Temper problem O1

Stromberg Knives

Stromberg Knives

strombergknives.com
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Jan 3, 2015
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I've been heat treating O1 coupons today since I can't seem to get my O1 HT as I want.


My recipe is as follows:



  • Preheat to 650 degC/1200 degF and hold for 20 min (to get oven evenly heated)
  • Insert blade and soak for 10 min (at 650 degC/1200 degF))
  • Ramp to 815 degC/1500 degF (not full ramp so I don't overshoot temp) and hold for 20 min
  • Quench in Canola oil at 55 degC/130 degF until blade is same temp as oil


At this stage, when I clean the blade up (up to trizact A45) and do a hardness test I get around 64-66 HRC. Which seems normal enough.


But when I temper, my hardness drops drastically. If I temper at 180 degC/360 degF my blade comes out at around 59-60 HRC. According to all temper charts I should get a higher hardness at this (low) tempering temp.


Does anyone see any problem with my routine?
I have a 24" Paragon oven for heat treating and a small household oven with a PID for tempering (with the TC mounted in a flat piece of aluminum in the middle of the oven).
 
Are you heat cycling first? Annealed O-1 needs a high heat cycle to distribute the carbides......like 1650F.
Darcy
Edited to add. I don't use it much either. But I always need to temper at 400 minimum or it's likely to chip the edge. I don't have hardness testing equipment. Pass the salt.
 
Last edited:
2 Possibilities

1) slightly under-soaked/hardened (less than O1's eutectoid amt of carbon in solution). If so, increase 1500F soak to 25 minutes.

2) Is 59-60rc after 1 or 2 temper(s)? If only 1, do 2nd temper and test again. If 2, I suspect RA is a tad high and dislocation still too high (even after precipitation stress relieved from 1st temper) . Try cryo if avail, otherwise try 400-425F temper 2 times.
 
I usually full ramp to 1650ish,put the blade in my oven and let the temp rebound, then cool to black, 1600, cool to black. 1550, cool to black, 1500 and soak for 15-20 minutes then quench in Parks AAA. Temper around 400f x2 and I end up around 60hrc. Truthfully I don't use a lot of O-1 so take this with a grain of salt!
 
O1 generally comes fine spheroidized and does not need to be normalized at all. All the normalizing was done when the steel was rolled out, then it was annealed resulting in a fine spheroidized matrix. O1 comes in just about the best condition you could hope for. It's very soft for machining, and is ready to harden (with that soak). 52100 usually comes coarse spheroidized, and needs the normalizing.

O1 should be 65 or so as quenched, so no problem there. Personally I do think it's best, with the simple cross section of a knife blade, to warm your kiln to austenitizing temp (1475 instead of 1500 for O1, but that's OK), and then insert the blade, starting soak time when the readout rebounds to 1475....that way there is NO way of temp overshooting. But that doesn't help with the tempering problem you're having.

I would suggest make sure the decarb layer is thoroughly removed before the post temper hardness reading, verify the oven temp isn't off. No real help to offer. Kind of strange to me too.
 
bluntcut said:
2 Possibilities

1) slightly under-soaked/hardened (less than O1's eutectoid amt of carbon in solution). If so, increase 1500F soak to 25 minutes. (He soaked at 1500 for 20 minutes...that's plenty if his temp is on target...note his post quench RC reading)

2) Is 59-60rc after 1 or 2 temper(s)? If only 1, do 2nd temper and test again. If 2, I suspect RA is a tad high and dislocation still too high (even after precipitation stress relieved from 1st temper) . Try cryo if avail, otherwise try 400-425F temper 2 times.
Click to expand...

You think he'll get a higher RC reading after the 2nd temper? How can RA be too high when 1500 is used as an aus temp? How can RA be a problem if he undersoaked/underhardened? refer to his post quench RC reading of 66.
 
Last edited:
bluntcut said:
2 Possibilities

1) slightly under-soaked/hardened (less than O1's eutectoid amt of carbon in solution). If so, increase 1500F soak to 25 minutes.

2) Is 59-60rc after 1 or 2 temper(s)? If only 1, do 2nd temper and test again. If 2, I suspect RA is a tad high and dislocation still too high (even after precipitation stress relieved from 1st temper) . Try cryo if avail, otherwise try 400-425F temper 2 times.
Click to expand...

The 59-60 is after two tempers. So you think I should try a temper at a highter temperature?
 
samuraistuart said:
O1 generally comes fine spheroidized and does not need to be normalized at all. All the normalizing was done when the steel was rolled out, then it was annealed resulting in a fine spheroidized matrix. O1 comes in just about the best condition you could hope for. It's very soft for machining, and is ready to harden (with that soak). 52100 usually comes coarse spheroidized, and needs the normalizing.

O1 should be 65 or so as quenched, so no problem there. Personally I do think it's best, with the simple cross section of a knife blade, to warm your kiln to austenitizing temp (1475 instead of 1500 for O1, but that's OK), and then insert the blade, starting soak time when the readout rebounds to 1475....that way there is NO way of temp overshooting. But that doesn't help with the tempering problem you're having.

I would suggest make sure the decarb layer is thoroughly removed before the post temper hardness reading, verify the oven temp isn't off. No real help to offer. Kind of strange to me too.
Click to expand...

I would think the decarb layer is removed. For my latest test I used 60, 120, A100 and A45 before performing the hardness test.

I just put another thermometer inside my oven and it shows the exact same values as the PID.

It's very strange, indeed.
 
Rockwell C-scale is a macro type of indentation test. RA pockets & regions can intersperse in a high dislocation matrix, where matrix displacement from indenter get high reading from pileup. Think, a bunch of big irregular shaped rocks next to each others and gaps filled with mud. It's would be hard to poke a pole through. Tempered alleviated/smooth edges of those rocks, hence rapid loss pileup displacement resistant (hardness).

However if 64-66# is a nano indentation#, then yeah, I wouldn't suspect RA problem...

samuraistuart said:
You think he'll get a higher RC reading after the 2nd temper? How can RA be too high when 1500 is used as an aus temp? How can RA be a problem if he undersoaked/underhardened? refer to his post quench RC reading of 66.
Click to expand...
 
I would re-harden using same ht procedure and temper at 300F. Gradually increase temper temperature to target hardness. I suspect 325F provides best outcome in your case.

currenthill said:
The 59-60 is after two tempers. So you think I should try a temper at a highter temperature?
Click to expand...
 
I use 1475 with O1. Going higher results in retained austentite, and decreased hardness. Would 25f make a difference? Don't know. I did a small blade in O1 yesterday. Had to temper at 425f to get Rc61. 1/8" steel.
 
bluntcut said:
I would re-harden using same ht procedure and temper at 300F. Gradually increase temper temperature to target hardness. I suspect 325F provides best outcome in your case.
Click to expand...

I followed your advice and used the same procedure, except for lowering temp to 800 degC and added another 5 min soak. This gave me 66 HRC.

Then i tempered at 160 degC and it came out as 62 HRC.

Thank you all, I'm glad it worked. But I still can't understand why I need these lower temperatures when tempering.

But hey, as long as it works... [emoji106]🏻
 
me2 said:
Do you have a chemical analysis for your O1?
Click to expand...

Yep, here it is:

Code: 
O1 (W1.2510) Precision Ground Diameters
Available in 1000mm and 2000mm Lengths. Precision Ground to a H8 Tolerance.

Average Analysis:

Carbon    0.95%
Silicon   0.25%
Manganese 1.10%
Chromium  0.55%
Vanadium  0.10%
Tungsten  0.55%
 
If you try again, see about lower temp, 1450-1475, and longer time, 30 min
 
Quick question:

Since I'm experimenting with temper. Would it be possible to do temper after temper with an increased temperature and measure hardness between each run?
 
Sure. I am zeroing-in 64rc for D2 & 3V blades right now by 25F increment and test hrc between each step.
currenthill said:
Quick question:

Since I'm experimenting with temper. Would it be possible to do temper after temper with an increased temperature and measure hardness between each run?
Click to expand...
 
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