AEB-L Soak time

[Stromberg Knives]

So if I read that correctly it says pop it in the oven and start the timer for the time listed next to the thickness.

That’s how I understand it also.

 

[Ken H>]

So if I read that correctly it says pop it in the oven and start the timer for the time listed next to the thickness.

I'd think it means to pop in oven, then once the temperature has recovered to spec'd temp, THEN start the timer. If your oven doesn't lose any heat and is still at spec'd temp after closing door, start timer. My oven (18" Evenheat) will drop temp and take a few minutes to stabilize at spec'd temp.

 

[DevinT]

Soak time will vary from furnace to furnace.

Hoss

 

[javand]

Soak time will vary from furnace to furnace.

Hoss

Yeah definitely, I've always considered "soak time" to be the time after the furnace temp has finished bouncing, i.e; it goes down when I open the door and place the piece inside, then it comes back up and overshoots, then it goes back down to slightly below the target temp, once it rebounds this time, that's when I start my soak timer.

 

[J. Hoover]

I heat treat AEB-L at 1960F. with a five minute soak time. For the steel to be at it's best it needs a cryo in liquid nitrogen or dry ice and denatured alcohol for thirty minutes between tempering cycles
I have noticed that on thin blades, less than .100 the blade may remain flexible as everything settles in after heat treat for several minutes. Once the cryo and temper cycles are complete the blade RC is good. Temper for two 1 hour cycles minimum.
If you are not using cryo with AEB-L your not getting the best out of the steel it needs it.

 

[JTknives]

So speaking about rebound would it not be better to do a dry run with out any steel in the oven to see what the rebound is without the cold steel in the oven then add that time to the time for the knife. This way you know how long it takes to get back to where the oven should be with a cold knife in the oven. It's my understanding that thy take into account the time it takes for the steel to heat up and that's included in the total time. With thin blades thy heat rather quick and could be close to temp by the time the oven is done rebounding which then means if you then held the required time you would in fact soak for longer then thy say.

 

[javand]

So speaking about rebound would it not be better to do a dry run with out any steel in the oven to see what the rebound is without the cold steel in the oven then add that time to the time for the knife. This way you know how long it takes to get back to where the oven should be with a cold knife in the oven. It's my understanding that thy take into account the time it takes for the steel to heat up and that's included in the total time. With thin blades thy heat rather quick and could be close to temp by the time the oven is done rebounding which then means if you then held the required time you would in fact soak for longer then thy say.

My experience (and I believe this is what Devin was alluding to) is that rebound; is highly dependent of each oven. I can't see how it would be possible for them to factor volume, wattage, cycle times, etc, into the "soak time" variable. Some ovens have enough mass, enough output, enough pre-heat, to make rebound nearly inconsequential (i.e. those belt furnaces, started at the beginning of the work day, and run until the end, or never shut down potentially the case of really large operations).

IMO, soak time is time at "actual temp", which in of itself can be somewhat vague, but bear in mind, that the tip of a thermocouple, is always going to be more responsive than a larger workpiece of metal. I view the rebound as representing the "equalizing" of that temp as heat is sucked out of the tip of the TC into the work, before it's stabilized.


Obviously, when we start getting into the specifics of each kiln, it gets murky, where even TC type, placement, mass, up-time, cycle rates, workpiece dimensions, etc, can all be a factor. I think the HT recipes provided by the steel manufacturers are just guidelines, assuming all things being equal, since that's the best objectivity that can be offered, in a world where they never are. It's up to the maker to figure out, with the best of their knowledge and understanding of their equipment and process; When, they are actually, at heat.

 

[Natlek]

Some ovens have enough mass, enough output, enough pre-heat, to make rebound nearly inconsequential

Well whole inside of oven is refractory bricks so there is nothing to hold temp .I read that someone use to put inside THICK piece of steel to keep temp high when open/close door .. What if say floor and ceiling of oven have say 1/2 inch thermo-accumulation bricks / I don t know right word for that kind of bricks/ . Oven will reach the temperature more slowly but will have more constant temp. in open/close ... Sorry for off-topic

 

[javand]

Well whole inside of oven is refractory bricks so there is nothing to hold temp .I read that someone use to put inside THICK piece of steel to keep temp high when open/close door .. What if say floor and ceiling of oven have say 1/2 inch thermo-accumulation bricks / I don t know right word for that kind of bricks/ . Oven will reach the temperature more slowly but will have more constant temp. in open/close ... Sorry for off-topic

The inside of most knifemaker kilns are, many industrial ht kilns I've seen have some hard brick furniture, and are typically better insulated, all of which will affect things.

Adding thermal mass will make getting to initial target temp slower, but will aid in rebound time and should soften the swing of temp, as long as you insulate well on the other side of the thermal mass. Hard fire brick of some kind (non-insulating, i.e. acquire heat), would be a good choice probably yes.

My old Blue M kiln has an entry (door opening) of specially made hard brick, to keep it from getting damaged, and is insulated beyond that, it also has ceramic element modules around the the wires, which add thermal mass also. This kiln is so well insulated that even after I shut it off and come back the next day, it's usually still very hot (hundreds of degrees F) the next day, unless I leave the door open for a while. It rebounds much quicker, and with less extreme, because of the extra mass also, compared to my knifemaker's kiln which is similarly sized, in terms of chamber size.