The role of microstructure in the corrosion-fatigue crack growth behaviour in structural steels

This paper presents an experimental investigation of the microstructural effects on the fatigue crack growth (FCG) behaviour in ferrite-pearlite steels. The study was carried out in the Paris region under sinewave and hold-time fatigue loading. The role of the microstructure in accelerating or retarding fatigue crack growth rate (FCGR) and the phenomena responsible for the variations in the FCGR are comprehensively examined. The effects of the material phase morphologies, environment, waveform, crack-tip loading condition, corrosion products and the influence of cyclic microplastic zone on FCGR are also discussed. The microstructural analyses were performed using scanning electron microscopy and the observations are interpreted in conjunction with the experimental results obtained from FCG tests performed in air and seawater (SW). This work suggests that the nature of the microstructure of ferrite-pearlite steel has a strong influence on the FCGR in the Paris region of the da/dN vs. ΔK sigmoidal curve both in air and SW. This study is important in the design of fatigue resistant steel for marine applications.