no Sub zero AEB-L?

Pablo is correct !

It isn't a sin to have RA . RA adds some toughness to the steel and is desired in certain applications .A problem is to have RA convert to martensite , especially in large amounts ,during use as untempered martensite is brittle and invites cracking !
 
Exactly. RA isn't something to worry about in knives. Knife steels that HT at 1400-1500F don't create high levels of RA in the quench. I feel that the gain in toughness balances out any loss in hardness. I have no problem with 3-5% retained austenite.

I didn't reply to Stuart's marshmallows analogy, but that isn't isn't how it works. It is all steel. The austenite is tougher and the martensite is harder It is nothing like rocks vs marshmallows. It is more like cement with quartz rocks and granite rocks. The two combine in a matrix to make the steel blade stronger and the edge may actually hold up longer due to less micro-chipping.

I failed to point out the one major advantage of placing all your knife blades in the freezer overnight - You will be able to find them in the morning. I sometimes spend 20 minutes trying to find where I left them the night before.
 
I sometimes spend 20 minutes trying to find where I left them the night before.
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only 20 minutes? You're doing good - I've gave up, then find them later {g}
 
Ken H> said:
Link didn't work for me - what steel are you using?

Ken H>
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Eh, it should work. Sharing is set to view for everyone. Try this link and find in Tempering graph. Usually I use N690, N695, Elmax or Sleipner. All Bohler/Uddeholm steels with similar tempering characteristic.
 
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The literature describes retained austenite as being "soft but tough" compared to the martensite matrix around it. And again, from what I understand RA is never a good thing at the edge of the edge of the edge of the...the apex. For a number of reasons. It isn't as hard as even the martensite (not to mention the carbides), it will convert over to untempered martensite over time or if shocked by impact, both of which aren't ideal for a fine edge apex.

I wouldn't want 16-18% RA in my A2 or D2 blades. The idea is to HT and get rid of as much of it as possible. Some applications it may be OK to leave that much RA, like a sword or machete. But not a kitchen knife.
 
Jesenius said:
We call it secondary hardness. I do it for almost all of My knives. I don't hunt for highest hardness so 56-60 Rc is good for Me. I temper at about 530°C (986F) at least 2x 2 hours. As You can see on the chart no cryo or sub-zero is needed for good made blade.

https://lh3.googleusercontent.com/7...aOTtrlpaUQL7X2JQc9BwDIC2DuYod5YA=w502-h479-no
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Thank link worked nicely - I went back and checked first link and it still gives a blank page for me using Chrome browser. Might be a setting in my browser or something if everyone else is getting the link. BUT - I did get this last link you posted.

Thank you,

Ken H>
 
samuraistuart said:
... Some applications it may be OK to leave that much RA, like a sword or machete. But not a kitchen knife.
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Why not kitchen knives? What is so special on them? Do You like damascus kitchen knives? I do. They are made from mixed steels, one (or more) harder and one (or more) softer. I will compare them to knives with some percent of RA. RA don't stay at the edge it's mixed through whole steel. imho... :)
 
When I found out that CPM 10V increased wear resistance over 100% with cryogenic treatment, I was impressed.
 
Jesenius said:
Why not kitchen knives? What is so special on them? Do You like damascus kitchen knives? I do. They are made from mixed steels, one (or more) harder and one (or more) softer. I will compare them to knives with some percent of RA. RA don't stay at the edge it's mixed through whole steel. imho... :)
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I believe that is due to the desire for kitchen knives to be both harder and with a thinner thickness overall.
 
Kevin's answer is along the right lines. And actually, I take my comment back about swords and RA. Ideally, you don't want a steel with RA in it, simply because you need to impart some sort of "toughness". The correct approach would be to choose a steel for the application, like a eutectoid steel that will essentially have ZERO RA to begin with. It isn't the best approach to take a hypereutectoid steel, and let it have some RA in it, for added "toughness".

Ideally, for knife applications, you want to reduce RA to as minimum of a level as you can practically/efficiently accomplish. RA is detrimental to a fine, stable, hard, thin edge. How much? Depends on the RA %. 5% probably not so noticeable. A2 without sub zero/cryo, or D2 without sub zero/cryo, will have almost 20% RA. No thank you. Best to do the sub zero/cryo get it down as much as possible. Yes, RA is mixed thru the whole steel, just as much at the apex of an edge as it is at the spine, as far as I know.
 
Kevin, Samurai: Thank You for explain to Me. Could You take a look at this blade (closer look)? I made this knife five years ago and it wasn't treated to secondary hardness. I think that bright lines is RA and I guess it is between 15-20%. I performed all My standard tests (cutting, chopping, batoning, bending) and I didn't felt any weakness. What is Your guess, what You think about it?
 
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Jesenius said:
Kevin, Samurai: Thank You for explain to Me. Could You take a look at this blade (closer look)? I made this knife five years ago and it wasn't treated to secondary hardness. I think that bright lines is RA and I guess it is between 15-20%. I performed all My standard tests (cutting, chopping, batoning, bending) and I didn't felt any weakness. What is Your guess, what You think about it?
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That's not retained austenite.
 
Thank You for answers. So My second guess is that lines are alloys as Stacey wrote. Because it is not PM steel they are not very well mixed. Am I correct?
 
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As a follow up to my original post. I followed Devin's recipe on my last batch. I just took it to a local machinist and he tested the hardness. With a 350°F temper I was shooting for RC of 58. Guess what? 58 right on the money. I know this doesn't address the retained austenite issue. Regardless, the validation made my day. Thanks for all the input.

74c43f5456a20d23b45dda52be1b481b.jpg
 
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