PSI - Issue 38

Tobias Jonsson et al. / Procedia Structural Integrity 38 (2022) 411–417 Jonsson, Narström and Barsoum / Structural Integrity Procedia 00 (2021) 000 – 000

413

3

2. Advanced High Strength Steels – Strenx® 1100Plus Advanced High Strength Steels (AHSS) are specially design steels that aims to improve specific mechanical properties such as strength, flexibility, fatigue attributes or other properties. These steels are complex combinations multiphase microstructures and meticulous selected components. This way each steel is tailor made to maximize the desired mechanical property. The 3rd generation of AHSS are currently under development with the aim of achieving yield strength > 1200 MPa and ductility > 30% elongation. Strenx® 1100 plus is AHSS specially design to improve weld properties. With matching filler material, the fusion zone and the heat affected zone receive similar mechanical properties as the base material. 3. Specimen manufacturing, static and fatigue testing Two plates with Strenx® 1100Plus steel were cut in to three pieces each. The six slabs were prepared for welding and with MAG 135 welding, the pieces were welded as a Double V joint type. In the welding processes Mison 18 was used as sheilding gas and Union X96 as electrode, small scrap pieces of steel were used as start and stop point for the welding to insure continuous welds along the whole joints. Two out of the three welds were then post treated with TIG dressing and HFMI respectively. After the treatments all three pieces were then laser cut into specimens. In figure 2a used for the tensile testing is presented.

Figure 2. Test specimen for a) static testing and b) fatigue testing. The fatigue testing was carried out in a Rumul 500 high frequency test rig. The testing was carried out at 90 Hz with R =0.1. The machine was set to stop when a 1.5 Hz frequency drop occurred, and the specimen was considered as failed. Run out limit was set to 5 million cycles and if this happened the load was increased, and the specimen was run again. An equivalent stress was then determined with Palmgren-Miner linear damage theory. The fatigue test specimen is shown in figure 2b where L = 400 mm, L 2 = 182 mm, the width W = 85 mm and the out-of-plane thickness is 8 mm. In order to avoid edge crack failures, a cut out with radius R = 10 mm was made. Figure 3a-c shows the as-welded, TIG dressed and HFMI treated butt welds, respectively. Winteria® qWeld, a digitized weld quality laser scanner system, was used in order to evaluate the weld quality in the as-welded condition and the improved weld quality according to the Volvo weld quality standard (181-0004, 2016) quality levels. This standard has five classes for different levels of weld quality; VS for static loading, VE, VD, VC and VB are for dynamic loading with VB being the highest quality and VE the lowest. All the classes asses the same features on the weld as undercut, weld toe radius, linear misalignment etc.