Experimental Study on Tensile Deformation Process of Graphitized High Carbon Steel Sheet

This work studies high carbon steel sheet with carbon content of 0.67 wt %. It has been demonstrated that the mechanical properties of specimens manufactured in different directions with respect to the rolling direction of the considered high carbon steel sheet are in fact the same. That is, for specimens tested for tension in various directions, the ratio of yield stress σ 0.2 to the ultimate strength σ u is 0.73; the index of strain hardening is n ≈ 0.24; the coefficient of plastic deformation is r ≈ 0.83. This indicates that the considered sheet is not characterized by obvious anisotropy of mechanical properties. During tension at the segment of uniform deformation, the plastic deformation is localized in graphite and during necking is transferred also into the ferrite matrix. When elongation increases, micropores are formed between the graphite inclusion and ferrite grain along the direction of the axis of tension, and these micropores propagate along the direction perpendicular to the axis of tension. The number of slip lines in ferrite grain gradually increases and the distance between them gradually decreases. Upon breakage of specimen, a large pit is formed on the surface with the core composed of graphite inclusion; in addition, minor pits are observed inside ferrite grain. Ferrite grain near the surface of breakage is covered with slip lines, which indicates that the ferrite matrix has been subjected to strong plastic deformation before the breakage.