Page 11 - Дисертація ГРЕДІЛЬ_ФМІ

11
has been disclosed, which consists in weakening adhesion between nonmetallic

inclusions and the matrix by hydrogen, with their further delamination and

deformation-driven growth and coalescence of pores due to a rising hydrogen

pressure inside them. The damage development is considered the crucial factor in

reducing the resistance of the operated pipe steels to stress corrosion cracking.
A semi-field method has been developed for assessing hydrogen

embrittlement of carbon steels of thin-walled gas distribution pipelines. The

method implies prolonged exposure of specimens to hydrogen gas under pressure

in a pipe at a test stand, subjected to climatic temperature variations close to

operational ones. Its implementation results in a significant increase in hydrogen

concentration in steel specimens and a decrease in fracture toughness of the

operated metal, especially the welded joint. The conditions for enhancing the

sensitivity in assessing hydrogen embrittlement of low-strength pipe steels have

been systematised: (i) preliminary hydrogen charging, (ii) specimen cutting

transversally to the pipe axis, (iii) using thin plane tensile specimens. The

methodological approach to the transversal specimen preparation from thin-

walled pipes has been introduced.
A corrosion-mechanical technique has been developed for fatigue crack

arrest in structural steels in a wide range of stress intensity factor values. It is
based on the interaction of the active component of the technological environment

(tannin) with crack edges under fretting conditions, which leads to filling up the
crack cavity with the solid interaction products and thus producing artificial crack

closure.

The anisotropy of corrosion resistance has been revealed for reinforcing

cold-drawn pearlite wires, which manifested in a higher polarisation resistance of

their side surface compared to the cross-section. The regularities and the

mechanism of the corrosion-mechanical fracture of the wires at the intermediate

stages of the cold drawing process have been established. Contrary to the first

three stages of cold drawing, where the crack is initiated from the side surface and

gradually propagates through the wire cross-section, at the later stages another