Strato Posted August 2, 2012 Share Posted August 2, 2012 We have a 80 pound steel casting (0.3% C max, 1.85%Mn max, Si 1.5% max) that is quenched and double tempered. Is there a test (hardness, microstructure, etc.) we can do to determine if it was double tempered or tempered just once? Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted August 2, 2012 Share Posted August 2, 2012 None that I have heard of...I wouild rely heavy on the reputation of the place thta did the heat treat process. Quote Link to comment Share on other sites More sharing options...
metal99 Posted October 3, 2012 Share Posted October 3, 2012 Tempering twice is a pretty good practice so I would assume that it would be done. Testing the hardness isn't going to tell you if it was tempered once or a hundred times because after the transformations are done and your left with no un tempered martensite re-tempering at the same or lower temps will do nothing to the steel. Seeing that's its got such a small amount of carbon makes me think that either way its not really going to matter. With only .3% carbon the metal isn't going to be overly brittle even if it was not tempered. Quote Link to comment Share on other sites More sharing options...
Woody Posted October 3, 2012 Share Posted October 3, 2012 Since tempering is a function of time at temperature, with that big hunk of metal i would be more concerned with how long it was held at temperature rather than the number of times it was heated to temperature. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted October 3, 2012 Share Posted October 3, 2012 It's a very low function of time at temp and a high function of cycles as the cycling can help "knock" structures that didn't temper the first time into tempering the second or third time. Or that's what they told me in my Mat Sci classes at Cornell... Quote Link to comment Share on other sites More sharing options...
Woody Posted October 4, 2012 Share Posted October 4, 2012 you can read the whole thing here, http://en.wikipedia.org/wiki/Tempering this is just one excerpt from the article, but once again there is no memtion or repetition that most of the knifemaking world is caught up in. "Precise control of time and temperature during the tempering process is critical to achieve the desired balance of physical properties." Quote Link to comment Share on other sites More sharing options...
Timothy Miller Posted October 4, 2012 Share Posted October 4, 2012 It's only 80 lbs temper it again in your home oven then you'll be sure it was tempered twice. 1 hour per inch of thickness. you may have to beef up the rack though. This may sound unprofessional but it is valid. Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted October 4, 2012 Share Posted October 4, 2012 If you bought the item(s) with the understanding that it should be heat treated a certain way then the supplier should provide a certificate of conformance stating process conditions and results. If you don't trust their certs then pick another supplier. Quote Link to comment Share on other sites More sharing options...
Patrick Nowak Posted October 6, 2012 Share Posted October 6, 2012 In industry it is not uncommon to double temper, though that is very much a function of grade and desired mechanical properties. Some grades do in fact respond fairly dramatically to being double tempered at the same or even slighlty LOWER second tempering temperatures. Unfortunately, there really is no test that one can do to confirm that a second temper was performed. All you can do is confim that hardness and mechancal properties requirements have been met. Patrick Quote Link to comment Share on other sites More sharing options...
John McPherson Posted October 7, 2012 Share Posted October 7, 2012 As a Certified Welding Inspector with just enough Non-Destructive Testing background to be dangerous: No. No known test can determine the number of thermal cycles. The component either meets end user requirements for Rockwell Hardness/X-ray/Magnetic Particle/Eddy Current/UltraSonic/etc. tests or it does not. You are relying on vendor reputation and history here. If you do *anything* else to it, you are assuming the blame for any later failures. Quote Link to comment Share on other sites More sharing options...
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