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Brian Madigan

AISI 1084 carbon steel

36 posts in this topic

1 hour ago, Alan Longmire said:

All steels benefit from slow air cooling after the tempering step.  It may only be a miniscule benefit, but it's better than quenching.

I'd just amend this to say most steels.  There are some that definitely need a water quench after a temper.  Generally these are not blade steels though.  

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Okay, that's what I thought but as I've been watching more and more Youtube videos and such I'd seen a lot quenched. Just wanted to make sure I wasn't missing something. Thanks!

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5 hours ago, Alan Longmire said:

All steels benefit from slow air cooling after the tempering step.  It may only be a miniscule benefit, but it's better than quenching.

Alan--I used to  think the same way but I've been told by those who know much more than I  that it really doesn't make any difference.  I've  not done any testing to know one way or  the other.

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Duly noted!  You and Jerrod certainly know more than I do.B)

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For the record, my take on quenching after a temper is this:

1)  Avoid the blue brittle range as much as possible.  If you have martensite it should spend as little time as possible between 500-900 F (the exact edges of this range are under debate and are likely alloy dependent).  So 4325 quenched then tempered at 1150F must be quenched.  Anything tempered at 450 or below doesn't need it.  Anything that doesn't have martensite (like 1010), isn't affected by this rule.  

2)  Other than following the above guideline, quenching or not after a temper cycle is all about convenience.  Letting it slow cool will continue the tempering (depending on thermal mass and temperature this may not be significant), quenching will end it right away.  Blades at temperatures under 500 F are good either way.  

Somewhere I'm sure there is an odd alloy that doesn't fit into these, but I haven't played with it yet.  

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One advantage that I  have  used a  time  or two is when the blade does a  slight bend during tempering.  By running water over the outside or convex side of  the bend, I have been able  to  straighten it but this is seldom relevant.

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Gary, that is a great idea!  I seem to always get a slight bend when quenching.  Is that something that can be attempted after the first tempering cycle, or do you wait until at least the second?

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On 2/15/2017 at 10:10 AM, Alan Longmire said:

All steels benefit from slow air cooling after the tempering step.  It may only be a miniscule benefit, but it's better than quenching.

It also has the potential to cause warping and cracks from what I've heard. I haven't experienced it myself, but I also don't quench them again after temper.

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It's interesting that Stacey, the moderator at bladeforum, suggested quenching after tempering or between tempers.  I pressed him on this, and it was said there is a miniscule advantage to it, though things got very technical at that point and I pressed no further.

I started quenching between tempering cycles, and the one difference I've been able to discern is it is quicker... Pull the blade out of the oven, quench, stick it right back in for another round.  Other than that, I can't see any difference, good or bad.

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On 9/26/2016 at 9:14 AM, Alan Longmire said:

A PM from a new guy made me revisit this thread, especially since I just got back from Ashokan where I heard a most excellent lecture from Kevin Cashen on heat treating stuff. Here is what I said, and I think it needs broader exposure since this is starting to happen a fair bit these days:

 

First, have you read this? http://www.bladesmit...showtopic=26523 (note: that is this very topic, don't click the link!)

 

Second, there's a whole book about that by Dr. Paul Verhoeven called "steel metallurgy for the non-metallurgist."

 

Third, did you look at this:http://www.cashenbla...ttreatment.html , http://www.cashenbla...steel/1084.html, http://www.cashenbla...metallurgy.html

 

Finally, here's the short version:

 

Nonmagnetic occurs at 1417.73 degrees F in iron alloys, because magnetism is a physical property unrelated to alloy content (except, of course, for 300-series stainless steels which are not magnetic to begin with). The critical temperature is a crystalline phase transformation which depends entirely on the alloy involved, which is why that pipe trick mentioned in that first link works so well. You can SEE it happen, so you don't need a magnet. This is a good thing because critical for 1084 is around 1475 degrees F, a little over nonmagnetic. Critical for 5160 is 1660 F, a LOT over nonmagnetic. Magnets are not your friend.

 

1084 is a simple alloy and has the exact amount of carbon that can go into solution with none left over, which is why it is such a good steel for those of us with less-than-high-tech setups. It requires no soak at temperature (the instructions Brian gave in the first link are in per inch of thickness, and since knives are thin you can safely ignore soak times on simple alloys. By the time you see the transformation it's soaked enough). It doesn't require a spheroidized anneal because there's not enough extra carbon to form carbide clumps that wreck drill bits, and the vanadium content is just enough to pin the grain boundaries so you don't have as much problems with excessive grain growth unless you soak the hell out of it or overheat it. Which leads me to your exact questions...

 

Heating 1084 to 100 degrees above nonmagnetic is what you want to do.

 

Letting it cool in still air leaves a small grain size and evenly distributed carbon. This is normalization.

 

Leaving it in the forge to slow cool can result in massive grain growth and severe decarburizing if it is too hot. Carbon prefers oxygen to steel, and will leak off the surface at high heats, especially if held there for a long time. It's just a bad idea and you will not find anyone who knows what they are talking about recommend that you do this.

 

Putting it in a bucket of hot ash is called a lamellar anneal. The carbon will precipitate into the grain boundaries and form sheets of pure carbide, which actually make it more difficult to grind, file, or drill. The iron part will be soft, but the carbon in the grain boundaries will be crunchy, which leads to ragged holes and tearout when filing.

 

So: A triple normalization from descending heats (way hot, a bit hot, and barely critical) will make your grain size uniform and small with evenly distributed carbon. This is what you want. The result will not be quite as soft as a spheroidized anneal, but neither you nor I have the equipment to do that and the difference is not enough to bother with for the things we do. If we were working with 4" thick blocks, then yes, it'd be slightly better for machineability to spheroidize it, but for simple filing, grinding, or drilling normalization is all you need.

The part of this post where you/he says critical for 5160 is 1660* and magnets are not your friend. Does this mean 5160 does NOT become non magnetic in the 1400* range??

Or am I adding 2 and 2 together and coming up with 22. lol

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All steels become nonmagnetic around 1425 degrees.  Nonmagnetic is not the same as critical temperature, which varies quite a bit between steels. That is why a magnet does not help with 5160.

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