PSI - Issue 54

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Paulo Mendes et al. / Procedia Structural Integrity 54 (2024) 340–353 Mendes et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 1. Geometry of the evaluated samples: a) J30 welded joint with root steps; b) J30 fully welded joint; c) J60 welded joint with root steps; d) J60 fully welded joint.

B Microhardness tests were also performed to evaluate the hardness of specific microstructure constituents in the welded joint. With this analysis, it will be possible to acquire a better understanding of each type of microstructure. Using the INNOVATEST Falcon 400 equipment, this test was carried out with an HV0.1 Vickers indenter, correspond ing to a 0.1 kgf (0.9807 N) force applied for 15 seconds. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) was employed to characterize the microstructure of specimens extracted from di ff erent regions of the welded joint. The SEM analysis involved a metallographic preparation with a P320–1000 grit sili con carbide sandpaper sequence, followed by a polishing step with 6 and 1 µ m cloths and their respective diamond suspensions. E F D C A A B

3. Hardness evaluation

3.1. Hardness test analysis - High-force Vickers hardness test

The main goal of this experiment was to investigate how the heat input of the final steps a ff ects the preceding ones concerning tempering heat treatment. Tempering typically reduces hardness values, making macrohardness tests a valuable tool for comprehending the evolution of this mechanical property. This is also a crucial stage in process quality control, as heat input can significantly influence the microstructure and mechanical properties to the point where the weld becomes unusable for industrial applications. ISO 15608:2017 (International Organization for Stan dardization (2015)) is a standard that provides guidelines for the selection and qualification of welding procedures for metallic materials. According to this standard, S690QL steel belongs to the 3.2 group, which means that it requires a high level of testing and inspection to ensure its quality and safety. It has a maximum hardness value of 450 HV10, according to ISO 15614-1:2017 (International Organization for Standardization (2017a)), which means that it is re sistant to wear and tear, as well as the ability to withstand high levels of stress and pressure. However, it is important to note that proper welding procedures must be followed to ensure the integrity of the material and prevent potential defects or failures. Twoa ffi liations, A and B, were carried out near the upper portion and near the root of the welded joints. These tests were conducted in a complete welded joint and in a welded joint only with the root steps. A ffi liation B is expected to have the most significant di ff erence in results between the complete and incomplete procedures. Vickers hardness tests were conducted for the root procedure and the fully welded J30 joint, as shown in Figure 4 and 5. The hardness profiles shown in both figures reveal significant di ff erences between the two procedures, indicating the direct influence of the multipass welding process on mechanical properties in various regions. The hardness profile for the welded joint with only the root steps is nearly identical for a ffi liations A and B, suggesting that the heat input of the steps in section A was insu ffi cient to induce tempering and gradually lower the hardness values in B. The most notable variations in the hardness values occurred in the HAZ, but it also had the biggest data discrepancy, indicating an uneven cooling rate along this zone. This observation is also supported with the microstructural characterization findings, which reveal a diverse array of morphologies and constituents within the HAZ.