52100 Heat treatment question

Robert Erickson

Robert Erickson

Knifemaker / Craftsman / Service Provider
Joined
Feb 2, 2014
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I recently purchased an Evenheat oven with TAP controller and have started to HT my own blades. I have a question on fine tuning my protocol.
I have read all the threads in the stickies on 52100 HT protocols and so that's where I started. I used this one from Stuart Davenport:
1. 1650F, cool to black, quench in water.
2. 1500F, cool to black, quench in water
3. 1400F, cool to black, quench in water
4. (if needed) 1250 for annealing and stress relieving. (I didn't do this step)
5. Harden at 1475, soaking for 10-15 minutes, and quenching in medium speed oil that has been warmed to 130F. (I used McMaster-Carr medium speed oil warmed to 130F)
I got the blade to 62RC out of quench. I was hoping for 65RC. My hardness tester is a Grizzly G9645 that is calibrated. I've also tested some blades that were HT'd by Peter's and it is measuring them as expected.
I know that I should do a group of coupons to help fine tune my protocol to my oven/quench oil. The question is, of the 4 or 5 coupons that I'll do, how should I vary the parameters? Any suggestions?
 
What is the starting point of the material prior to the heat treatment you performed? Was it forged before you followed this procedure? Did you grind the surface of the specimen before you performed the hardness test?
 
Are you certain you ground through all of the decarb before testing?
 
Larrin said:
What is the starting point of the material prior to the heat treatment you performed? Was it forged before you followed this procedure? Did you grind the surface of the specimen before you performed the hardness test?
Click to expand...
The steel is from Aldo, 0.09" thick, profiled but not ground or forged.
kuraki said:
Are you certain you ground through all of the decarb before testing?
Click to expand...
I took it to my surface grinder attachment and ground down to clean steel with first 100 grit then 200 grit. I'm not sure exactly how much steel I took off. I could go back and grind it down a bit more and retest.
 
did you just take one measurement point location?
this normalizing quench in water is interesting, I've never done that samuraistuart samuraistuart , care to elaborate?
was your soak 10? or 15? or in between?
 
I think the issue is the medium speed oil. my experience with 52100 showed best results with oil rated for 12 seconds or less.
 
Robert Erickson said:
The steel is from Aldo, 0.09" thick, profiled but not ground or forged.

I took it to my surface grinder attachment and ground down to clean steel with first 100 grit then 200 grit. I'm not sure exactly how much steel I took off. I could go back and grind it down a bit more and retest.
Click to expand...

Quick etch would show if there is still decarb without regrinding. It was just a lot deeper than I expected the first time I went through the steps you did without using foil or antiscale during normalizing/cycling.
 
The quench in water was ALWAYS at a black heat, and I no longer take that step. It was just a way to speed things up a bit, instead of waiting until the blade became ambient again, like some of us do during tempering. The water quench, once cooled below the black heat, does nothing good or bad metallurgically speaking, so I don't do that any longer.

Medium speed oil seems to work great for 52100. That is the recommended quench for that steel. I've used P50 with success, but with more distortion problems that medium speed oil. If you have a faster oil, by all means give it a go.

Also my cycling is different now with better info from Cashen. After the normalizing, all thermal cycles are closer to 1475f. As in 1500, 1475, 1450. I no longer cycle below 1425f. With that said, Robert, your HT is good, and would expect 65+ post quench. Decarb is a devil.

Just FYI for the thread, my bevels are usually ground pre HT.
As for my soak, technically it is 12-13 minutes. Insert blade, let readout rebound, let the blade come up to temp (takes 2 minutes thereabouts), begin 10 minute soak.
And all cycles/hardening done with ATP-641. Will be changing to foil for cycling in the future, and ATP for hardening.
 
Good idea on the quick etch, thanks Kuraki!
Thanks Stuart so if I understand correctly you do:
1. 1650F, cool to black.
2. 1500F, cool to black
3. 1475F, cool to black
4. 1450F, cool to black then harden at 1475 for 12-13 min. => quench in medium oil
Do you still heat your medium speed oil to 130 or go with room temp.
 
Robert, that's exactly what I am doing now. I do heat up the oil. 130°F. Good luck!

Just to add: If you're doing any machining after the normalizing/cycling, then to a subcritical anneal: On the last thermal cycle of 1450F (or whatever temp you're using), quench. Then into the oven at 1200F for 2 hours. You'll now have a fine spheroidized structure ready for machining and hardening. I usually prefer hardening from pearlite over spheroidite, tho.
 
Let us know if you find out harder steel grinding it down further... it is most likely.
You might be able to see decarb through an etch, but your rockwell will definitely show high and consistent readings once you had ground all the decarburation layer...of course under coolant, still in the as quenched state.
Be also sure your sample sits clean and flat on its bottom on the Rockwell cleaned anvil
 
Glad you got it working for you.

If you want to reduce the time it takes to thermal cycle, you don't have to cool to black in between cycles. Once the structure changes to "something else" it is ready to cycle back up. As soon as it becomes magnetic again, you are good to go. I also throw a quench on the last cycle to "lock it in" then subcritical anneal or "redneck spheroidize".

My current recipe... after forging

1650F, Cool to magnetic
1525F, Cool to magnetic
1475F, Quench in oil
Heat to dull red(still magnetic) three times cooling to black in between.
Grind, drill, file, etc...
1350F, check for straightness
1500F, hold for 5min, Quench.
 
Good to know Rick, thanks.
Another question I have is when you're thermal cycling how do you know how long to leave the blade in the oven other than magnetism? I left the blade in the oven roughly 5 min at each step so the oven was able to recover temp, but that doesn't necessarily mean the blade is up to temp right?
 
Decalescence is the single most reliable way to determine that steel is at the critical temperature. Learn how to recognize it. Open the door(slightly) and see if the shadows are flickering along the blade. When they stop, start your timer. I desperately want to install a viewing window in my kiln.
 
Rick Marchand said:
Decalescence is the single most reliable way to determine that steel is at the critical temperature. Learn how to recognize it. Open the door(slightly) and see if the shadows are flickering along the blade. When they stop, start your timer. I desperately want to install a viewing window in my kiln.
Click to expand...

Thank you sir! I'm not going to lie I had to look up Decalescence :confused:. Learn something new every day!
Is this a fair definition: a sudden decrease in the rate of temperature rise of heated metal after a certain temperature has been reached (795°C for iron) due to greater absorption of heat.
So probably turn the lights out to able to see this phenomenon better, I would guess.
 
Oh yeah... lights out. You need control of the light in your shop. Best to do it at night if you don't have blackout shades.

As your blade heats up and turns red, you with notice a "shadow" form. It is not a loss of heat but rather a momentary plateau. You'll see the heat start to creep back in like a wave. In a kiln, the ramp up rate is much slower and you often see a "flickering" affect.

What is also neat(and easier to see) is Recalescence. Pull a red hot blade out of your kiln/forge and watch it cool down in the dark. It'll get duller and duller red, then out of nowhere a bright band will glide across the piece. So cool.
 
Since 52100 is hypereutectoid a magnet works just as well for determining when the austenite transformation is complete.
 
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