Clamping blades straight after interrupted quench

nickandersonart

nickandersonart

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Aug 5, 2014
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It seems a lot of people address warpage during tempering, but i really like the idea of straightening while the blade is converting to martensite because it's so flexible.

I've read a lot about people straightening blades using gloved hands directly out of an interrupted quench while the blade is still hot, and tried it myself a handful of times with moderate success.

I'm working on a short sword now and as a means to avoid warpage I decided to do an interrupted quench, and immediately out of the quench clamped the blade (lightly) between two pieces of thick steel.

I let it cool for about 10 minutes between the bars of steel and upon removing was happy to see that it was perfectly straight.

I'm thinking now that I'm going to do this for all of my blades. Is there any reason that this would cause issues? Are there other makers doing this as well?


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Trugrit sells plates for tempering. They use plates when needed to straighten blades in tempering and my blades always come back straight.

Many people recommend a heat treater that actually takes a torch to their blades in an attempt to "straighten" them, it blows my mind they tolerate that being done to their knives.
 
Torch straightening ?? Yes there is a valid method for doing it on A36 construction steel ,but thats a low carbon ,non -HTing grade . I've seen it attempted on a high carbon tool steel --a total disaster !!

Better to stress relieve before HT then HTin a way that doesn't add stresses.!!
 
mete said:
Torch straightening ?? Yes there is a valid method for doing it on A36 construction steel ,but thats a low carbon ,non -HTing grade . I've seen it attempted on a high carbon tool steel --a total disaster !!

Better to stress relieve before HT then HTin a way that doesn't add stresses.!!
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Yep, they do it to stainless blades.

It was discussed here awhile back when a member had moon shaped marks on his stainless blades, back from the heat treater, and got the reason why.
 
I don't usually get any warping but just to make sure, I do a oil/plate quench on my W2 blades. I quench in oil for 8 seconds using a up and down motion only. I then pull the blades out, quickly scrape the clay off with a chisel and then clamp between two 1" thick aluminum plates that are attached to the jaws of a woodworkers vise. I have removed warps during the draws and it seems to work fine as well.

As for the torch straightening, I was shown a technique for straightening with a torch with the cutting edge in water by a highly regarded Mastersmith. It is the same technique used to draw the spine back except you put some pressure on the blade to remove the bend. I expect it is also taught at the ABS school.

Bob
 
I clamp my blades between 2 sections of aluminum angle irons. They are mounted in a "loose" table vice. This gives them enough play to conform to distal tapered pieces. Personally, I wouldn't use thick steel plates as they would draw out the heat too quickly.
 
Thanks for the responses guys :) just to be clear, the method I'm referring to is closest to what RangerBob and Rick are talking about, which is clamping straight immediately out of the quench and then letting it cool between the plates. An oil/plate quench essentially.

As for straightening in temper, I would then try that if there was still warp after this method.

As for straightening with a torch, seems kinda risky. it just seems way better to heat the whole blade to tempering heat before straightening instead of doing it locally with a torch flame. Not sure I'd go that route unless it was part of the handle or something that doesn't need to stay hardened.

Is it possible that the clamping between plates after the oil could cause issues with martensite conversion due to it affecting the cooling rate of the steel?


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Rick Marchand said:
I clamp my blades between 2 sections of aluminum angle irons. They are mounted in a "loose" table vice. This gives them enough play to conform to distal tapered pieces. Personally, I wouldn't use thick steel plates as they would draw out the heat too quickly.
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We are talking about tempering with a steel plate, not quenching.

Trugrit used coolant cooled aluminum plates for quenching
 
I've clamped my blade in between to pieces of steel angle iron while it was tempering in the oven and it came out very straight. I was an ungrounded gyuto profile that took a long, shallow bend. Came out fine after the temper.
 
AVigil said:
We are talking about tempering with a steel plate, not quenching.

Trugrit used coolant cooled aluminum plates for quenching
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I believe it is quenching. He wants to interrupt the quench in oil, then clamp the blade straight during the martensite formation phase. I do this for longer/thinner blades all the time. Stacy, put me on to that.
 
Rick Marchand said:
I believe it is quenching. He wants to interrupt the quench in oil, then clamp the blade straight during the martensite formation phase. I do this for longer/thinner blades all the time. Stacy, put me on to that.
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I do the same thing. Quench and agitate for about 8-9 seconds, then into the aluminum plates to keep it all flat. I haven't seen any Ill effects during testing.
 
Rick reminded me that I also have a pretty nifty setup for clamping longer blades with distal taper. I learned it from J.R.Cook and it is two aluminum bars attached to the drop in floating jaws on a parrot vise. I'll try to post a photo later; that Parrot vise is a handy little deal.

Bob
 
Rick Marchand said:
I believe it is quenching. He wants to interrupt the quench in oil, then clamp the blade straight during the martensite formation phase. I do this for longer/thinner blades all the time. Stacy, put me on to that.
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I reread what he wrote, yep do not use steel for the quench.
 
Use two 18" long pieces of 1.5"X1/8" angle iron as the straightening jig. Set the hot blade ( below 900F, but above 500F) between them and clamp with two or three strong spring clamps.

When using this jig to straighten a blade during temper, use two or three small "C" clamps.

There is probably no reason aluminum wouldn't work, but I like the slightly slower cooling rate of the steel.
 
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As you quench -below the critical temp but above the Ms temp -you are in the austenite range .In this area [ see the TTT diagram for that steel ] you have a shorttime to straighten the blade by hand.Once it reaches the Ms you can't bend it easily .
 
Doesn't this method eliminate the benefits of marquenching, though? As I understand it, the point of the interrupted quench is to beat the pearlite nose in the quenchant, and then let the blade transform to martensite evenly and slowly in the air, imparting greater toughness to the blade. Putting it against a heat sink seems like it would nullify that.
 
Tenebr0s said:
Doesn't this method eliminate the benefits of marquenching, though? As I understand it, the point of the interrupted quench is to beat the pearlite nose in the quenchant, and then let the blade transform to martensite evenly and slowly in the air, imparting greater toughness to the blade. Putting it against a heat sink seems like it would nullify that.
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What is your definition of "marquenching"? If you mean simply pulling the piece out below the nose and above the Ms, I would just call that an "interrupted quench". I believe you would need to interupt with a low temperature salt bath above Ms and hold, for it to be considered marquenching. I think you mean the former, "interrupt" method. It won't nullify it but I would imagine it has some affect. I have not noticed any difference by the standardized, highly calibrated, caveman testing I employ in my shop.
 
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Tenebr0s said:
Doesn't this method eliminate the benefits of marquenching, though? As I understand it, the point of the interrupted quench is to beat the pearlite nose in the quenchant, and then let the blade transform to martensite evenly and slowly in the air, imparting greater toughness to the blade. Putting it against a heat sink seems like it would nullify that.
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Not necessarily. I was thinking about this as well but remembered that when I was doing some heat transfer simulations of blades, the majority of heat lost during quenching is actually via Radiation and not natural convection of still air. Above 350 C, radiation plays a more significant role in heat exchange but below that, it's about equal and decreases at an equal rate as well.

If you clamp two plates for straightening, it will indeed act as a heat sink. It would also cancel out the natural convection portion (disrupts flow of air - basically 50% of the loss when below 350 C) and depending on the quality of the surface, it may reflect radiation back.

If you use a thin piece of steel with one side coated with refractory material and the other side polished for clamps, natural convection would be disrupted (~50% heat loss gone). Once the heat sink equalizes in temperature with the blade, there's no more difference in temperature to drive thermal conduction and there would be minimal radiation losses between it and the blade to the surrounding pockets of air. Also, the refractory should prevent the majority of heat loss via radiation from the clamp to the environment. Theoretically, the cooling rate would be even lower than in still air.

Might be worth it to slather on some refractory on the exposed surfaces of the clamps.
 
Marquenching is quenching into a media that is at around 400-500F. It is called marquenching because the quench is at the martensite start point.Molten salt is the normal media. The steel is then allowed to equalize in the salt pot, and slowly cooled in air. This somewhat auto-tempers the steel and makes a slightly tougher structure. In some industrial products where dimensional change and toughness is important, this is an advantage. In a knife blade it makes nearly zero difference. That is why marquenching isn't a common knifemaking practice.

Interrupted quenching is when you quench to below the pearlite nose at 1000F, and once the blade is around 900F remove it from the quenchant. It is then either cooled in still air or placed in a media that will allow slow cooling. This reduces warping, and slightly increases toughness.

Clamping the blade at 900F between straightening plates is somewhere between a regular quench and an interrupted quench. Its main advantage is straight blades on long thin knives.


I suppose if you wanted to warm the plates to above 400F it would be a called an interrupted-mar-plate quench.
 
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