PSI - Issue 13

M.S. Khoma et al. / Procedia Structural Integrity 13 (2018) 2184–2189 2187 4 M.S. Khoma, V.R. Ivashkiv, M.R. Chuchman, Ch.B. Vasyliv, N.B. Ratska, B.M. Datsko / Structural Integrity Procedia 00 (2018) 000–000

Н Table 2. Susceptibility of steel У8 to stress corrosion cracking in NACE solution. Influence of static loads on hydrogenation of steel У8 in the solution (С  Н  /С 0  )*. Structure Time to destruction in air/NACE, min  a /  e * С � 0 Н  /С Н  pearlite 124/26 4.8 1.3 sorbite 199/43 4.6 1.4 troostite 130/31 4.2 1.8 martensite 129/23 5.5 - *С   - hydrogenation under load 300 MPa; С 0  - hydrogenation without load. Consequently, resistance to hydrogen sulfide corrosion cracking of steel У8 is defined as the degree of hydrogenating, as well as the localization of corrosion processes, which can enhance or weaken each other's actions. Table 3.Microelectrochemical properties of steel У8 in the initial state (  Е) and after corrosion (  Е  ) in the solution NACE Structure  Е, mV  Е  , mV pearlite 10…25 10…120 sorbite 15…35 20…70 troostite 10…25 70…300 martensite 10…30 25…250 3.2. Corrosion and hydrogenating of steel 45 in the NACE solution Corrosion rate of ferrite-pearlite steel 45 in the NACE solution is 2.3…5.1 g/(m 2 /h) (Table 4). Hydrogenating of steel after 720 h is 13.8 ... 19.4 ppm (Table 5). Corrosion rate of sorbite, troostite and martensite is ~ 60 ... 65% lower than pearlite (Table 4). Hydrogenation of the troostite and martensite is ~ 2 times lower than pearlite-ferrite, and sorbite ~ 3 ... 4 times. The part of diffusion hydrogen is ~ 75%. Н Н

Table 4. Corrosion rate and hydrogenation of steel 45 in the NACE solution (t = 720 h) Structure ferrite-pearlite sorbite

troostite 1.9…3.1 4.9…6.5 6.5…10.7

martensite 1.8…3.2 3.7…8.8 7.1…10.4

Corrosion rate, g/(m 2 ∙h)

2.3…5.1

1.6…2.9 2.3…5.7 3.1…7.2

C H200

10.0…11.9 13.8…19.4

hydrogenation, ppm

С Н 

Sulfide films were fixed on the surface of steels after exposure in corrosive solution (Fig. 3). The most homogeneous films with low defects are formed on the surface of sorbite and ferrite-pearlite (Fig. 3). Films on troostite and martensite have numerous defects; consist of large clusters of crystals, which are chaotically layered on the surface (Fig. 3c). Fig. 4 shows the susceptibility of steel 45 to corrosion cracking in the solution of NACE. Corrosion of steel under sulfide film has an ulcerous nature. The depth of ulcers is the smallest on the surface of the sorbite and ferrite- pearlite structures, the largest on troostite.

Figure 3. Microstructure of sulfide films on the surface of steel 45 of ferrite-perlite (a); sorbite (b); troostite (c); martensite (d) structures after exposure in NACE solution for 96 hours.