Influence of point defects on intergranular fracture of steel

At present, it has been established that the ageing process of pipe steel is multistage. The first stage is characterized by the release of carbon atoms from the metal grains. The second stage is determined by the removal of inter-nodal atoms to the grain boundaries. This removal mechanism is related to the diffusion of carbon through the inter-domain space, facilitated by point defects such as vacancies. The most optimistic estimates give an unrealistically long time of the ageing process of steel. Thus the diffusion mechanism remains unclear. The aim of this study is to construct a mechanism that would adequately describes this phenomenon. The authors believe such a mechanism should be related to point defects (vacancies). The leading method used in this research is theoretical analysis, which has led to the proposal of an effective way of influence of point defects in intergranular corrosion failure of steel is proposed.Under conditions of uphill diffusion in the linear approximation, mass transfer develops slowly and cannot enrich the adjacent grain boundary layers with impurities. The presence of defects makes the diffusion nonlinear.This study considers thermodefects generated by a temperature gradient. Based on changes in the magnetic properties of the samples, conclusions about the formation of the structure with the participation of carbon impurities displaced in the process of hydrogen introduction were made. The results of this study can be used in the development of methods of increase of service life of pipe steels.