A2 blades split down the middle at the butt end after heat treat

Proper terms - dry ice gives you "sub-zero quench " [~ -100 F ]
- Liquid nitrogen gives you "cryo " temperature [ - 300 F ]
A complete metallurgical exam should be able to find the problem. Many steps could cause that problem but probably it's the steel, inclusions or other non-homogenous things .Send it to Aldo.
 
Crazy! I wouldn't a' believed it if I hadn't seen it! Deffinately a problem with the steel prior to your work.
 
I just had a great conversation with Aldo. He gets his A2 from Latrobe. Where Latrobe gets it, who knows. We discussed cryo and the time needed. I left mine in the cooler until the dry ice melted. He will talk to Peters tomorrow to get some input and get back to me. I'll keep you guys informed. Thanks to Aldo for his help.
 
What was your aust. temp.? and how long was the soak.?
A-2 is a high Mn. steel. High Mn. steels seem more prone to
tear themselves apart than lower Mn. steels.
I've seen this occur with O-1, Cruforge-V, and 1084/15N20 Damascus....
all were High Mn, and all occurred during extended soaks at -105f.
 
I held the steel at 1750 for 45 minutes. I kept the knives in dry ice until the ice melted. Around 8 hours in a cooler with denatured alchohol
 
I remember not to long ago a member posted a pic of an A2 blade that just about came all the way apart down the middle. I was looking for the post but could not find it. I have never had a problem with A2 and it's allways been quite stable for me. I personally don't see how a heat treat problem would cause that. I have seen blades warp so bad that thy snap but across the spine not along it.
 
Your soak is probably about 20 min too long, according to Carpenter.
Also, try your dry ice treatment w/o liquid. Insulate the blades w/paper towels
and sandwich them between two layers of dry ice for 2 to 4 hours, and then check.
A slight insulation will inhibit cooling to be more in line with proper quench rate
for A2.
 
I get different opinions on the soak. I've read that it's 30 minutes for 1/8 inch and 45 for thicker. These are 1/4 inch. To take it even further, the blade edge is nowhere near these measurements. I find 45 minutes a little long as well. If the goal is simply to ensure the steel is heated throughout (plus a little more), then it is definitely too long. If you think about it, the steel is already been soaking (to an extent) on the temperature rise to 1750. Depending on the ramp rate of your oven, the steel would be very near the soak temperature or at it if you do your final soak at the high end of the acceptable soak range. There are so many opinions out there. When Aldo speaks to Peters Heat Treat today, he is going to give me a call. I will update all of you guys on the conversation. As far as the dry ice goes, again if you think about it, once the lid to the cooler is closed, the inside temperature of the cooler will become the temp of the dry ice and hold it there until it completely sublimates back to gas. Technically no liquid is needed since air is a liquid and will surround the blades. I have read only one opinion that does not recommend liquid such as acetone, kerosene, or in my case denatured alcohol. I would be more than happy to simply use the ice if it's capable of doing the job. Which theoretically it should be.
 
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I'd still say it's a steel issue... I forgot an A2 blade in my HT oven once, and it soaked for an hour and a half before I took it out. Since it was already an experiment at that point I dipped it in my dewar overnight. No problem what so ever. I carried that knife for about a year and it held up great.

That was a piece of Starrett A2 if it makes any difference
 
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