Heat Treating - Can someone help me understand what Murray Carter is doing?

S

Steve98

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Dec 23, 2015
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Hi, I was watching this youtube video:

https://www.youtube.com/watch?v=HrasEQhVOLo

...and at about 12:40ish, Murray goes to heat treat the knife. First he coats the entire blade in some kind of clay or dirt wash, and then heats it and quenches it.

I assume the clay wash is to prevent scaling in the forge.
Murray doesn't say in this video, but based on his other videos I assume he's working with a hypereutectic steel (I think his steel is over 1% carbon). I would assume that means it'll have a TTT profile similar to 1095, and thus require really quick quenching to harden properly. Why isn't the clay interfering with the heat treat?
Will any clay do the job?

Note that earlier he also anneals the blade by letting it cool in a bucket of straw ash. I know that people also use vermiculite. Can I use really any kind of ash and get the same effect? I have neither straw nor vermiculite but can get regular old wood ash.

Can anyone help me understand the details a bit better?

Thanks in advance,

Steve.
 
Yes it's a thin 'wash' of clay used to eliminate scale and decarb. But the clay is very thin and have little effect on the quench.
Straw ash is not significant except that it insulates the blade so it cools slowly .Any insulating material would work.
 
As I understand it, a thin clay wash can actually speed up the quench a bit as well.
 
From what I understand of yaki-iri, the thin clay wash creates many sites of nucleation for the vapor jacket ( nothing todo with nucleation in steel grain). This allows the transfer of heat to be faster and the jacket collapse to be quicker. All of my water quench steels get a thin wash of satanite. I do it on some blades quenched in Parks #50, too. It is done as the first step in putting on the clay for a hamon.
 
Steve98 said:
Note that earlier he also anneals the blade by letting it cool in a bucket of straw ash. I know that people also use vermiculite. Can I use really any kind of ash and get the same effect? I have neither straw nor vermiculite but can get regular old wood ash.

.
Click to expand...

I don't care for the super fine dust in wood ash.

Plus vermiculite has all those cancer/asbestos warnings


Try Perlite from a garden store or the garden section of Home Depot
http://www.homedepot.com/p/Vigoro-2-cu-ft-Perlite-Soil-Amendment-100521091/205655210

I've seen people pick up old metal Coleman coolers at garage sales for that.

The sealing lid would retain heat and be convenient.

I'm still looking for one on the cheap, but they are vintage and retro now...
Big ammo cans might work though.
 
Rick Marchand said:
As I understand it, a thin clay wash can actually speed up the quench a bit as well.
Click to expand...

That was always my understanding. makes the quench faster and more "even", less harsh on the blade. We use wood ash's to anneal in or if its the right time of day we'll stick it in the heated kiln at the end of the night to cool slowly overnight. That works very well too.
 
The thing to consider is that slow cooling annealing works for steels with less than 0.84% carbon.
For hypereutectoid steels it will do harm and you should spheroidize instead. An home brew to do this (without proper equipment) is trough repeated heats below critical with air cooling in between...if the steel becomes magnetic you'll have to start again.
 
12345678910 said:
I don't care for the super fine dust in wood ash.

Plus vermiculite has all those cancer/asbestos warnings


Try Perlite from a garden store or the garden section of Home Depot
http://www.homedepot.com/p/Vigoro-2-cu-ft-Perlite-Soil-Amendment-100521091/205655210

I've seen people pick up old metal Coleman coolers at garage sales for that.

The sealing lid would retain heat and be convenient.

I'm still looking for one on the cheap, but they are vintage and retro now...
Big ammo cans might work though.
Click to expand...

I think the ash he uses is from the rice plant. Read one of his books a year or so back and can't remember specifically.
 
Rice straw ash is he traditional material for many shop processes in the Japanese method. It produces a fine ash with a high silica content. This is used for making clays, as a flux, as a insulating material, and as a cleaning agent.There is no magic to the material, but it is always available and always consistent, so it is what they use.
 
Steve98 said:
Hi, I was watching this youtube video:

https://www.youtube.com/watch?v=HrasEQhVOLo

...and at about 12:40ish, Murray goes to heat treat the knife. First he coats the entire blade in some kind of clay or dirt wash, and then heats it and quenches it.

I assume the clay wash is to prevent scaling in the forge.
Murray doesn't say in this video, but based on his other videos I assume he's working with a hypereutectic steel (I think his steel is over 1% carbon). I would assume that means it'll have a TTT profile similar to 1095, and thus require really quick quenching to harden properly. Why isn't the clay interfering with the heat treat?
Will any clay do the job?

Note that earlier he also anneals the blade by letting it cool in a bucket of straw ash. I know that people also use vermiculite. Can I use really any kind of ash and get the same effect? I have neither straw nor vermiculite but can get regular old wood ash.

Can anyone help me understand the details a bit better?

Thanks in advance,

Steve.
Click to expand...

I didn't watch the video, but in general I think most all of Murray Carter's knives are either white paper or blue paper steel, laminated to a lower carbon steel. Yes, the carbon content on these types of steel is similar to 1095, and they do require a fast quench. If you are thinking of using a fast quench steel and are just starting out, I would recommend you try and get some parks 50 quench oil. When I quenched 1095 in water, more blades cracked then came out good, but then again none were laminated, and that may help.
 
stezann said:
A home brew to do this (without proper equipment) is through repeated heats below critical with air cooling in between...if the steel becomes magnetic you'll have to start again.
Click to expand...

You must have meant to say non-magnetic.
 
Steve98 said:
I assume the clay wash is to prevent scaling in the forge.

and thus require really quick quenching to harden properly.
Why isn't the clay interfering with the heat treat?
Will any clay do the job?

Note that earlier he also anneals the blade by letting it cool in a bucket of straw ash. I know that people also use vermiculite. Can I use really any kind of ash and get the same effect? I have neither straw nor vermiculite but can get regular old wood ash.
Click to expand...

you can read my writeup here - http://www.bladeforums.com/forums/showthread.php/1397121-laminated-Hitachi-White-and-Blue-Steel-Heat-Treat-Process?p=16104069#post16104069

"prior to hardening , thinly coat blade with clay slurry

I use a clay slurry that I made myself based on some online research and my experience of what Carter uses. This prevents the vapor barrier from forming when the hot steel in inserted into the quench water. The mixture is mostly ball clay, iron filings, charcoal powder, iron oxide. Most items were purchased from Aardvark Clay and Supplies in Santa Ana. The clay tends to get thicker (and settles to the bottom) as the water evaporates, so just add some water and stir everytime you use it. The clay slurry is very thin and it’s a light, almost see-thru coating). Again the purpose is to help the blade cool faster.

Dip the blade into the clay slurry, use the mixture to clean the blade by rubbing the blade back and forth in your fingers. Only the blade needs to be coated, not the tang.
With tongs, place the wet coated blade into the forge to dry and harden the clay coating. The clay will change color as it dries up. This only takes 20 seconds or so. The clay dried should be thin enough to “see through”. Set the blade on a rack or brick."

so answers are

1) no
2) the steel doesn't "require" water quenching, he does to get the maximum performance out of the steel.
3) it prevents a vapor barrier and aids in the quench, not interfere
4) no
5) i think your ash would be suitable
 
stezann said:
The thing to consider is that slow cooling annealing works for steels with less than 0.84% carbon.
For hypereutectoid steels it will do harm and you should spheroidize instead. An home brew to do this (without proper equipment) is trough repeated heats below critical with air cooling in between...if the steel becomes magnetic you'll have to start again.
Click to expand...

Stezann, the process annealing (slow cooling annealing) that Murray uses does work,
I use it myself on all laminated steels. I'm not aware of what harm it does,

spheroidize heat treat has its place but I would say it's not required with the high carbon laminated steels

regards
 
Last edited:
HSC, I'm curious to hear your experience; around what temperature would you say Murray annealed his blades at? (I know the manufacturer specs for shirogami steel say 740-770 C for annealing, but it's not clear to me whether they are actually recommending a rice ash anneal at these temps). Would you say the blades were sub-critical when going into the ashes or was the temp similar to what he quenches at?

I believe a sub-critical rice ash anneal would be fine for hypereutectoids, since this isn't going to lead to carbide precipitating in the grain boundaries.
 
Tenebr0s said:
HSC, I'm curious to hear your experience; around what temperature would you say Murray annealed his blades at? (I know the manufacturer specs for shirogami steel say 740-770 C for annealing, but it's not clear to me whether they are actually recommending a rice ash anneal at these temps). Would you say the blades were sub-critical when going into the ashes or was the temp similar to what he quenches at?

I believe a sub-critical rice ash anneal would be fine for hypereutectoids, since this isn't going to lead to carbide precipitating in the grain boundaries.
Click to expand...

definitely subcritical
in the dull cherry red color range is what I look for
 
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