PSI - Issue 30

G.N. Sleptsov et al. / Procedia Structural Integrity 30 (2020) 154–161 Sleptsov G.N. et al. / Structural Integrity Procedia 00 (2020) 000–000

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Also, to research the influence of the development and occurrence of cold cracks at low temperatures. Technological samples Tekken were welded at positive and at low ambient temperatures up to -48 ° С . The thermal cycle parameters were recorded on the TERKON universal precision instrument mentioned above. In turn, during the testing of Tekken technological samples, to monitoring the kinetics of the destruction process, were recorded signals AE from the Expert 2014 complex. The reliability of the obtained data was realized by locating AE signals on the samples, using acoustic antennas from three or more AE sensors (see Fig. 2b). On Fig. 4 shown a typical fracture of a welded joint on a technological sample Tekken, obtained during welding at naturally low temperatures, in particular -42 ° С . For example, after moving sample to a room with a temperature of + 20 °C from a workshop with a temperature of -42 °C, where it was welded and observed using the AE method, high activity of AE signals and a visually observed growing crack were recorded (Fig. 4, “development of crack” zone ). The crack developed within 2 days. AE signal recordings were stopped only after the signal activity stopped. It is characteristic that the crack propagation at room temperature was shifted to the heat affected zone with the base metal and propagated along the edge of the weld. The crack is shifted to the heat affected zone, where, according to the experimental conditions, was to be ensured the localization of diffusion hydrogen that approved by the Sleptsov O.I. (2019). At present, with a high culture of welding, the main sources of hydrogen entering the weld are welding materials. The main ways to reduce the hydrogen content in the weld metal and the measures that contribute to its removal into the environment can be classified as follows: the choice of welding materials and their preparation before welding (calcination), optimization of welding conditions, and the use of preheating and post-welding heating. In welding practice, the effect of hydrogen on the tendency of welded joints to form cold cracks is mainly characterized through the content of diffusion-mobile hydrogen in the deposited metal or in the weld. In the work by Sleptsov O.I. (1989), according to degassing conditions, the main methods for determining the content of diffusion mobile hydrogen in welded samples can be divided into methods with hydrogen evolution: in a blocking liquid, in a technical vacuum, in a carrier gas medium. The most widespread because of the simplicity of execution are methods related to the first group. These methods, in turn, are divided into eudiometric and volumetric. In the eudiometric method, hydrogen released from a welded sample immersed in a blocking liquid is collected on its surface into gas bubbles, which, upon reaching a certain volume, float and collect in a measuring burette. According to Russian River Register (2019), in our country, glycerin or ethanol is most often used as a locking fluid in eudiometers. 2.3. Determination of the concentration of hydrogen.

Fig. 3. General view of the destruction of the technological sample Tekken