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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 09-16-2017, 02:39 PM
epicfail48 epicfail48 is offline
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Heat Treating AEB-L stainless

I'm sure this has been discussed before but I couldn't find much, can anybody recommend a good heat treatment regiment for the aforementioned steel? I'm just getting started with stainless, different beast from the 1095 I usually play with. So far my planned process is as follows, blades are .110 thick AEB-L sourced from aldo;

1. Profile and rough grinds the blade and bevels
2. Wrap knives in stainless steel foil with a little paper in there to eat up excess oxygen
3. Place knives in electric kiln preheated to 1950, soak for 15 minutes at temperature Here's the first thing I'm wondering about, a few of the HT recipes I've seen recommend a preheat at ~1500, then ramping to 1950. My kiln is a little slow on temperature ramps, I'm hoping skipping the preheat won't compromise the results.
4. Quench. Little fuzzy on this one too, from what I understand I can go air, plate or oil quench. Of the three I'm inclined to go oil, Parks 50 in particular since that's what I have. I'm wondering if that's too fast of an oil and I'm asking for warp or crack issues. I'm also wondering, can I go straight from the kiln to the quench, or should the blades be removed from the foil first?
5. Once blades are cool to room temp, soak in dry ice/alcohol bath overnight
6. Temper for 3 cycles at 300f to hopefully get 60-61 RHC
7. Finish grind, polish

So, can anybody see any issues with that process, or answer either of those questions?
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  #2  
Old 09-18-2017, 01:17 AM
epicfail48 epicfail48 is offline
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Still looking for tips, if anybody has any to share
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  #3  
Old 09-18-2017, 10:18 AM
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cnccutter cnccutter is offline
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Good morning.

Your right, Stainless is a beast of its own.

The 1500 step is usually put in the give your blade time to catch up and have a even temp through the core of the steel. Then ramp up the the top temp where you hold for a short time to give the blade metal structure time to fully go through its change.

I would also caution you about putting a wraped blade into a preheated oven. The wrapping on the blade sometimes wants to puff up. I've seen them actually tear open slightly which abviously voids the air tight goal, ha.

The question has also been brought up as to what kind of stress we are putting the blades under putting them into a heated oven? Could it lead to a warped blade?

You will find blade smiths that heat treat just like your laying out and have great success with it. My 2cents would be for you to go for it and test your recipe. Keep lots of notes and test your blade afterward.

You might want to fill in your profile a bit and at least a first name. You might have a maker right around the corner from you that you can talk with.

Erik
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Old 09-18-2017, 01:27 PM
jimmontg jimmontg is offline
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Epic, if you are quenching in oil, cut off the end of the foil to let the part drop into the oil is what I've been told to do (MUST have a METAL quench tank, will melt thru plastic) and as I had good snips it was easy, but regular household scissors may not be up to cutting through multiple layers of stainless. Fold up the foil so you have 4 layers (the creased edge will be 4 layers) and see if the scissors you have cut the end off with no problems and quickly, with as quick as you can being the most important thing. Leather cutting scissors work well too and be sure and pick it up by the folded foil at the butt end of the knife. I presume you don't have a hardness tester so the old standby of brass rod deflection test and skating a good file on the edge will have to do. Problem with the foil on is an uneven quench. I don't know about the foil on quench in oil as l have not tried with AEB-L. I've done plate quench with 440-C and the foil on, but that's another beast.

Now as for the dry ice I made a very thick walled ice chest for it (6") and it would last over two weeks if I didn't open it too much. If you are only doing 2 or 3 knives at a time you can simply put them in between two blocks of dry ice without the alcohol, dry ice is -105 F and AEB-L needs to be brought down to -95 and simply let soak through and remove and then temper. It is what I did because I only made 3 or 4 knives at a time and just leaving them in-between the blocks was more than sufficient, (they will make a snug imprint in the dry ice). You can leave them in as long as you wish if you are cooling your HT oven to do the temper, but once you let them come up to room temperature you need to temper them soon, I wouldn't wait to long as they might crack from internal stresses which is one thing the temper relieves. Oh oil should be about 120 degrees and then wipe and let cool in refrigerator and then freezer before the dry ice. It would be better than going straight from room temp to dry ice. 15 minutes in each and dry ice about 20 minutes just to be sure of soak thru. Check and straighten right after quench by hand is something I learned here and I'm sure it will work for this steel too, if not it doesn't hurt to try.

1975 is the sweet spot for this steel and hold for 5 minutes for the thickness you are using by the way, but with your slow ramp up speed you may be better served to watch the rise in temperature and see how long it takes to go from 1950 to 1975. If it takes much more than 5 minutes, like lets say 15, then remove and quench as soon after it hits 1975 would be my advice as overheating is possible. Temper for 2 hours at 400 and you should be in the 60+ HRC range. You can also temper twice at 325-50 for 2 hours, for the best effect put it in the dry ice between tempers. If the 400 temper is too hard, you can temper again for 1 hour at 400, I have had this metal come out too soft at 2 hours at 400 2x and I settled for the single temper and it was 61 HRC, we had a hardness tester. For some folks RC 61 is too hard, the 325 should leave you a point or two lower.

The 1500 soak is needed for temperature variation and again for .100 thick material about 15 minutes there. The slow ramp up is fine, a quick quench is where speed is needed. I used a strong magnet bolted to a rod to fish my blades out of the tank btw. If you use the house oven be sure and get a good thermometer to check it and a candy thermometer for the oil temp. An infrared temperature gun is best if you can afford one. They have some that are cheap and they only have a 2% accuracy range, but at 500 degrees that is only 10 degrees so I think that would be acceptable for a temper oven for this steel. Here's a link to one. The more accurate ones run significantly higher.
https://tempgunsdirect-com.myshopify.com/products/tgd-2

As you can see Epic there is more than one way to HT this metal, some say to take it as high as 1995 for austenizing, but 1975 is the sweet spot, like O1 alloy steel is 1475, but you can go as high as 1500 or low to 1450 and it's all good, but best is 15 min soak at 1475.
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Old 09-18-2017, 02:41 PM
epicfail48 epicfail48 is offline
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Thanks for the input guys! Good to hear my planned procedure isn't horrible. I figured that keeping the blade wrapped for an oil quench would be a no-go, but it never hurts to ask. So Jim, when you've plate quenched the 440c while its wrapped, has everything worked out alright doing that? I plan on moving to plates eventually, but at the moment I don't have any but I do have a bucket of Parks 50.

Speaking of the oil, is Parks 50 too fast of a quench for this breed of steel? I'd like to avoid warping as much as possible, would I be better served with a slower oil like canola?
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  #6  
Old 09-19-2017, 02:15 AM
jimmontg jimmontg is offline
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The Parks 50 is faster than the oil my company used

But it will be fine if you heat it up to m120-130. Pleases note I said you may be able to check and straighten right after quench. SamaraiStuart turned me on to that procedure for O1 steel and it works! I would guess it may very well work with AEB-L as it does work for D2. Wear gloves and see, the temp should be a bit uncomfortable for your bare hands at 120-130, just hurry as the effect doesn't last long. With this steel that is the most picky part of it, check and straighten then into the fridge it goes, or water with ice cubes in it, slowly. I am afraid of thermo shock, which is why I worry about going direct to the dry ice, some makers say it doesn't make a difference, but I made knives out of 3/16ths thick or .187 and I did have a blade go Tink! when I placed it directly on the -105F dry ice. Never had that problem if I put it into the 0 degree freezer first. Thickness determines time in freezer.

I worked in a machine shop and had access to 2" thick aluminum plates and I left them in the fridge to cool off a bit. I used plate quench for D2 steel and it worked rather well, same as the 440C. To be honest I did a ton more D2 than 440C or AEB-L. Same for O1 tool steel, which I consider one of the easiest steels to HT if you have an oven.
AEB-L is the easiest stainless steel to HT. The simple dry ice cryo is a great addition to the steel. Without dry ice I wouldn't even use this steel. The alloy makes great knives and is probably the most used steel for knives in Scandinavia. It was originally made to make razor blades. I moved recently and when, or if I am able to get a HT oven, AEB-L will be at the top of my list for stainless knives and O1 for high carbon steel. The highest price I ever got was for a set of knives made from AEB-L, at RC 59-60 it is a good kitchen knife, but does need a diamond sharpener at that hardness. Most commercial knives do not come close to that degree of hardness plus decent toughness and wear resistance. There are better steels, but for simplicity AEB-L is hard to beat and it does its job well.
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Old 09-19-2017, 03:46 AM
epicfail48 epicfail48 is offline
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Quote:
Originally Posted by jimmontg View Post
But it will be fine if you heat it up to m120-130. Pleases note I said you may be able to check and straighten right after quench. SamaraiStuart turned me on to that procedure for O1 steel and it works! I would guess it may very well work with AEB-L as it does work for D2. Wear gloves and see, the temp should be a bit uncomfortable for your bare hands at 120-130, just hurry as the effect doesn't last long. With this steel that is the most picky part of it, check and straighten then into the fridge it goes, or water with ice cubes in it, slowly. I am afraid of thermo shock, which is why I worry about going direct to the dry ice, some makers say it doesn't make a difference, but I made knives out of 3/16ths thick or .187 and I did have a blade go Tink! when I placed it directly on the -105F dry ice. Never had that problem if I put it into the 0 degree freezer first. Thickness determines time in freezer.

I worked in a machine shop and had access to 2" thick aluminum plates and I left them in the fridge to cool off a bit. I used plate quench for D2 steel and it worked rather well, same as the 440C. To be honest I did a ton more D2 than 440C or AEB-L. Same for O1 tool steel, which I consider one of the easiest steels to HT if you have an oven.
AEB-L is the easiest stainless steel to HT. The simple dry ice cryo is a great addition to the steel. Without dry ice I wouldn't even use this steel. The alloy makes great knives and is probably the most used steel for knives in Scandinavia. It was originally made to make razor blades. I moved recently and when, or if I am able to get a HT oven, AEB-L will be at the top of my list for stainless knives and O1 for high carbon steel. The highest price I ever got was for a set of knives made from AEB-L, at RC 59-60 it is a good kitchen knife, but does need a diamond sharpener at that hardness. Most commercial knives do not come close to that degree of hardness plus decent toughness and wear resistance. There are better steels, but for simplicity AEB-L is hard to beat and it does its job well.
Again, thanks for the advise! I did know i should be able to straighten after quench, ive had to do that with a few (a lot...) of my 1095 blades, its just something i prefer avoiding where possible. Id like it to come out as straight as possible to avoid having to mess with it, ive lost one too many blades trying to straighten them... I may end up just taking a trip down to the local metal supply and picking up a bar of aluminium to make some quench plates so i dont have to stress.

Ive heard fantastic things about AEB-L, which is ironic given i barely knew it existed until a customer of mine made a request about it. Seems right up my alley too, ive always been resistant to working with stainless because i prefer the sharper edge of carbon steels. From what ive heard though, AEB-L may as well be a stainless carbon steel for the edge you can get in it. I look forward to seeing if thats true! Ive got high hopes though, data sheets put it pretty close to Sandviks 14C28N, which is the same stuff my favorite pocket knife is made from.

Im still wondering though, would plate quenching while the blade is still in the foil work? May be carryover from working with 1095 where oven to quench has to be done as fast as possible or it doesnt harden right, but I cant shake the feeling it would end up taking me too long to get the foil off
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Old 09-19-2017, 10:47 AM
jimmontg jimmontg is offline
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As long as you have the foil on with no wrinkles a plate quench is fine. We are talking about a steel that can be air quenched as well. Aluminum plates need to be about 1" thick or close.


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Old 09-21-2017, 02:26 AM
epicfail48 epicfail48 is offline
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Quick update, turns out ill be able to skip trying the oil quench. I made the mistake of using the knife supply places prices for quench plates ($50 for a set), and was thinking i wouldnt have the cash for a bit. Quick trip to my local metal supply and i picked up a 1"x2"x18" bar of aluminium, cut it in half and face milled one side of each plate for a nice flat surface, all for the princely price of $15. Think i need to start selling these myself...

Did decide to do a quick test of my heat treatment kiln, just to make sure id be able to hit that 1975f temperature. I knew i should be able to, when i built my kiln i took it up to 2100f just to see if i could, just wanted to make sure that the elements werent getting worn. Went pretty well, up until the temps hit 1750 and then just stuck there for 2 hours. Seemed a little weird to me, given that the inside was glowing bright yellow. Then i remembered that my 1200c thermocouple burnt out a few months ago and i had to drop in one that was rated to 800c.

Yeah, whoopsie. Think i may have melted the thermocouple... Either that or my kiln is 200f short of where i need it to be. Off to order a new thermocouple!
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Old 09-22-2017, 11:57 PM
jimmontg jimmontg is offline
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I never had a problem with a bad thermo-couple, or temp measurement tool, BUT it happens. You can order a Tempil Stick up to the temperature you require. They sell them up to 1800, but you can order a special temperature stick for your target temp. I have used these sticks and they are quite accurate if you want to save some money. They last a long time, just a touch is all they take, if it melts you are there. Order a stick 50 degrees above your target temp and if it doesn't melt you are in the range you need.

http://www.markingpendepot.com/tempi...ormarkers.aspx
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Old 09-23-2017, 01:53 AM
epicfail48 epicfail48 is offline
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Originally Posted by jimmontg View Post
I never had a problem with a bad thermo-couple, or temp measurement tool, BUT it happens. You can order a Tempil Stick up to the temperature you require. They sell them up to 1800, but you can order a special temperature stick for your target temp. I have used these sticks and they are quite accurate if you want to save some money. They last a long time, just a touch is all they take, if it melts you are there. Order a stick 50 degrees above your target temp and if it doesn't melt you are in the range you need.

http://www.markingpendepot.com/tempi...ormarkers.aspx
I can't call it a bad thermocouple, it PS not like it didn't work. Only issue is it was only rated to 1200f, pretty sure that 500 degrees out of range was just too much to even think about getting an accurate read, least not for me to trust it. Had I not had my kiln on for 3 hours without it budging a degree after 1745 I'd be less leery, but I'm pretty sure it just stopped reading.

Nice tip on the tempil stick, though it wouldn't work for me here. Trying to get up to 1950-75, looks like those sticks max out at 1800. Work comes to worse I can drop some copper in there, if that melts its hot enough!
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Old 09-25-2017, 08:01 AM
jdale jdale is offline
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When you use the plates make sure you HT before you grind the bevels. The steel needs to be in direct contact with the aluminum to draw the heat. I learned this the hard way and had a nice hardened spine and tang with a almost annealed cutting edge. The blade definitely failed my chopping tests
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Old 09-25-2017, 12:04 PM
samuraistuart samuraistuart is offline
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That is absolutely NOT true. AEBL has a pearlite nose of 2 minutes. That means that bevels cut already equals a thinner edge (much thinner) than if straight profiled. Hence a simple air cool will cool the edge fast enough without plates, as it doesn't have the mass. As long as the steel gets below the pearlite nose in 2 minutes, you will achieve max HRC.

Peter's and other professional HT places do not use plates. I thought they did, turns out I was wrong. They hang them in still air (Peters anyway) Every single AEBL blade I've sent to Peter's, with the exception of 2, had bevels ground prior to HT and an edge width of 0.015". All came back at the exact HRC I requested, 62. They do test on the flat (Ricasso), as you cannot test HRC on an already ground bevel, unless that bevel is dead flat and square to the penetrator.

You can make plates contact pre ground bevels, unless you have a hollow grind. In which case you would need plates with the same radius as your hollow. But again, if the bevels are already cut, then the temp drops even faster, thus allowing for the pearlite nose to be beaten even faster than if the edge was full thickness.

Last edited by samuraistuart; 09-25-2017 at 12:07 PM.
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Old 09-26-2017, 01:02 PM
jdale jdale is offline
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I posted about a failed AEB-L HT in earlt 2016 and it was Ray Rogers position that the reason for the non hardened edge was the use of the plates on a pre ground blade. The steel may have a 2 min nose but all i know is i followed the HT recipe to a T with my evenheat oven and the edge was little harder than in its annealed state when finished.
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Old 09-26-2017, 07:55 PM
jimmontg jimmontg is offline
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I never had that issue with 440C still in the foil, BUT I did put my plates in the Fridge first to drop them down to about 40 degrees. I was always told to never quench in oil while the foil was still on so I never did, but maybe if one were to leave the blade in the foil and put it into 70 degree oil it wouldn't be so uneven?
Stuart what do you think?


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Last edited by jimmontg; 09-26-2017 at 08:05 PM.
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