Study of the stress corrosion cracking of low-carbon low-alloy steels using the eddy current method

Abstract

The results of studying the processes of stress corrosion cracking (SCC) of low-carbon low-alloy steels are presented. It is shown that the use of eddy current method (ECM) allows one to evaluate even small structure changes associated with the processes of the SCC crack nucleation and growth. It is noted that the process of stress corrosion cracking exhibits a two-stage character, which is distinctly displayed in the electromagnetic characteristics. The first stage of the destruction characterizes the processes of accumulation of micro-damages in the material and ends with the formation of one or more cracks having the size of several grains. At the second stage the formation and growth of the macro cracks is accompanied by a rapid change of the electromagnetic characteristics. The dependences of the SCC incubation time on the value of the macroelasticity limit ( σ 0 ) are given. It is noted that an increase in the o0 value entails an increase in the time prior to the formation of the first crack. This can be explained by the fact that the limit of the macroelasticity determines the onset of microplastic flow in the material that actively affects the stress corrosion cracking. An analytical dependence of the SCC incubation period on the value of the macroelasticity limit is obtained using experimental data. The calculation error did not exceed 10%. A parameter is proposed to assess the state of the material prone to SCC which allows detecting the stages of accumulation of micro-damages and exhaustion of a significant part of the material resource before the appearance of multiple surface macro-cracks proceeding from the data of eddy current measurements. It is shown that the eddy current method apart from determination of the macro cracks present on the surface provides identification of the stages of the material destruction under the simultaneous action of corrosive medium and static tensile stresses.