Effect of Corrosion on the Fatigue Behavior of G20Mn5QT Cast Steel Welded Connections and Fatigue Life Evaluation Model

Corrosion fatigue experiments were conducted on a welded connection constructed of G20Mn5QT cast steel in 3.5% by weight NaCl solution. The corrosion fatigue fracture mechanism of the welded connection was determined. Surface defects (casting defects and welding defects) and surface corrosion pit are the main reasons for the corrosion fatigue failure of welded connections. For non-load-carrying cruciform welded connections, casting defects and welding defects are the main causes of crack nucleation under a larger stress level (>170 MPa). At a smaller stress level (≤170 MPa), surface corrosion pits are the main cause of crack nucleation. For load-carrying cruciform welded connections, surface defects and corrosion pits lead to corrosion fatigue failure at all stress levels. The stress level at 2×106 cycles of load-carrying cruciform welded connections decreased by 15% compared with the non-load-carrying cruciform weld connections due to the welding defects at the weld root. The fatigue life evaluation model of the welded connection was established by the Stromeyer model and three-parameter Weibull distribution model. The accuracy of fatigue life evaluation for the non-load-carrying cruciform welded connections based on the three-parameter Weibull distribution model improved by 57.53% compared with the Stromeyer model. The three-parameter Weibull distribution model can be a powerful tool for corrosion fatigue life evaluation.