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the pits is characteristic for the troostite and martensite structures. It is 150 ... 200 and

250 ... 125 microns respectively. This is accompanied by the increasing of the surface

microelectrochemical heterogeneity of steel. In the case of 0.8%C steel it is from

10 ... 30 to 250 ... 300 mV, while in 0.45%C steel case it is from 10 ... 35 to 170 ...

250 mV.

The corrosion rate and hydrogenation of 0.8%C steel increases in a number of

structures: perlite, sorbite, troostite and martensite. For 0.45%C steel corrosion rate

2
and hydrogenation for most ferrite - perlite and are 5.1 g / (m ∙h) and 19.4 ppm,
respectively, and for sorbite, troostite, martensite and lower 30 ... 50%. The main

contribution in process of hydrogen absorbing is made by diffusible hydrogen. Its

share in the total amount of absorbent reaches ~ 65 ... 74% for perlite, 50 ... 54%

sorbite, 64 ... 78% troostie and ~ 67% martensite steel structure of 0.8%C steel.

Microscopic studies of the surface of samples of 0.8%C and 0.45%C steels

with different structures after corrosion in solution of NACE for 96 hours showed

that corrosion, regardless of structure, has an ulcerative nature. The maximum depth

of the ulcers for them is characteristic for the structures of the troostite ~ 150 and ~

200 microns and martensite ~ 250 and ~ 125 microns, respectively. This is
accompanied by the growth of microelectrochemical heterogeneity of the surface of

0.8%C steel from 10 ... 30 to 250..300 mV. After corrosion of 0.45%C steel in the
solution of NACE, its microelectrochemical heterogeneity increases on ferrite -

perlite - twice, sorbite and martensite in 2.0 ... 5.5 times, and troostite - in 7.0 times,
indicating significant damage to the surface and the appearance of sites local

corrosion, but less than for 0.8%C steel.

The best resistance to hydrogen sulphide corrosion cracking have a 0.45%C

steel with ferrite-pearlite and sorbite, and 0.8%C steel with sorbite and troostite

structures. However, taking into account the impact on the fracture both factors like

hydrogen embrittlement and the corrosion localization, the most suitable for use in

hydrogen sulphide media are 0.45%C and 0.8%C steels in a sorbite structures.

Consequently, hydrogen sulfide stress corrosion cracking resistance of these steels is