The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

This experimental work investigates the tensile behavior of friction stir spot welded joints from 3 mm thick aluminum alloy AA6082-T6 sheets. Taguchi L9 Orthogonal array was used for process parameters - Tool rotational speed (TRS), Dwell time (DT) and Shoulder diameter (SD) with consideration of three levels. Friction Stir Spot Welding (FSSW) was performed on vertical milling machine. Tensile shear test was conducted on Universal testing machine (UTM) to find out the tensile shear failure load (TSFL). The optimal combinations of parameters were at tool rotational speed of 2,000 rpm, dwell time of 15 seconds and tool shoulder diameter of 16 mm. Tool rotational speed had a substantial effect on tensile shear strength of FSSW joint. Scanning Electron Microscopy (SEM) tests revealed that the changes in microstructure in different zones of FSSW joint were observed. Tensile shear specimen was analyzed using SEM to observe the behavior of fracture surfaces. Significant ductility in the fracture surface was an evident in the fractography. In this article, attention is focused on the influence of joining parameters on the mechanical behavior of the friction stir spot weld under the tensile shear load condition. Keywords: Fractography; friction stir spot welding (FSSW); heat affected zone (HAZ); scanning electron microscopy (SEM); thermo-mechanically affected zone (TMAZ).

The T92 martensitic steel is utilized in thermal power plants because of its better mechanical properties, and it is needed to enhance the strength and improve the properties using heat treatment. The research aims to determine how the microstructure changes in T92 martensitic steel when normalized at 1000 °C for an hour and tempered at 760 °C for 2 hours using various cooling techniques, including air cooling, furnace cooling, and water quenching. It is characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), and optical microscopy (OM). Tensile strength, hardness and toughness measurements were also performed on the heat-treated T92 steel specimens. After tensile testing of heat-treated samples of T92 steel, the fracture surface was characterized using SEM to determine the fracture mode. The strength and hardness of T92 material increased with a normalizing of 1000 °C, whereas they decreased with a tempering of 760 °C. Compared to various material conditions, the tempering of 760 °C with air-cooled hold the tensile strength of 887 MPa, hardness of 267.42 HV and toughness of 135 J was shown to be the optimal combination.

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