Duplex stainless steels are materials with high mechanical strength, toughness, and corrosion resistance, properties that make them rather appealing for the application on chemical and petrochemical industries. However, the exposure of such materials to high temperatures promotes the precipitation of deleterious intermetallic phases that cause significant damage to the mechanical and corrosion properties of these materials. In this study, the UNS S31803 duplex stainless steel received a thermal treatment at a temperature of 830 °C for 30, 90, and 180 minutes. After the treatment, the precipitates were characterized by backscattered electrons (BSE) and chemical composition mapping, and the properties of impact toughness were assessed by Charpy V-notch test for the different treatment conditions. The corrosion resistance properties were assessed by cyclic potentiodynamic polarization study. The thermal treatments at 830 °C resulted in a considerable reduction of impact toughness, and the corrosion resistance was also reduced in longer treatment times along with the loss of the passivation ability of the materials treated.

Friction Stir Welding (FSW) is an excellent alternative for joining dissimilar and similar materials in comparison to conventional welding processes. In this sense, this work aims at qualifying FSW to similar AA5083-O and AA5052-O aluminum alloys, with 6.35 mm thickness, in a CNC machining center. Therefore, four welding experiments were undertaken. At first, two types of plate surface finish were considered before joining. Afterward, two tool probe geometries, and changes in the base material position were evaluated. Hence, the welds were mainly analyzed by metallography, tensile testing, and bending tests. Results showed that the machining step to oxides removal and plates alignment is beneficial for the weld processing and the factor that has significant influence to achieve suitable joints is the tool probe geometry. Finally, by obtaining an average ultimate tensile strength (UTS) of around 191 MPa, enhanced microhardness, and bent angle of approximately 150°, the best joint was chosen.

Tensile armor in flexible pipes consists of two or more layers of steel wires. Damage to the outer sheath may cause ingress of seawater in the annular space and thus corrosion of the armor wires. This work focused on the susceptibility of these wires to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) using a slow strain rate test (SSRT) under a bending load in an environment that contains chlorides. The behavior of two different microstructures was compared: martensite and pearlite plus ferrite. Furthermore, the materials were mechanically and metallurgically characterized. The results indicate that martensitic steel is more sensitive to both hydrogen embrittlement and stress corrosion cracking than pearlitic-ferritic steel.

Abstract The reliable determination of materials' mechanical properties is a fundamental factor for their application in engineering, and the estimation of the measurement uncertainty in testing laboratories has a direct impact on the interpretation of the results. Recent literature demonstrates that one of the most widely used methodologies for uncertainty estimation, the Guide to the Expression of Uncertainty in Measurement (GUM), has limitations, especially in cases where the mathematical model has a high degree of non-linearity. Furthermore, it makes approximations for the final probability distribution. In these cases, it is recommended that the measurement uncertainty is determined by the Monte Carlo Method (MCM), which considers the propagation of the distribution rather than the propagation of uncertainties. Thus, given the limitations of the GUM method and the importance of estimating the measurement uncertainty of mechanical tests, this work aims to implement the measurement uncertainty estimation for the plane-strain fracture toughness (KIC) test of metallic materials through the Monte Carlo Method. The results of the work confirm the importance of estimating the measurement uncertainty of fracture toughness tests.

Dissimilar Al-Cu joints are desirable due to the combination of the good electrical and thermal properties of copper with the economic advantages of aluminium. However, different chemical, mechanical and thermal properties turn dissimilar welding into a challenge with traditional fusion welding techniques. Friction stir welding appears to be a good alternative to welding dissimilar materials. Most of the works in Al-Cu FSW have been performed with Al on top. This work investigates the influence of heat input on the shear strength of aluminium-copper lap joints produced by FSW with a copper over aluminium lap configuration. Welds produced with the ω/ν rate of 200 rev.mm-1 or 500 rev.mm-1 resulted in the melting of the base materials and material leaking. Joints with shear tensile strength varying from 76 to 85% of the original resistance of AA6060 T5 were produced when the ω/ν rate was varied from 80 to 110 rev.mm-1. The fracture was governed by tension overload on the aluminium sheet, resulting in little influence of welding defects, such as tunnelling, on the joint strength.

Friction welding is a solid state technology which has been used worldwide. Potential advantages may be recognized as reducing welding project costs, weld weight, environmental impact and to promote enhanced mechanical properties. However, traditional welding methods are still a common practice in many engineering areas. In this sense, this work aims to present the technical advantages for replacing gas metal arc welding (GMAW) by friction welding for joining hydraulic cylinder tubes. The feasibility of friction welding was demonstrated by microstructural analysis, mechanical properties and hydrostatic pressure testing. The results showed enhanced mechanical properties for the friction welded tubes. In addition, macro and microstructural features presented distinguishable process characteristics which reflect in different microhardness values. The friction weld exhibited a better behavior in bending as well as hydrostatic tests.

This work presents a study about the correlations between the characteristics of the acoustic waves and the mechanical properties of low carbon hot rolled steel bars, through the comparison between the wave velocity or attenuation and the tensile strength, yield point or elongation of the material. The aim is the possibility of using this technique to predict the production quality of ASTM A36 steels. Acoustic velocity and attenuation measurements by gain acquisition were carried out with the use of longitudinal waves and transducers of 5 and 15 MHz. Samples of hot rolled reinforcement steel bars with one inch diameter were used. A metallographic study of grain size and inclusion content was made along with chemical composition to verify the influence of these factors to the acoustic measurements. Results indicated that it is possible to use the presented methodology to estimate the mechanical properties, in especial, the tensile strength in steel rebars.

Neste estudo, um aço TRIP 800 foi soldado através do processo SPFMM usando três diferentes velocidades de rotação da ferramenta, 1600, 2000 e 2400 rpm, e mantendo-se o tempo de mistura fixo em 2s. Foram mostradas as microestruturas resultantes em cada zona formada, assim como a variação de dureza através delas. Maiores valores de dureza foram obtidos na menor velocidade de rotação, 1600 rpm, onde o aporte de energia teoricamente foi menor e, portanto, a taxa de resfriamento foi maior. Porém, nesta velocidade de rotação também houve formação de ferrita alotriomorfa na microestrutura. Nos ensaios de cisalhamento, amostras soldadas nas velocidades de 1600 rpm e 2400 rpm não atingiram o valor de força mínimo recomendado pela norma AWS D8.1M, o que foi atribuído ao menor comprimento da linha de ligação e à menor distância entre a parede do furo deixado pelo pino e a linha de zinco formada na zona de mistura, uma vez que durante a fratura a trinca propaga através desta linha e a microestrutura só possui algum papel no processo de fratura quando ela não existe mais.

A TRIP 800 steel was friction stir spot welded using three different tool rotational speeds, 1600, 2000 and 2400 rpm, and the dwell time was kept constant in 2s. The resultant microstructures formed in each weld zone were analyzed, as well as their hardness. Higher hardness values were observed for the lowest rotational speed, 1600 rpm, where the heat input in theory was lower and, therefore, the cooling rate was faster. However, for this rotational speed allotriomorphic ferrite was also observed in the stir zone. In the lap-shear tests, samples welded at 1600 rpm and 2400 rpm did not reach the minimum value recommended by the AWS D8.1M standard, which was attributed to the lower bonding ligament length and also lower distance between the keyhole left by the pin and the end of the zinc line, which is formed in the stir zone. The fracture of the samples occurred along this line. As a result the influence of the microstructure on the failure process could only be inferred when the zinc line disappeared.