PSI - Issue 68

Paolo Ferro et al. / Procedia Structural Integrity 68 (2025) 988–1002 Ferro et al./ Structural Integrity Procedia 00 (2025) 000–000

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Both figure 13 and 14 highlight the great variation of mushy zone (MZ) size moving from 5 mm/s to 25 mm/s welding speed with the lowest value for the 5 mm/s welding speed. However, in MZ the longitudinal stress is positive and about 1.5 MPa, while using the 25 mm/s welding speed, in the corresponding MZ a compressive RS stress is calculated, equals to about -10 MPa. Even the thermal stresses in the sub-solidus zone are extremely different (tensile in Fig. 14a and compressive in Fig. 14b) and can play a role in hot cracking formation. 3.4. Effect of butt-welded joint geometry on longitudinal residual stress By keeping constant the plate thickness (2 mm), P-HT (500 °C) and welding parameters (P = 1250 W, v = 25 mm/s), both the width (W) and the length (L) of the plate were varied with the aim to study their influence on longitudinal RS ( s yy ). Results are summarized in Fig. 15. By observing Figs. 15a and 15b, no influence of the width (W) on the longitudinal RS distribution is observed. On the other hand, by doubling the joint length the RS increases and reach a plateau along the welding line (Figs. 15c and 15d) which value is in the range of those observed in Figs. 6 and 7 for P-HT lower than 450 °C.

RS (MPa)

RS (MPa)

Fig. 15. Longitudinal residual stress (MPa) as a function of geometrical parameters of the welded joint with P-HT = 500 °C: a,b) W = 30 ÷ 15 mm and L = 20 mm; c,d) W = 30 mm and L = 40 mm (P = 1250 W, v = 25 mm/s)

Further parametric analyses were carried out by rising the P-HT to 600 °C to search for RS reduction even in the 40 mm length plate, both at constant laser power (1250 W) and constant weld pool width, as described above. It was found that by keeping laser parameters constant, the P-HT of 600 °C effectively reduces the RS (compare Fig. 15 with Fig. 16) even if a high RS peak (above 1200 MPa) remains. By reducing the laser power to maintain constant the FZ width (Fig. 16), RS at P-HT of 600 °C tends to be comparable with that obtained at P-HT = 500 °C but with a higher power.