PSI - Issue 38

Tuomas Skriko et al. / Procedia Structural Integrity 38 (2022) 393–400 Skriko et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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NB PB TIG

nota bene

horizontal position

tungsten inert gas UHSS ultra-high-strength steel

2. Experiments The performed experimental researches comprised the determination of appropriate laser dressing parameters for the studied fillet-welded joints, the preparation of fatigue test specimens with suitable methods and parameters and, along with related measurements and analyses, such as joint geometry and residual stresses, the execution of the fatigue tests. All the experiments were carried out in the laboratory environment and circumstances. 2.1. Materials A direct quenched S960 grade UHSS was used for the base material of the fatigue test specimens. Nowadays and in the future, this type of structural steel is increasingly applied in lightweight and energy efficient products, such as mobile machines, cranes and transportation equipment. For the welding of the test specimens, a slightly undermatching solid wire filler metal compared to base material in terms of nominal yield and tensile strength was used, and the applied shielding gases were argon-based mixed gas (Ar + 10 % CO 2 ) and pure argon (99.99 % Ar) in welding and laser dressing, respectively. The nominal chemical compositions and mechanical properties of the base material and filler metal are shown in Table 1 and Table 2, respectively. Table 1. Nominal chemical compositions of the base material and filler metal (%). Presented proportions are standard maximum values apart from Al content of S960MC, which is a minimum content value. (EN 10149-2, 2013; EN ISO 16834, 2012) C Si Mn P S Al Nb V Ti Cu Cr Ni Mo B Base material S960MC 0.20 0.60 2.20 0.025 0.010 0.015 0.09 0.20 0.25 1.00 0.005 Filler metal G 89 5 M21 Mn4Ni2.5CrMo 0.13 0.80 2.10 0.015 0.018 0.12 0.03 0.10 0.30 0.60 2.80 0.65

Table 2. Nominal mechanical properties of the base material and filler metal. Presented properties are standard minimum values. (EN 10149-2, 2013; EN ISO 16834, 2012) Yield strength Ultimate strength Elongation Impact strength R p 0.2 [MPa] R m [MPa] A [%] T [°C] KV [J] Base material S960MC 960 980 - 1250 7 -40 27 Filler metal G 89 5 M21 Mn4Ni2.5CrMo 890 940 - 1180 15 -50 47

2.2. Test specimens The applied fatigue test specimens were non-load-carrying fillet-welded cruciform joints, of which shape and dimensions, in addition to welding and laser dressing sequences and directions, are presented in Fig. 1. The plate thickness of laser cut sheet metal parts was 7.8 mm and a robotized gas metal arc welding (GMAW) and laser dressing was applied to make the weldments. The used process parameters are shown in Table 3. The wire diameter of the filler metal was 1.0 mm and a nominal throat thickness of 5 mm for each weld was produced with a single-pass welding. In addition, the interpass temperature between welding and laser dressing runs were kept below 50 °C, and a horizontal