Research on Low Temperature CTOD Fracture Toughness and da/dN Properties of S355N and S355N-Z25 Structural Steel Plate

Adopting three-point bend SE(B) and compact tensile C(T) specimen,through crack-tip opening displacement CTOD fracture toughness test at-20℃ and fatigue crack propagation rate da/dN test,resistance to crack initiation and propagation of S355N and S355N-Z25 structural steel plates were studied.The results manifested that S355N steel is stronger in resistance to crack initiation and prophase growth than S355N-Z25 steel,but is weaker to crack anaphase propagating.When stress strength factor ΔK is less than 34.3MPa·\sqrt \rmm ,S355N steel has less fatigue resistance than S355N-Z25 steel.When ΔK equals 34.3MPa·\sqrt \rmm ,both have the same fatigue resistance.When ΔK is more than 34.3MPa·\sqrt \rmm ,the former has stronger fatigue resistance than the latter.These information may provide reference for the steels as used in safety-assessing of engineering structure.