Heat Treat Question

CDHumiston

CDHumiston

KNIFE MAKER
I just heat treated two Alabama Damascus blades. I ramped my oven to 1550 and soaked the blades for 5 minutes. I quenched in AAA oil heated to 120. I finished the cooling in aluminum plates to avoid any warps. I tempered the blades at 350 for one hour and let the oven and blades cool to room temp.

I cleaned the blades and made sure there was no scale build up. My HRC reading on both blades was right at 51. Not good for me.

I decided to heat treat them again. Second time same procedure, but I cleaned them right after the aluminum plate cool down. Both are at 59 HRC.

I did a drop test on the blades to see if they are fragile and they had no issues with multiple drops at 5' on to a concrete floor.

Now the question...should I temper the blades again???
 
The info I’ve got could be wrong, but I was told that Rockwell test results on Damascus were mostly inaccurate and you couldn’t trust them. There may be others here that have different mileage, but that’s what I was told by a well-known maker before he died. As far as tempering goes, I generally would recommend multiple cycles, especially if the cycle time is only one hour. Tempering them again is not going to make it harder though.
 
I just did some Alabama Damascus yesterday, here’s how I go about it. Bring the oven to 1550…then put the blade in, let soak for about five minutes, crack the door open and check with an extendo magnet. It’s usually good, 0 magnetization. Close the door and let the oven get back up to 1550, usually 1 minute, pull it out and straight into parks 50 within 2-3 seconds, straight down tip first, hold for about 4-5 seconds and onto the plates. Temper twice for one hour each at 370. I don’t let the blade cool with the oven, it comes out to cool. As for Rockwell testing, I sand my blade down to 400 grit then test, taking several test moving the blade around under the diamond, some will read low some won’t, this last blade read 59. Etched a couple hours ago and soaking in coffee now.
 
bladegrinder said:
I just did some Alabama Damascus yesterday, here’s how I go about it. Bring the oven to 1550…then put the blade in, let soak for about five minutes, crack the door open and check with an extendo magnet. It’s usually good, 0 magnetization. Close the door and let the oven get back up to 1550, usually 1 minute, pull it out and straight into parks 50 within 2-3 seconds, straight down tip first, hold for about 4-5 seconds and onto the plates. Temper twice for one hour each at 370. I don’t let the blade cool with the oven, it comes out to cool. As for Rockwell testing, I sand my blade down to 400 grit then test, taking several test moving the blade around under the diamond, some will read low some won’t, this last blade read 59. Etched a couple hours ago and soaking in coffee now.
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Not understanding why you would open the oven and check to see if it’s non magnetic since that’s at 1425 degrees and the oven is at 1550? I’m not questioning your method just curious as to why.
 
bladegrinder said:
As for Rockwell testing, I sand my blade down to 400 grit then test, taking several test moving the blade around under the diamond, some will read low some won’t, this last blade read 59.
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Do you think the places that read low Rc were in the 203e material? I understand 203e is low carbon and shouldn't harden. I've read some folks say in forging and folding for Damascus the carbon level evens out thru all the layers allowing the 203e to harden.
 
opaul said:
Not understanding why you would open the oven and check to see if it’s non magnetic since that’s at 1425 degrees and the oven is at 1550? I’m not questioning your method just curious as to why.
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Just something I've been doing for years. I've had some thicker blades still tugging at a magnet when I assumed they were at temperature to quench. just something I always do and seems to work for me, I've never had any problems doing it like this.
 
KenH said:
Do you think the places that read low Rc were in the 203e material? I understand 203e is low carbon and shouldn't harden. I've read some folks say in forging and folding for Damascus the carbon level evens out thru all the layers allowing the 203e to harden.
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I couldn't say Ken but I have found that taking several readings with a rockwell tester over one area will usually vary, compared to doing the same testing on a mono steel.
 
KenH said:
Do you think the places that read low Rc were in the 203e material? I understand 203e is low carbon and shouldn't harden. I've read some folks say in forging and folding for Damascus the carbon level evens out thru all the layers allowing the 203e to harden.
Click to expand...

I'm not sure. I tested two blades that were heat treated exactly the same in multiple test locations and got the same reading across the board.

Second heat treat has got me up to 61 HRC prior to tempering. Just trying to decide if I should temper again...

I think I'm going to go for one temper for one hour at 350F.
 
YES!!! From what I've read even with a low Rc (60/61) the steel still needs a temper cycle (or 2) to reduce the strains from quenching even if it doesn't drop the Rc much at all. With a 61Rc I'd think about tempering at 325°F for an hour or, check Rc and if it didn't drop any, perhaps another temper cycle at 350°F to drop Rc to 60? You need tempering so "the carbon atoms move out of the spaces between the iron atoms in the martensite to form the iron carbide particles. The strain within the martensite is relieved as the carbon atoms move out from between the iron atoms in the martensite" (copied from someplace)
 
After one temper cycle for one hour at 325F I now have a 59HRC.

I think I'll stay here on this one...if it wasn't expensive Damascus, I'd snap one of the blades for a test!
 
Bühlmann said:
I don’t know for sure, but I would be willing to bet that your hardness would stay stable at 59 with a second temper cycle. I get why you don’t want to, though.
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Yep, as long as the 2nd temper is at the same temp of 325°F the Rc shouldn't change. The 2nd temper allows the more of the RA to convert.
 
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