Analysis Of Inverse Fracture Occurring In Hammer-Impacted Region During Drop-Weight Tear Test Of A High-Toughness Linepipe Steel

This study aims at analyzing inverse fracture occurring in the hammer-impacted region during drop-weight tear test (DWTT) of a high-toughness line-pipe steel. A pressed notch or a chevron notch was introduced into DWTT specimens, some of which had a back slot. The DWTT results indicated that the shear area of the pressed notch DWTT specimens was larger than that of chevron notch DWTT specimens. In the hammer-impacted region of all the DWTT specimens, abnormal inverse fracture having a cleavage fracture mode appeared, and its fracture area was correlated well with hardness and work hardening exponent. The formation of this inverse cleavage fracture raised the fracture propagation transition temperature by decreasing the shear area measured in accordance of the API 5L3 specification, which was confirmed by relating to the Charpy impact test data of pre-strained steel specimens. In order to forecast actual FPTT of line-pipe steels more precisely and to properly evaluate the resistance to unstable ductile fracture, therefore, continued research efforts are required to modify the current DWTT methods or to develop new test methods that well match with actual fracture behavior of line-pipe steels.