PSI - Issue 54

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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HAZ Heat-a ff ected zone SEM-EDS Scanning electron microscopy with energy-dispersive X-ray spectroscopy R p 0 . 2 Yield strength R m Tensile strength Ac 1 ,Ac 3 Intercritical temperatures CCT Continuous cooling transformation

1. Introduction

The increased popularity of high-strength steels in o ff shore structures can be attributed to their advantageous strength-to-weight ratio, which reduces the overall structural weight and fabrication costs. However, the weldabil ity of these materials can be challenging, owing to their lower toughness and higher susceptibility to cracking in the heat-a ff ected zone (HAZ) and weld material (Weman (2011); Sefcikova et al. (2015); Arsic et al. (2015); Micˇian et al. (2021); S´ lezak and S´ niez˙ek (2017); Dobosy and Luka´cs (2019)). Lahtinen et al. (2019) investigated the impact of di ff erent welding conditions, specifically heat input, on the fatigue behavior of metal active gas welds of a thermo mechanically processed 700MC modern ultra high-strength steel. Costa et al. (2010) conducted a fatigue study on three di ff erent welding conditions on high-strength steel transverse butt joints. Shiga et al. (2014) focused on im proving the fatigue properties of high-strength steel gusset welded joints. Akyel et al. (2018) investigated the fatigue strength of repaired welded connections made from S690QL and other grades of high-strength steel. Pijpers et al. (2009) performed fatigue tests on V-shape welded hybrid plate specimens composed of S460, S690, and S890 rolled steel plates. Sorger et al. (2018) discussed the weldability of high-strength steels and the limitations they face due to their loss of strength, toughness, and fatigue properties focusing on the microstructure and fatigue properties of 6-millimeters thick S690 and S355 steel plates joined by friction stir welding. Therefore, it is important to recog nize the factors that determine the weldability of high-strength steels and develop appropriate strategies to improve their performance in welded joints. Also, the weldability of high-strength steels directly a ff ects the fatigue behavior of o ff shore welded joints. The microstructure and properties of the weld are a ff ected by the weldability of the high strength steel, which in turn a ff ects the fatigue strength of the joint. For this reason, the fatigue behavior of o ff shore welded joints has been the subject of extensive research (Aidibi et al. (2021); Vieira A´ vila et al. (2022); Karthik and Mahendramani (2021); Heinemann et al. (2021); Zhang et al. (2016); Chang and Dover (1999)). Joint geometry and process parameters, such as travel speed, welding current, voltage, pre-heating and interpass temperature, should also be carefully considered to ensure the optimal performance of high-strength steel welds (Partes et al. (2020); Wang et al. (2017); Mike Lord (1999); Peng et al. (2012); Li et al. (2019)). Hardness is a critical factor that a ff ects the mechanical properties and performance of welded joints. Hardness testing can indicate the extent of deformation and strengthening that occur during welding. Hardness testing can provide insights into deformation, strengthening, stress concentration, and crack initiation at the weld toe, all of which are crucial for understanding fatigue crack propagation (Guo et al. (2018)). To achieve the desired degree of hardness and fatigue resistance, it is crucial to understand the link between the hardness and fatigue characteristics of welded joints and optimizing welding conditions and post-weld treatments are crucial in light of existing knowledge. Several methods for estimating fatigue strength based on hardness testing have been proposed (Remes et al. (2020); Lee and Song (2006); Roessle and Fatemi (2000); Masuda et al. (1986); Konuma and Furukawa (1989)). Fatigue testing is a complex and time-consuming process that requires specialized equipment and significant resources, particularly in the very high-cycle fatigue regions (Bandara et al. (2016); Dantas et al. (2023)). Hardness can be correlated with other mechanical properties, such as yield strength and tensile strength (Rozumek et al. (2020); Silva et al. (2021); Xin et al. (2021)). In general, harder materials tend to exhibit higher yield and tensile strength. The microstructure of high strength steel joints is influenced by the welding process, the base material composition, the heat input, and the post weld heat treatment. Di ff erent microstructures, such as martensite, bainite, austenite, and carbides, can have varying e ff ects on the strength, toughness, fatigue resistance, and corrosion resistance of joints (Sun et al. (2022); He et al. (2012); Weglowski et al. (2020)). Ahiale and Oh (2014) compared the microstructure and fatigue life of weldments in advanced high-strength steels with di ff erent strength levels and investigated crack formation in weldments in relation