The API 5L X70 steel is used in high-pressure gas transmission pipelines. Because of this, knowledge of presence of residual stress and their magnitude is important to assess the material integrity in service. For the pipeline manufacturing, tubes need to be curved which is often made using the hot induction bending process. This process can introduce different residual stress depending of tube position. For this research, in order to evaluate the residual stress, was used an API 5L X70 tube that was previously curved by hot induction process. Samples were taken from the extrados, intrados, neutral line and straight section of the curved tube. Residual stresses were studied by two conventional methods: X-Ray Diffraction (XRD) and Hole-Drilling, which are destructive and non-destructive methods, respectively, in order to assess their qualitative responses. Each of these methods presents particular methodologies in sample preparation and material analysis, but also they differ in factors such time consumption and cost of the analysis. The qualitative responses obtained by the two different methods were comparable and satisfactory and pointed out the existence of a compressive residual stress state in steel pipe.

This study aimed to evaluate the potential use of elemental powders, Ni oxyreduction and Ti HDH (hydration-dehydration) to obtain the NiTi shape memory alloy in cylindrical specimens from additive manufacturing process by Selective Laser Melting with laser power and energy density under control (100 to 150 W and 25 to 40 J/mm 3 ). Scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) conjugated analyses showed that all processing parameters yield samples with Ti enriched regions surrounded by alloy layers associated to Ni 3 Ti, Ni 3 Ti 2 , and NiTi 2 intermetallic. This evidence suggests that the parameters applied were not enough to promote the complete fusion of Ti particles, indicating that the samples presented a melting microstructure with evidence of defects located due to lack of fusion due to the irregular voids and Ti islands that resemble the irregular morphology of the starting Ti HDH powder, and pores depending on the retention of gases in the fusion pool. Each explored condition presented in its structure a set of different phases in nature and proportion, without the NiTi intermetallic. Also, justifies the apparent and real density values not compatible with the NiTi intermetallic theoretical density, but the density resulting from the mixture of different Ni-Ti system phases formed. Observing the decrease in the cracks and pores, and the real densities measured, compared with the theoretical density of the NiTi intermetally, the specimens that represent the best conditions are those produced with 125 and 150 W with 30 J/mm 3 , in order not compromising the SMA properties, and would allow microstructural evolution for the formation of the NiTi through heat treatment. Although the most favorable parameters, the NiTi system did not exhibited an austenitic matrix, and then the adoption of the proposed elementary powders mixture will be promising when followed by solution heat treatment, which is one of the works under development by our research group.

The present study shows a comparison between two sintering processes, microwave and conventional sintering, for the manufacture of NiTi porous specimens starting from powder mixtures of nickel and titanium hydrogenation–dehydrogenation (HDH) milled by mechanical alloying for a short time (25 min). The samples were sintered at 850 °C for 15 min and 120 min, respectively. Both samples exhibited porosity, and the pore size results are within the range of the human bone. The NiTi intermetallic compound (B2, R-phase, and B19′) was detected in both sintered samples through X-ray diffraction (XRD) and electron backscattering diffraction (EBSD) on scanning electron microscopic (SEM). Two-step phase transformation occurred in both sintering processes with cooling and heating, the latter occurring with an overlap of the peaks, according to the differential scanning calorimetry (DSC) results. From scanning electron microscopy/electron backscatter diffraction, the R-phase and B2/B19′ were detected in microwave and conventional sintering, respectively. The instrumented ultramicrohardness results show the highest elastic work values for the conventionally sintered sample. It was observed throughout this investigation that using mechanical alloying (MA) powders enabled, in both sintering processes, good results, such as intermetallic formation and densification in the range for biomedical applications.

The crystallographic texture developed during cold rolling and subsequent annealing of interstitial free sheet steels aims to increase conformability. For this, it is necessary to obtain partial α-fiber and continuous and homogeneous γ-fiber texture components. In this work, the influence of symmetric (SR) and asymmetric (AR) cold rolling on crystallographic texture and mechanical properties of an interstitial free steel (IF) was investigated. Symmetric cold rolling yields α-and γ-fibers, which are enhanced as deformation increases. Moreover, α-fiber weakening occurs due to recrystallizations, improving formability. The same fibers are produced by asymmetric cold rolling, but in this case, the γ-fiber is slightly shifted in psi, which is one of Euler angles second ROE's notation 1,2 , and more homogeneous than in symmetric rolling. The best mechanical properties were achieved by asymmetric cold rolling/annealed with about 80% deformation.

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