PSI - Issue 30

K.V. Stepanova et al. / Procedia Structural Integrity 30 (2020) 167–172 Stepanova K.V., , Petrov P.P., Platonov A.A. / Structural Integrity Procedia 00 (2020) 000–000

169

3

The diffraction spectrum was recorded in a �  2� scanning scheme with Bragg - Brentano focusing in the range of angles 1230° - 1250° in Co К α radiation (wavelength λ = 0.179020 nm) using a graphite monochromator in the secondary beam. The width of the slit restricting the incident beam horizontally is 10 mm, vertically is 0.50 mm; Seller slits on the incident and diffracted beams - 0.50 mm; the width of the slit restricting the diffracted beam vertically in front of the receiving slit is 0.50 mm. A rectangular beam with a size of (1 x 0.2) mm is focusing on the sample. The operating mode of the X-ray source: U=40 kV; I=40 mA; scanning speed is 0.1 deg/min with 0.01 deg. interval, scan axis: 2 θ / θ . The international diffraction data base PDXL - 2 was used to analyze the diffraction patterns. In order to obtain the profile of the X-ray line corresponding to planes with rear reflection angles, a plane with (hkl) = (220) was chosen. The total width of the diffraction peak at half height was determined (taking into account the standard). Instrumental broadening was detected experimentally by X-ray under the same conditions a reference sample in which the physical broadening is close to zero (D> 0.15 μ m, ρ <10 8 с m -2 ). The standard is made of working samples material by recrystallization treatment. Umanskiy (1982) reported that the residual stresses are characterized by uniform compre ssion or extension (deformation in the elastic zone) of the crystal lattice of metals and alloys and they lead to a uniform change in the interplanar spacings (d) by ∆ d, and therefore to a shift in X-ray interference by an angle ∆θ . Based on this relation, for uniaxial tension, the stress value is determined by the Gorelik (1994) equation (1): where E is Young’s modulus Е = 2.17 * 10 5 MPa, ν is Poisson’s ratio ν = 0.3, d is interplanar distance, ∆ d is the interplanar distance change of the deformed sample, θ 0 is the position of the diffraction line in the absence of deformation, θ is the position of the diffraction line at deformed sample, ∆θ is the shift in the diffraction maximum position of the deformed sample relative to the standard. The microstructure of weld metal was observed by Altami Polar 312 optical microscope. Nitric acid and ethanol in proportion 1 ml HNO 3 per 4 ml C 2 H 5 OH was used for metal etching. The Brinell hardness was determined by MET U1 ultrasonic hardness tester. 3. Results and discussion It has been empirically demonstrated in the surfacing materials, the most vulnerable areas are the weld bead (point 1 in Fig.1) and the lower boundary of the weld (point 2 in Fig. 1).      2 1  0 0 2 * * ctg θ * * ctg * 2   1 * sin   1 sin E d E E d                  (1)

Fig. 1. The schematic picture of the sample with locations of X-ray.

Weld metal obtained by flux-cored wire of Composition 4 has the highest strength properties, hardness is 183 HB, and the minimum segregation sizes at the fusion bo undary reaching 76 μ m are also observed (see Table 2) relative to other compositions. At the same time, the values of residual tensile stresses in the area of the weld bead and in the lower boundary of deposited metal reach 112.4 MPa and 104.4 MPa, respectively, and the level of stress-