RCAAP Repository

The application of hardfacing brings the reduction of the wear and therefore increases service life of components and reducing the maintenance shutdowns. This work aims to study the wear resistance of hardface applied by welding, by using the process FCAW (Flux- Cored Arc Welding) Self-Shield Double Wire. Three types of consumables were used (FeCrC, FeCrC+Ti and FeCrC + Nb) with diameter 1.6 mm in twelve coating conditions. The coating was applied by welding on a steel SAE 1020 with and without E308lSi buttering, with metal transfer mode in short circuit. It was compared the deposits made with each condition. It was constructed specimens for the evaluation of wear in the laboratory with Rubber Wheel according to ASTM G65-00. The wear evaluation was made via mass loss. It was also carried analysis hardness and microhardness of the coating microstructure. The best wear resistance results were obtained with the use of two wires electrode with the same composition (FeCrC + Ti). The presence of Ti in the coating has fewer cracks and improves wear resistance in this study. The conditions with buttering have not shown good results with respect to wear resistance of coatings.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Currently companies working with the transformation of raw materials into finished products had to redo their general planning and adequate to a new reality to become competitive. They undergo considerable change in production environments, driven by the dynamic behavior of the market, primarily by customer demand and due to increased competitiveness. Faced with this new scenario, it has become even more necessary to reduce production costs, working whereever possible, since the purchase of raw materials, tools and machinery up to in increasing the efficiency of the manufacturing processes. In this work, two important machining fartores were considered, the geometry of the cutting tool wedge and cutting fluids. The geometry of the cutting wedge, particularly the angles measured in the orthogonal plane (side rake angle, wedge angle and side clearance angle) has a key role for a successful operation, since it determines the resistance of cutting tool wedge and the amount of heat generated by friction between the chip-tool-workpiece system. Although some machining operations occur without a cutting fluid, sometimes it does not need fluid or it hinders the process, sometimes because of environmental and economic issues, the cutting fluid can be vital in certain processes. The lubricant and cooling functions are often crucial to ensure necessary conditions for the cutting tool to perform machining. When the machining occurs with the use of a cutting fluid, it can be applied in the form of jet (flooding) or the formo f a spray, technically called MQF Minimum Quantity of Fluid. The objective of this work is to develop an experimental study to optimize the wedge geometry of high-speed steel - HSS tools, using the Brandsma rapid facing method in ABNT 1045 steel, evaluating the influence of lub-cooling conditions. The output parameter considered was the diameter of collapse of the tool, which determines the critical cutting speed. The results found allowed comparisons between the lub-cooling conditions and check the influence of rake and clearance angles in the in diameter of collapse of the tool. The values of the side rake and side clearance angles of the tool that maximizes the diameter of collapse depend on the lubri-cooling system used. In general, the combination of a side clearance angle of 9° with a side rake angle also of 9° when using flood cooling system (90 l / h) gave the best result. These results are important to contribute to the knowledge of the process, enabling cost savings, because it indicates the best tool wedge geometry and lubri-cooling condition that can be applied for part production in companies / industries.

More complex and bigger structures have increased the applicability of low alloy high strength steels due to weight and cost reductions in these projects. One of the requirements for the use of these materials is the preservation of performance after welding. Meanwhile, the norms on which the Welding Procedures Specifications (WPS) are based have not yet considered the development of modern steel and its new production process, resulting in unnecessary welding costs that diminish the profits of the application of this type of steel. This thesis aimed to develop and evaluate an experimental methodology to guide the creation and control of welding procedures for structural steel through a microstructural atlas of the heat affected zone (HAZ) in a thermomechanical control process (TMCP), 65 ksi steel (ASTM A572 Grade 65). This steel was used in the project of an industrial building for CBMM in Araxá, Minas Gerais, Brazil. It is proposed that through a microstructural atlas of a given steel, it is possible to determine the range of cooling rates that the steel may suffer during welding without affecting mechanical properties and without risking cold cracks. When comparing the microstructure of steel welds performed in field conditions, it is possible to determine the heat input range for a given process in the preparation of a WPS. The selected case study is from a high strength low alloy class 65 ksi steel (ASTM A572 Grade 65) that was used in the structure of an industrial building. The steel was produced using TMCP. The atlas was created via the construction of a continuous cooling transformation diagram using physical simulation (dilatometer and Gleeble) of the coarse grain HAZ (GCHAZ). The characterization of the simulated region was performed by metallography and mechanical tests. The microstructure of real welds made by a qualified WPS were compared to the atlas in order to certify the correct use of parameters and to validate the method. The methodology was also qualified and the potential economic benefits were quantified (based only on the reduction of consumables used and the increased availability of the welding process machine) for the selected industrial project. The mapped microstructures varied from martensite (at high cooling rates) to pearlite/ferrite with large grain size (at low cooling rates). There was remarkable prevalence of bainitic microstructure in a wide range of cooling rates, consistent with the chemical composition of the steel studied. Comparisons with real weld microstructures showed the atlas is compatible with them, and that it can more accurately describe the effective thermal cycle xi that occurs in the coarse grain region of the HAZ (other regions were not included). The application of this methodology in the development of new WPS would allow greater flexibility in the welding procedures, including welding without preheating. In this respect alone, it was possible to forecast savings of approximately R$200,000.00, 1,000 hours of processing and 172 tonnes of carbon equivalent emissions.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Conselho Nacional de Desenvolvimento Científico e Tecnológico

The large Brazilian territory and the increasing demand for oil and gas consumption created a national challenge for the fast and reliable expansion of pipelines. The need for construction and maintenance and of new pipelines require welding processes with high productivity, reliable, that produce quality welds, to the detriment of the coated electrode process, currently the most used in the pipe union. Therefore, this work presents the study of girth welding of carbon steel pipes (API 5L, 2012) with 8\" nominal diameter and 8.0 mm thickness. The welds were carried out in downhill progression by using orbital displacement device (mechanized welding), ER70S-6 wire with 1.2 mm diameter and Ar+25%CO2, as shielding gas. The material was deposited on butt V joint with 15º bevel, 1 mm of root face and 3 mm root opening, without backing. For the proposed joint, GMAW processes with short-circuit metal transfer were assessed in both conventional and derivative modes by using commercial power source namely STT (Surface Tension Transfer). In this context, welding parameters were investigated for root pass and filling pass. The analysis were obtained from visual inspection and mechanical tests (uniaxial tensile test, root and face bending, nick-break, charpy V-notch impact test, macrography test and hardness profile) with objective to qualify both processes. In addition to the qualification of welding processes, it was also necessary to make improvements in the experimental rig, the test-pipe assembly and the existing electronic system. Among such improvements, it was carried optimization the trigger synchronism between the power source, the data acquisition system and the orbital machine; the elimination of equipment shutdown during welding; the optimization of automatic adjustment control of the contact tip to workpiece distance (DBCP) and the elimination of visual narrowing of the heat zone caused by fixtures. Pre-tests were carried to qualitatively evaluate the temperature decay on both sides of the welded joints motivated by the excessive frequency of defects (lack of side fusion) previously observed. The results showed that the temperature decay rate on one side of the pipeline does not affect the welding. Finally, only the derivative process (STT) was capable to obtain a robust set of parameters for the proposed joint, in accordance to the acceptability criteria of standard API 1104 (2010). On the other hand, the conventional process GMAW was capable only to obtain a set of parameters for the root pass.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior