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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.

Below is a "picture summary" of what  was found.  The  schematics of Charpy impact specimens were all prepared from one weld.  Dr. Nelson placed the Charpy specimens to locate the "V" notch such that there was about 50% refined material in all specimens.  However some had single refined material, some double refined areas (those shown in yellow) and most important the refined material was placed at the outer edges for the specimens. 

Doubly refined material placed at the specimen edges produced  the highest toughness values!  Still maintaining about 50% refined material in the location of the Charpy "V" he placed single refined material in the center of the specimen, the least effective location and only 7 ft-lbs were achieved!

Want to know the theory behind the differences?  A Free 7 Page Report is available as a PDF download.  It also shows graphs of the toughness values versus refined and unrefined material from our original work.  This original data indicates why this further study was conducted with Dr. Nelson. 

Click for a Copy    

 

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* US Patent  # 6,610,957;  "Welding Shielding Gas Saver Device" August 26, 2003,  Patent Pending in other countries.   The "Flow Rate Limiter" device is
 covered by 2008 US patent #7,462,709.  Other site material may be covered under our 2006 US Patents # 7,015,412 or # 7,019,248 .
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Last modified: 09/08/10

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