INFLUENCE OF DEFECTS ON THE STRUCTURAL-PHASE STATE OF WELDED JOINTS AND PARAMETERS OF ACOUSTIC EMISSION SIGNALS IN STRUCTURAL STEELS

The work was performed using physical methods of materials science, destructive and non-destructive testing. Samples of structural carbon and low-alloy steels of grades St3sp, 10, 09G2S, 17GS have been studied. The analysis of changes in the structure of welded joints made of structural steels under the influence of plastic deformation is carried out. The material for artificial defects was graphite and crushed glass, which were introduced into the welding bath. The results of the study of samples with artificial defects and defect-free samples made by manual arc welding and modulated current welding are presented. Based on the mathematical patterns of changes in the parameters of acoustic emission (AE) of the signal for the studied steels of grades St3sp, 10, 09G2S, 17GS, a four-parameter three-level criterion for determining the stage of plastic deformation has been developed. The criterion under consideration allows us to qualitatively assess the degree of plastic deformation during stress tests of pipelines (throughout the AE location area), which is especially important for pipes with different wall thinning. In the fine structure of the zone of thermal influence of welding at the fusion line and in the deposited metal, bending extinction contours were revealed, indicating the presence of internal stresses. The number of contours increases as you approach the fusion line. The morphological components, regardless of the welding method, in the structure of the base metal are lamellar perlite and ferrite, in the structure of the seam metal – lamellar perlite, ferrite and martensite (the volume fraction depends on the welding method).

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