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High-Performance Blades Sharing ideas for getting the most out of our steel.

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  #1  
Old 02-09-2003, 10:05 AM
jethro jethro is offline
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Question Tempering D2

I had a friend heat treat my D2 blades yesterday. They ended up at 65 rc. I brought them home and tempered them at 300 deg. for two hours. I am doing the same thing this morning. I do not have a hardness tester so, do you think that this will be enough to get back to 60 rc?

Mike
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  #2  
Old 02-09-2003, 10:24 AM
Jan Dox Jan Dox is offline
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Mike,
according to the Uddeholm charts for their D2, and just going by the temperature of the temper, The hardness would have dropped from 65HRC to somewhere between 60 and 62. 400?f would more likely give 60HRC.
If the initial hardness was 65 the graphic shows the hardening temperature would have been about 1900?F.

Jan
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  #3  
Old 02-09-2003, 06:28 PM
jethro jethro is offline
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Thanks Jan. I have had Bob do some heat treating for me when I visited his shop and he does a double temper at 300 deg. but I don't think that my other blades were that hard to start with. I guess that by tempering them a second time I really haven't helped them any have I?

Mike
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  #4  
Old 02-10-2003, 02:31 PM
Jerry Hossom Jerry Hossom is offline
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According to Crucible Steel, hardening at 1850F and tempering at 300F should give you Rc62. A fast quench may up that a point, but certainly not get you to Rc65. What was the hardening temp? Tempering at 500 should bring it down to Rc60, according to the chart.


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  #5  
Old 02-10-2003, 03:11 PM
jethro jethro is offline
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Jerry, the 65 was aftrer the air quench, before the first temper. We took it to 1850 and soaked for 45min. I had to run after they were cool, so I did not get to test them after the first temper. I guess I am probably OK with two temperings of 300 deg. for two hours each.
The odd thing was, that I did five blades at the same time- three from one pc. of D2 and these two from a bar of D2. The other three came out at 57 rc. straight from the oven.

Next time I won't mix blades made from different sheets or bars.

Mike
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  #6  
Old 02-10-2003, 06:13 PM
Jerry Hossom Jerry Hossom is offline
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I'd say it's a pretty good bet that the three that came out at Rc57 are not D2. D2 should be Rc65 or higher after hardening at 1850.


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  #7  
Old 02-11-2003, 02:00 PM
Jan Dox Jan Dox is offline
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Uddeholm advises tempering at minimum 360?F and this for 2 cycles of 2 hrs and cooling to room temperature in between.Some even advise a third temper , so you did well tempering twice.
(Bob Dozier does triple tempers too)

Jan
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  #8  
Old 02-11-2003, 03:03 PM
jethro jethro is offline
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Thanks again Jan. Bob has always been kind enough to help me with this stuff. I actually decided to go ahead and call him today and got his opinion on the three knives that only went to 57 rc. It turns out that these were likely some A2 that they had laying around instead of D2. The two were from a bar that had been standing in a corner of my shop for a couple of years.

I will make sure I know what I am getting on any knife that I am making for a customer. I don't mind using A2 as long as I know what it is.

Mike
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  #9  
Old 02-11-2003, 09:55 PM
shgeo shgeo is offline
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D2 heat treat

I have been getting great results with D2 from Uddeholm (Flatground.com) by hardening at ~1870 degrees F, then doing an interupted oil quench finished in cold water. This gets the blade below the boiling point in 10 to 15 seconds. I follow this with a cold treatment on dry ice for 8 to 12 hours, then triple tempering at 400 degrees F for two hours each time.
The fast quench minimizes the grain size, to give maximun strength.
I have been using a similar technique on S30V hardened at 2000 degrees F with very impressive results.


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  #10  
Old 02-12-2003, 06:10 AM
Jerry Hossom Jerry Hossom is offline
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Shgeo, welcome to the forums. I'm curious how you are dealing with debarburization. I ass-um-e you're not using tool wrap with the oil quench.


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  #11  
Old 02-12-2003, 06:57 AM
shgeo shgeo is offline
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decarburizing prevention

I started using turco 2 from K & G recently, which freed me from unwrapping the steel foil and allowed the speedy quench.
The stuff seems to work very well. I dip normal size blades a couple of times until the coverage looks good and use a brush for larger blades.
You should use it in a well ventilated aream its pretty aromatic stuff. The container has no information on it and I just went by guess...


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  #12  
Old 02-12-2003, 09:21 PM
Jason Cutter Jason Cutter is offline
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Interesting info.

I'm learning heaps from this thread. I'm using D-2 heat treated by my local HT-er's who do a lot of work for knifemakers. But they won't harden / temper past 59-60HRC and they only do single tempers.

Those temperature ranges are simple enough for me to stick in my home oven for 2 more cycles at 400F at 90minutes each. Those guys also tell me that they don'gt subzero quench D-2 as they haven't found any extra gains, but will gladly do it on 440C, ATS-34 etc.

I gather than the extra 2 cycles will help the steel some, or is it a lost cause since the steel is already starting off at 59Rockwell after a single cycle at their shop ?

I also apply a coat of KGI Gunkote Moly which is baked at 325F, I'm presuming this won't change things much ?

Hope I'm not taking anything away from the original post.

Thanks. Cheers.


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  #13  
Old 02-13-2003, 07:05 AM
shgeo shgeo is offline
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D2 cont.

Jason,
Uddeholm reccommends a cryo/freezing treatment at -80 degrees C (dry ice temp) to gain 1-3 points HRC and also a minimum of 2 tempers for two hours each.
Some people like to snap temper D2 before the freeze, but that allows some of the retained austenite/carbon solution to form bainite and pearlite which I am trying to avoid. The reason is simple, there is a lot of carbon in D2 and it can and will form large carbide crystals. These create sites where crack-tips can nicleate, increasing the chances of chipping/adhesive wear. When snap tempered, D2 will show "orange peel texture" from polishing much sooner than with immediate cryo treatment. This is a sort of pitting that is from the carbides being plucked from the surface of the steel.


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  #14  
Old 02-13-2003, 08:35 PM
Jason Cutter Jason Cutter is offline
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Hmm...

I'd say that makes sense, but I don't know much about metallurgy or cryogenics. I might see if I can convince the guys to do the cryo quench before the first tempering cycle.

For those of you interested, the local HT-er's I speak of are Hills Heat Treat in Bayswater, Victoria, Australia (03) 97626233. Not only are they accustomed to knifemaking steels, they are great fellows and always ready with some advice and happy to accommodate your HT order. It helps that they are just around the corner from where I work and open at 6am on weekdays and also work on weekends !

Thanks shgeo. Cheers.


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  #15  
Old 02-15-2003, 07:34 AM
Jan Dox Jan Dox is offline
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Those professional HT's around the corner are a luxury, Jason.

Uddeholm and others in the toolsteel buisiness, be it steelmaker, distributor or heat treater told me the main advantage of of the cryo-treatment is maximum dimentional stability, which is most important in measuring tools like gauges or certain structural components (quote Uddeholm).
The guys at Doerrenberg advice triple tempers (MINIMUM 2)and say cryo is not needed for knives.
I want my D2 knives at 60HRC, final hardness. If up to 3 points are gained by cryo, do we have to temper at a higher temperature or not?

Now the tricky question: Is a knife, made of D2,at 60HRC, better with cryo and two tempers than a knife without cryo after tree tempers?
If so, in what specific aspect: edge holding, toughness, stain-resistance? more or less orange peel?
Would it make any difference for the user?

I know we're talking high level practical metallurgy here and the knives of D2 treated correctly eader way will serve very well (If the maker has done his job right of course).



Jan
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