PSI - Issue 36

Sergiy Kozulin et al. / Procedia Structural Integrity 36 (2022) 247–253 Sergiy Kozulin et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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2. Methodology The methodology of the research included the following steps:

• We produced MESW CN samples of 290, 480 and 620 mm thickness made of 35L and 34L-ESH steels at specific unit energy of 110...170 kJ/cm 2 . Welding wires 08G2C and 10G2 were used as filler materials. Welding was performed using AN-8M flux; • Thermal cycles were measured according to the known method by self-recording device KSP-4, using tungsten thermocouples, WR 5/20 grade, which were fixed along the axes of the holes to be welded at a distance of 45 mm from the edge for welding; • Templates were cut from welded specimens to produce cross-sectional and longitudinal macroscales, as well as specimens for testing weld metal, ground metal and base metal for impact toughness (KCU); • Analysis of the microstructure of welded joints was performed using MIM 7 microscope; • Macro-hardness of characteristic areas of welded joints was determined using portable dynamic hardness tester TEMP-2; • Quantitative assessment of the effect of automatic heat treatment on the welds metal and HAZ was carried out by measuring HAZ width and areas of zones reheated with 0.01 mm accuracy, using Kompas-3DV12 program. The scheme of cutting specimens for testing welded joints for impact toughness is shown in Fig. 2.

Fig. 2. Scheme of cutting specimens from the transverse temple for mechanical testing of welded joints made by MESW CN: 1...4 – order of execution of welds; 5 – HAZ; 6 – specimens for impact bending tests (KCU). 3. Results and discussion The results of the measurements of thermal cycles of HAZ metal for 35L steel are shown in Fig. 3. Analysis of thermal cycles showed that the cooling rate w 6/5 of HAZ metal of each weld within the temperature range 600...500 ° C does not exceed critical values for 35L steel, and also decreases as subsequent passes are made (Fig. 3, b), indicating the lack of risk of martensitic formation in these areas. In this case, the character of the thermal cycle effect is also d istinguished by the conditions of slow heating of the base metal (0.3...0.4 °С/s). These conditions can be considered relatively close to the equilibrium conditions (Kozulin et al. (2013)). The analysis revealed the multilayered macrostructure of the weld (Fig. 4), which is characterized by columnar crystallization with predominant development of axial crystals, as demonstrated by Kozulin et al. (2013). In the first joint, thin crystals of small cross-section were found, as well as equiaxed crystals. In the second seam, crystals were elongated and enlarged close to the fusion zone. In the third weld, larger, branching crystals were found. In the fourth weld, the largest branching crystals were observed. This crystal structure is characteristic of electroslag