• Malinin, A. V.
• Khaziahmetova, D. R.
• Makatrov, A. K.
• Sitdikov, V. D.

Abstract

<jats:p>The work analyzes the influence of certain types of metal microstructure defects on the value and nature of distribution of the active residual macro-stresses of the σ in the tubing sleeve. The tubing coupling was made of pre-eutectoid steel, and to improve corrosion resistance, a bainite structure was formed in it. As defects of the metal microstructure, the most common cases in the manufacture of a coupling were considered, such as the structural gradient of the formation of constituent phases (upper and lower bainite, martensite tempering, martensite, etc.) along the thickness of the tubing wall, as well as non-metallic inclusions and pores in the material wall. To assess the residual macrostresses on the selected coupling surface, a non-destructive X-ray scattering method modified by the authors was used. At the same time, the modernization of this method consisted in the use of a micro-X-ray parallel beam (diameter 0.5 mm) in estimating the σ value, in measuring the spectrum of reflexes at inclined surveys at given coordinates (pitch 1.0 mm) for different directions of the φ plane, in determining the value of macro-stresses at each point and constructing their surface distribution with superimposed power lines. In order to take into account the anisotropy of the acting residual macro-stresses of the σφ on the analyzed surface of the coupling, in the measurements of the reflex (222), the sample was rotated about an axis perpendicular to the analysis plane. As a result of applying the modified macro stress estimation approach for the initial tubing sleeve having no process defects, it is found that the distribution of residual macro stresses in the longitudinal section of the wall is symmetrical. It is shown that residual compressive-type macro stresses of minus 341 MPa are formed in the inner part of the tubing coupling wall, and the tensile type — with the value of plus 347 MPa acts on the outer side of the coupling wall, the absence of macro stresses is detected in the middle part of the material wall. It has been shown that the presence of a structural gradient, i.e. the presence of martensitic plates in the near-surface layers of the coupling with a content of about 12 %, increases the active residual macro-stresses in these areas by more than 1.3 times. It was found that the presence of pores and non-metallic inclusions in the near-surface layers concentrated on the thickness of 170 μm of the coupling wall increases the residual macro stresses 1.6 times from the outside and 1.4 times from the inside of the wall. It has been shown that increased pore size and increased pore content, which are analyzed by raster electron microscopy, are factors in the increase of macro stresses from the outside of the coupling wall.</jats:p>

Topics

• impedance spectroscopy
• microstructure
• pore
• surface
• corrosion
• inclusion
• phase
• steel
• electron microscopy
• X-ray scattering
• tempering