PSI - Issue 40

E.E. Abashkin et al. / Procedia Structural Integrity 40 (2022) 1–6

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Abashkin E.E. / Structural Integrity Procedia 00 (2022) 000 – 000

«Metals. Tensile test methods ". Tensile stress, yield strength, and relative elongation when bending the specimens were determined in the AG-X plus SHIMADZU versatile testing machine at constant velocity of the grippers of 0.05 mm/s.In the course of the work, it was revealed that the value of the yield strength ( Ϭ v = 342 MPa) and tensile strength ( Ϭ t = 465 MPa) are higher for specimens obtained when using flux-cored wire with aluminothermic filler in mode 3. The experimental method used in comparison with the traditional method of welding with a solid wire at similar current-voltage characteristics allows to increase the tensile strength by 5%, and the yield strength by 20%.

Fig. 2. Influence of thermal exposure on impact strength KCV of permanent joint specimen of St3sp steel plates.

AXIO VERT A1 optical microscope with an AxioCam ERc5s digital camera was used to determine the microstructure of the weld metal and the heat- affected zone (with a magnification range of ×200). It was identified, that the specimens of the obtained permanent joints have a ferrite-pearlite structure. According to (GOST 8233-56) scale 7 the ratio of pearlite and ferrite is estimated at 7 points. The weld zone has a columnar (dendritic) structure, with the grain size growth due to current increase, it reaches a value of 40 μm. The weld junction and excessive heating zone are characterized by a ferrite-pearlite structure with a larger grain size and as opposite in recovery and recrystallization zones the grain size decreases. The length of the heat-affected zone is 10 mm. Figure 3 shows the specimen microstructures obtained from the weld zone of St3sp steel plates with mode 3 applied: a - center of the weld; b - weld junction and excessive heating zone, c - zones of recovery and recrystallization. The structures of the weld and the heat-affected zone obtained with an experimental flux-cored wire with an alumothermic filler are similar to the zones of permanent joints obtained by the traditional welding method (Abashkin et al., 2019; Komarov et al., 2016). The heat generated by the heating source during metal welding due to thermal conductivity is distributed to the areas of the steel plate adjacent to the fusion zone – followed by that parent metal becomes heated to the highest temperatures. When the heating source being removed, the temperature of the metal decreases. The parent metal parts, contacting the surfacing material, experience rapid changes in the structure and, consequently, the properties change occurs. The influence of a temperature drop to the weld junction zone affects negatively on the formation of strength properties as well as determines the nature of the specimen rapture. Thus, the structure of the metal obtained during these tests is a factor that determines the combination of strength characteristics and its possible destruction. The nature of specimen distraction can be estimated by fractographies presented in Figure 4. Fractographies are made from rupture surfaces in deposition zones of permanent joints, using the scanning electron microscope ZEISS EVO MA-10.