Property Distribution Map to understand HAZ CTOD Toughness

Study on Micro-crack Initiation Properties in Steel HAZ having Microscopical Heterogeneity in Strength (Report 2)

Abstract

To visualize the fracture initiation characteristics in the multipass weld heat affected zone (HAZ), the yield strength distribution map and the CTOD toughness distribution map were drawn up graphically by a computer, based on a series of HAZ simulation test results. The comparison between these computationally estimated property distribution maps and the real HAZ CTOD test result revealed that:
The fracture of the HAZ CTOD specimens was initiated from a peripheral part of a local hard zone (LHZ), which does not always correspond to the most brittle point on the crack front line, and
The critical CTOD value derived by the full-thickness specimen was adequately represented by the local critical CTOD level at its fracture initiation point.
The result of this study suggested that the fracture initiation is prevailed not only by the local brittleness but also by the heterogeneity in strength in the HAZ.