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

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  #1  
Old 10-18-2010, 11:58 AM
Boshi Boshi is offline
 
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Differentially hardened D-2

I've been experimenting with differentially hardening air hardening steels lately. This is my latest experiment with D-2. It's almost there. Body is in the mid 40's RC, Need the blade edge up a bit more though it's in the mid 50's. BTW this is etched with nitric acid. The high chromium carbide count in the hardened area resists oxidation so the hard blade area stays shinny while the rest gets gray.



One interesting thing to note. Conventional D-2 has a natural tendency to form a wootz pattern because of the high alloy & high carbon content especially vanadium. In the transition area a pattern can be seen because it lacks the chromium carbides but still has a high iron carbide content. As any bladesmith who has tried to buff D-2 to a mirror polish will tell you, It always ends up with an ?Orange peel? texture to the surface. That is the wootz-ish patterning showing through. If they were to etch it with a chromium cutting acid they would see a basic element banding seen in wootz steel. This can be enhanced by (room temperature) cold forging the bar prior stock removal. Cold forging can also be done after rough shaping a blade by stock removal. A hot forged blade will tend to be too dense & work hardened to deform enough to enhance the patterning. This work extremely well on any conventional steel with a reasonable amount of Vanadium. Molybdenum will also enhance the ability of the carbides to form in linear bands. And if you don't use a stainless it's even easier. There is at least one maker that uses this method to manufacture Wootz from conventional bar stock. Basically all you need do is bang the crap out of it with a hammer, grind it to shape, do factory recommended heat treatment, polish & acid dip. ?Poof Wootz.?
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Old 10-22-2010, 04:48 PM
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Ed Caffrey Ed Caffrey is offline
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Interesting....I don't know what your experience level is, but many folks have tried differentially heat treating D2 in the past, including myself, and the steel just does not lend itself to that process. I can only speak for me, but assume most others found the same thing.....when attempting to differentially heat treat D2, there is always some undesirable characteristic that manifests itself as a result of attempting to differentially heat treat D2...and that usually far outweighs any perceived advantage.

Even though the body might read out in the mid 40s RC, it will be VERY brittle and will generally be fairly easy to break. I'm not trying to discourage you, just trying to relay experience.


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Old 10-24-2010, 10:44 AM
Boshi Boshi is offline
 
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Thanks for the input. I've been studying blades & blade making for around 20 years. Been making for about 15 years.

Because this was just a test blade I did an impact test on the softer areas to test the toughness. I struck with force using a ball peen hammer. The ball end dented the steel much as one would expect of a standard "right out of the mill" bar would. No signs of cracking or chipping were seen.

My previous attempts have been unsatisfying to say the least. Because D-2 is such a deep hardening steel even a standard edge quench won't do the trick as I'm sure you know all to well. So I started playing around with different ideas to over come the strengths & weaknesses D-2 has that keep it from differentially hardening, & showing a distinct transition.

Obviously I haven't nailed it at this point, but I think I've come up with a method that will do it. No doubt it needs some fine tuning, but if it does work, it's a very reproducible method. Probably even mass producible.

I think I'm on the right track at this point, but obviously not to my desired results yet. Thanks again for the input. I know the odds are against me pulling this off, but hey I love a challenge.
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