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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 01-16-2015, 07:36 PM
ss caustic ss caustic is offline
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Question : heat treat

Ok, so I've been researching heat treating info and process logic and ran across this site , seems to be a great resource .

-http://www.navaching.com/forge/heattreat.html

I did come away with a question on heat treat though and it has to do with once you get past the "nose" of the s curve from 1450f down to 900f in the example ( from web site), what effect does cooling all the way down quickly to 125F have , alternately what effect does following the s-curve more closely to the 125F.

is it only about managing the thermal shock or will one :

1) have a higher HRC #.?
2)have a finer grain structure ?
3)have any thing else different ?

I'll re-read the pc. in case it is staring me in the face , but in the mean time anyone willing to clarify would be much appreciated

hope this makes scene , thanks
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  #2  
Old 01-20-2015, 11:11 AM
samuraistuart samuraistuart is offline
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Once the PN is reached by the quench medium.....you'll have max RC. Reaching the PN in the correct time gives max RC. Not anything to do with cooling below PN.

Grain structure is not affected by heat below 1350F.

Anything else different by speeding up the cooling from 900 to 400? NOPE. Except maybe internal stress may be greater.

It is that 900 to 400 range where the steel is flexible enough to be bent by a gloved hand for straightening. Until it hits about 400 or so where martensite begins to form.
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Old 01-21-2015, 06:08 AM
WBE WBE is offline
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"It is that 900 to 400 range where the steel is flexible enough to be bent by a gloved hand for straightening. Until it hits about 400 or so where martensite begins to form."

Not sure about other steels, but 01 can be straightened by hand well below 400? with about a five minute or longer window to work in.
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Old 01-22-2015, 01:12 PM
ss caustic ss caustic is offline
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thanks guys , I've recently found a copy on line of

"Metallurgy of Steel for Bladesmiths & Others
who Heat Treat and Forge Steel
John D. Verhoeven"

tonnes of info to digest in there.

your replies are much appreciate

Last edited by ss caustic; 01-23-2015 at 11:28 AM.
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  #5  
Old 01-23-2015, 11:11 AM
samuraistuart samuraistuart is offline
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Martensite Start temp of simple carbon steels like O1 is around 400F or so. It is at 400F that martensite begins forming until it reaches about 200 or 100F where martensite finish is reached.

Last edited by samuraistuart; 01-23-2015 at 11:15 AM.
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Old 01-24-2015, 06:44 AM
WBE WBE is offline
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Yes Stuart, kinda, sorta, but actual MF with 01 can be 15 to 20 minutes, possibly longer, after it reaches ambient temp, or below 100?. In my experience with it, I don't bother to file check for at least 15 minutes after it has cooled to ambient. A twenty minute soak at 1475?, into 130? AAA, and removed after close to a minute. Maybe a tad sooner.
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Old 01-26-2015, 09:16 AM
Kevin R. Cashen Kevin R. Cashen is offline
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A good number of informational resources for knifemakers suffer from odd inconsistancies in the quality of information, there will be pages of really good information and then a page or two of stuff that makes no sense whatsoever. The last time I looked the resource cited in the original post was no exception, so please take all information with a grain of salt until you can triangulate and verify.

First point to consider is that transformation temperatures are highly depended on chemistry so the first crucial bit of information you need before any of it can be useful is what alloy you are working with. For simplicity I am going to start with something like 1084. Austenitizing temp can be anywhere from 1450F to 1500F from here you quench, and it is when the steel goes below the surface of the quenchant that the clocks starts. The idea here is to cool fast enough to outpace any of the rapidly forming phases from around 1200F to 600F, to be safe(although with 1084 you can stop worrying around 900F).

It is not necessary to cool all the way to the oil temp (90-130F) but many folks do with little trouble. Rate of cooling from 900F to 450F will make little difference in anything because if you cooling was fast enough to avoid any transformations above 900F all you have is austenite still. At 400-450F (depends on how thoroughly you soaked the steel at temp, the more carbon in solution the lower will be this temp) the steel will begin to harden. I would like to lose the word ?flexibility? in favor of something like ?plastic? or ?ductile?, in any case at this 400-450F range the blade is able to be easily deformed, or pushed straight because it is still austenitic (check it with a magnet, it won?t stick yet). The farther the blade cools below this temp. it hardens (forms martensite) more, and more, until it reaches the maximum hardness it can achieve at room temp., and with 1084 even freezing it shouldn?t produce more hardness, unless your heat was WAY out of line ( and few more things to boot).

This is all in continuous cooling, which is important in the if all you want to do is fully harden the blade. Changing the rate of cooling should only be done where isothermal conditions will give you a desired effect, and you don?t want it anywhere from 1200F to 600F. If all you want is a hardened blade, ala martensite, then increase that to 1200F to 450F. There are some phases in that limbo that are not desirable for maximum hardness, and one that can form from 900F to 700F that really stinks for both strength and toughness.

Once you get to 400F to 450F, cooling can be slower but it should be continuous to keep the transformation moving forward, without having to do something goofy like freeze a simple carbon steel blade. It is here where you can really overstress a blade and so there are advantages to slowing things down here. The hardening process involves a different type of transformation mechanism that induces enormous strain inside the steel, so the gentler it is done, the better.

With an alloy, like O-1, things change. The alloying changes how things go into solution and also how they come out, so everything takes more time. You still have to worry from 1200F to 600F but not as much, (cooling can be much slower) and the threat is pretty much same throughout the range as the pearlite is suppressed other phases get their chance. At Ms things are more interesting because it can be less predictable (even more dependent on austenitizing temp.), but mostly things temp to be pushed lower by the alloying so it is easier to create a situation where you may see changes if you freeze O-1, but you still messed up somewhere if you have to do this. With even more alloying than this freezing becomes necessary for maximum hardness since the range is pushed below room temperature.
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Old 01-26-2015, 09:37 AM
ss caustic ss caustic is offline
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thanks Kevin, I've read a bunch of your stickies on blade forum.

thanks so much for you contribution to the community and the internet knowledge base in general!
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Old 01-27-2015, 12:15 PM
Kevin R. Cashen Kevin R. Cashen is offline
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Quote:
Originally Posted by ss caustic View Post
thanks Kevin, I've read a bunch of your stickies on blade forum.

thanks so much for you contribution to the community and the internet knowledge base in general!
You are very welcome, I am glad if I have been able to help. I hope to make 2015 a year of greater progress in some of my projects to help bring more information to the knifemaking community. You are getting good input from Wick and Stuart, we all spend some time chatting about things at various friendly places around the internet, I look forward to you joining us in some of those chats.
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