Page 12 - Дисертація на здобуття наукового ступеня доктора філософії

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hydrogenated steel, while the relative elongation δ and reduction in area (ѱ) decreased

by 17% and 40%, respectively. However, with the combined effect of restoration and

hydrogenation of steel on its strength characteristics σ UTS and σ YS, the positive effect

of restoration (compared to operated steel after hydrogenation) remained at the level

of 16% and 9%, respectively. According to the plasticity characteristics (δ and ѱ), the

positive effect of the restored steel after its hydrogenation was 39% and 41%,

respectively.

Using fractographic analysis, it was confirmed that the deterioration of the

properties of both steel variants under the influence of hydrogenation of the specimens

was due to the presence of damage in them. In the operated steel, such defects were

formed due to the decohesion of large carbides along the grain boundaries from the

surrounding matrix. In the restored steel, the defects were remnants the remains of

pores on large inclusions that were not healed during heat treatment due to the complete

loss of their cohesion with the matrix.

However, as a result of complete recrystallization of the steel, the remaining

unhealed defects moved from the boundaries into the grains, which was considered a

positive structural sign of steel restoration. This is due to the fact that defects located
along the grain boundaries, as a rule, have a stronger negatively effect on the steel's

tendency to creep than those within the grains. It is clear that these defects became
energetically favorable traps for the accumulation of hydrogen, inside which it is

molized, creates pressure and contributes to the destruction of steel. It is also important
to consider the effect of adsorption reduction of steel strength and its possible hydrogen

embrittlement under the influence of hydrogen accumulated in these traps. The

presence of such damage along grain boundaries (especially at the junctions of the

boundaries of three grains) in the structure of 12Kh1MF steel, operated in the stretched

bending zone, contributed to the appearance of transgranular cleavages on the fracture

of the hydrogenated specimen, which were clearly distinguishable against the

background of its generally dimple relief. On the contrary, in the restored steel,

transgranular cleavages were initiated only from large non-metallic inclusions, which,