Grain size variance

[mking0919]

I am having an issue that is beyond my limited knowledge of metallurgy. My company makes extruded fin tubing for use in heat exchangers. I was given a sample of a raw copper tube that was too soft for our operators to run it. It was being crushed as it passed through the machine. My boss wanted me to verify that the material was nonconforming and there for rejectable. When I analyzed the sample I expected to see grains that were larger than what was specified in the purchase order. What I found however were clusters of small and medium sized grains surrounding larger ones. I was wondering if anyone might know what would cause this. I have never had this issue before and I'm stumped.

 

[EdStainless]

Which copper alloy?
Sounds like partial recrystallization after cold work.


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P.E. Metallurgy, consulting work welcomed

 

[mking0919]

Thanks for the reply. It was C122.

 

[blacksmith37]

An old Copper Development document shows C 122 tubing can be ordered to ASTM B- 68 ,75, 88, 111, 280, 306, 359, 360, 395, 447, or 543. I expect some of the ASTM specs have been discontinued but there are still many options from annealed to hard drawn. Tubing yield strength can be from 10,000 to 50,000 psi. What exactly was ordered?