Resumo O aço ASTM A572 Grau 50 é utilizado na fabricação de conjuntos soldados para aerogeradores, por este motivo, a realização de alívio de tensões é de grande importância para correção dos impactos causados pelos processos de soldagem, bem como, o conhecimento das propriedades finais obtidas com a realização deste processo. O objetivo desse estudo é comparar as propriedades mecânicas e tensões residuais (método de furo cego) em amostras de aço ASTM A572 Grau 50, soldadas pelo processo de arco submerso, submetidas ao alívio de tensões na condição térmica (PWHT) e na condição como soldado (SST), seguindo os requisitos normativos da AWS D1.1-2015. Os resultados da condição PWHT referente a dureza, limite de escoamento, resistência a tração e tensões residuais são menores e os valores de alongamento e energia absorvida ao impacto são maiores do que a condição SST. Ambas as condições foram aprovadas no ensaio de dobramento lateral. Os resultados obtidos demonstram a importância do processo de alivio de tensões que minimiza os efeitos indesejados dos processos de soldagem aos componentes.

Abstract The ASTM A572 Grade 50 material is used in welded structural components in the manufacture of wind turbines. In this way, it is important to apply the stress relief process to correct the effects caused by the welding processes, and then assess the final properties obtained with this process. The objective of this article is to evaluate the mechanical properties of specimens of the ASTM A572 Grade 50 material welded by the submerged arc welding, comparing the thermal stress relief condition (PWHT) with the as welded condition (SST), following the normative requirements of AWS D1. 1-2015. Tensile testing, impact test, lateral bending, hardness and residual stresses measured by hole drilling method for the conditions tested. The results showed lower values of hardness, residual stress, yield strength, and ultimate tensile strength of the PWHT specimens. On the other hand, the values of elongation and impact energy absorbed of the PWHT specimens were higher than those of the SST specimens. Both conditions tested were approved in the lateral bending test. The results demonstrate the importance of the stress relief process, which reduces the unwanted effects of the welding processes, thereby delivering better quality of the components.

This work was based on the surface integrity analysis of hardened steel, AISI 4317 case carburized, quenched and tempered with 58 HRC, obtained by a turning operation executed with CBN (cubic boron nitride) tool, varying three basic cutting parameters (cutting speed, feed rate and cutting depth). The surface integrity characterization was conducted analyzing the behavior of the surface roughness Ra, residual stresses and with layer presence after turning. Also, the cutting forces were measured. The experimental planning used was a central composite design. The results and data were statistically treated by the Statistica software, enabling the generation of a mathematical model, relating the dependent variables with the independent variables. The roughness values Ra obtained after the experiments ranged from 0.31 to 2.8 µm, providing an indication that is possible to replace grinding process by hard turning using CBN tools that could reduce machining time and costs. The hard turning process generated compressive residual stresses profiles and white layer formation, from 1.1 to 5.1 µm, on the surface of the samples. The penetration force showed the highest values for the turning forces measurements. The lowest values for the cutting parameters represented the optimized surface integrity of the AISI 4317 steel.

This study presents the effect of the welding parameters variation on the results of forces, temperature, residual stresses and Vickers micro hardness of dissimilar butt joints of AA2024-T3 and AA7475-T761 welded by friction stir welding (FSW). The tool rotational speed, feed rate and tool tilt angle were investigated using the Design of Experiments method. The obtained results of penetration force, temperature in the weld zone compared with the microscopic analysis of the microstructure showed that it is necessary a minimum amount of force and heat input to obtain a defect free weld zone. It was also notable that, friction stir welding has a wide stability range of its most significant parameters - rotational speed and feed rate - which grantee this minimum condition. Micro hardness’ profiles showed the effect of the grain size refinement towards the thermo-mechanically affected zone as well as, the effect of recrystallization inside the nugget. Residual stresses’ profiles showed a tensile stress peak at the shoulder contact area due the pressure with the base material on thermo-mechanically affected zone and the stress relief effect caused by high temperatures in the nugget resulting in a decrease in residual stress value. The most significant variables for residual stress results were rotational speed of the tool and welding feed rate, once their interaction rule the heat input in the weld zone.

This study aimed to analyze the residual stresses and roughness in finishing milling of AISI 4140 steel, quenched and tempered up to hardness of 58 HRC. Machining operations were performed with the use of CBN inserts and by varying three basic cutting parameters (cutting speed, feed per tooth and cutting depth). Hardened materials are typically machined by abrasive processes, which in turn are more expensive and complex to be studied due to the undefined cutting geometry of the grinding wheel. A series of machining tests with milling process and CBN tools was implemented in order to study the resultant condition of the specimen´s surface. An experimental design was used and the results were statistically treated, enabling the generation of a model that aims to obtain roughness values due to the optimization of three adopted cutting parameters. The roughness values found in the range of Ra 0,16 to 0,4 µm indicate that it is possible to use the milling process with CBN tools for finishing, reducing machining time and the cost of the machined part. The generated residual stresses were compressive and the feed per tooth parameter showed greater influence in this result. The research was limited to test only one type of CBN insert, which was constantly replaced, preventing the influence of tool wear on responses. The geometry of the tool as well as the use of cutting fluid were not considered. Milling process with CBN inserts is confirmed as a possibility for replacing grinding process for finishing machining leading to significant gains in machining time. An optimized model was derived to predict the value of the roughness and three optimizations were made to specify the best cutting parameters to desirable answers such as better roughness, higher compressive residual stresses and low cutting forces, for example.