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

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  #1  
Old 08-19-2004, 03:25 PM
VSMBlades VSMBlades is offline
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Heat Treating O-1

I was looking at a T-T diagram for O-1 steel from Taylor Specialty Steels. It appears that you have almost a full 10 seconds to get the steel from 1250 degrees to 400 degrees. I had always read that O-1 was very forgiving to heat treat but never realised you had so much time. That is alot of time isn't it? And after you get past the "nose" on the chart you could take even more time to cool it and still get a fully hard blade. Just thought that was interesting.


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  #2  
Old 08-20-2004, 10:16 AM
Guy Thomas Guy Thomas is offline
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Not sure what those temperatures are about, O1, just like most carbon steels, doesn't even begin to go austenitic until around 1320-1330 degrees F and needs to be taken to 1450-1500 degrees F before quenching. I don't have O1 data at hand at the moment, but time to cool to 400 degrees is irrelevant to a degree as long as cooling was fast enough to miss the pearlite nose, so the crucial cooling time is from the austenitizing temperature, lets just say 1500 degrees F, to below 800 degrees or so and I rather doubt it has 10 seconds to do that. As long as the pearlite nose is missed, martensite will form but it doesn't begin to form until around 400-450 degrees F. I mentioned earlier that the cooling time coming down to 400 degrees after missing the pearlite nose was irrelevant, that's not exactly true because if you hold the steel above 400-450 degrees for extended periods you will begin forming bainite.

I haven't used O1 much and I don't have it's preferred heat treating temperatures and times handy so perhaps someone who does will post them. I'll look around also. The temperatures I used above are generalizations only.

Can you post a link to the data you were looking at?


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Old 08-20-2004, 11:08 AM
VSMBlades VSMBlades is offline
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Here is the diagram I was looking at.



The Text included with picture is

The diagram illustrates the time required for transformation of austenite to commence and it may be usefully employed in determining the correct temperatures and holding times for interrupted quenching treatments. (Austenitised at 800?C)

I realize the scale is logrithmic but it appears as if the nose is just a little on the left of the 10 second mark.

I will also say that this chart may be totally incorrect but it did spark some interest.

Hope the picture posts.


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Old 08-20-2004, 11:18 AM
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SteveS SteveS is offline
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Cool chart Joe, Thanks.

Boy that does seem like the nose is out of proportion for a oil hardening steel.

One thing that puzzles me, is people get great hamons with o1. But if this chart is true, the steel is practially air hardening and I don't see how you could get the sharp transition you see on 01 clay treated blades. I mean the martensite would travel right under the clay to the spine at that rate!

Or I'm really confused.

Steve


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Old 08-20-2004, 02:41 PM
Guy Thomas Guy Thomas is offline
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Well that chart certainly shows the nose right at about 900 degrees F and the time somewere around 8-9 seconds (hard to tell for sure).


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Last edited by Guy Thomas; 08-20-2004 at 02:43 PM.
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Old 08-30-2004, 05:50 PM
paul harm paul harm is offline
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i've used it quite a bit , and yes you do have 10 seconds . worked in a heat treat room that did all their work for a tool room . we used to go from salt bath to a preheated oil tank . boy did i get spoiled . will it air harden ? don't know how hard it got , but when first starting to make knife blades , i ruined many a band saw blade by cutting too fast - that 01 would harden right in front of the blade and ruin it . what i've never tried , but wanted to bring it down to 400 to 500 and put in a preheated oven at 450 and leave it there for a couple of hours . would you get banite ? i do preheat my draw oven to 425 and shove it in , but have never tested it . someday maybe . paul


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  #7  
Old 08-31-2004, 12:13 PM
Quenchcrack Quenchcrack is offline
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O1 IT curve

If that curve is accurate, it says you have even more time than 10 seconds. If you draw a straight line from the point where 800C is on the vertical axis down to where it just misses the pearlite nose, and continue the projection down to where it intersects the horizontal Ms line, you find you have more like 60 seconds! I also find that remarkable but I found another IT curve for O1 in "Atlas of Isothermal Transformation and Continuous Cooling Curves" from ASM. It confirms the time to quench at about 1 minute. The chemistry listed for the curve is: C=.85, Mn = 1.18, Cr = .50, W = .44. In a thin blade with forced air, you might just get this to air harden.


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Old 08-31-2004, 02:30 PM
paul harm paul harm is offline
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that long time is why it's so easy to get it hard ,unlike the straight carbon steels . if you notice the W - that's tungsten [ wolfram ] - it gives the 01 a small , dense grain structure [ good cutting edge ]. but it also keeps it hard at high temps , harder to forge . it's also a bit " red short " , prone to crack at too high a temp [ yellow heat ] . haven't had that problem yet , knock on wood . it h.t.s nice , a bit harder to forge . paul


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Old 08-31-2004, 02:39 PM
AwP AwP is offline
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Quote:
if you notice the W - that's tungsten [ wolfram ] - it gives the 01 a small , dense grain structure [ good cutting edge ]. but it also keeps it hard at high temps , harder to forge . it's also a bit " red short " , prone to crack at too high a temp [ yellow heat ] .
Makes me glad I started on scrap . I used some O1 reciently and it felt like butter compared to some of the steels I've used before. It might be a little red-hard, but it's got nothing on HSS, heh.


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Old 09-10-2004, 05:11 PM
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Yes the curve is correct and yes O-1 is very suitable for bainite .BTW you could do a O-1/L-6 damascus and you can get bainite for both at the same time ! While all steels are made to a range for each element a mill might aim at the high or low side of the range for any element . Also for some tool steels ,like O-1 there are optional elements that a mill may use . The result of all this is that the same tool steel made by two different mills may react to forging and heat treating very differently.
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