Stupidity Check

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mpcoppin

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Dec 8, 2017
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I'm getting ready to do a HT on a blade made from a farrier's rasp. This is my first rodeo so I'm looking for the obvious mistakes and dangerous stupidity.

Based on my shop, my budget, and my research of this forum (and others), here is my plan...

1- Low expectations: As this is "found" steel and my 1st try, I'm not expecting anything exceptional; I'll settle for "good" and some experience.

2- Safety first, I'll have gloves, glasses, apron, fire extinguisher, disapproving spouse w/ 911 on speed dial, etc...

3- Heat the blade to approximately 1500 - 1600 degrees in my little kiln & let it sit for a few minutes (the kiln tops out at about 1600).

4- As quickly as possible, move the blade from the kiln to a pot of Canola oil that has been pre-heated to about 130 degrees (I anticipate I can make this move in about .5 seconds).

5- Let the blade cool to about 100 - 200 degrees

6- Pop the blade in the oven at about 400 degrees for 2 hours (or until a golden brown).

7- Allow to cool and repeat the tempering process at 400 degrees.

Did I miss anything critical? Am I going to burn my house down?
 
1- Low expectations: As this is "found" steel and my 1st try, I'm not expecting anything exceptional; I'll settle for "good" and some experience.
As you say, it is a mystery, so you don't know. That said, most farrier rasps will make a knife.
2- Safety first, I'll have gloves, glasses, apron, fire extinguisher, disapproving spouse w/ 911 on speed dial, etc...
A garden hose nearby is a good idea.
Also, consider where the oil will go if knocked over and on fire.
IMPORTANT - don't pull the blade form then oil any sooner than 8 seconds or it may combust into a flaming torch. If that happens, just stick back in the tank under the oil to put out the flames ... and keep it there for a while longer.
A pair of tongs or long handled pliers is needed to safely hold the blade. The long pliers from Harbor Freight have been "first tongs" for many new makers.
3- Heat the blade to approximately 1500 - 1600 degrees in my little kiln & let it sit for a few minutes (the kiln tops out at about 1600).
I would use 1525F as a target temp.
4- As quickly as possible, move the blade from the kiln to a pot of Canola oil that has been pre-heated to about 130 degrees (I anticipate I can make this move in about .5 seconds).
Don't rush and do anything in a jerk movement or run to the quench tank. A hot blade flying out of your pliers is not a good thing. That said, try to get it in the quench as soon as possible. The best method is to put the kiln near the quench tank before starting the HT. About four feet away s good. That will cut your transit time to about one second. It is best to do the quench outside, as there can be considerable smoke.
5- Let the blade cool to about 100 - 200 degrees
Just leave it in the oil to cool. If desired, you can pull it ot of the oil after 8 seconds and check for a warp. It can be hand straightened ( heavy gloves on hands) easily down to 400F. It will start to stiffen at that point and should be set aside to finish cooling to room temp.
6- Pop the blade in the oven at about 400 degrees for 2 hours (or until a golden brown).
Carefully wash it off well with dish soap first. It will still smell a bit, but not as bad as if you don't clean off the oil first.
7- Allow to cool and repeat the tempering process at 400 degrees.
Since you don't know the stele type, I would temper at 425-450F.
When you take it out of the tempering oven, just cool off in running (or a bucket) water. Dryit off and stick right back in the oven. No need to let it cool slowly. Do the same when taking it out after the second temper.
 
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You don't have to be in a huge hurry going from heat to the oil. The clock doesn't really start ticking in the quench until you drop below the Curie temperature. Don't go real slow but you have time, be safe.
 
Don't panic if your canola oil starts burning when you enter with the blade into the oil. Flames should stop when the blade is completely in the quench.
For all cases, keep a metall cover at hand to cover the oil. And of course, don't use a plastic bucket or container for the oil.
 
And the results are in:

FAIL (it didn’t get hard)

Oh well. I’ll try again later. I guess the experience was worth something.

You know what they say...
Experience is what you get when you don’t get what you wanted.
 
mpcoppin said:
And the results are in:

FAIL (it didn’t get hard)

Oh well. I’ll try again later. I guess the experience was worth something.

You know what they say...
Experience is what you get when you don’t get what you wanted.
Click to expand...

Can you explain how you did your heat treat?

If you put your blade in, keep checking it with a magnet. Once it gets to non-magnetic, note the colour and keep the blade in a little bit longer. Once the blade gets a shade brighter than when it was non magnetic, take it out and quench.

That said, not all farrier rasps are good for making knives.

I have quite a selection of old files for knife making. From my research old files are better. Look for Globe brand, black diamond, etc .
 
Are you file testing? If so file a little deeper at the edge and verify that there isn’t a layer of decarb. What i mean is it may be hard, but you are filing on a layer of decarb which is softer.
 
S.Alexander said:
Can you explain how you did your heat treat?.
Click to expand...

I have an old (so old I can’t read the mfg. stamping) 8” kiln.

  1. I ran it up to a temp between 1500 & 1600° (verified by #11 & #16 pyrometric cones).
  2. I let it soak for about 10 minutes
  3. I pulled it out of the kiln and stuck it in 2 gallons of canola oil that were pre-heated to 130° in a 12qt stock pot.
  4. I swished it around in the canola oil for about 20 seconds and pulled it out.
  5. I file tested it and it was still soft.
  6. Sad “wah-wah” trombone sound played in my head.

v8r said:
Are you file testing? If so file a little deeper at the edge and verify that there isn’t a layer of decarb. What i mean is it may be hard, but you are filing on a layer of decarb which is softer.
Click to expand...

I was hoping that was the case but I got rid of the carb & it was still soft.

So far my theories are:
  1. Not enough soak time.
  2. To much time to get to the quench (in light of the size of the blade and the ambient temperatures).
  3. I’m dealing with something other than a simple high carbon steel.
 
Update 2:

Upon further research, it appears that my file may not harden unless I do it in brine.

My file is a Simonds and others have had similar problems.

Now to research brine solutions.
 
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