Fatigue Crack Propagation Characteristic and Fatigue Fracture Toughness in 5.5% Ni Steel Weldments at Low Temperature

Fatigue test and fracture toughness test in 5.5% Ni steel weldments in the temperature range from 98K to room temperature were experimentally carried out. Both the tests were performed with a compact tension specimen by using a program-load-controlled 0.98MN fatigue testing machine. The main results obtained are summarized as follows: (1) Fatigue crack propagation rate in weld metal zone is very larger than that in both base metal and HAZ (heat affected zone.) On the contrary, fatigue life, Nƒ in weld metal zone is lower than a half-value of that in both base metal and HAZ. (2) Within the temperature range from 98K to room temperature, the power coeffinient, n of da/dN=A⊿Kn is related with 1/T as n=b1+a1/kT, and da/dN shows Arrhenius type. Apparent activation energy, Q is related with ⊿K as Q=U-a1ln⊿K within the same tremperature range. These trends are in good agreement with the dislocation dynamics theory of fatigue crack propagation. (3) Fatigue fracture toughness, KƒC and fracture toughness, KC in base metal are larger than those in both weld metal zone and HAZ