PSI - Issue 40

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V.P. Gulyaev et al. / Procedia Structural Integrity 40 (2022) 180–184 Gulyaev V.P. at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 1. Geometry, dimensions, and area of X-ray photography of 09G2S structural steel samples

The profiles of diffraction lines were obtained from the polycrystalline structure of the laboratory samples on a Rigaku Ultima IV X-ray diffractometer with a high-precision horizontal goniometer in the operating mode of the X ray tube of the diffractometer: voltage U = 40 kV; current I = 40 mA. X-ray photography was performed according to the θ − 2θ scanning scheme with Bragg - Brentano focusing in the angle range of 123° ... 125°, using the Co anode of the X-ray tube with the following scanning characteristics: speed – 0.1°/min, step – 0.01°, scanning axis – 2θ/θ . The geometry of the survey was provided by Soller slits, which limited the incident beam, 10 mm horizontally, 0.5° vertically. The slits in the incident and diffracted beams are 5°. The width of the slit that limits the diffracted beam vertically in front of the receiving slit is 0.5°. The established survey geometry provided the X -ray line profile from the sample surface area 3×1 mm in size. The software of the diffractometer ( PDXL-2 ) approximates the diffraction line profile in the coordinates " I – 2  " by the pseudo-Voight function, compiles a table of numerical values of the 2  angle (in degrees) of the profile peak, interplanar distance d (in angstroms), maximum intensity Imax of reflected radiation (in pulses/s), half-width of the FWHM profile (in degrees), and other characteristics. X- ray photography of the samples, 60 × 10 × 7 mm in size subjected to the preliminary tension by loads causing an elastic stress state in the working part, was performed three times at one central point. The reference characteristics of the diffraction line profile were also registered at the center point of the frontal plane of the initial (unloaded σ = 0) sample, which was thermally treated according to the recry stallization annealing mode. 6. Results The results of multiple analyzes and processing of the shapes of the diffraction line profiles obtained from samples of structural materials subjected to elastic deformation in the range of loads (0.3 ... 0.9) σ 0.2 [6, 7] have revealed changes in the shape of the profiles, as well as their relative broadening. The diffraction line profiles registered by a diffractometer of geometrically identical samples of 09G2S steel, but with different levels of the elastic-stressed state, are shown in Figure 2. The numerical values of the profile characteristics are presented in Table 1. X-ray diffraction of 09G2S steel, which was performed after a short-term stress field in the test section of the samples in fractions of the physical yield point σ = 0,3σ 0,2 , σ = 0,5σ 0,2 , and σ = 0,9σ 0,2 , shows that stresses of this level cause distortion in the system of crystallographic planes (220) recorded by a diffractometer (Fig. 1, Table 1). The distortions of the “fine” structure of the crystal structure on an area of 3 mm 2 of the studied surface of the samples are revealed not only when comparing the FWHM values with the original, the reference sample, but also with the FWHM values of the samples with different stress levels (Table 1). FWHM broadening of the diffraction line profiles reflected from the system of crystallographic planes of the second-order (220) indicates that the response of the set of lattice planes (220) is not linear at different levels of the elastic stress- strain state in the range of nominal external stresses from 0 to 0.9σ 0.2 . Herewith, there is a significant change in the broadening of the FWHM profile of the diffraction line in the range from 0 to 0.3σ 0.2 . Consequently, the laboratory studies of physical processes caused by low external loads and recorded by X-ray diffraction methods can substantiate defined values of the safety coefficient established by calculating the strength of machine parts and metal structures. Thus, it can be affirmed that the safety coefficient n T = 1.5 recommended for calculating the