For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

RESUMO Neste trabalho foram investigadas as influências de alguns dos principais fatores do torneamento sobre o acabamento da superfície e a rugosidade de uma peça torneada. Foram analisadas barras de aço SAE 1045 torneadas em um torno controle numérico computadorizado (CNC), com auxílio da técnica de Planejamento de experimentos (DOE) para formar trinta e duas diferentes combinações de fatores, analisar suas interações e sua influência no acabamento de cada amostra. Os fatores de usinagem investigados foram: (1) avanço, (2) velocidade de corte, (3) raio de quina, (4) ângulo de saída e (5) região de medição da rugosidade. Por meio do DOE foram realizadas duas análises fatoriais: a primeira avaliou a influência dos cinco fatores na rugosidade média, representada por Ra, e a segunda avaliou a eficácia de cada conjunto de fatores em obter o acabamento alvo. Para isso, foi criado um índice que relaciona a rugosidade teórica de cada processo com a rugosidade medida pelo rugosímetro. Os resultados mostraram que o avanço e o raio de quina possuem elevado efeito padronizado em ambas as análises. Porém, enquanto a aplicação de um menor avanço (ou maior raio de quina) produziu superfícies com baixa Ra, por outro lado também prejudicou a eficácia do torneamento, pois contribuiu para obtenção de uma rugosidade significativamente maior que a rugosidade teórica. Já o fator velocidade de corte foi benéfico ao processo em ambas as análises. Não foi encontrada relevância da região de medição da rugosidade sobre a rugosidade média, Ra.

ABSTRACT This paper investigated the influence of some of the main turning parameters in surface finish and roughness of turning samples. The 0.45%C (SAE 1045) steel bars samples, turned on a CNC turning machine, were analyzed using Design of experiments (DOE) approach to produce a total of thirty-two parameters combination, analyze its interactions and influences in each sample’s surface finish. Machining parameters investigated were: (1) feed rate, (2) cutting speed, (3) nose radius, (4) rake angle and (5) region of roughness measurement. Two factorial analyses were conducted through the DOE data. The first one evaluated the influence of those five parameters in the average roughness, represented by Ra, and the second one evaluated the accuracy of each parameters combination to achieve the expected surface finish. For this measurement, an index was created to compare the theoretical surface roughness of each process with the surface roughness measured by rugosimeter. Results showed that parameters as feed rate and nose radius have strong standardized effect in both factorial analysis. Results shown that reduction of the feed rate (or increase in nose radius) was able to produce lower roughness average (Ra) but, on the other hand, it also contribute to generate a surface roughness significant higher than theoretical roughness. The increase in cutting speed was beneficial to both, achieving a lower roughness average and improving process accuracy. The region of roughness measurement was found not significant to influence the roughness average, Ra.

In this work, the corrosion resistance of Inconel 625 coatings applied to AISI 4140 steel plates was evaluated. Coatings were produced by High Velocity Oxygen Fuel (HVOF) by use of two different equipment which use either kerosene (liquid) or propane (gas) as fuel. The resulting coatings were evaluated in two conditions: as-deposited and after a surface finishing process by grinding. Residual stress distributions in the coatings were characterized by X-ray diffraction and their morphology was verified through metallography and roughness measurements. Potentiodynamic polarization corrosion testing complemented their analysis. The results show a strong influence of the surface finishing process on the corrosion performance of the coatings.

Resumo A utilização de materiais nobres é requisito básico em aplicações onde existe um ambiente agressivo como na indústria do petróleo e nuclear. Neste panorama, a liga Inconel 625 é frequentemente utilizada como material de cladeamento no revestimento interno de dutos rígidos. Assim, as superligas de níquel exercem papel fundamental nos campos de exploração de águas profundas e, por isso, o conhecimento de métodos modernos de soldagem aplicados a estas ligas e suas consequências nos estados de tensões residuais é importante. Portanto, o presente trabalho faz uma avaliação das tensões residuais após a Soldagem por Fricção e Mistura Mecânica (SFMM) em chapas soldadas de Inconel 625. A união das chapas foi realizada com rotação da ferramenta 200 e 1200 rpm e velocidade de soldagem constante (1mm/s). As medições de tensões residuais na superfície das juntas soldadas foram investigadas através da técnica de difração de raios-X. Além disso, foram avaliadas as macroestruturas e o aporte térmico de acordo com os parâmetros de soldagem empregados. Embora não existam muitos trabalhos relacionados ao processo SFMM para ligas de Inconel, provavelmente devido à sua dificuldade de soldagem, tem sido percebido um aumento na aplicação da soldagem no estado sólido como excelente alternativa para as superligas à base de níquel. Os resultados mostraram que diferentes parâmetros de processo produziram juntas soldadas distintas e, consequentemente, variações na distribuição de tensões residuais. Por fim, um aumento na velocidade de rotação da ferramenta ocasionou um aumento nas tensões residuais na zona de mistura.

Abstract The use of noble materials is a basic requirement in applications where an aggressive environment such as offshore industry and nuclear energy. In this scenario, the Inconel 625 is often used as clad material in rigid pipes. Thus, nickel superalloys play a fundamental role in the deepwater exploration fields and, therefore, understanding of modern welding methods applied to these alloys and their consequences in the residual stress states is very important. Hence, this work evaluates the residual stress distributions after Friction Stir Welding (FSW) applied on Inconel 625 sheets. FSW was performed with tool rotational speed in the range of 200 to 1200 rpm and welding speed constant. Measurements of superficial residual stresses were investigated by X-ray Diffraction. In addition, macrostructures and heat input were evaluated. Although there are only few reports related to FSW applied on Inconel alloys, probably due to this welding process difficulty, it has been regarded that there is cumulative application of a solid state welding as an excellent alternative for nickel superalloys. The results showed that different welding parameters produced distinctly welded joints and consequently changes in the residual stress distributions. Finally, an increase in the tool rotation speed increased the residual stress in the stir zone.

The residual stress state of a mechanical component is an important factor in its production planning and in estimates of its lifecycle since it can be responsible for geometric distortions and degradation of fatigue properties. Therefore, the development of reliable methods for non-destructively quantifying these stresses remains in the interest of most manufacturing industries; Barkhausen magnetic noise measurements have been investigated in several applications and remains a viable option. However, its effective implementation has occurred mostly in components with simple geometries and insignificant microstructural gradients; even in these cases, successful industrial adoption of the method depends on previous calibration with samples that are often difficult and costly to prepare and validate. This work aims at investigating the capability of the method of characterizing the residual stress state in a simple but generally useful application: samples of hot-rolled steel sheets collected at two different stages of processing in an industrial mechanical conformation and heat treatment plant. In this analysis Barkhausen noise measurements were compared to X-ray diffraction results, and statistical analysis tools were used to correlate the results.

Typically, for automotive shafts, shape distortion manifests itself in most cases after the induction hardening by an effect known as bending. The distortion results in a boost of costs, especially due to machining parts in the hardened state to fabricate its final tolerances. In the present study, residual stress measurements were carried out on automotive drive shafts made of DIN 38B3 steel. The samples were selected in consequence of their different distortion properties by an industrial manufacturing line. One tested shaft was straightened, because of the considerable dimensional variation and the other one not. Firstly, the residual stress measurements were carried out by using a portable difractometer, in order to avoid cutting the shafts and evaluate the original state of the stresses, and afterwards a more detailed analysis was realized by a conventional stationary diffractometer. The obtained results presented an overview of the surface residual stress profiles after induction hardening and displayed the influence of the straightening process on the redistribution of residual stresses. They also indicated that the effects of the straightening in the residual stresses cannot be neglected.

In this work, a drawing processed was simulated to calculate forces and the resulting residual stresses in the material. The calculated residual stresses were compared with experimentally measured residual stresses by the Neutron Diffraction Method. The modeled process was the Wire Drawing. The necessary parameters to model the process were taken from an industrial currently used process. Rods of an AISI 1045 steel with nominal diameters of 21.46 mm were reduced to 20.25 mm by drawing with an drawing angle of 15°. Compression tests were used to determinate flow curves of the real material an used in the simulation models. The possibility to estimate drawing forces by numerical simulation was evaluated by comparing simulated results with values from empirical equations given by the literature. The results have shown a sufficient accuracy for the calculation of forces, but the comparison of residual stresses has shown differences to the experimentally determined ones that can be minimized by the consideration of high strain rates in the compression tests, anisotropy of the material and kinematic hardening.

In this investigation a DoE (Design of Experiments) analysis of distortion for a typical manufacturing process of pre-straightened, cold drawn and induction hardened AISI 1045 cylindrical steel bars was carried out. A careful characterization of the material, including residual stress states and geometrical changes, was done for the different manufacturing steps. In order to identify effects and correlations on distortion behavior, the investigated variables included the drawing process itself with two different drawing angles, a stress relief treatment, which was applied to one part of the samples, and, finally, induction hardening with two different case depths. Main and statistically significant effects on the distortion of the induction hardened samples were found to be in this order, the drawing angle, the stress relief treatment and the induction hardening depth. It was also found that the distortion potentials are transmitted from the drawing process to further manufacturing steps and, consequently, from one production site to the next.