Modeling the Brittle Crack Arrest Toughness in TMCP Processed Steel Plates for Shipbuilding

Micro-alloyed steel plates with thickness (t) from 80mm to 100mm were produced via thermo-mechanical controlled processes (TMCPs). Microstructural characterizations and mechanical properties tests were conducted in the mother plates as well as in the butt weld assemblies prepared by submerged arc welding processes (SAWs). Pellini drop weight tests were carried out to measure the nil-ductility transition temperature (NDTT). Wide-plate temperature-gradient double tension (DT) tests were conducted to evaluate the brittle crack arrest toughness Kca(t). Brittle crack-initiation toughness Kc in the coarse-grained heat affected zone (CGHAZ) across the entire thickness was evaluated by using crack tip opening displacement (CTOD) approach for each weld assembly. Kca(t) at -10°C greater than 190 MPa√m was achieved in each test plate. An eigenvalue of the NDTT (TNDTEig) was proposed to represent the nil-ductility transition temperature across the thickness of the plate as a whole. The mean value of Kca(t) at a specific temperature was then indexed by TNDTEig of the heavy plates leading to an empirical model for predicting Kca(t) over temperatures of engineering interest. Further, the results of the DT tests were used to determine the master curve, which enabled the prediction on the distribution of Kca(t) over a temperature range wider than that applicable for the empirical model. By direct comparison between Kca(t=100mm) in the mother plates and Kc(t=100mm) in the actual weld CGHAZs, it is concluded that once a brittle crack initiated in the CGHAZ, its propagation will be arrested in the mother plate.