FORMATION OF ZONES OF STABLE DEFORMATION LOCALIZATION IN WELDED JOINTS OF STRUCTURAL STEEL, CHARACTERISTICS OF NON-DESTRUCTIVE TESTING

10.25712/ASTU.1811-1416.2023.01.010

Abstract

The paper reveals the features of the formation and development of Chernov-Luders bands (CLB), as well as zones of stable localization of deformation in samples of low-carbon steel 20, including those with structural-phase inhomogeneity in the form of welds made by arc welding. Recently, there has been increased interest in the study of the formation and propagation of CLB as the initial stage of deformation. In fact, it is impossible to do without studying the physical nature of the elastoplastic transition in metals and alloys, since many engineering structures (especially with welded seams) used in technology operate in the area of elastoplastic deformations and significant residual deformations accumulate in them. The microstructure and mechanical properties of the material under uniaxial tension were analyzed, mechanical tests were carried out with registration of strain localization patterns and metallographic studies. The studies were carried out on two batches of flat samples with heads made of steel 20. The dimensions of the working part of the samples are 40×4×3 mm. The second batch was made of steel 20 (pipe Ø159×18 with a welded seam). The product was not in operation (initial state). The third batch of samples was cut from the steam outlet pipe of heat power equipment, also with a welded seam. Pipe size Ø159×18, operating life 198 thousand hours (after operation). Mechanical tests were carried out on a Walter+Bai AG LFM-125 testing machine at room temperature. The speed of movement of the movable grip was 0.4 mm/min, which, with the used working length of the specimens, corresponded to a strain rate of 1.67×10^-4 s^-1 (quasi-static tests). It has been established that in the metal of welded joints, the deformation criteria for failure are lower than in the base metal.