PSI - Issue 36

Odarka Prokhorenko et al. / Procedia Structural Integrity 36 (2022) 290–297 6 Odarka Prokhorenko, Serhii Hainutdinov, Volodymyr Prokhorenko et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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A joint analysis of the kinetics of temperature and phase processes in an arbitrarily selected node 63153 located on the weld axis with coordinates x = 200 mm, y = 0 mm will be performed. At the heating stage, a sharp rise of the temperature curves predetermines the corresponding changes of the structural phases of the welded metal (Fig. 4).

(b)

(a)

Fig. 4. The kinetics of temperature and structural phases in node 63153 on the weld axis: (a) ferrite and austenite; (b) bainite and martensite.

During time interval t = (0...70) s in node 63153 at T = 20 °C the proportion of ferrite is equal to 1. At t = 97.5 s the temperature raised to T = 981.375 °C and the proportion of ferrite sharply decreased to 0.0206559 value with the simultaneous appearance and increase of the austenite structural phase in the node, from the initial value of 0 to the value of 0.979344 (dashed line in Fig. 4 a). At T=100 °C, the proportion of austenite reaches its maximum value of 0.999239. Ferrite turns into austenite with the ferrite lattice is re-arranged into the austenite lattice due to the diffusion of carbon atoms into the centers of the cube faces. These processes of ferrite reduction to the value of 7.606e -4 and the appearance of austenite with the increase in its proportion to 0.999239 value occur when the node is heated until the time t =100 s to a temperature of T = 1300 °C, which can be seen in Fig . 4a. Further, at time interval t = (122.5… 200.43) s the temperature in the node drops from 1300 °C to 532.79 °C with the sharp decrease of the austenite phase from to 6.23291е -4 value, with the simultaneous sharp increase to 0.999377 value in the ferrite proportion (dash-dotted line in Fig. 4a). From the time t = 200.43 s, the changes in the proportions of the ferrite and austenite phases, as it can be seen from the course of the curves of the corresponding charts, sharply slow down, since at t = 200.43 s martensite began to appear in the node (Fig. 4b) due to the decrease of austenite. At the time t = 1200 s when the node is almost cooled, the proportion of austenite decreases from the value of 6.23291e -4 to the value of 1.67111e -6 . A part of this proportion, in the value of 6.2162e -4 , is converted into martensite, as the increase in its amount in the node was observed and the only source of this can be austenite, as there is no change in the proportion of ferrite in the node in this case. Bainite is completely absent, the line for bainite in Fig. 4b coincides with the abscissa. The final value of the martensite proportion in the node is 6.2162e -4 . The sum of the phase proportions in the metal structure during the process of transformations is always equal to 1, which compiles with the overall balance of the structural phases in the node. The calculated distribution data, in the residual state, of the austenite and martensite phases in the weld and HAZ in longitudinal sections at |y| = 0; 5; 10; 15; 20 and 25 mm are shown in Fig. 5. The charts shown in Fig. 5 reflect the complexity of the kinetics of temperature and metallurgical processes occurring during the heating and cooling of the metal during welding. Proportions of the austenite (Fig. 5a) and martensite (Fig. 5b) phases in the weld and HAZ along the entire length of the welded joint is in a narrow range of values which are (0…0.0003)% and (0...0.1)%, respectively. Obviously, these are small values, which means that during welding by such technological scheme austenite and martensite almost do not appear in the weld and HAZ, but instead of that ferrite (Fig. 6a) – (99.44...100)% and bainite (Fig. 6b) – (0...0.54)% are formed. Moreover, there is almost no bainite in the longitudinal sections at |y|  10 mm. From these data it can be seen that the weld and HAZ consist of ferrite by (99.44...100)%, and all other phases are account for (0...0.56)e10 -3 or (0...0.056)% in percentage. Integrally averaged over the length of the welded joint, the proportions of ferrite, austenite, bainite and martensite in the residual state in longitudinal section along the weld axis y = 0 mm and sections at |y| =5; 10; 15; 20 and 25 mm during one direction welding are shown in Fig. 7.