# Effects of High Toughness and Welding Residual Stress for Unstable Fracture Prevention
## 2 Experimental Procedure  
### Materials  
In previous research [8; 22; 23], the brittle crack propagation path was determined by the influence of the welding residual stress, regardless of plate thickness. By measuring the welding residual stress distribution along the thickness of the plate, it was observed that: (a) in the case of high heat input (HHI), the tensile residual stress was predominantly distributed in this direction, thereby directly accelerating brittle crack propagation (b) and, in the case of low heat input (LHI), the compressive welding residual stress was distributed along the thickness, thereby arresting and preventing brittle crack propagation. As shown in Figure 1, the crack stopped for the LHI specimen and propagated straight for the HHI specimen, regardless of plate thickness. The residual stress distribution along the thickness, which was obtained through previous research, is shown in Figure 2, in which a comparison of the LHI and HHI welding residual stresses in the loading direction are also given. The transverse direction (TD) is the loading direction in the ESSO test and the longitudinal direction (LD) is the welding direction, as shown in Figure 2. The HHI presents tensile stress along all the directions of thickness, while the LHI exhibits tension and compression residual stresses. According to previous research [22; 24], the distribution of the residual compressive stress can prevent unstable fractures. Therefore, avoiding unstable fractures was achieved in this study by distributing the compressive welding residual stress using a special welding consumable. Tables 1 and 2 present the chemical composition and mechanical properties of the base metal. The Charpy impact toughness was 255 J on an average, at a base metal temperature of \(-40\)\({}^{\circ}\)C.  
Figure 1: Brittle crack propagation path and crack arrest locations in low heat input (LHI) and high heat input (HHI) weld joints with 50 mm and 80 mm thick steel plates. (**a**) LHI weld joints of crack propagation path with 50 mm; (**b**) LHI weld joints of crack arrest position with 50 mm; (**c**) HHI weld joints of crack propagation path with 80 mm; (**d**) HHI weld joints of crack arrest position with 80 mm. A window frame-type ESSO test was used to evaluate the welded joint and prevent the brittle crack from deviating into the base metal via the welding residual stress at the initial stage, as suggested by the SR147 committee (1978) [24]. Figure 3 shows the shape and dimension of the ESSO test specimen. The specimen length and width were 1200 mm and 1200 mm, respectively, and it had a special welding zone to avoid brittle fractures. Figure 4 shows the schematic diagram of the special welding zone of each specimen. The special welding part was manufactured through a combination of large toughness welding consumables, as listed in Table 3. To secure the weld joint, 2-3 types of welding consumables with different toughness values were welded with different materials for each layer (as shown in Figure 5, demonstrating an example of a macro section with different welding consumables with different toughness values); this was to suppress the propagation of brittle cracks through the heterogeneity of toughness by applying a welding consumable with large toughness. The welding consumable used to arrest the brittle crack propagation was selected as a welding consumable with a high Ni content and excellent fracture toughness. The chemical composition and mechanical properties of each welding consumable are shown in Tables 4 and 5. Most welding consumables were guaranteed to have a toughness of more than 27 J at \(-60\)\({}^{\circ}\)C or \(-196\)\({}^{\circ}\)C as Charpy impact energy values. In contrast, specimen-5 attempted to deviate from the brittle crack propagation path into the base material by generating residual compressive stress near the weld through the LTT welding material. Table 6 presents the welding conditions for each test specimen.