O presente trabalho teve por objetivo realizar ensaios de desgaste abrasivo em juntas soldadas pelo processo MAG, em dois aços estruturais de alta resistência e baixa liga utilizados no transporte ferroviário de minério, os quais apresentavam diferentes propriedades mecânicas. No aço de menor resistência (Aço A) foram utilizados os metais de adição AWS ER70S-G (Aço A-70) e AWS ER80S-G (Aço A-80), enquanto no aço de maior resistência (Aço B) os metais de adição AWS ER80S-G (Aço B-80) e AWS ER110S-G (Aço B-110). Os conjuntos soldados foram caracterizados quanto às suas microestruturas, dureza e resistência ao desgaste abrasivo em ensaios de degaste roda de borracha e ensaios de desgaste por deslizamento a seco e com adição de um meio corrosivo (NaCl 0,05M, água arti cial ). Os resultados obtidos a partir dos ensaios de desgaste roda de borracha mostraram que para o Aço A a junta soldada do Aço A-70 apresentou melhor resistência ao desgaste, enquanto para o Aço B a maior resistência ao desgaste foi obtida na junta soldada Aço B-110. Dos resultados dos ensaios de desgaste por deslizamento a seco, as zona afetada pelo calor de grãos grosseiros (ZAC-GG) foram as regiões que apresentaram a maior resistência ao desgaste. Das condições soldadas no Aço A, o metal base (MB) apresentou a menor resistência ao desgaste, entre os metais de solda (MS), o MS do Aço A-80 apresentou a maior resistência ao desgaste. No Aço B, o MS do Aço B-80 apresentou a menor resistência ao desgaste, e o MS do Aço B-110 apresentou a resistência ao desgaste similar ao MB. Foi observado um maior desgaste para as amostras que foram submetidas ao ensaio de desgaste por deslizamento com solução, comparativamente às amostras submetidas aos ensaios a seco, o que, de acordo com a literatura, está associado ao efeito sinérgico entre corrosão e desgaste. / The present work had the objective perform abrasive wear tests on GMA welded joints in two high strength low alloy structural steels used in rail transport of ore, which presented di erent mechanical properties. The AWS ER70S-G and AWS ER80S-G wires were used in the lower strength steel (Steel A), whereas the AWS ER80S-G and AWS ER110S-G wires were used in the higher strength steel (Steel B). The welded joints were characterized in terms of their microstructures, hardness and abrasive wear resistance in dry sand/rubber wheel tests and sliding wear tests dry and with a corrosive medium (0.05M NaCl, arti cial water ). The results obtained from the dry sand/rubber wheel tests showed that for Steel A the welded joint with the wire AWS ER70S-G showed better wear resistance, while for Steel B the highest wear resistance was obtained with the AWS ER110S-G wire. From the results of dry sliding wear tests, the coarse grained heat a ected zone were the regions that presented the highest wear resistance. In Steel A, the base metal (BM) showed the least resistance, and between the weld metals (WM), the WM Steel A-80 showed the highest wear resistance. In Steel B, WM Steels B-80 showed the least wear resistance, while the WM Steels B-110 showed the wear resistance similar to BM. It was observed a higher wear for the samples that were submitted to the sliding wear test with solution, compared to the samples submitted to the dry wear test, which, according to the literature, is associated with the synergic e ect between corrosion and wear.

Mechanical properties of polymers are reviewed and the phenomenon of the abrasive wear is analyzed in the literary part. The researches of other authors on the abrasive wear and their results are surveyed. Laboratory equipment for carrying out the abrasive wear researches is introduced. Optimal mount of laboratory simulation for modeling polymeric material wear in the abrasive environment is chosen. The testing materials‘ properties are characterized. The results of researches on polymeric materials, used in enginery, on the wear in the abrasive environment are presented. The carried out research showed that wear results of the same materials under different testing conditions (“polymer-abrasive”, “polymer-steel disc” ASTM G176-03) the dependence of wear on hardness end on the coefficient of friction differs. That is influenced by the choice of polymeric materials. The scope of the work is 62 pages: 57 pictures, 1 table, 7 appendixes are included, 25 sources of literature were referred to in this work.

Titanium carbide (TiC) and titanium carbonitride (Ti(C,N)) are both common components in hard, wear resistant ceramic-metal composites, or cermets. In this study the intermetallic nickel aluminide (Ni3Al) has been used as a binder for the production of TiC and Ti(C,N) based cermets. These cermets offer several improved characteristics relative to conventional WC-based ‘hardmetals’, such as lower mass and improved oxidation resistance, which are also combined with high fracture resistance, hardness and wear resistance. The cermets were produced using an in-situ, reaction sintering procedure to form the stoichiometric Ni3Al binder, with the binder contents varied from 20 to 40 vol%. However, for high N content Ti(C,N) cermets, the wettability of molten Ni3Al is relatively poor, which leads to materials with residual porosity. Therefore various amounts of Mo2C (1.25, 2.5, 5 and 10 vol%) were incorporated into the Ti(C0.3,N0.7)-Ni3Al cermets, with the aim of improving the densification behaviour. Mo2C was found to improve upon the wettability during sintering, thus enhancing the densification, especially at the lower binder contents. The tribological behaviour of TiC and Ti(C,N) cermets have been evaluated under reciprocating sliding conditions. The wear tests were conducted using a ball-on-flat sliding geometry, with a WC-Co sphere as the counter-face material, for loads from 20 to 60 N. The wear response was characterised using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy, and focused ion beam microscopy. Initially, two-body abrasive wear was observed to occur, which transitions to three-body abrasion through the generation of debris from the cermet and counter-face materials. Ultimately, this wear debris is incorporated into a thin tribolayer within the wear track, which indicates a further transition to an adhesive wear mechanism. It was found that Mo2C additions had a positive effect on both the hardness and indentation fracture resistance of the samples, but had a detrimental effect on the sliding wear response of the cermets. This behaviour was attributed to increased microstructural inhomogeneity with Mo2C additions.

Baigiamajame magistro darbe apžvelgti laboratoriniai ir praktiniai abrazyvinio dėvėjimosi tyrimų metodai. Sumontuotas ekskavatoriaus kaušo dantų abrazyvinio dėvėjimosi stendas, sudaryta nauja tyrimo metodika. Tyrimas buvo atliktas su šešiais ekskavatoriaus kaušo dantimis: trys aplydyti „Anykščių vario“, du ESAB firmų elektrodais, vienas dantis neaplydytas. Darbe ištirtos neaplydyto ir aplydytų skirtingais elektrodais ekskavatoriaus kaušo dantų abrazyvinio dėvėjimosi charakteristikos, pateiktos išvados ir rekomendacijos. / The final magistracy work review laboratory and field abrasive wear test methods. New excavator bucket teeth abrasive wear tester was mounted and new research method was created. Research was developed with six excavator bucket’s teeth: three teeth were coating with “Anyksciu varis” company electrodes, two teeth were coating with ESAB company electrodes and one tooth wasn’t coating. In this work are analysing teeth that are coating with several types electrodes or without them, abrasive wear performances. It was present conclusion and recommendation.

Titanium carbonitride (Ti(C,N)) cermets have become more popular in recent research due to their mix of high hardness, high hot hardness, good ductility, chemical stability, and low densities. These mechanical properties make Ti(C,N)-cermets especially desirable as a replacement for current ‘hardmetals’, such as tungsten carbide cobalt (WCCo), as it is known that WC-Co exhibits poor mechanical behaviour at elevated temperatures. Additional interest and research has been conducted in reference to binders which enhance the cermet’s capability to retain strength at high temperatures while remaining ductile. One such binder, Ni3Al actually increases in yield strength up to a temperature of ~900°C. In this thesis, the production method utilizing melt infiltration for TiC, Ti(C0.7,N0.3), Ti(C0.5,N0.5), and Ti(C0.3,N0.7)-based cermets with Ni3Al binder contents of 20, 30 and 40 vol. % have successfully been developed and utilized. This process produced high density samples at each nitrogen content for all binder contents, excluding Ti(C0.3,N0.7). Ti(C0.3,N0.7)-Ni3Al samples at 20 and 30 vol. % suffered from poor infiltration and could not be tested. The reciprocating wear mechanisms were examined, using a ball-on-flat test, utilizing WC-Co spheres with a diameter of 6.35 mm as a counter-face, and test parameters of 20 Hz, 2 hrs., and applied loads of 20, 40, 60 and 80 N. The wear tracks were examined using optical profilometry, SEM, and EDS to determine the volumetric wear rate, and the dominant wear mechanisms. The wear volume, and wear mechanisms were compared with the effect of binder content, nitrogen content, and applied load.

The wear process in three-body contact causes problems of abrasion such as volume loss and changes of geometry of the triboelements. The wear problem leads to increased failure and high costs for repairing or replacing equipment. To understand the nature of the wear behaviour and to predict the wear rate in advance, experimental investigation and numerical simulation of the wear process are required. In this work, the wear process is analysed and the influencing parameters governing the wear behaviour are investigated experimentally to develop a new wear model. Main influential factors are considered such as kinematics of abrasive particles, contact stiffness of the particle layer, friction characteristics, and wear factors. The experiments to study kinematics of particle layers are performed on a new observation tester. To define the contact stiffness of abrasive particles, experiments are conducted by the uniaxial spindle compression tester. Moreover, a tribometer test rig with applied load up to 200 N and velocity up to 1000 mm/s is used to investigate the friction characteristics and the wear behaviour of three-body tribosystem. Analyses of influential factors on the wear behaviour in dependency of predefined process parameter are carried out. Additionally, based on the results of the experimental investigations, approximation equations representing the relation of the influential factors and the process parameters are determined. A three-body wear model is build up to represent the wear behaviour by physical wear laws. Furthermore, these approximation equations and the relevant parameters obtained by experimental investigations are included in the Fleischer’s wear equation to simulate the wear process. With the coupled model the wear process of the sample can be simulated twodimensional over the sliding distance. It is possible to predict the wear depth and the wear intensity, which can be used to estimate the wear rate. Additionally, from the results of the wear simulation the worn surface and the local contact pressure in the contact region are determined which provide a deeper insight into the wear process. With this simulation the understanding of the wear behaviour can be improved which is important to solve wear problems.

O objetivo desta pesquisa é realizar um estudo sobre o desgaste abrasivo do ferro fundido branco alto cromo de acordo com a norma ASTM A532 II D, submetidas à diferentes faixas de temperatura de austenitização, decompondo a faixa de 950 a 1.150 ºC, amplamente usada nas fundições, em intervalos de 50 ºC. Esta liga foi escolhida para estudo em virtude de sua extensa aplicação na indústria de mineração, possuindo como principal característica a utilização em revestimentos de moinhos e martelos de britadores, onde a resistência ao desgaste abrasivo é exigida. Os corpos de prova foram caracterizados através de análise química, dureza, e estrutura metalográfica, avaliando as mudanças na microestrutura, e consequentemente, alterações nas propriedades de resistência ao desgaste abrasivo do material. Na avaliação das amostras, foi utilizada a microscopia ótica e, para simular a condição de desgaste abrasivo, determinando a perda de massa, foi empregando o abrasômetro do tipo roda de borracha, seguindo a norma ASTM G65. Os testes práticos demostraram que o ciclo de temperatura é uma etapa importante na determinação da dureza, que por sua vez, é uma característica fundamental à resistência ao desgaste abrasivo, visto que para o material estudado, quanto maior a dureza, maior foi a resistência ao desgaste abrasivo. / The objective of this research is to perform a study on the abrasive wear of high chromium white cast iron according to ASTM A532 II D, submitted to different austenitizing temperatures, in the range of 950 to 1150 ºC with 50 ºC steps, widely used in foundries. This alloy was chosen for study because of its extensive application in the mining industry, having as main characteristic the use in mill and hammer coatings of crushers where abrasive wear resistance is required. The specimens were characterized by chemical analysis, hardness, and metallographic analysis, evaluating the changes in the microstructure, and consequently changes in the abrasive wear properties of the material. In the evaluation of the samples, optical microscopy was used and, to simulate the abrasive wear condition, determining the mass loss, the rubber wheel type abrasive test was used, following the ASTM G65 standard. The practical tests demonstrated that the temperature cycle is an important step in determining the hardness, which in turn is a fundamental characteristic to the abrasive wear resistance, since for the material studied, the higher the hardness, the higher the resistance to abrasive wear.

Os aços Hardox possuem microestrutura de martensita revenida e são caracterizados pelas elevadas dureza e resistência à tração, sendo empregados em situações que requerem alta resistência ao desgaste. Entretanto, os processos de soldagem alteram significativamente a sua microestrutura e propriedades. Assim, o objetivo deste estudo foi avaliar a resistência ao desgaste de juntas soldadas de um aço Hardox 500 produzidas através do processo MAG convencional e, juntamente, com o Hardox sem soldagem (metal base), para comparação. A soldagem ocorreu utilizando dois consumíveis, um recomendado pela empresa fabricante do aço, o AWS ER80S-G, e outro de maior resistência mecânica, o consumível AWS ER120SG. As propriedades mecânicas das juntas soldadas foram avaliadas através de perfis de microdureza, ensaios de tração e dobramento. Ainda, foi realizada uma análise da superfície de fratura dos corpos de prova do ensaio de tração, em microscópio eletrônico de varredura. Foram executados ensaios de desgaste por um abrasômetro do tipo roda de borracha. Análises através de microscopia óptica e microscopia eletrônica de varredura foram utilizadas para verificar os mecanismos de desgaste nas superfícies submetidas à abrasão Nos ensaios de dobramento, constatou-se que a condição soldada com o arame de menor resistência apresentou maior ductilidade. Verificou-se, também, que com a soldagem houve uma diminuição da resistência mecânica das juntas em comparação ao metal sem soldagem. Em relação aos ensaios de desgaste, com o uso do arame de maior resistência foi atingido um melhor desempenho no desgaste abrasivo em comparação ao de menor resistência, pois as taxas de desgaste foram de 0,058 e 0,083 mm³/m, respectivamente, mas o comportamento foi ainda inferior ao exibido pelo aço Hardox 500 sem soldagem, que apresentou uma taxa de desgaste de 0,031 mm³/m. Constatou-se, também, que os mecanismos de desgaste foram dúcteis em todas as condições estudadas, pois as superfícies desgastadas mostravam predominantemente micro sulcamento e regiões com micro fadiga; essa última parece ter aumentado de tamanho à medida que a dureza do material testado aumentava. / The Hardox steels have a martensite microstructure and are characterized by high hardness and tensile strength. This steel has been used in situations that require high resistance to wear. However, the welding processes significantly alter their microstructures and properties. Thus, the purpose of this study was to evaluate the wear resistance of welded joints of Hardox 500 steel produced by the conventional MAG process and with Hardox without welding (base metal), for comparison. The welding took place using two consumables, one recommended by the steel manufacturer, the AWS ER80S-G and another with higher resistance, the consumable AWS ER120S-G. The mechanical properties of welded joints were evaluated through micro hardness profiles, tensile and bending tests. In addition an analysis of the fracture surface of the tensile test specimen was carried out by scanning electron microscopy. Wear tests were performed by a rubber wheel type abrasometer. Analyses by optical microscopy and scanning electron microscopy were used to verify the mechanisms of wear on surfaces subjected to abrasion In the bending tests, it was verified that the welded condition with the filler metal of lower resistance presented greater ductility. It was also verified that with the welding, there was a decrease in the mechanical strength of the joints in comparison with the base metal. In relation to the wear tests, with the use of the higher strength wire, a better performance was obtained when compared to the lower one, since the wear rates were 0.058 and 0.083 mm³/m respectively, but the behavior was lower in the Hardox 500 steel without welding, which presented a wear rate of 0.031 mm³/m. It was also observed that the wear mechanisms were ductile in all the studied conditions, since the worn surfaces showed predominantly micro plowing and regions with micro fatigue, the latter seem to have increased in size as the hardness of the tested material increased.

O presente trabalho teve por objetivo realizar ensaios de desgaste abrasivo em juntas soldadas pelo processo MAG, em dois aços estruturais de alta resistência e baixa liga utilizados no transporte ferroviário de minério, os quais apresentavam diferentes propriedades mecânicas. No aço de menor resistência (Aço A) foram utilizados os metais de adição AWS ER70S-G (Aço A-70) e AWS ER80S-G (Aço A-80), enquanto no aço de maior resistência (Aço B) os metais de adição AWS ER80S-G (Aço B-80) e AWS ER110S-G (Aço B-110). Os conjuntos soldados foram caracterizados quanto às suas microestruturas, dureza e resistência ao desgaste abrasivo em ensaios de degaste roda de borracha e ensaios de desgaste por deslizamento a seco e com adição de um meio corrosivo (NaCl 0,05M, água arti cial ). Os resultados obtidos a partir dos ensaios de desgaste roda de borracha mostraram que para o Aço A a junta soldada do Aço A-70 apresentou melhor resistência ao desgaste, enquanto para o Aço B a maior resistência ao desgaste foi obtida na junta soldada Aço B-110. Dos resultados dos ensaios de desgaste por deslizamento a seco, as zona afetada pelo calor de grãos grosseiros (ZAC-GG) foram as regiões que apresentaram a maior resistência ao desgaste. Das condições soldadas no Aço A, o metal base (MB) apresentou a menor resistência ao desgaste, entre os metais de solda (MS), o MS do Aço A-80 apresentou a maior resistência ao desgaste. No Aço B, o MS do Aço B-80 apresentou a menor resistência ao desgaste, e o MS do Aço B-110 apresentou a resistência ao desgaste similar ao MB. Foi observado um maior desgaste para as amostras que foram submetidas ao ensaio de desgaste por deslizamento com solução, comparativamente às amostras submetidas aos ensaios a seco, o que, de acordo com a literatura, está associado ao efeito sinérgico entre corrosão e desgaste. / The present work had the objective perform abrasive wear tests on GMA welded joints in two high strength low alloy structural steels used in rail transport of ore, which presented di erent mechanical properties. The AWS ER70S-G and AWS ER80S-G wires were used in the lower strength steel (Steel A), whereas the AWS ER80S-G and AWS ER110S-G wires were used in the higher strength steel (Steel B). The welded joints were characterized in terms of their microstructures, hardness and abrasive wear resistance in dry sand/rubber wheel tests and sliding wear tests dry and with a corrosive medium (0.05M NaCl, arti cial water ). The results obtained from the dry sand/rubber wheel tests showed that for Steel A the welded joint with the wire AWS ER70S-G showed better wear resistance, while for Steel B the highest wear resistance was obtained with the AWS ER110S-G wire. From the results of dry sliding wear tests, the coarse grained heat a ected zone were the regions that presented the highest wear resistance. In Steel A, the base metal (BM) showed the least resistance, and between the weld metals (WM), the WM Steel A-80 showed the highest wear resistance. In Steel B, WM Steels B-80 showed the least wear resistance, while the WM Steels B-110 showed the wear resistance similar to BM. It was observed a higher wear for the samples that were submitted to the sliding wear test with solution, compared to the samples submitted to the dry wear test, which, according to the literature, is associated with the synergic e ect between corrosion and wear.

Made available in DSpace on 2016-12-08T17:19:25Z (GMT). No. of bitstreams: 1 Rafael_Silva.pdf: 11456819 bytes, checksum: 6b16187fff0cfd80ae2de57337e8105c (MD5) Previous issue date: 2015-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Sand cores are widely used at automotive foundries. The impact of sand on the surface of the tooling caused by the injection pressure causes wear on internal geometry, that interferes in the assembly of sand cores and dimensional of casting, and the maintenance of tooling is a bigger concern of the automotive foundries. When a core box show wear, some procedures may be applied for re-use of tooling, but, however, a better understanding of the wear process that occurs on the surface of the inserts will improve the life time of the core box. The purpose of this study is to better understand the wear mechanism that suffers tooling and form a knowledge base of wear on foundry tooling. In this study was present a comparative study on wear resistance among 05 different types of steels used in the manufacture of foundry tooling. The wear resistance has studied by tests on steel specimens used in the manufacture of foundry tooling in the rubber wheel abrasometer, as the pattern set by the technical ASTM G65-04. / Núcleos de areia são largamente utilizados em fundições de peças automotivas. O impacto da areia sobre a superfície do ferramental causado pela injeção sob pressão provoca desgaste na sua geometria interna, o que interfere na montagem dos núcleos de areia e dimensional da peça fundida, sendo que, a manutenção dos ferramentais é uma das grandes preocupações da fundição de peças automotivas. Quando uma caixa de macho apresenta desgaste, certos procedimentos podem ser aplicados para reutilização do ferramental, mas, no entanto, o melhor conhecimento do processo de desgaste que ocorre na superfície dos insertos irá melhorar a vida útil da caixa de macho. O objetivo do trabalho é entender melhor o mecanismo de desgaste que o ferramental sofre e formar uma base de conhecimento sobre desgaste em ferramentais de fundição. Neste trabalho foi realizado um estudo comparativo na resistência ao desgaste entre 05 diferentes tipos de aços utilizados na confecção de ferramentais de macharia Cold Box. A resistência ao desgaste foi estudada através de testes em corpos de prova de aços utilizados na fabricação de ferramentais em abrasômetro do tipo roda de borracha, conforme o padrão estabelecido pela norma técnica ASTM G-65-04.