numero25

A. Shanyavskiy, Frattura ed Integrità Strutturale, 25 (2013) 36-43; DOI: 10.3221/IGF-ESIS.25.06 38 case of rolling contact [15]. This case also related to hydrostatic pressing. For the introduced consideration in discussed case of external loading condition, the carbon diffusion in crack takes place because of carbides destruction. Now it is clear that the carbon diffusion in area of crack is main process for steels that followed subsurface cracking. Figure 1 : View of Fine-Granular-Area under high magnification [13]. Spherical particles are dominant of the surface pattern. Let be discussed metals composition in the depth direction in FGA. It is clear that the same spheres or ellipsoids that have been discovered by the fracture surface followed metals subsurface cracking in the depth direction from the crack edges [2]. This type of nano-structures cannot be suddenly appeared in metals. It should be developed in time some process of their formation in the thin layer of FGA where UHP has taken place. Then in matrix develops specific process of fracture surface formation by the border of this structure. This fracture mechanism ought to be considered as the one of the step in nano-structure formation process based on earlier introduced consideration of spherical and elliptically shaped particles formation during fatigue crack propagation [16, 17]. Earlier the same type of fracture surfaces patterns as ellipsoidal and spherical particles have been discovered in Al-based alloys subjected to biaxial cyclic loading. The spherical or ellipsoidal particles had occurring because of specific process of metals deformation and destruction under local rotation when intensive pressing of material volume is occurred. In all cases of metal cracking under cyclic loads there has non-conventional manner of matrix fracture along the crack front. In the discussed case of FGA formation for steels or other metals there is appearance of the same particles formation mechanism, Fig2. Figure 2 : Schema of the spherical particles formation in FGA origin after ultra-high-plasticity in some metal’s volume After metals experienced UHP in area of the crack origination, inside of the plastically deformed volume there starts the rotation deformation process of local volumes inside the area of UHP. If critical density of defects is exceeded, by the border of rotated volumes appeared in homogeneity with spherical shape of fracture surface formation and with spherically or elliptically shaped particles too. During rotations in volume which will be in a further failed with FGA formation, there takes place heating and inside of the volume can go carbon, rest gases and other elements of decomposed matrix.