PSI - Issue 36

Odarka Prokhorenko et al. / Procedia Structural Integrity 36 (2022) 254–261 Odarka Prokhorenko , Serhii Hainutdinov, Volodymyr Prokhorenko et al. / Structural Integrity Procedia 00 (2021) 000 – 000 7

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slightly differ from each other with a decrease in the maximum values as the longitudinal section moves away from the weld axis. In longitudinal sections, away from two cone-shaped surfaces with the highest values of phase proportions, the distribution along the joint length of the phase structure parameters is relatively regular, as, for example, for the longitudinal sections at y=10 and 20 mm.

Fig. 5 . Phase composition of the welded joint in longitudinal sections at |y|=0, 5, 10, 15 and 20 mm after welding by «Fr_ 8 2» scheme.

Consider the kinetics of phase structure components for 5 characteristic nodes on the weld axis at the joining locations of the welded sections during welding and cooling by “Fr_82” technological scheme. Localized circular shape regions with a diameter of ~(20...25) mm are formed around each of these nodes, the kinetics of temperature in which is differs by the presence of two maximum values on the temperature curve T(t), which complicates the kinetics of phase processes and affects the residual distribution in the metal of the structural phases proportions in HAZ along the length of the plate on both sides of the weld. Node numbers and geometric coordinates of the short sections joint location on the front surface of the plate, along the X-axis in the XYZ coordinate system, are as follows: 69997 (x=-200 mm, y=0 mm), 69797 (x=-100 mm, y=0 mm), 62757 (x=0 mm, y=0 mm), 62953 (x=100 mm, y=0 mm), 63153 (x=200 mm, y=0 mm). This is clearly seen in Fig. 6 (a), which shows the kinetics charts for the structural phase of ferrite in the short sections joining nodes the back-step weld. At the beginning of welding of the first back-step weld section from the first node 69997, a sharp increase in temperature can be observed in the node up to 1300 °C. The ferrite proportion in the node from the initial value of 1 is sharply decreases to value 8.27129 e-4 during time interval of 2.5 s and remains unchanged until t=21 s. Further, the ferrite proportions change at the indicated nodes in accordance with the curves and reach their different maximum values (up to ~99.9%) at different for each node time, which is shown in Fig. 6 (a). In the next node 69797, this process for the ferrite phase shifts in time by 22 s and the minimum proportion of the ferrite phase in the node reaches the value of 7.49258e-4. This is due to insignificant fluctuations in the temperature minimum on the T(t) curve. The proportion of decreasing ferrite in the nodes is replaced by the proportion of austenite (Fig. 6 (b)) in the time range of t= (0...220) s in accordance with the maximum and minimum values of the ferrite phase, the kinetics of which in the nodes is shown in Fig.6 (a). For the first node 69997 T min =~630 °C, the residual propor tion of ferrite is 0.996724. For the second node 69797 T min =~658 °C, the residual proportion of ferrite is 0.998073. For the subsequent nodes 62757, 62953 and 63153, T min =~659 ° C, ~658 °C, ~666 °C with the ferrite proportion of 0.99894, 0.999377, 0.999201, respectively. The kinetics of bainite at the joining nodes of the welded sections is shown in Fig. 6 (c). For node 69997, the maximum value of the bainite phase is equal to 2.46532e-3 and is formed at t=120 s (end to of the welding process), for nodes 69797 and 62757, the maximum values are 1.01177e-3 (at t=137 s) and 0.129962e-3 (at t=161 s), respectively. There is no bainite phase in nodes 62953 and 63153. Somewhat later in time, part of the bainite transforms into martensite, the proportion of which gradually approaches the value