PSI - Issue 13

V. Pokhmurskii et al. / Procedia Structural Integrity 13 (2018) 2190–2195 4 V.Pokhmurskii, M.Khoma, V.Vynar, Ch,Vasyliv, N.Ratska, T.Voronyak I. Stasyshyn / Structural Integrity Procedia 00 (2018) 000–000

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Comparison of the height change in Armco-iron and У8 steel under desorption (Fig.3) indicates that the maximum changes in the surface layers of ferrite occur within one day and gradually slow down. In У8 steel the profile changes occur for a longer time, since the cementite in the pearlite structure creates numerous barriers to the movement of hydrogen.

Fig. 3 . The changes in ordinates of local point on the surface of Armco-iron (1) and У8 steel (2) during the desorption of hydrogen.

At the presence of diffusion hydrogen, the width of the friction track of Armco-iron increases by 20 ... 25% compared with the initial state. There are numerous damages on the friction surface. At the presence of residual hydrogen, the friction track is narrower, and there is less damage there (Fig. 4b, 5). Friction tracks width of steel У8 after hydrogenating is 3-5% lower than in the initial state.

initial diffusion hydrogen residual hydrogen

initial diffusion hydrogen residual hydrogen

250

0.4

200

100 Track width,  m 150

0.3

0.2

friction coefficient

50

0

0.1

ferrite

pearlite

ferrite

pearlite

b

а

Fig.4. Friction parameters of hydrogenated ferrite and pearlite: 1 - non- hydrogenated metals; 2 - at the presence of diffusion hydrogen; 3 - at the presence of the residual hydrogen. Friction coefficients (a) and track width (b). Diffusion hydrogen initiates more damage of the friction surfaces than the residual. This is due to the defect and instability of hydrogenated layers, the combined effect of external loads and internal stresses caused by hydrogen. Wear products indicate a fragile destruction of hydrogenated surfaces of friction (Fig. 5e). As result, resistance to wear and the coefficients of friction Armco-iron are reduced. The coefficients of friction of steel У8 are increased, because the hard particles of cementite fall into wear products and play the role of abrasive. Partial renewal of mechanical properties of metal may occur after desorption of hydrogen at room temperature and normal pressure. When the load is took off, hydrogen removes from the local traps, and fragility reduced [Shashkova (2013)]. The wear resistance of iron and steels increases at the presence of residual hydrogen. It can be explained by relaxation of stresses in a crystalline lattice and reducing of its damages.