Abstract
CTOD property of 780MPa class high strength steel weld HAZ was investigated by means of HAZ thermal cycle simulation. CTOD property improves as hardenability of steel increases as well as charpy impact property does in case the CTOD specimen fractures in brittle manner.
As the hardenability of steel increases, fracture mode changes from brittle to ductile one. However, steel with high hardenability shows low CTOD value, less than 0.2mm, even with ductile fracture mode. CTOD value with ductile fracture mode (δm) decreases with increasing hardness of steel.
Decrease in δm due to increasing hardness is attributed both to deterioration of CTOD value at ductile fracture initiation (δ1) and ductile crack growth resistance (K).
δm value can be estimated from strain hardening exponent, ductile fracture properties (δ1, K) and initial ligament size of a CTOD specimen.
