Fatigue behaviour of G20Mn5QT cast steel and butt welds with Q345B steel

A total number of 44 fatigue tests were conducted under total stain control, 26 for G20Mn5QT cast steel and 18 for butt welds between G20Mn5QT cast steel and Q345B steel. Based on the test results, cyclic stress response, plastic strain energy, strainlife curves and Coffin-Manson equations were presented. Comparing with hot rolled steels widely used in steel construction, the fatigue behaviour of G20Mn5QT cast steel is poor, the reason for which was imputed to the defects caused by the casting process. The welds between G20Mn5QT cast steel and Q345B steel exhibited similar fatigue performance as G20Mn5QT cast steel. Fatigue crack tends to initiate in the heat affected zone (HAZ) at the cast steel. Microstructure observations using optical and scanning electron microscope showed that casting defects are the common fatigue source for both G20Mn5QT cast steel and the butt welds between G20Mn5QT cast steel and Q345B steel.