# Effects of High Toughness and Welding Residual Stress for Unstable Fracture Prevention
## 3 Brittle Crack Arrest Test Results and Discussions
### Welding Residual Stress Effect in Brittle Crack Propagation  
To prevent straight propagation of the brittle crack, compressed residual stress was added to the front of the brittle crack propagation by applying a LTT welding consumable. In the case of specimen-5, listed in Table 7, the brittle crack that initiated at the weld joint propagated along the weld line, reached the special weld part to prevent brittle fracture, failed to further propagate in a straight line, and then deviated from the base material, thereby arresting the propagation. Figure 9 shows the brittle crack propagation path and its arrest position. In the test specimen image, the brittle crack met the LTT welding consumable after propagating in a straight line along the weld and the crack then deviated from the base material and was arrested. As shown by previous research [8,25], the brittle crack propagation path was changed due to the influence of the welding residual stress. In this study, it is suggested that the brittle crack was arrested because its progress was hindered by the influence of the residual compressive stress distribution at the running crack tip. The LTT welding consumable applied in this study has an excellent fracture toughness, with 10% Ni and 9.6% Cr as its main components. Figure 10 shows the microstructural characterization of the LTT weld joint. The locations for the optical microscopy were 0 mm (weld metal), 30 mm (heat affected zone: HAZ), and 60 mm (base metal) from the top surface along the weld centerline, as marked by squares 1, 2, and 3. The microstructure of the weld metal exhibits a strong grain orientation due to the elongated grains along the thickness of the weld. The grain size is mostly over 200 um in the face regions. To characterize the localized phase transformation behavior, thermal dilation experiments were performed using samples 3 mm in diameter and 10 mm in length, with LTT welding and commercial welding (CWC) consumables. Thermal expansion and contraction were recorded during heating to 1300 \({}^{\circ}\)C at a rate of 1 \({}^{\circ}\)C/s, were maintained for 5 min, and then cooled back down to room temperature at a rate of 1 \({}^{\circ}\)C/s. Figure 11 shows the thermal dilation experiment results with LTT and CWCs. It was confirmed that phase transformation occurred in both of the welding consumable tests. However, the phase transformation temperature was different in their specimens. For the LTT, phase transformations occurred at around 100 \({}^{\circ}\)C, whereas they occurred at around 600-700 \({}^{\circ}\)C for the CWC. Figure 8: Charpy impact test results of welding consumables B and G. (**a**) welding consumable B; (**b**) welding consumable G.  
Figure 9: Brittle crack arrest position of specimen-5. Figure 12 presents the welding residual stress distribution of the weld joint along the thickness with the LTT and CWC, using neutron diffraction. The welding residual stress was measured using neutron strain scanning in the Residual Stress Instrument at Korea Atomic Energy Research Institute. Figure 12a,d show the welding residual stress distribution of WM with LTT and CWC. Generally, the welding residual stress distribution of weld metals has a large tensile residual stress, as in Figure 12d. However, the LTT exhibits compressive welding stress, as shown in Figure 12a, from which a clear reduction in the residual stress can be observed in cases of longitudinal residual stress (LD). For example, the tensile stress of 600 MPa changes to a compression of \(-200\) MPa in LTT. Figure 12b,e show the residual stress distribution in HAZ. Compared to commercial welding consumables, which have a  
Figure 11: Thermal dilation experiments using specimens extracted from the low transformation temperature and commercial welding consumable. Figure 10: Cross-sectional macrostructure of the low transformation temperature combined with a high heat input weld specimen. large tensile residual stress distribution in HAZ, LLT demonstrated a relatively small tensile stress distribution.