Investigation of fracture of borated low-carbon steel specimens

Studies have shown that the deformation in specimens with brittle homogeneous layer and plane interface profile causes a system of transverse quasiperiodical cracks in the surface layer when under tension. As such, the influence of coating structure and thickness as well as the presence of intermediate layer between the coating and matrix on the pattern of stress concentrator distribution at the interface is critical. Analyses of stress-strain curves have shown that development of plastic deformation in studied specimens was substantially defined by coating thickness. It also shows the dependencies illustrating changing of specimen mechanical characteristics with hardened layer thickness increasing. From the results, we have concluded the following: 1) Quasiperiodical thin borated layer cracking under active tension is defined by propagation of Luders band and by the presence of second (plane) interface, 2) The difference of secondary borated layer cracking for specimens with thin and thick borated layers is determined by smaller plasticity of compositions with hardened layers, and 3) Fine cracking covering the most working part of specimens with thin borated layers allow to escape from significant deformation localization with new crack appearances and does not promote decreasing of surface hardened specimens plasticity.