Dreaded Brine Quench--Need Help

bpiatt

bpiatt

Joined
Jun 17, 2010
Messages
644
Hey guys,

I am currently working on a hunting style knife that I would like to gift to a very close friend. The steel is 1095, dimensions are .130in thick, 7.5in overall length, plunge line to tip is 3.5in, and the blade width is 1.069in. The blade is a Full Flat grind and the spine tapers from .130 at the plunge to .050 at the tip. I have left the edge at .075 nearest the ricasso but its .050 at the tip prior to heat treat. My question is concerning heat treatment.

I have an electric heat treating oven, although it does not have digital temperature control. The manufacturer calls it "infinitely adjustable", i played around with all the settings on the dial and have figured out where the dial needs to be to hold certain temperatures. The accuracy of the oven is +/- 20 degrees Fahrenheit.

I wanted to see what you more experienced knife makers think about the process I would like to attempt prior to me attempting it. The biggest thing I am concerned about is that I plan to quench in Brine Water. I got a brine recipe out of the Machinists Bible, it says to add 3/4LB rock salt per gallon of water and allow to dissolve for 2 hours, stirring every half hour or so. I plan to use 5 gallons of water, and 3.75LB of rock salt. I have used canola oil on 1095, blade didn't crack but I did not feel I obtained maximum hardness. I have also tried a brine solution although I used standard table salt and lets just say I was unsuccessful on multiple blades.

I plan to follow this procedure:

Slowly heat knife up to 1550*F, once there let soak for 10 minutes, then remove and allow to Air Cool. (Normalize)

Once knife and Oven are room temperature i plan to place knife back in oven and heat to 1500*F, once temperature is reached I plan to Soak for 20 minutes and Quench in Brine Solution.

I then plan on tempering in a toaster oven at 400*F for two 1 hour cycles. I plan to achieve a final hardness of 58-60.

Questions:

A) Is the +/- 20 degree oven accuracy going to hurt me?
B) Do you feel I left enough thickness at the edge to prevent warping/cracking?
C) Does my brine solution recipe sound accurate?
D) What do you think of my procedure? What would you change?
E) On a blade of this size is there a need to soften the handle of the blade, or will I be ok leaving it the same hardness through out?

I appreciate everything you guys do for us! Thank you!
 
The fastest brine is a 10% salt [table salt will do] in water] Effectiveness will decrease if heated . Don't know about lbs /gallon.
 
I use 7% brine when I do it. That is 2.5 pounds in 5 gallons of water. Just mix with room temp water and stir until it is dissolved. Any rock salt or table salt will work. The brine should be warm...about 80-100F...no more.
For such a small blade, I would use one pound of salt and 2 gallons of water.

As to your procedure and questions:
Those "infinite control" ovens are fine, but you have to watch the temp gauge. They will not hold perfectly at a certain setting. Also, do not put the knife blade in the oven while heating up. It may greatly overheat the blade edge. Those ovens heat up by a timer that governs the on/off time. There is no reading of the temperature to the control...just on for X off for Y. The +/- 20 degrees is fine...but watch the temp readout, adjusting the dial as needed if it drifts up or down too much.
For tempering, they work fine, but you need to let the oven sit at the desired temp for at least 15 minutes to get soaked inside before putting in the blade. Then watch the temp as it recovers from the door being opened and adjust it after about five minutes if needed. Check every ten-fifteen minutes to adjust as needed for the two hour temper cycle. When the first cycle is done, don't touch the dial. Remove the blade and quench in water to cool the blade to room temp ( or your brine...it doesn't matter at 450F). Wipe dry and place back in the oven for another two hours. Remove and quench to cool again. The blade should be ready to clean up and finish,now.

The blade edge is pretty thick as it is now. I would use about .040-.050 for a brine quench. It will not be worse in the quench as is, just more metal to thin down when it is hard.

On a small blade, there is no need to soften the tang unless you are doing some particular function...like drilling the holes you forgot to drill :)
If the whole knife is properly tempered at 450F, the tang and blade will be hard and tough.

Bring the oven to 1500F for at least fifteen minutes, and place blade in oven.
Allow the oven to return to 1500F and soak for 10 minutes.
Remove and let cool in the air. Turn off the oven, keeping the door shut.
Place knife blade back in the oven when the temp reaches 1450F. Set temp control to 1 number less than the 1500F setting. Let sit for ten minutes. Adjust setting on oven if needed to keep between 1400F and 1450F.
Remove and quickly quench in oil ( canola will be fine). Turn off oven .
Place back in the oven when the temp drops to 1350F. Let sit for 10 minutes ( temp drop will be OK, but keep above 1250F). Remove and air cool.
Set oven at the setting to hold at 1450F, let sit at 1450F for 15 minutes, place blade in oven. When oven returns to 1450F, soak for 10 minutes and quench in the warm brine.
Temper at 450F for two hours twice.
 
bladsmth said:
I use 7% brine when I do it. That is 2.5 pounds in 5 gallons of water. Just mix with room temp water and stir until it is dissolved. Any rock salt or table salt will work. The brine should be warm...about 80-100F...no more.
For such a small blade, I would use one pound of salt and 2 gallons of water.

As to your procedure and questions:
Those "infinite control" ovens are fine, but you have to watch the temp gauge. They will not hold perfectly at a certain setting. Also, do not put the knife blade in the oven while heating up. It may greatly overheat the blade edge. Those ovens heat up by a timer that governs the on/off time. There is no reading of the temperature to the control...just on for X off for Y. The +/- 20 degrees is fine...but watch the temp readout, adjusting the dial as needed if it drifts up or down too much.
For tempering, they work fine, but you need to let the oven sit at the desired temp for at least 15 minutes to get soaked inside before putting in the blade. Then watch the temp as it recovers from the door being opened and adjust it after about five minutes if needed. Check every ten-fifteen minutes to adjust as needed for the two hour temper cycle. When the first cycle is done, don't touch the dial. Remove the blade and quench in water to cool the blade to room temp ( or your brine...it doesn't matter at 450F). Wipe dry and place back in the oven for another two hours. Remove and quench to cool again. The blade should be ready to clean up and finish,now.

The blade edge is pretty thick as it is now. I would use about .040-.050 for a brine quench. It will not be worse in the quench as is, just more metal to thin down when it is hard.

On a small blade, there is no need to soften the tang unless you are doing some particular function...like drilling the holes you forgot to drill :)
If the whole knife is properly tempered at 450F, the tang and blade will be hard and tough.

Bring the oven to 1500F for at least fifteen minutes, and place blade in oven.
Allow the oven to return to 1500F and soak for 10 minutes.
Remove and let cool in the air. Turn off the oven, keeping the door shut.
Place knife blade back in the oven when the temp reaches 1450F. Set temp control to 1 number less than the 1500F setting. Let sit for ten minutes. Adjust setting on oven if needed to keep between 1400F and 1450F.
Remove and quickly quench in oil ( canola will be fine). Turn off oven .
Place back in the oven when the temp drops to 1350F. Let sit for 10 minutes ( temp drop will be OK, but keep above 1250F). Remove and air cool.
Set oven at the setting to hold at 1450F, let sit at 1450F for 15 minutes, place blade in oven. When oven returns to 1450F, soak for 10 minutes and quench in the warm brine.
Temper at 450F for two hours twice.
Click to expand...

Thank you for such a detailed response Blad, I am going to follow these instructions exactly. Can you please explain to me what happens to the steel when I quench in the canola, then put back in oven, and then air cool? Also, what will my projected hardness be tempering at 2-2hour cycles at 450? Thank you so much for the support!
 
Those three steps - 1500/1450/under1350 are to normalize the blade and get the grain structure small for the final quench. At the 1500F step, the blade air cools into pearlite. At 1450F, it is quenched into a medium fast oil and becomes martensite ...with some pearlite hanging around. The grain structure should be fine and even. At 1350F, and an air cool, you remove all stress from the blade and end with a fine grain pearlite blade. Straighten if any is needed and then do the final HT quench in brine.

The dreaded "PING" may still happen, but you did everything you could to avoid it. I feel that you will be fine on a small blade like this.

I did not mention it, but you should get the blade into the tempering oven as soon as possible after the final quench. 1095 that has been water/brine quenched can crack just sitting there before tempering. I set the kitchen oven to 450F and have it on before I do the quench. After checking the blade, and washing it off, I immediately place it in the oven within minutes of the final quench. If doing yaki-ire, this is very important.

I would suggest you do a clay coated spine and shoot for a hamon ( yaki-ire) since you are doing a brine quench anyway. That will also give you a softer spine and tang. On a small blade like yours, take the thicker clay to about 3/8" to 1/2" from the edge in a simple slightly wavy line. Adding some ashi is OK, but probably not needed. See tutorial below for explanation.
Here is a tutorial I put up a while back:
http://www.bladeforums.com/forums/showthread.php/712415-Hamon-Formation
 
Thanks again, Stacy. I've never attempted a hamon before and this sounds like the perfect knife to give it a shot on. I am going to pick up some Satanite and give it a shot. I noticed in the thread you provided that I should coat the entire blade in thin slurry and then apply thicker satanite to the spine. What is the reason for the thin coating over the entire blade? Does it help decrease the difference in cooling between spine and edge so its not so drastic? Also, will a hamon help decrease my odds of hearing "ping", or increase them?
 
The thin coating actually speeds up the quench, and helps prevent cracking. It is just a thin coating of buttermilk thick slurry. Let it dry well and then apply the thicker layer to the spine. The thicker layer isn't all that thick, BTW, 1/8" max.
 
mete said:
The fastest brine is a 10% salt [table salt will do] in water] Effectiveness will decrease if heated . Don't know about lbs /gallon.
Click to expand...

If you can measure in metric, 10% is pretty easy

10 grams of salt in 100ml of water

or 378 grams in 3.78 litres
Which is 378 grams in a US gallon

13.5 weight oz in a US gallon
 
Ok, thanks again Stacy. Tommorrow I'm going to see if I can pick up any Satanite locally , if not ill order some online. Ill be sure to take some pictures and let you guys know how I make out. I appreciate the help, its nice having so much knowledge in one place where answers to questions are near instant.
 
I leave the edge thick and quench vertically and have had great luck with brine quenching. I actually like brine quenching, no oil that makes stinky smoke and no foil wrap.

I just quenched 2 this way on Friday, it is always exciting.
 
Daniel Fairly Knives said:
I leave the edge thick and quench vertically and have had great luck with brine quenching. I actually like brine quenching, no oil that makes stinky smoke and no foil wrap.

I just quenched 2 this way on Friday, it is always exciting.
Click to expand...

Awesome! Glad to hear you had success, how big were your blades? Did you try for a hamon?

Also, sorry if this is a dumb question but I just wana make sure I do this right as this knife is special to me since its for such a close friend. I apply the clay after I normalize, right?
 
bpiatt said:
Awesome! Glad to hear you had success, how big were your blades? Did you try for a hamon?

Also, sorry if this is a dumb question but I just wana make sure I do this right as this knife is special to me since its for such a close friend. I apply the clay after I normalize, right?
Click to expand...

The most recent ones were about 6 and 7 inches long. With long blades there is more chance for warp in my experience.

I'd apply the clay after the last normalizing cycle but I am no hamon pro, I am just looking for a full quench on water hardening steels.

Good luck, it is satisfying when it all goes well!
 
Daniel makes a good point. Even if you don't put a thicker area of clay to get a hamon, putting a wash of clay over the whole blade will give a better water/brine quench.
 
Have you considered an interrupted quench? I have had good luck with brine for about 4 sec then into canola oil. I think you get the best of both worlds the speed of brine when it counts, and the safety of canola
 
Nebulae said:
Have you considered an interrupted quench? I have had good luck with brine for about 4 sec then into canola oil. I think you get the best of both worlds the speed of brine when it counts, and the safety of canola
Click to expand...

Honostly, I've never given that any thought. Do you feel you still achieve maximum hardness this way? Is it more for larger blades or do you use this method on all of them?
 
Metallurgically, an interrupted quench going from brine to canola is not going to make much difference for a shallow hardening steel.
If you quench 1095 in the brine for 4 seconds, the pearlite nose is passed. Removing it from the brine for a few seconds allows it to stop the cooling and equalize the temperature differential between the spine and the edge a bit. It will be about 700F at that point. After that, you can put it back in the brine or in canola...or any warm coolant, and it will drop down past the Ms at about 400F. The type of coolant will be of minor difference at this point. The oil may be a bit milder, but there will be likely little difference on a small blade like this. It is the cooling rate between 400 and 200 that makes the most difference in controlling warp in long blades. This is where a low temp salt pot is superb. On a long blade, I could see some reason to try a brine to oil switch.

What I do is use multiple interruptions. In for 3-4 seconds, out to inspect and straighten, in for a few seconds, out,in,out in, until it stops steaming off the water ( below 200F). then I put it in and let it sit for a few minutes and after a quick inspection, temper immediately. Any secondary straightening is done at temper temp on the first and second temper.
 
I forgot to mention I do an interrupted quench, usually 5 in, 5 out repeated a few times until it is almost hand cool, the steam point as pointed out. I then hang the knife from a nail in still air and cool to room temp, after that I temper immediately with water hardening steels.
 
Ok I decided to normalize and heat treat the blade today with out trying a hamon only for the fact I didn't want to wait for clay. Normalizing went great and I did not get the ping when I quenched in brine. I have no cracks but the blade did warp to one side. Its not horrible but it definitely needs correction. I currently have the knife in the tempering oven at 425 degrees. After 2 hours I plan to remove it and use a "C" clamp to clamp it to a thick piece of aluminum. I then plan to temper at 425 again for 2 hours. Is this how you guys would fix a warped blade of 1095?
 
bpiatt said:
Ok I decided to normalize and heat treat the blade today with out trying a hamon only for the fact I didn't want to wait for clay. Normalizing went great and I did not get the ping when I quenched in brine. I have no cracks but the blade did warp to one side. Its not horrible but it definitely needs correction. I currently have the knife in the tempering oven at 425 degrees. After 2 hours I plan to remove it and use a "C" clamp to clamp it to a thick piece of aluminum. I then plan to temper at 425 again for 2 hours. Is this how you guys would fix a warped blade of 1095?
Click to expand...

That will probably work, you may need to shim it and over correct the bend depending on the severity and a few other variables.
 
also the aluminum should be pretty thick, its not to strong, and looses what strength it has very quickly with heat. just make sure you are not bending the aluminum
 
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