Problem heat treating 80Crv2

ashwinearl

ashwinearl

Knifemaker / Craftsman / Service Provider
Joined
Nov 9, 2006
Messages
562
Hi all,

I am working with 80Crv2 and following a heat treat recipe from here
I have an old Paragon small kiln with the original thermocouple/analog gauge. It says that it gets up to 800c (easy to read on the analog guage) but have not verified with another thermocouple. I went with a about a 7 minute soak

Quenching is in Canola oil warmed to 130F in a small steel container on a hot plate. The container is pretty small and does not even hold half a gallon.

I tempered in kitchen oven 3x 375 for 15 minutes each. Initial testing with hardness files show it at 40Rc and was expecting in the higher 50s-60

Can you suggest area to consider for what went wrong?
1) kiln is not getting as hot as I think
2) canola oil container too small
3) canola oil spoiled
4) temper oven temperature not right

Thanks
 
I would guess #1 or #5 being if the steel came from anywhere but AKS, it likley requires a bit of thermal cycling before the final quench.
I also would recommend 2 temper cycles of 1 hour each.
 
E.Carlson said:
I would guess #1 or #5 being if the steel came from anywhere but AKS, it likley requires a bit of thermal cycling before the final quench.
I also would recommend 2 temper cycles of 1 hour each.
Click to expand...
It is from Alpha and this is stock removal for reference
 
Did you file check after the quench? I always file the edge after quenching. It may not tell you if you're 62 RC or 66 RC but it will tell you you're in the ball park. Now you have no way of knowing how hard it was when it went into the temper oven.

I also wonder if you're hardness testing clean steel or decarb. 90% of the time people come in here with "My knife isn't hard" it's because they didn't grind anything off before hardness testing.
 
The first thing that jumps out is the quench. You need a gallon or more on most blades. Canola will work, but you need enough of it.

I would check the kiln to verify it is in the ballpark. A few pieces of rock salt set on a piece of scrap steel in the kiln should melt around 801C. Set the oven at 810C and let the salt sit for 10-15 minutes once the oven is at 810C. If it melts, then the oven is hot enough. To complete the check, put in some new salt and set the oven for 790C. If the salt doesn't melt after 10-15 minutes at 790C, you can safely believe that the kiln gauge is reading accurately.
As a general rule, I suggest putting in a new TC on any old used oven, regardless of the current accuracy.

I would temper twice at 400F. Do each temper for 1 hour.

As kuraki suggested, check the blade right out of the quench by filing on the edge. The file should slide along with a screeching noise, not a grinding/filing noise.
After the temper, you have to grind an area clean of decarb to test that hardness.

I find hardness test files almost useless for testing hardness .... heck, they don't even work well as files.

Other likely cause:
Make sure the blade has soaked at 800C for 10 minutes after the kiln has rebounded to 800C. Don't start the count when you put it in. If in doubt, soak for 15 or even 20 minutes.
If your blade is truly Rc40, I suspect this was the main issue.
 
Last edited:
Yeah, I don't know where he got that unless he misread the 15 minute soak time on a HT recipe.
 
“Normalizing” is what is needed to take care of the carbon steel from Aldo. Not “thermal cycling”. Thermal cycling technically speaking is any heat operation (tempering included). But for our parlance, a “thermal cycle” is for grain refinement, around critical temp, and will not do anything for a coarse spheroidized steel like Aldo sells. A “normalizing” heat is what is needed, and is 100f-150f above usual “thermal cycling” temperature. If a person only “thermal cycles” a coarse spheroidized steel and doesn’t normalize it, they will just exacerbate the problem by reducing hardenability.

“Normalizing”: around 1600-1700f, depending on steel, and will help bring carbon in solution on coarse spheroidized steels. It frees carbon from the heavily annealed steel so that it is ready for the hardening operation. Normalizing “may” cause grain growth.

“Thermal cycling”: around critical temp 1500f. Helps to refine aus grain that “may” have been enlarged by the high normalizing heat. If Moly, Tungsten, vanadium carbides are in the steel, the normalizing heat probably will not cause grain growth. If it’s just chromium carbide or cementite carbides, normalizing probably will enlarge aus grain.
 
Spalted said:
This is the first time I have seen a 15 minute temper used
Click to expand...
I got the 15min temper from this post "80CrV2 was sold for years by Alpha Knife Supply as 1080+. my best results were preheat furnace to 1500F, put blade in furnace for 5 minutes or so(enough time to heat thru), quench in warm oil. with carbon a 0.8%, it is eutectoid and does not need super involved heat treat. did some tests and found two 15 minute tempers at 375F with cold water quench in between gave Rc62-63. only surprise is cost, while not high, it is still more expensive than AEB-L at AKS."
 
Stacy E. Apelt - Bladesmith said:
The first thing that jumps out is the quench. You need a gallon or more on most blades. Canola will work, but you need enough of it.

I would check the kiln to verify it is in the ballpark. A few pieces of rock salt set on a piece of scrap steel in the kiln should melt around 801C. Set the oven at 810C and let the salt sit for 10-15 minutes once the oven is at 810C. If it melts, then the oven is hot enough. To complete the check, put in some new salt and set the oven for 790C. If the salt doesn't melt after 10-15 minutes at 790C, you can safely believe that the kiln gauge is reading accurately.
As a general rule, I suggest putting in a new TC on any old used oven, regardless of the current accuracy.

I would temper twice at 400F. Do each temper for 1 hour.

As kuraki suggested, check the blade right out of the quench by filing on the edge. The file should slide along with a screeching noise, not a grinding/filing noise.
After the temper, you have to grind an area clean of decarb to test that hardness.

I find hardness test files almost useless for testing hardness .... heck, they don't even work well as files.

Other likely cause:
Make sure the blade has soaked at 800C for 10 minutes after the kiln has rebounded to 800C. Don't start the count when you put it in. If in doubt, soak for 15 or even 20 minutes.
If your blade is truly Rc40, I suspect this was the main issue.
Click to expand...

Thanks so much. I Used a thermocouple from a digital multi-meter and it showed it get up to 1520+ F. So I think it is capable of a simple heat threat? It is an old Paragon with no temperature control , just plug it in and let it run. It take a long time to reach that temperature and looked to be still increasing a hair.

I really need to install a digital PID controller to make this more useable.

M9jPlbgb.jpg


I agree, my major shortcomings are 1) not enough oil, 2) not soaking it properly. I am going to redo with 1 gallon container, start soak timer when temperature has stabilized after inserting blades, hold soak for longer, and check with file after initial quench. I will also go with 400 degree temper 2x1 hour per suggestion and report back.

Very Respectfully.
 
That looks like an old jewelers burnout oven. If iy barely reaches 1520°F, it probably isn't going to work well for HT.

To use it this is what you will have to do:
1) Adjust the oven to run at 1500F and let it hold there for at least 15 minutes (30 would be better).
2) Quickly open the door, set in the blade, and close the door. The temperature will drop about 20°F ( about 10°C), to around 1475°F/800°C.
3) Watch the temperature climb back up, and start timing when it is at 1465°F/795°C. It should continue to climb slowly.
4) Time the soak for 10 to 15 minutes, watching the temp climb. Lower the setting knob if it gets to 1480°F/805°C.
5) When the blade has had its 110-15 minutes soak at this range, pull out and quench in at least one gallon of canola oil.

The quench tank should be at lest 4" wide and 3" deeper than the blade. For small blades, a gallon paint can ($5 at Home Depot) works well, and all you have to do is put the lid on for storage. A great permanent quench tank is a cut off oxygen/compressed gas tank. You can often find them at the scrap yard for a few bucks. Some welding suppliers will give you an old out of date tank for free. Make a metal lid for it, or use an old pot lid that covers the end.

You had asked about the life of canola oil. Commercial oil quench is made from mineral oils that do not go rancid easily. These also have stabilizers and other additives that give them a long life. Buying a bucket of commercial quench oil is often a one time purchase for many hobby makers.
Canola oil is a low acid vegetable oil made from rapeseed ( CAnadian Oil, Low Acid). It last a long time as a quenchant as long as you keep it tightly covered when not in use and keep water/moisture out of it. You will know by the smell if it goes bad. The other thing that can happen to it is if it is degraded by burning. It will turn very dark. As long as it is somewhat clear and doesn't smell bad, it is still good.
 
ashwinearl said:
I got the 15min temper from this post...
Click to expand...

Temper for at least 1 hour. Most of us have found through our own testing that for low alloy carbon steels two tempers, two hours each is the point of diminishing returns, but two cycles of one hour each can be sufficient. In short, tempering is a product of time and temperature, the higher the temperature, the less time required for diffusion to occur, and the temperatures we're using to maintain high hardness (<500F) are relatively low temperatures in the scheme of things, meaning they require a certain amount of time.

If you want to learn more Larrin posted an excellent, if rather deep, article here: https://knifesteelnerds.com/2018/04/23/what-happens-during-tempering-of-steel/
 
I think I identified another process error. I had multiple blades in the oven at a time. When I pulled one out, I closed the door quickly, but it didn't fully latch which is hard to do one handed. I'd quench the blade I took out and then go to the next blade.

The temperature drops so fast when the door opens, I believe the remaining blade were cooling quickly prior to quench. Each time I made the same mistake in not latching the door fully.

This leads to my question, when heating multiple blades in an over at a time, what is your process to quench them? Do you take one out, fully close the door, quench it, and then ensure that the oven has rebounded to your original set point and then take another out for quench?
 
ashwinearl said:
I think I identified another process error. I had multiple blades in the oven at a time. When I pulled one out, I closed the door quickly, but it didn't fully latch which is hard to do one handed. I'd quench the blade I took out and then go to the next blade.

The temperature drops so fast when the door opens, I believe the remaining blade were cooling quickly prior to quench. Each time I made the same mistake in not latching the door fully.

This leads to my question, when heating multiple blades in an over at a time, what is your process to quench them? Do you take one out, fully close the door, quench it, and then ensure that the oven has rebounded to your original set point and then take another out for quench?
Click to expand...

Yes, to the best of your ability. If you can't get it latched one handed, then quench, go back and latch it, then twiddle your thumbs while it comes back up to temperature before quenching the next one. Everyone's oven is different with how much heat is lost, how fast it comes back, etc, so if you ask people specifically what they do you'll get a variety of answers. But they all boil down to assuring the next blade has gotten back to the set temp before removing and quenching.
 
The temperature has to rebound to the target ( say 1475F) before you pull the next blade. It doesn't have to soak for any long amount of time, but has to get back up evenly for a proper austenitization. I would allow it to equalize for about 1 minute once the temp is back to the target, then pull the next blade. Your particular oven has a very slow rebound at the target, so it may take longer. Just watch the needle - "Good things come to those who wait." (Guinness)

Most of the time the quench, checking for warp and straighten while still hot, and setting in the quench plates or setting/hanging on a cooling rack takes about the required time for an oven to come back up ... provided the door was closed immediately after removing the blade, and provided the oven has sufficient power for a fast rebound.
 
Honestly I don t like this .......For one blade you need at least about five minutes to quench ,check hardness , check straightness , straighten while still hot .....etc .If I have say six blade in oven last one will be inside too long ?
 
Not really. As long as the oven stays around the set point, you will be fine.

You will find the time on each blade will average less than 5 minutes. Each will probably take less time than the last.

Even if it is five minutes a blade, the extra soak of 25-30 minutes at 1475F (eg) will not harm any of the steels we use for a knife blade. 80CrV2 will be fine.
Significant grain growth takes many hours at that temperature. Once the temperature gets over 1700F, the grain growth increases in speed. It really gets faster at 2000F.
 
I more mean on decarburization Stacy . Open/close door will bring every time fresh air inside ? Once I try to triple quench 52100 blade and I have to do lot sanding to get rid of soft core..... ?? Decarburization occurs when the metal is heated to temperatures of 700 °C or above when carbon in the metal reacts with gases containing oxygen or hidrogen
 
The only real way I've found to resolve decarb issues is to apply an anti-scaling compound to the blade(s), or running an argon injected oven. Probably my favorite option is ATP-641, which is a watery clay that you apply to the blade before putting it in the oven. It should be applied very thinly, as to not affect the quench process. It seems to do a very good job at preventing scale and decarb from forming. If I don't use an anti-scaling compound, a blade that soaks for more than 5 mins in my Evenheat oven will start to form scale and decarb. The type of steel seems to have an effect on this as well... The Cru-forge V I have decarbs like no other steel I have used.

Most of the time however, it's not really a concern to me and probably a lot of guys here, because I grind after heat treatment. With a few exceptions like blades with hamons, I grind everything post heat treat and this resolves any scale or decarb worries. All of it will be ground past and the only steel remaining will be the hardened core. Decarb was one of the main catalysts for me grinding post heat treat, and after doing so, I've found that I like it more and it seems to save me a lot of time grinding. That said, grinding post heat treat requires some practice, good equipment, and expensive ceramic belts--bonus if you have a mister, dripper, or liquid cooled platen.
 
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