Influence of V and V–N Addition on the High‐Cycle Fatigue Performance for EH40‐Grade High‐Strength Hull Structure Steels

As the demand for polar ships with long‐term service in ice environment increases, the steel materials are required to have key properties of high strength, toughness, and fatigue properties. The mechanical properties of hull structure steel with three different composition systems are investigated by tensile test, impact test, hardness test, and high‐cycle fatigue test, and the microstructure is observed and analyzed by optical microscope, scanning electron microscope–electron backscatter diffraction, and transmission electron microscope. The results show that the addition of V and V–N elements improves the mechanical properties of steel plates, especially the fatigue performance. The fatigue limits of V0, V and V–N steels are 250, 275, and 292 MPa, respectively. The microstructures of the steel plates are composed of ferrite and bainite, and the proportion of ferrite in steels increases with the addition of V and V–N elements. The fatigue cracks initiate in the soft phase nearby the soft/hard phase interface and propagate along the soft phase to form transgranular fracture. The fatigue limit of steels is elevated by doping V and V–N elements which increases the strength of ferrite. Moreover, the enhancement effect of V–N compound addition is better than that of V individual addition.