Corrosion fatigue behaviour and microstructural characterisation of G20Mn5QT cast steel in 3.5‐wt% NaCl solution

Abstract

Corrosion fatigue behaviour and microstructural characterisation of G20Mn5QT cast steel are investigated in simulated seawater. Fractography is performed by using scanning electron microscopy (SEM). The macroscale fracture surface and microstructure of the failed specimen are acquired including the crack initiation, crack propagation, and pitting evolution. The maximum cyclic stress (S) versus number of cycles to failure (N) curves is derived by three‐parameter fatigue curve method. Fatigue life is predominantly controlled by the corrosion pitting‐induced crack initiation when tested in simulated seawater at lower stress levels. As the maximum cyclic stress is less than 185 MPa, the chloride ion erosion is the main influence factor, which affects the fatigue failure of the G20Mn5QT cast steel in simulated seawater.

Effect of corrosion on the fatigue behaviour of butt welds of G20Mn5QT cast steel and Q345D hot rolled steel in 3.5‐wt% NaCl solution

“…The S‐N curves are also plotted comparing the welded specimens with the cast steel base materials in 3.5‐wt% NaCl solution 4 (see Figure 4). The results indicate that the welded specimen and the cast steel base material have similar corrosion fatigue properties.…”

“…After the corrosion fatigue experiments, the corrosion products on the surface of the specimens are washed in distilled water and absolute ethanol. The fractured welded specimen is cut at a distance of 5 mm from the fracture and then washed at room temperature 4 . The overall corrosion fatigue fracture, macroscopic fracture surface and microscopic fracture surface are analysed with a Hitachi S‐3400N scanning electron microscope.…”

“…The fatigue strength ( S AIR )in laboratory air and that ( S COR ) in 3.5‐wt % NaCl solution are derived with the same cycles to failure acquired by S‐N curves (Equations 1 and 2) to investigate the corrosion fatigue behaviour 4,37 . The relationships between S AIR and S COR are plotted in Figure 11.…”

“…Both a corrosive solution circulation system and a fatigue testing machine are used in the corrosion fatigue tests (see Figure 2). 4 The corrosive solution is stored in an airtight container. Because the internal pressure remains constant, the corrosive solution can be continuously circulated.…”

“…Then, the acquired cyclic stress versus number of cycles to failure ( S ‐ N ) curves of the materials are used to evaluate the fatigue behaviour and develop the fatigue design. Han et al 3,4 studied the fatigue behavior of cast steel in laboratory air and in simulated seawater. They found that casting defects inside the cast steel were the main reason for fatigue crack nucleation in laboratory air.…”