A2 troubleshoot heat treat

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Rythorne

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Sep 27, 2015
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So I am using a paragon KM14d. My process was preheat to 1100 put blank in, hold at 1100 5 minutes giving me time to get the blank in and for it to begin heating ect. Ramped full to 1775 and held 35 minutes. Blank was in a stainless pouch. I pulled the pouch out and hung it. I could somewhat see the outline of the blade in the pouch from it being orange. I let it hang in the pouch until I could handle it then removed the blank. Initially I filed off a very thin coating of Im assuming scale which was extremely soft. At first I thought the blade had not hardened at all but soon realized I was just digging out this material. After grinding the belt to 65x Norton and file testing I could tell it was hardened. The issue is it doesn't seem anywhere near as hard as my 1084 blades which are post temper. Any ideas on things I could try or change? My next plan was to preheat to 1400F and hold for 10 minutes. I got this process from an experienced and successful knife maker and I trust his results however it doesn't seem to be the same to me. Could this steel really be that much different that 1084 as far as maybe its tougher but not as wear resistant or something and that's what I'm seeing? My file is almost incapable of effecting my 1084's with the A2 if I push I can get scratches and get the "hung up on something" feeling as the file sweeps across the blade.

Also, any ideas on the average time it takes a kiln such as the km14d to evenly soak a blade to temp, meaning, If I stick a room temp blade in a 1100 degree oven, how long would it take to get to 1100 degrees? Further if its in an oven ramping to 1775 how long would it take to bring the blade temp up as the kiln temp increased to 1775? If I was a soak for 35 minutes at 1775, should I add a certain amount of time to the actual program at 1775 in order to account for the time it takes for the blade to actually REACH 1775.

I've read that an experiment was conducted on tool steel and that OVER soaking(in time not temp.) it had no negatives, merely diminished returns as to make it not worth it, while under soaking is when you run into issues so I don't want to be on that side however I'm also looking for the most economical way of treating blades.

For the record I am already planning on recording my programs and testing numerous blades to get what I want, just was hoping for someone to help me out with your experiences. Thank You in advance
 
I'll let others chime in, since i have not much direct experience treating air hardening steels.
Troubleshooting an heat treatment it is not an easy task to begin with, since we need to make a lot of assumption on things we have not seen, that have be done.
Your aust.temperature seems too high (better 1700-1730 for A2) and without subzero treatments immediately post quench will lead to worth noting amounts of retained austenite. Retained austenite will have your file doing what it did.
Air hardening should be read as "at least to be plate quenched", possibly with positive air pressure, or even better oil quenching, if we are talking edged tools.
As far as you soaking concerns i'd say that you could start timing as soon as your kiln had rebound to the setpoint temperature....plus i'd skip the presoak and put the blade directly in the preheated austenitization temperature kiln....but if you have a secon kiln waiting in temperature, in that case the presoak is very ok. What it is not good is having the blade inside the cool kiln while the kiln adjust itself, since you can overshoot the setpoint. You want to reach austenitization temperature as quick as possible without overshooting the setpoint, for some main reasons: austenitization begins as soon as your steel goes in the range of 1450 °F and because this your soaking time will be skewed; then your ausgrain is kept smaller the quicker your aus.ramp is.
 
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The fact you had found the "skin" of your steel softer than the core, to me, confirm the effect of overshooting the target temperature due to oven accomodation.
Seems that the outer surface has had the time to be oversaturated by carbon in solution than the core, during oven rebounds, and consequently showed more RA in the outer layer. In the core, the thermal inertia just allowed less overheating.

1084 shouldn't be harder or more wear resistant than A2, the other way around!!! But know you know why they say 1084 is easier to heat treat than more complex steels.

I hope my thoughts may lead you in a useful direction, but definitely ask for other's opinion/advices :)
 
I'm not a knife maker but a long time stamping die designer and builder. I have been heat treating A-2 and D-2 weekly, if not daily for 2 decades. This is what I would do differently. I would never throw
steel into a hot oven. Preheat is a misleading term. This is how I would do it. Bag the steel (I like to double bag) Put it in a cool oven turn it on to 1350F. When it reaches that temp let it soak for 20 or 30mins.
This is a critical stage IMO. Turn the oven to 1775F after it reaches that leave it in for no less than 30 no more than 45. I literally use an old kitchen timer. Pull it out of the oven and cut the bag open as fast
as you can safely do so. If you have a little desk fan you should keep hot air gently moving away from it. Let the oven cool down to below 300 before you put it in for draw. I typically get 62 to 65 HRC out
of A-2. I let them soak at 375 for two hours that gets me about 60-61.
 
Auetenitize at between 1725-1740 if you are not doing a sub-zero quench. Oil quench. The soft outer layers are from decarb, which can come from the mill. Because knife blades are not complicated shapes, you can put them in a preheated oven without the preheat step.

Hoss
 
Three posts ? Stefano is really learning stuff !
You have to have the whole oven heated not just the air. Give it more than 5 min. I would rather HT in foil and plate quench. Check to see if the problem is decarb ! When you buy it , is it annealed or spheroidize annealed , or is it also ground decarb free ?
Don't panic about grain growth with long time soaking as the grain growth is not much of a problem Unless you go over temperature !! Cutting open a hot bag to air quench is not very convenient since the quench is good between plates in the bag. Remove from bag , check hardness, temper about 400 F 2+2. Try that.
 
So I adjusted my formula and got a very hard piece of steel. I file checked and it didn't make a mark, even to the minor discoloration on the blade from the heat. No Scale at all on this one.

New Schedule -

1. Foiled knife blank into oven.
2. Ramp to 1350, hold 10 minutes
3. Ramp to 1775, hold 35 minutes
4. remove and hang in foil
5. When blank is still hot but able to be easily manipulated I quickly cut it out of the envelope but it was still too hot to touch bare handed so I rehung till it was cool

This schedule when I took it out I could see the entire blade through the foil. Also It seemed like the blade took much longer to fully cool. The first blade that was soft had a very thin layer of carb I assume. This was clean. Also the first blade had soot, Im assuming carbon, left over in the bottom of the envelope (like someone dropped a cigarettes ash in the bottom). Rockwell tester will be used probably tomorrow, and I have plates en route to test that aswell. Things are looking up.


Last question for now...with plates if I have say 10 blades do I have to use different plates to quench? Can I use the same plates in the same spot for 10 times in a row? Seems it would be self defeating to put a hot blade blank on hot ass aluminum which is my experience gets hot real fast and stays hot.
 
ktmbigfan said:
I'm not a knife maker but a long time stamping die designer and builder. I have been heat treating A-2 and D-2 weekly, if not daily for 2 decades. This is what I would do differently. I would never throw
steel into a hot oven. Preheat is a misleading term. This is how I would do it. Bag the steel (I like to double bag) Put it in a cool oven turn it on to 1350F. When it reaches that temp let it soak for 20 or 30mins.
This is a critical stage IMO. Turn the oven to 1775F after it reaches that leave it in for no less than 30 no more than 45. I literally use an old kitchen timer. Pull it out of the oven and cut the bag open as fast
as you can safely do so. If you have a little desk fan you should keep hot air gently moving away from it. Let the oven cool down to below 300 before you put it in for draw. I typically get 62 to 65 HRC out
of A-2. I let them soak at 375 for two hours that gets me about 60-61.
Click to expand...
Thank you for this experienced information, I am working a d2 combat/"rat" style knife and the heat treat is coming soon.
 
4.remove and hang in foil
If you cool it in foil you must use plates ! For multiple blades cool the plates in water .
 
Based on the soot in my first envelope it may be decarb. I'm gonna refire a blade with the same program making sure my envelope is air tight.
 
My "crappy" blade came out at 60hrc. Lol high expectations I guess. That was after a two hour temper.
 
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