AEB-L Soak time

[JTknives]

Any one looked at the 13C26 data sheet lately. 13C26 is the same as AEB-L but made by sandvik not uddeholm. The general word on the street is 15min soak at 1940°. But thy say 3min at 1940°

 

[Larrin]

Those are required times for a "belt furnace" where the required time is highly sensitive; more time requires slowing down the furnace. You can visualize these by thinking of an oven in a sandwich or pizza shop where they stick it in one side and it moves through until it is "cooked" on the other. As it states there, it is 3 min for a 1.0mm thickness. However, this page lists different times based on thickness: http://smt.sandvik.com/en/products/...ening-programs/sandvik-13c26-piece-hardening/

In a "batch" furnace, which is more typically what a knifemaker would use, Sandvik recommends 30 minutes: http://smt.sandvik.com/en/products/...ening-programs/sandvik-13c26-batch-hardening/ In this case they are recommending a relatively long time to ensure the piece is sufficiently heated through and has time for dissolution of carbides, etc. The time is likely longer than necessary but grain growth is minimal as long as the austenitizing temperature is correctly chosen (not too high). Notice the recommended temperatures in the hardening guide for a belt furnace are higher than for batch hardening, likely to compensate for these differences in holding time.

 

[Greenberg Woods]

D DevinT

 

[JTknives]

Those are required times for a "belt furnace" where the required time is highly sensitive; more time requires slowing down the furnace. You can visualize these by thinking of an oven in a sandwich or pizza shop where they stick it in one side and it moves through until it is "cooked" on the other. As it states there, it is 3 min for a 1.0mm thickness. However, this page lists different times based on thickness: http://smt.sandvik.com/en/products/...ening-programs/sandvik-13c26-piece-hardening/

In a "batch" furnace, which is more typically what a knifemaker would use, Sandvik recommends 30 minutes: http://smt.sandvik.com/en/products/...ening-programs/sandvik-13c26-batch-hardening/ In this case they are recommending a relatively long time to ensure the piece is sufficiently heated through and has time for dissolution of carbides, etc. The time is likely longer than necessary but grain growth is minimal as long as the austenitizing temperature is correctly chosen (not too high). Notice the recommended temperatures in the hardening guide for a belt furnace are higher than for batch hardening, likely to compensate for these differences in holding time.

I don't think that's correct. I think thy have 2 different times because in a batch there are a bunch of blades together and the time for the oven to come back up to temp is longer. Where a belt does not have a large mass to heat all at once. Also thy only have one data sheet for it. And it says 1940deg with a hold of 3 min. Yes that's 1mm thick, but its still saying that 13c26 does not need much of any soak time by default. Other steels are X min plus X per inch of thickness. This does not say that, it basically says as the steel gets thicker the time goes up. That accounts for the time it takes for the thicker stock to come up to temp. I would waiger a bet that at least in my situation I'm more like a belt furnace. My oven has soaked for 1hr and is nice and even. I open the door quickly and insert the bade. The temp drops but comes back about 2min later. i set the blades right next to the thermal probe. it seams like the temp drop is due to the blade not the exchange of air. If I open the door and close it without a blade the temp pops right back up. The higher temps seem to be for the steel that get the cold treatment. The non cold treated steel are very close from batch to belt. The way I'm reading it, thy are accounting for the time it takes to heat from cold steel.

 

[Larrin]

I don't think that's correct. I think thy have 2 different times because in a batch there are a bunch of blades together and the time for the oven to come back up to temp is longer. Where a belt does not have a large mass to heat all at once. Also thy only have one data sheet for it. And it says 1940deg with a hold of 3 min. Yes that's 1mm thick, but its still saying that 13c26 does not need much of any soak time by default. Other steels are X min plus X per inch of thickness. This does not say that, it basically says as the steel gets thicker the time goes up. That accounts for the time it takes for the thicker stock to come up to temp. I would waiger a bet that at least in my situation I'm more like a belt furnace. My oven has soaked for 1hr and is nice and even. I open the door quickly and insert the bade. The temp drops but comes back about 2min later. i set the blades right next to the thermal probe. it seams like the temp drop is due to the blade not the exchange of air. If I open the door and close it without a blade the temp pops right back up. The higher temps seem to be for the steel that get the cold treatment. The non cold treated steel are very close from batch to belt.

If you email Sandvik and they same the same thing I did, will I still be wrong?

 

[Larrin]

Sandvik says that piece hardening in a furnace is similar to a belt furnace. What you are learning about here is how temperature is typically more important than time and that things tend to "saturate" where a range of times are acceptable.

 

[DevinT]

JT, Larrin is my oldest son. His first word as a baby was not ma-ma or da-da, it was aeb-l, that's how long we've been talking about aeb-l. He has a PhD in metallurgy and currently works for US Steel developing new steels.

Steels in the annealed condition have twice the carbide volume as heat treated steels. The reason for soaking steels at temp before quenching is to dissolve certain types and amounts of carbide so that carbon and alloy go into solution. Carbon goes into solution to allow hardening, chrome goes into solution making steels stainless etc.

Steels with large amounts of primary carbide require longer soak times because of thier size and type. In the manufacturing of aeb-l, the carbides dissolve and precipitate back as secondary carbides, which means they are small and don't require the same amount of soak time as D2. Most carbon and low alloy steels also have secondary carbides which is why they don't need much soak time.

Temperature is more important than time but too short a soak will result in under hardening. Run a few coupons at different times to determine what is best for your furnace.

I run two furnaces, one at 1600', and one at 1950'. I pre-heat for 20 minutes at 1600' and then transfer to the higher temp for 8 to 30 minutes depending on thickness and overall size.

Hoss

 

[JTknives]

Thanks, I was just confused by what I was seeing.

 

[DevinT]

Thanks, I was just confused by what I was seeing.

Thanks for all of your contributions here on the forum, you're very unselfish.

Hoss

 

[Ken H>]

Good discussion on both sides, and with Hoss and Larrin chiming in on the technical aspects, we mere mortals get LOTS of good info. Thank you to Hoss 'n Larrin.

JT has been such a good contributor to the forum I've learned a lot from him also. Ya'll handled the discussion in a very polite manner - I LOVE to see that happen in a forum setting.

Ken H>

 

[Darrin Sanders]

OOPS, wrong thread. Sorry guys.

 

[JTknives]

I love the forum and want to contribute as much as I can. Thanks for the kind words.

Yeah I just downloaded the PDF and was going through it and was a bit stumped by the time listed. I personally have been doing a 12min soak. 2 to heat and 10 at temp. Been working real good. But thank you for the general gloves lol

 

[Larrin]

This is an old thread, but someone reminded me of it today while saying I had been unnecessarily confrontational. After reading through it again, I agree with his assessment. I don’t remember feeling particularly argumentative at the time, and this may have been an issue where emojis would have helped the situation. However, our actions are more important that our intentions, and I apologize for being impolite.

 

[JTknives]

All is good man, no worries. I did not think you where being impolite at all. I know how easy it is to take things the wrong way on the forum. I have adopted the philosophy that unless told otherwise everyone typing out of kindness. Life is to short to get all worked up over what you think someone might have ment.

 

[Stacy E. Apelt - Bladesmith]

As said, Larrin is correct.
On thing that knifemakers get confused is that the parameters used for industrial process are not for the equipment we use. JT's assumption that there is a recovery time because they HT in large batches is such an assumption. In a little knifemakers kiln, that would be so. In a industrial belt furnace, HTing thousands of pieces, the temp never changes a bit. Those ovens are HUGE compared to what we think of as a HT oven.

 

[Stromberg Knives]

Since Sandvik is kind enough to describe their definition of the belt furnace and batch furnace setups, why not show it for everyone to read.

Furnace types
Knife steel can be hardened in two different ways, depending on the equipment used:

• Piece hardening in a small furnace, or on a belt furnace. The hardening procedure, times and temperatures, is the same for both furnace types.
• Batch hardening of larger batches, e.g. in a vacuum furnace.

Regardless of the method used, the purpose is the same: to heat treat the material to increase hardness and improve corrosion resistance.

Piece hardening
Piece hardening of individual blades in a small furnace or a belt furnace is normally carried out by heating the steel to 1080°C / 1976°F (for Sandvik 12C27) and the time during which the blade is held (soaked) in the furnace depends on the material thickness.

The table below shows the approximate soaking times in the furnace as a function of the material thickness. When the blade has been soaked in the furnace for the specified time, it is removed and immediately quenched, preferably in oil intended specifically for quenching.

In belt furnaces, the pieces are either placed together on a long belt, or the knife blades are placed on a mesh belt that transports them through the furnace. The most critical operation for hardening in a belt furnace is quenching, which should be given extra attention for an optimal result.

Thickness Thickness Time in furnace
mm in. minutes
Soaking times (approximate)
2.50 0.100 5
3.00 0.118 6
3.25 0.128 7
3.50 0.138 8
3.75 0.148 10
4.00 0.157 12
When the blade has been soaked in the furnace for the time specified above, it is removed and immediately quenched, preferably in oil intended for quenching.

In belt furnaces, the material is either placed together on a long belt, or the knife blades are placed on a mesh belt that transports them through the furnace. The most critical operation for hardening in a belt furnace is quenching, which should be given extra attention for an optimal result.

Batch hardening
When larger batches are hardened, there is a risk of temperature difference within the batch. The material should therefore be given a chance to achieve uniform temperature by soaking it at 850°C (1562°F) during the heating process. The material should also be given a longer soaking time and slightly lower temperature in relation to piece hardening.

Quenching is equally critical in this type of hardening, and it is very important that the furnace equipment has high cooling capacity in order to meet the requirement for lowering the temperature to 600°C (1112°F) within 2 minutes.


https://www.materials.sandvik/en/pr...teel/hardening-guide/the-hardening-procedure/

 

[JTknives]

That looks like thy are grouping us into the belt category.

 

[Larrin]

The plot thickens!

 

[javand]

That looks like thy are grouping us into the belt category.

It also seems to imply (the way I'm reading it) that equalizing temp at 1562, is only necessary for "batch" hardening. Which honestly makes sense to me.

 

[JTknives]

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.