Cold cracking delay times for single pass weld metal
The study of hydrogen assisted cracking in steels has received considerable attention although certain aspects still elude academia and industry. The aim of this paper is to communicate physical research undertaken at The University of Wollongong (UOW) and the subsequent analysis at BMT Fleet Technology in relation to small scale testing of single pass weld deposits. The work presented entails the use of 4-point bend testing to derive hydrogen weld metal cold cracking delay times. It is proposed that a maximum delay time before cracking, rather the prediction of a single delay crack time for one condition, may provide more realistic expectations. Two loading regimes were investigated. The first constituted a 5mm/min incremental load increase and the second regime ensured that the crosshead displacement was maintained when a specified load was reached. The results from the mechanically strained samples suggest that hydrogen-dislocation interactions deliver a significant influence on the expected delay times. It is argued that these interactions will then contribute to the variations in delay times observed for specimens welded and tested in near identical conditions. Other possible reasons for variations in weld metal delayed crack times will briefly be discussed and images from scanning electron microscopy will be presented to show fractured surfaces.
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