Re: Metallography of Cracked Viggen Pistons..... - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Metallography of Cracked Viggen Pistons.....
Posted by Steven (more from Steven) on Mon, 4 Apr 2005 19:46:28
In Reply to: Metallography of Cracked Viggen Pistons....., KB900psi, Mon, 4 Apr 2005 16:24:30
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You can probably section the cracked piston (near the crack initiation site), or if you can't determine that, the area that looks most burnt.. ;-)
Since you probably can't find out from the GM dealer what the alloy is, you'll have to guess. Cut up a good one (good idea if its not from the same engine) and compare the microstructure. Keep in mind to compare the same area, as the grainsize might be drastically different in the different areas of the same piston!
As you've said, comparing the grain size of the HAZ in the cracked part will let you estimate the temperature it spent in the known run time before failure. However, you might have to do some experiment... (anneal some virgin samples to get a good feeling for what temperature/time will cause the grain growth you observed).
Its a big project, and you'll need many many bad/good pistons to build a case...
Maybe check the oil first? (oxidation, metallic content) You can get an idea of how hot it got (up to a point).
posted by 68.61.39...
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