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Triple quench?


James R.Fuller

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Jerrod

You might have trouble finding a general figure for carbide dissolving temps as each carbide ( IE chromium carbide, cementite, vanadium carbide etc ) have wildly different heat/ time ranges that they will dissolve in. I think for specific figures you will need to look up each carbide that could be present in each alloy individually.

MP

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Yeah I know, those are hard to find. Especially since many have multiple different configurations and it is hard to know what you have at any given time and in what quantities. M23C6, M7C3, M3C2, etc. Those listed are all forms typical of chrome-carbide and I am sure they dissolve at different temperatures and different rates. For things that just have one major (non-iron) carbide former it is hard enough, but then you move into stuff with multiple (chrome, moly, vanadium, tungsten) and good luck! The scientist in me wants to know what exactly is going on, the part of me that likes sharp objects wants to shut that part up and just follow a known "recipe". Good or bad, the scientist part is the more stubborn of the two.

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LOL isn't metallurgy fun? In practice I think knowing exact temps is not real necessary just general ranges as I would guess that just about all of the forms of carbide for each alloy will break down with in the same temp range of a few hundred deg.

MP

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"A few hundred degrees" is pretty big. Also, we can see from the Fe-C diagram that Fe3C can dissolve at 1333F when C<0.83%, but can survive up to ACM when C>0.83%, and up to 2097F when C>2.06%.

 

So in 5160 your Fe3C goes away well before you need it to for hardening, but your Cr-carbides may not completely dissolve until 2000F or higher. Then 52100 gets even more variable. This is what makes multiple quenches not just a "snake-oil" type thing. Depending on how hot you get you could really change some carbide structures and retained austenite. It is also, in many cases, highly dependent on how the steel was treated before-hand. My gut feeling is that it really boils down to "good enough". If you do a triple normalize and single quench to get 99% ideal structure (random number pulled out of thin air, I'm not saying this is what it takes), then is it really worth a bunch of effort to get that last 1%? Personally, I would have to say no. If I could every get to within 95% of "perfect/ideal", I would consider it a huge success. Now if it is the difference between 90% of ideal and 99% be doing something different that is another story. I'm not sure how to even put a number on "ideal" though. Grain size is a factor, as is carbide size; but what is the ideal ranges and/or ratio of those? Also, there tends to be a trade-off that lends itself to design intent (e.g. hard=brittle but holds edge, etc.).

 

And yes, metallurgy is fun. Not once have I regretted my career choice, or hobby. That doesn't mean either have never made me really thirsty for a stiff drink. :)

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Whoa...Ask a simple question.... have your brain fried... You guys are so knowledgeable on this stuff. I feel so fortunate that this forum exists!

-=JF=-

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Good question,Jerrod! :) I think something cold to drink is in order for me as my brain is starting to overheat a bit...

To become old and wise... You first have to survive being young and foolish! ;) Ikisu.blogsot.com. Email; milesikisu@gmail.com mobile: +27784653651

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