# MAG Welding Tests of Modern High Strength Steels with Minimum Yield Strength of 700 MPa
## 2 Materials and Methods
The elongation results correspond to the elongation at break of the test specimen and it was measured as the ratio between changed length after breakage and the initial 70 mm distanced two marks equidistant from the centre of the weld. The yield tensile strength results correspond to the offset yield point with a 0.2% plastic strain. For the welds of the S700 MC-1, extended tensile tests were implemented in specimens extracted in the locations represented in Figure 3. The extended tests are mainly focused on the evaluation of the mechanical strength properties along the weld axis and general bending behaviour, depending on the welding conditions. Considering that all the welding technological parameters and procedures, component's geometry, and material's physical properties are similar, it is sufficient to use one of the three materials being investigated. The modern TMCP steel S700 MC-1 was the one selected. These results from the extended tensile tests were made with digital image correlation (DIC) measurements, at the frequency of 2 Hz, using a Lavision Imager Pro X camera system. The strain and its localization were estimated by analyzing the images using DaVis software. The main objective of these extended tests was to assess the differences in strength values along the weld seam. Therefore, tensile test specimens were extracted from the welded plate focusing on the transient region of the start and end of the weld. One specimen was removed from the stationary middle region. Figure 2: Schematic presentation of the weld joint: (**a**) joint design; (**b**) welding sequence. All dimensions in [mm]. Three-point bending tests were implemented for the material S700 MC-1 using an MTS 810 and following the ISO 5173:2009. All four different heat inputs were tested. The dimensions of specimens were 8 \(\times\) 20 \(\times\) 140 mm. The edges were rounded and reinforcements were removed by milling on both face and root sides avoiding reduction of plate thickness. The test set was made of one loading anvil and two supporting roller anvils, with 50 mm in diameter, and a support span between the center of the two supporting roller anvils of 122 mm. The velocity of loading anvil was held constant at 0.33 mm/s. Both face and root side bending tests were implemented. In this study, Charpy-V sub-sized specimens were used. The sub-sized specimens extracted from welds had a thickness of 5 mm (i.e., 5 \(\times\) 10 \(\times\) 55 mm). The sub-sized specimens from base material had a thickness of 7.5 mm (i.e., 7.5 \(\times\) 10 \(\times\) 55 mm) and were extracted transversally to the final rolling direction. To enable an equivalent analysis, the results obtained with the sub-sized specimens were corrected to the full-sized specimens (i.e., 10 \(\times\) 10 \(\times\) 55 mm) by multiplying the energy value by 3/2 in case of 5 mm thick, and by 6/5 in case of 7.5 mm thick sub-sized specimen, according to [27]. The specimens were prepared according to the standard SFS-EN ISO 148-1 [28]. The dimensions, the direction and the notch locations are illustrated in Figure 4. The notches were placed at the weld metal (WM), fusion line (FL) + 1 mm, FL + 3 mm and FL + 5 mm. The specimens having the notch at the FL + 1 mm were tested at \(-\)20, \(-\)40 and \(-\)60 \({}^{\circ}\)C. Specimens having the notch at WM, FL + 3 mm and FL + 5 mm were tested only at \(-\)40 and \(-\)60 \({}^{\circ}\)C.  
Hardness profiles were determined using the Vickers hardness test, HV5. Face side and root side hardness profiles were measured separately, so that the distance from the face side measuring line to the top of the plate was 1.5 mm and, respectively, the distance from the root side measuring line to the bottom of the plate was 1.5 mm. Distances between the points were 0.5 mm. Figure 4: Charpy-V impact test specimens: (**a**) dimension; (**b**) notch locations with red vertical lines representing the locations: WM (veld metal), FL (fusion line) + 1 mm, FL + 3 mm and FL + 5 mm.