Aebl trouble

mnavarro

mnavarro

Joined
Nov 21, 2013
Messages
288
I made a couple drop points in aebl and think I overheated them. I did an oil quench at 130 degrees. . The problem is that when I went to grind them out the blade portion of the blade seemed to loose its magnetism. Everything behind the part I did not quench still had its magnetic properties.

I have a small paragon kiln. I wrapped them in foil, and held them at 1975 for 9 minutes exactly.
I tempered at 450 for 2 hours. What do you guys think happened? I would appreciate your feedback.
Thanks
 
At high temperature , above the Curie temperature of about 1400 F , it will be austenite [non-magnetic ]. When you quench it will convert to martensite which is magnetic ! Did you somehow miss the quench ?
Did you quench in foil ? Did you quench in foil but not in plates ?
 
I took them out of the foil and quenched them in oil. It took no longer then 30 seconds to cut the foil package and quench them.
The thing that is interesting is that the handle portion of the knife is still magnetic and the blade portion which I quenched is not. I don't know I'm going to try to reheat treat the blades and see what happens.
Thanks for the feedback
 
It sounds like the blade has a very high amount of Retained Austenite. Austenite is non-magnetic.


Did yo do any sub-zero treatment after quench? There has been some discussion that AEB-L doesn't need it, but as far as I know, it benefits greatly in RA reduction by sub-zero treatmenyt. The hardness goes up considerably, too.

Did you fully quench the blade under the oil?

Are you sure it is AEB-L?


Your 9 minute soak seems very short to me. Wast there a pre-soak?
I have my AEB-L doene by Peters now, but I used to place the blades in a pre-heatyed oven at 1500F and equalize, then ramp to 1920F and soak for 30 minutes, then ramp to 1975F and soak for 15 more.
 
That is weird, but i had similar issues normalizing an hypereutectoid steel. Also i tought i got significant RA since i was waiting long time the steel to regain magnetic as it was cooling to black...eventually it become magnetic but with a weak force.

Perhaps one could come up with a magnetic testing procedure to measure the RA amounts ;)
 
You have retained austenite. You need to do a sub-zero or cryo quench from that temperature. Try 1925-1950 aus temp if you are not doing a sub-zero quench.

Pre-heat your furnace to the temperature you want, place the blade in at that point, soak for 7-8 min at temp, quench. Total funace time is ~12-14 min.

Longer soak or ramp times will cause more RA. Double seal the foil, leave blade in foil, quench foil and blade in water for a faster quench. A faster quench = less RA.

Temper at 350-375
Hoss
 
Thanks Devin, I had forgotten that you have shared your procedure with lower soak times and no pre-heat.

The need for sub-zero is almost assuredly where his problem lies.
 
Yep, most stainless and alloy steels benifit from longer ramps and soaks. Aeb-l has very little or no primary carbides that require longer soak times to dissolve.

Hoss
 
Thanks for all the feedback. I think for now I will send out stainless blades for heat treat since I do not have the ability to do a sub zero quench. I will try a few though with Devins, process.
Thanks you all again.
 
If you only do 1 or 2 blades, subzero can be as simple as putting blades between 2 slab of DI - Crunchy SubZeroSteel Sandwich© ® - hahaha. Grab some DI at Praxair. I wouldn't waste time/resource cutlery ht aebl and other high alloy steels (no secondary hardening temper option) w/o subzero or cryo quench.
 
Locally, two grocery stores carry dry ice. If the is a Harris teeter or Weis near you, see if they have DI

Sent from my XT1095 using Tapatalk
 
I've had to battle warpage when using slabs of dry ice.
A much better backyard method is to pulverize it and either make a slurry with the recommended solvent, or simply make a container of "snow."
I use a welding rod can, packed with dry ice snow- results seem very good.
 
Having liquid mixed with the dry ice is more efficient at cooling the blade. I use denatured alcohol.
 
I have a praxair that's near me so I will have to check them out this week. I am going to heat treat these two blades again and try the dry ice and denatured alcohol method. I have done aebl blades in the past the same way and the results turned out good. This go around I was just confused on what happened.
Either way thanks for all the great feedback. I Really appreciate it.
 
Sub-zero done with dry ice needs to be a liquid slurry. Use denatured alcohol and crushed dry ice. It will not work the same as a solid or powder.

Place liquid in a container and put in the crushed dry ice. Place blade in and let sit for 5-10 minutes. That is all the time needed for sub-zero treatment. Containers like a six-pack cooler or a long shallow pan ( I use a "whole fish" pan) work excellent.

The alcohol can be used over and over again. Let the dry ice all sublimate, then pour back in the can. Put the cap on a little loose and let it warm back up to room temp. Shake the can a bit to release trapped CO2, then tighten the cap. I label the can "HT".


What is going on in stainless steels that needs a sub-zero treatment is that the martensitic finish point (Mf) is not around 200°F as it is with carbon steel. It is around -95°F. A dry ice slurry at around -100°F will reach this temperature just right.

Cryo, done in liquid nitrogen at near -350°F, will first reach the Mf, and then go down lower to gain some other effects on the carbides. Cryo is a good thing on most stainless steel.

AEB-L has low carbon and relatively low alloying, so the primary carbides are not an issue. Cryo won't hurt it, but it won't gain anything over dry ice.
 
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