Heat treating methods for A2

Matt Logan

Matt Logan

Joined
Aug 4, 2017
Messages
11
Hello everyone, I'm brand new to the forum. I've been making knives for a few years now, and I don't know why I haven't joined sooner! Recently, I started doing my own heat treating with my Paragon furnace.

I'm having trouble with my blades warping a little at the spine. I'm following paragon's recommended recipe for A2, which is ramp up full speed to 1750, then soak for 20 minutes. Then I plate quench, then temper at 500 for 1 hour.

I haven't been preheating, I've just been heating the blade in the furnace at full speed to 1750.....I wander if that could be my problem? Also, I forgot to mention that I leave my blades plenty thick at the edge, so I don't see thinness as an issue.

When I plate quench, I use a 30lb dumbell on top of the plate....maybe I need more weight?

I would like to get some opinions on this, and maybe you could share your recipes as well.

Thanks,
Matt
 
I normally HT A2 at 1775 with a 1475 preheat step.
Your temper seems a bit high as well, I usually temper at 425 or so depending on the knife.
I'm surprised you're having warpage issues with A2 though, it's about the most stable steel I've ever worked with. I usually grind it basically to final dimension before HT and never have an issue.

That said your plate quench isn't near enough force. Even standing on the plates is a bit on the light side. I use a big pipe vise, but a couple of large C clamps would work as well. You really want to squeeze the crap out of the plates to force the steel flat, and keep it there
 
Geoff Flato said:
I normally HT A2 at 1775 with a 1475 preheat step.
Your temper seems a bit high as well, I usually temper at 425 or so depending on the knife.
I'm surprised you're having warpage issues with A2 though, it's about the most stable steel I've ever worked with. I usually grind it basically to final dimension before HT and never have an issue.

That said your plate quench isn't near enough force. Even standing on the plates is a bit on the light side. I use a big pipe vise, but a couple of large C clamps would work as well. You really want to squeeze the crap out of the plates to force the steel flat, and keep it there
Click to expand...

How long should I hold the preheat? And should I ramp up at full speed to preheat?

Thanks for the advice
 
I hold my preheat for 15 minutes.
And the other question has some debate involved. Some people argue for putting them in the oven at the preheat temperature, others put them in a cold oven and ramp up.
I've tried both ways, and could never seem to tell a difference in the finished blade... My understanding is putting them in at the preheat temp is considered the best practice though.
From preheat to soak temp I'll ramp as fast as possible.
The temps I suggested (at least according to my oven) deliver about rc60
 
Are you SURE your plates are flat? I had some that weren't and they had me scratching my head until I thought to check them. Also, very little pressure is required for a good quench if your plates are flat. The contact with the plates does the quenching through conduction, not pressure. Actually, too much pressure is more likely to cause a warp than just enough to maintain even contact.
 
Darrin Sanders said:
Are you SURE your plates are flat? I had some that weren't and they had me scratching my head until I thought to check them. Also, very little pressure is required for a good quench if your plates are flat. The contact with the plates does the quenching through conduction, not pressure. Actually, too much pressure is more likely to cause a warp than just enough to maintain even contact.
Click to expand...

Hey Darrin, thanks for the reply. I'm a little confused about the pressure required as well, because it's my understanding that some people quench without plates just with a fan? If that's the case, there wouldn't be any pressure to keep the blades flat. Also, another question I have is should I use a combustible inside the foil pack, or not?

Thanks,

Matt
 
Maybe I'm wrong, but I see plate quenching like this, at least in regard to A2 and other truly air hardening steels. Plates quench faster than still air, or blown air, when there is sufficient contact through conduction, but the primary reason I quench between plates is to prevent warp. Warping can occur from uneven cooling, and if that's the only cause for warping in the quench, then light pressure is sufficient to provide both conductive cooling and even cooling.

However, I don't believe uneven cooling to be the only reason for warp in the quench, and when plate quenching, I prefer to clamp them quite hard in a Kurt vise to constrain them flat and square. I surface grind them prior to heat treat so I have flat and parallel sides to clamp against. And doing this, in every instance even after the temper, when I go back to the surface grinder it's less than .005" to clean them back up.

So, light pressure: sufficient for conductive cooling and quenching evenly. Clamping: constraining the blade straight.

I don't understand how the rate of cooling in regard to hardening even becomes part of the equation until you start talking about steels that are borderline oil quench/air quench, especially in regard to the thicknesses we generally work in.
 
Matt Logan said:
Hey Darrin, thanks for the reply. I'm a little confused about the pressure required as well, because it's my understanding that some people quench without plates just with a fan? If that's the case, there wouldn't be any pressure to keep the blades flat. Also, another question I have is should I use a combustible inside the foil pack, or not?

Thanks,

Matt
Click to expand...
Air hardening steel is exactly that and as such it will harden in still air but plates provide a faster quench with the added benefit of eliminating warping if done properly. I just use plates, no fan needed. After the plates are clamped, the temp. will start to rise. Once the temp. of the plates stops rising (you can shoot the surface periodically with an IR thermometer) they have done all they can do and after that just insulate the blade from further cooling. Enough pressure to insure good contact is all that is needed and anything else is just overkill. I have my plates bolted to a cheap woodworkers vise attached to the end of my workbench horizontally. I have the plates opened wide enough to accept the foil wrapped blade, place it in, & screw the vise down until the plates are just snug and I never have a problem.
I never put anything combustible in the packages and never have a problem. However, I do add a light dusting of talcum powder (baby powder) to prevent the foil from sticking to the blade. The talcum is just powdered rock and wont burn or cause any other problems. Just don't use too much. Just dust em and shake out the excess before you seal the last seam in the pack. As long as I do all this properly, my blades come out arrow straight and clean as a whistle.
I'm sure that there are other and even better ways but this is what works for me and my equip. YMMV.
 
I used to give the blades a light spray of WD-40 before wrapping in foil, but stopped it because there was no real difference when I didn't do it. They had peacock colors on them either way.
 
I generally throw in a little scrap of paper in each, even though there wasn't much difference the few times I've forgotten to. Something I do for my own peace of mind more than anything else
 
I heat treat my blades in even numbers , that way when I plate quench I put 2 blades on the plates . Foil fold in the middle and blades toward the edges . This guarantees that the plates stay flat and even on the blades . I use about a 35 lb weight on top .
I do this because one time not paying attention with one blade in the center of the plate ,the top plate leaned over some and the spine of the blade lost contact with the plate. Now if I do one blade at a time , I add a small piece of steel the same thickness between the plates to keep them even .
 
forgot to say , temper at 425 for 2 hours , 2 times .
For soak time it depends on # of blades and thickness . I usually soak for 30 to 40 minutes depending on what is in the oven .
 
I treated a blade Friday evening and I used the following recipe: ramp up full speed to 1425 and preheat for 10 minutes...then ramp full speed to 1750 and soak for 45 minutes....then plate quench...then temper twice for 2 hours each time at 425.

This one came out much more straight, but I did preheat and put alot more pressure on the plates during quench.

Thankyou everyone, for all the great advice

Matt
 
Something to remember , keep a good amount of flat on the blade before heat treat , helps the plates keep them flat . Also , keep your grinds even , if they are not you will warp .
 
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