapid technological advancement in the steel industry / Tredje generationens avancerade höghållfasta stål representerar en möjlighet för dagens stålutveckling där lättare material med bibehållen styrka och seghet efterfrågas. De unika egenskaperna hos dessa material härrör ofta frän en skräddarsydd mikrostruktur. Vid fortsatt utveckling av dessa stål är det önskvärt att minimera användningen av legeringsämnen, vilket betyder att processdesign i form av korrekta värmebehandlingar blir  av  stor  betydelse.  Detta  arbete  fokuserar  på  Medium  Mn  avancerade höghållfasta stål med syftet att undersöka en av dessa värmebehandlingar, interkritisk glödgning,  vilken  har  en  avgörande  betydelse  för  att  uppnå önskad  prestanda. Experimentell  testning  av  glödgningseffekter  anses  vara  en  utmanande  process och avsikten med denna studie är att presentera ett nytt tillvägagångssätt för denna typ av test. Under experimentell utvärdering av glödgningseffekter används ofta det termomekaniska testsystemet  Gleeble  3800.  Provmonteringen  i  Gleeblen  resulterar i en  inhomogen värmefördelning i proverna vilket medför en temperaturgradient. Denna rapport syftar till att använda gradienten som en möjlighet att testa effekten av flera  glödgningstemperaturer  på  ett  enda  prov  och  därigenom  öka  effektiviteten i det  experimentella  arbetet.  Metoden  grundas  på  data  från  termoelement  fästa  på provet under Gleebleförsök, med avsikt att identifiera den termiska gradienten. Denna data kombineras sedan med XRD-mätningar där austenitfraktion efter värmebehandling utvärderas.  Termodynamiska  beräkningar  av  förväntad  austenitfraktion  efter interkritisk glödgning genomförs parallellt med experimentellt arbete. Resultaten  från  detta  arbete  påvisar  att  den  presenterade  metoden  är  genomförbar då omfattande data gällande interkritisk glödgningseffekt grundat på endast ett prov erhålls. Resultaten visar en tydlig termisk gradient och en motsvarande gradient av austenitfraktion längs provet, vilka är i överensstämmelse med tidigare experimentella resultat för samma material. Resultaten för austenitfraktion vid rumstemperatur uppvisar  betydande  likheter  med  de  termodymiska  beräkningarna, med  några  undantag. Orsaken till dessa variationer ¨ar troligen en otillräcklig glödgningstid, vilket gör att  materialet  inte  når  jämvikt.  Denna  hypotes  stöds  av andra  beräkningsresultat gällande austenitens sammansättning. Sammanfattningsvis presenterar denna rapport ett nytt tillvägagångssätt för att effektivisera experimentellt arbete, som med vissa förbättringar har potential att gynna det bredare forskarsamhället.

The feed rate at which a defect free friction stir weld can be run (friction stir weldability) on an HSLA steel plate can vary widely between heats that meet the same specified physical properties. Consequently, every time a new heat of HSLA steel is obtained, exploratory welds must be run to determine the proper feed rate for that plate. Previous research suggests that the varying levels of alloying elements related to high temperature physical properties between the different heats causes the observed change in friction stir weldability. Because of this, it was hypothesized that the high temperature physical properties of HSLA steels are related to their friction stir weldability.High temperature physical propeties of HSLA steels are a function of the alloying content of the steel. To determine the relationship between high temperature physical properties and alloying content, eight different heats of HSLA steel with different chemical compositions were obtained. In particular, percent additions of molybdenum, vanadium, niobium, and titanium were varied between the heats in a factorial design. Gleeble compression tests were run on each heat to determine their high temperature properties. Based on these tests, experimental models wereconstructed to estimate the high temperature properties of HSLA steels based on composition and temperature. These models were used to determine the high temperature physical properties of HSLA heats with known friction stir weldability. The high temperature physical properties werecompared to the friction stir weldability of each heat. No correlation was found in this study between the high temperature properties examined and friction stir weldability in HSLA steels.

Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.

Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.