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 3

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symmetrical welded butt joint was obtained, which made it possible to determine the temperature in the nodes of the mesh model, as well as the proportions of different phases in the weld and HAZ according to the Leblond et al. (2000), Koistinen and Marburger (1959) equations which taking into account the dependence of thermal properties on temperature for various phases. Structural steel DC04 belongs to the group of low-carbon ferrite-perlite steels and is widely used for the manufacturing of the various welded structures. The chemical composition, which determines the properties and behavior of phases during phase transformations and mechanical properties of the steel are given in SYSWELD (2015) Modern approaches to mathematical modeling of welding processes for solving the related thermal problem involve the use of volumetric models of heating sources. For arc welding, in nowadays, the most accurate model is considered to be a model of a distributed volumetric heating source, which was proposed by Goldak (2005). In the analytical model J. Goldak sets the normal (Gaussian) distribution of power density of the heating source in the body volume, which has the form of a double ellipsoid (Fig. 1). The butt joint welding parameters and the dimensions of the weld pool of the simulated heating source for a single-pass submerged arc welding of 10 mm thick plates are shown in Table 1.

Fig. 1. The J. Goldak model of the volumetric welding heat source.

Table 1. Butt joint submerged arc welding heat source parameters. Heat Input (J/mm) Welding current Welding voltage

Velocity (mm/s)

Efficiency

a f , a r ,b,c (mm) 16, 34, 10, 10

f f , f r

4000

730

35

5

0.8

0.6, 1.4

3. Results and Discussion 3.1. A back-step welding of a butt joint with three 200 mm long sections (technological scheme – «Fr_72») According to the phase transformations model used by the SYSWELD (2015), the mutual transformations of the following structural phases occur during welding of the steel DC04: ferrite, austenite, upper bainite (hereinafter bainite) and martensite. Distribution of phase structure components in the residual state, after welding and cooling, in longitudinal sections parallel to the weld, with coordinates |y|=0, 5, 10, 15 and 20 mm, is shown in Fig. 2. From Fig. 2 it can be concluded that all components of the phase structure have two characteristic cone-shaped surfaces of the maximum values of the phase structure considered parameter (ferrite, bainite, martensite, austenite) in a given node of the welded joint mesh model on the face surface z=5 mm, along the length of the plate. Cone shaped surfaces are localized in two places above the back-step weld in the vicinity of the junction of the two outermost sections of the back-step weld with the middle section, and their maximum values do not coincide with the coordinates of the junction points of the welded sections (x=-100 mm and x=100 mm). For example, on the weld axis at y=0 mm, the maximum phase proportion values correspond to nodes 69780 (x=-87.5 mm, y=0 mm) and 62978 (x=112.5 mm, y=0 mm). In addition, the coordinates of the maximum values of the phase structure proportions in the longitudinal sections (y=5, 10, 15, 20 mm) remote from the weld axis also slightly differ from each other with a decrease of the maximum values as the longitudinal section moves away from the weld axis. In the longitudinal sections, away from the two cone-shaped surfaces with the highest values of phase proportions, the