Dry Ice - warped blades!

K

KenH

Well-Known Member
I'm posting this in the "newbie" section because that's how I feel today. I HT'd 10 blades today and all in dry ice. Dry Ice is new to me, but it's not rocket science. Put some chunks of dry ice in styrofoam cooler, poor denatured alcohol in to make a nice ice/alcohol bath - check temp, see it's at -95ºF and drop blades in for 20 to 30 minutes. That's not hard is it?

Well, I had a batch of 6 steak knife blades for the wife - matched set. Hung them on wires by tang, wasn't careful at all about how they were lying in bath. Some on side, some propped over chunks of dry ice. take them out 30 minutes later and I've got 2 good blades. The other 4 blades look like a gun barrel made to shoot around corners! Nice even bow.

I KNEW 13C26 and AEB-L (and 14C28N) blades were limber as a wet dish rag when first out of quench plates - after cooling and in dry ice bath I forgot to be careful to MAKE SURE the blades were even on edge to prevent any bowing. Oh well - Sandvik says not to re-HT their steels. Not only did I have these blades profiled, I had them grind to a finish shape ready to sharpen with 800 grit finish. Just a tad of work is all it was take after HT.

This was my first "batch" of blades to HT with dry ice. Always before, I take blade out of quench plates, lay flat on granite slab, then transfer to deep freeze for a -5ºF soak (this is usually clamped against a freezer side), then to oven for tempering. All this takes place on a nice flat surface so no bowing. Now, in the dry ice bath I was not careful so wound up with 4 bowed blades.

Note to self: DO NOT ALLOW THIS TO HAPPEN AGAIN!

Thanks for allowing me to vent {smiling sadly}

Ken H>
 
Calvin - I'm not sure there is any "real" difference with dry ice vs a -5ºF freeze which I've always used. Per the Sandvik, there is a small amount of difference. I was going to try it and see "IF" I could tell any difference.

I've got a Kershaw 1670 liner lock folder that I got cheap off Amazon with a 420HC blade. I've made a 14C28N with a dry ice treatment (my first ever with dry ice) to there is a real difference (as expected) to the 420HC blade. Today I did a CPM-S30V blade with dry ice treatment, and later plan to make a 14C28N blade with just a -5ºF freeze treatment. Then I can switch the different blades in the same folder and get "some idea" how just how much difference there is from one blade to the other. Nothing scientific, just an "idea".

The blades today were mostly AEB-L and some 13C26 - I only used those vs 14C28N to get the thin blades - 13C26 (.052") and AEB-L (.082") for some paring/steak knives for wife. I'd read/heard so much about the AEB-L "had" to have at least a dry ice to get max from it. Many folks claim 12C26 and AEB-L are the same material because they have the same chemical composition. I'm not at all sure that is the case - even with same chemical makeup, wouldn't how the manuf handled the making have an effect on the final result?

I do think 14C28N is by far my favorite steel - at this time. This may well be my last time with Dry Ice - at least until I get a good setup so my blades don't warp.

Ken H>
 
Ken

First, you can straighten those blades in temper with a three point clamp up. Second, Sandvik aren't the only metallurgical engineers in the world. Their alloys aren't that different from - say Crucible. Crucible says long soak. Sandvik says short soak. Crucible says at least dry ice. Sandvik says 'Meh!' Crucible says go ahead and retreat as long as you didn't overheat or decarb. Sandvik says don't.

I'm not saying either one of them is right or wrong - but I wouldn't be giving up on those blades. If they don't straighten in a couple temper cycles, just redo them. What do you have to lose? In most things we knifemakers do, there are a few ways to get it right. Go for it!

Rob!
 
Right now you are looking at ruined blades. If you do nothing you will still have ruined blades. If you repeat the heat treatment to straighten the blades the worst thing that will happen is that you will still have ruined blades. However, you might succeed.

Doug
 
I put two of the blades in tempering oven with 3-point clamp this afternoon - helped some, but still not perfect. I expect I will reheat treat the blades to get them straight before long - I've not tossed them by any means.

Rob - do you think even with the same ingredients, it's not possible for 2 different cooks to turn out different dish?

Ken H>
 
Keep trying the fixture tempering and increase the counter-bend, as a last resort you can try upping the temp by 10 degrees or so and take a small hit on hardness. Some blades are stubborn but if you're stubborn AND patient you can usually get them straight.
 
KenH said:
I put two of the blades in tempering oven with 3-point clamp this afternoon - helped some, but still not perfect. I expect I will reheat treat the blades to get them straight before long - I've not tossed them by any means.

Rob - do you think even with the same ingredients, it's not possible for 2 different cooks to turn out different dish?

Ken H>
Click to expand...

Of course it's possible - and steel is a good example. ATS34, 154CM and CPM154 and RWL34 are all essentially the same alloy. I haven't used ATS34 for years, but it used to suffer from internal inclusions. 154CM is an excellent blade steel with good performance. CPM154 is made with Crucible's CPM process and is widely respected as a super steel - which as it turns out, is twice as tough for the same hardness and takes an even better mirror polish that 154CM.

My post isn't about the steel. It's about the engineers. Engineers remind me of the Justices of the Supreme Court of Canada. They are so freaking impressed with their own wisdom that they are convinced the rest of the world is just plain wrong. :31:

In your example of cooks, the question might better be; "Can two cooks turn out the desired dish using different techniques?"

Good conversation. :thumbup1:

Rob!
 
Rob - Yep, good conversation. Your comment about Canadian Supreme Court Justices are dead on about the US Supreme Court justices.... INCLUDING the Federal judges.

Justin - I've got two blades in oven now and upped temp to 450ºF to see what happens. If I do toss them, no big deal - not much money involved in the metal (small blades), about as much cost in belts as the metal. We can call them "practice" grinding blades. This is the first time (told you I'm a newbie) I've ground so many blades in one batch. Helped me learn a good bit about grinding free hand. Just part of cost of education..... still frustrating {g}

Ken H>
 
Quick update - the two blades in oven tempered again at 450F came out ok - even pasted the wife's inspection, and she's picky! Looks like I've only got 1 - maybe two blades to scrape from the batch.

Lesson learned.

Ken H>
 
Good thread, sorry about your experience. If I'm not mistaken AEB-L and 13C26 are the same steels.
 
Nope, AEB-L and 13C26 are not the same steels - they are of similar (same?) chemical composition, but are manuf'd by different companies. AEB-L is a Uddeholm, (NOT Crucible) steel while 13C26 is by Sandvik. Sandvik really focus on small carbides in their blade steel.

Even though they are by different manufactur companies, I'm told the end result is very similar. I don't know. That's what gave rise to Rob and I discussing if two cooks used same amount of same ingredients, could they come up with a different dish. I think they could, but did Uddeholm, (NOT Crucible) and Sandvik come up with different steels? That is the question - both are good steels.

Ken H>
 
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No thinking about it - you are correct, it is Uddeholm for AEB-L. I just had Crucible on my mind. Note to self - check facts before posting.

Ken H>
 
I wonder why Sandvik advises against re-ht their steels...knowing the WHY-NOT's may turns out into HOW-TO's, so to speak ;)
In my opinion they sell their 14c28n with a very nice carbon/carbide distribution setup as optimal starting place for ht, and once you get martensite and go for another austenitization chanches are that those carbides starts to enlarge at the expenses of the overall martensite carbon. Every time you repeat you have fatter carbides and leaner martensite.
This is just my guess, of course the answer may instead be related to the H, and i don't know pretty much anything about it's dynamics.
 
I have wondered that myself - why not re-HT? Surely there would be a way to make it work, if a person knew what was involved.

Ken H>
 
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