Explanation for Variations in Charpy Impact Test Results
Fabricators
often see significant differences in Charpy impact properties when
making procedure tests. This occurs even with the same welding
materials, plate and welding parameters. We encountered this situation a
number of years ago when exploring significant impact property differences
in multipass welds with process procedure variations that should not
have produced these differences.
At the time, Dr. Robert
Stout from Lehigh University was a consultant to our Welding R&D
Laboratory. We employed his suggestion of comparing the impact results with
the percent refined versus unrefined weld metal in each Charpy specimen.
This approach mostly explained the differences at the higher test temperature. But the procedure could not account for the difference of 44
ft-lbs to 8 ft-lbs found in the -50 degree F tests.
Our Senior Metallurgist,
Dr. E. C. (Ted) Nelson, postulated a possible reason for these differences.
We made a large multipass weldment avoiding any issues of plate dilution. Dr. Nelson
carefully located Charpy specimens in this weld and was able to duplicate
the impact property range we had encountered. One Charpy producing
7 and another 45 ft-lbs in the exact same weld metal. This web page
presents a
summary of the findings.