why the hatred for S.S. blades

I really don't want to touch the stainless/carbon thing with a 10 foot pole so I will be brief in simply saying that folks really need to be very careful in confusing "grains" with "carbides", they are not the same and preferably carbides should be much smaller than grains, otherwise you either have a truly incredibly small grain or a truly gargantuan carbide. You can abrade a portion of a grain (it is simply a group of atoms with the same crystalline orientation) unless its boundaries are filled with carbide, it is more difficult to abrade a portion of a carbide which will prefer to just leave the material if the surrounding matrix is not as strong.

The only reason I posted this is that this grain/carbide size vs sharpness confusion is the sort of thing that attention hungry voodoo pushers love to take advantage of in their PR of how their thermoelectrophasemechanolgial heat treating methods produce ASTM grain size in excess of 32 and thus make the finest cutting knives in history. Yet the common thread in most of their steels is that they form carbides! With simple equipment and little insight carbides can be more a liability than a friend. very complicated and voluminous carbides are the stuff for controlled ovens not forges...

...thus, and this is just a hunch, the unpopularity of such a material on a site called "BladeSmith Questions and Answers".
 
That's the long way of saying CPM154 is better than 154CM because of the smaller carbides !!!
 
Kevin R. Cashen said:
...I will be brief in simply saying that folks really need to be very careful in confusing "grains" with "carbides", they are not the same and preferably carbides should be much smaller than grains, otherwise you either have a truly incredibly small grain or a truly gargantuan carbide...
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Thank you. I know there's a difference but didn't know how to explain it.
 
Kevin and Mete . Please do jump in here . I'm getting ready to purchase an oven for the reasons of having that temp. control . I would like to know . Just finished reading your stickies and my nose and ears are bleeding from trying to absorb it all , but tomorrow I will be ready for more . Throw in some stuff on the cryo treatment also please .
 
If you're going to get a furnace make sure you get one that has the capability to go a couple of hundred degrees above the hardening temperature.The complex steels like stainless are often cryo'd to get the best performance .Check your area for sources of liquid nitrogen.
 
mete said:
If you're going to get a furnace make sure you get one that has the capability to go a couple of hundred degrees above the hardening temperature.The complex steels like stainless are often cryo'd to get the best performance .Check your area for sources of liquid nitrogen.
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That I will do . I'm several months away from this happening , so I starting my education process early . I'm may also consider a change in steel choices which is why I'm reading all I can now .

It has been interesting and I thank all for there thoughts and input .
 
While we are here. Let me ask about liquid nitrogen verses dry ice solutions. I have been doing my D2 with acetone and dry ice and getting what seem to be great results. I now have a Ames hardness tester and a certified test block and I checked a couple of my D2 blades and they were slightly harder than the test block which is 63.31. I was amazed and rechecked everything. I am thinking of upping my temper although I have had no edge chipping except a tiny one on one blade when I cut a 16 penny nail in half. I have done it with several blades. But, am I am mainly wondering here just how much of an improvement would I get with liquid N2
 
Yes know that part but, I am wondering about how much improvement you get with the extra 200 f. Am I getting 70% of the retained and would I get 100% or am I getting 50% and would get 60%. Am I getting 85% and would I get 90%???????????????. Would an extra 10% equate to an a 10% better cutting knife when I am already over 63 RC and have the carbides to content with anyway?
 
ib2v4u said:
Yes know that part but, I am wondering about how much improvement you get with the extra 200 f. Am I getting 70% of the retained and would I get 100% or am I getting 50% and would get 60%. Am I getting 85% and would I get 90%???????????????. Would an extra 10% equate to an a 10% better cutting knife when I am already over 63 RC and have the carbides to content with anyway?
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Great question Jim, I wish I knew the answer.

Tempered at low temps, D2 can have as much as about 15% RA without cryo. So you're at least 85%. But I can tell you, 85% doesn't work well.

I know how you're doing your HT, and I believe your RA has to be less than a couple percent. Would going colder improve that? Probably a bit. Would a sudden dunk into -300 have other possibly negative effects? Probably a bit.

Mf is an antiquated concept, but for the sake of discussion I have to doubt it is lower than -100 on D2 austenitized at 1850. Are there other effects from going colder than Mf? Many people postulate there is, but I honestly don't know.

If you wanted to experiment with higher austenitizing temperatures where RA starts being a killer, the LN might make all the difference.

In my testing of D2, with dry ice, or with LN, I didn't see enough difference to be able to say there was a difference. To be a proper test the two blades would need to be from the same bar, and have the same geometry, and austenitized at the same time, and tempered after cryo at the same time to reduce random influences, and I haven't done it to that degree. But so far, I have seen little difference.



If your blades are not chippy, I say HRC 63 is great. Diamond Blade claims 64-66 on their edge. I have tweaked my process to get the performance I want in my cutting tests and I settled on 62 as a Rockwell hardness for D2. But 62 or 63 is splitting hairs. And a HRC number doesn't tell the entire story with D2. The rate of quench affects the type of carbides formed and the timing of temper and cryo affects RA. So two blades of the same hardness can have very different properties.
 
The most important thing to control RA is the hardenung temperature. Above the recommended hardening range can result in very high RA.Even within the recommended range the higher you go the more RA you get .Steels vary in their sensitivity to forming RA.
Never use cryo to make up for improper hardening !!! RA is tougher than martensite so it will reduce brittleness a bit, besides you won't eliminate allof the RA.Get to know a particular steel and decide what levels are acceptable to you.
 
I have two comments from the peanut gallery... first of all, D2 at 62-63 HRC with no edge chipping is VERY encouraging to me... second, you guys are filling up my notebook fast. :) Thanks, gentlemen.
 
One thing I will say. I do believe D2 is a great steel. I don't think it can be made into the sharpest steel. But, it will get sharp enough to shave hair and it will stay that way for a long time. You won't bend it very far. I believe every decent knife steel has its place. If I was making a knife I had to use as my only knife in a survival application it would not be D2. I doubt I will ever really need such a knife. I may need to field dress and quarter a couple elk and I know a D2 knife will do a great job as will many others.
 
would multiple undercooling quenches/cryo trip off more RA.. ? i'm not sure that the -300F is necessary.. where is the Mf of D2... (obviously below room temp )
 
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