Figure 10 Thermal histories in correspondence of thermocouples: A, TC3; B, focus on TC3; C, TC4; D, focus on TC4; E, TC5; F, focus on TC5; G, TC6 and H, focus on TC6.

Figures 11A and 11B show the temperature distributions during the first and second passes at welding times of t = 66.67 s and t = 315 s respectively. The centre of the welding arc at these times is at the position of x = 0 mm and y = 104 mm. As it can be seen from the figures, the peaks of temperature around the welding arc, at the two instants, are calculated to be about 2460 °C and 2116 °C, respectively, suggesting that the material is melted in the fusion zone. High temperatures are present nearby the fusion zone (FZ), defining the heat affected zone (HAZ).

During the first pass, the thermal gradients are very steep in the proximity of the heat source, while they decrease during the second pass; furthermore, near the welding line, the distance between the isotherms increases as the cooling rate decreases and the welding pool also presents a very small area in front of the welding arc.