Using tempering salts to quench Elmax, M390, K390...

T

twistedneck

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Dec 22, 2005
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I was wondering if I can improve the heat treat of these exotic alloys by quenching them at some intermediate temperature using my tempering salts. I can hold that molten salt quench temp from about 300F to 900F...

A lot of these require a 4bar quench, or oil. I can do either although i've never used a 4 bar quench since i'm new to these exotic alloys air or water or salt always worked before.

Is there a benefit to salt pot quenching any of these alloys? I use it to grow bainite at good hardness levels with 52100, but I think these PM alloys are not really steel they are something different.

CPM 3V
K390

Elmax
M390
 
Not sure what the question is?
If you are familiar with salt quenching, you know the speed and evenness of salt. Were you concerned that it would be too fast?

BTW, they are steel alloys. Steel quenches in predictable ways depending on the alloy content. Salt pots can be quite useful for marquenching and austempering, but hold no magic beyond a very even and complete quench. Since PM high alloy steels are not candidates for marquenching or bainitic growth, I see no need for the salt pots in quenching 1900F steel that will cool nicely in air or slow oil. A good blower and a long section of 2-3" pipe will make a nice high air flow 4 Bar quench tank. Place the blower hose on one end and mount the pipe upright. Turn on the blower, and lower the hot blade into the tube. A pair of vise grips works nicely as a holder/clamp to suspend the blade in the tube. The air will cool the blade evenly and at a proper rate. Warpage is minimal this way.
 
bladsmth said:
Not sure what the question is?
If you are familiar with salt quenching, you know the speed and evenness of salt. Were you concerned that it would be too fast?

BTW, they are steel alloys. Steel quenches in predictable ways depending on the alloy content. Salt pots can be quite useful for marquenching and austempering, but hold no magic beyond a very even and complete quench. Since PM high alloy steels are not candidates for marquenching or bainitic growth, I see no need for the salt pots in quenching 1900F steel that will cool nicely in air or slow oil. A good blower and a long section of 2-3" pipe will make a nice high air flow 4 Bar quench tank. Place the blower hose on one end and mount the pipe upright. Turn on the blower, and lower the hot blade into the tube. A pair of vise grips works nicely as a holder/clamp to suspend the blade in the tube. The air will cool the blade evenly and at a proper rate. Warpage is minimal this way.
Click to expand...

I was hoping to use tempering salts as a jack of all trades quench and avoid bringing in oil and / or setting up a 4 bar quench tank since i have not studied those yet, but what you have just said clarifies what that is sounds like its a simple project and i know there is a lot of info on it here. I believe all of the stainelss alloys including exotics are ok to plate / air quench, time for me to learn that new skill.

I know some of the crucible heat treat sheets callout out quenching into 900F salt then air cooling in still air, but that sounds like more trouble than its worth as you know firing up a salt pot can be an undertaking and quite scary since I dont use a tapered rod.

Thanks for the reply.
 
For a bit more info . The cooling rates are critical .I don't have figures at hand for salt but for oil it's about 770 F /sec depending on type of oil. Copper plate will give 390 F/sec . Some of the stainless steel knife steels such as 12c27 and N690 have oil hardening recommended for best performance .
 
Did more research and found a better HT guide for elmax (and by hopeful rule of similarity - m390).


http://www.bucorp.com/files/Elmax__HTR_Rev_Jan16_2008.pdf

Alternate quenching method 1 is interruputed salt quench first in salt 390-900F (390F if i dont mind the risk of distortion and cracking) - i think the warmer the salt the less distortion but also less properties. After initial quench then equalize in salt bath then pull out and air cool to 150F and then room temp, then cryo for 3 to 4 hours and into the temper after it comes to room temp.

Looking at the alloys, the general difference in heat treat between Elmax and M390 is small - 2100F f or 15min then temper at 300F for Elmax, 2100F for 20min, temper at 250F for M390, so i'll give it a try and see if M390 works with salt quench also. I can get some micro's and harness readings, maybe decarb but i wont be able to do much impact testing except with my own knives. is there any way to tell from a specimen if you have made a bad heat treat with these extreme alloys?

K390 has similar quenching behavior but MUCH higher tempering temps - since there is no double hardness peak, but thats proably because it competes with the hot form steels. Why dont they recommend cryogenic treatment for K390?

http://www.crucibleservice.com/eselector/prodbyapp/tooldie/cpm3vt.html
Finally - cpm 3v demands hotter quenching salt, about 1000F, equalize then air cool and i can only hit about 900F safely so we'll see how that goes. No mention of cryo again, not sure if this is typical with carbon steel that no cryogenic is required.
 
That is what I was implying.
The salts will pull the temp down fast and evenly. There is no vapor jacket, so there is no uneven cooling. Once the blade drops to the salt temp, you will have to cool it in another media, most likely air, to get the blade to convert to martensite. Cryo will be needed to deal with the carbides and RA.

So.....the salt is just a cooling step in the quench, and can be replaced with cheaper and easier quenchants like aluminum plates, air , and Parks AAA.

So....while it will work, the salt pot will need to come up to temp, which can take a long time depending on your pot size and heating system......only be in use for about 60-120 seconds....hardly worth the trouble.
 
bladesmth, is there not an advantage cooling quickly from 2100f to 900F? In the Elmax heat treat guide from Buehler it states "quench as quickly as possible" - i think it means the first part of the quench not the second, but hell they both might be critical. I am still buidling an air quencher for obvious reasons you stated, and i am not sure if its BETTER to let the blade 'still air cool' after the salt or to do a 2 or 4 bar quench on it?

I'm sure there will be cracked blades, but thats the nature of the beast! any idea abou the min thickness the edge should be before heat treating these? i have Argon but i cant pump all the flow i want w/o causing the oven to cool below 2100F, so there will be decarb. whats the best way to limit it with my primative kf22 evenheat kiln? it decarbed the living hell out of 4130 until i cranked up the homegrown argon feed.

how do you deal with decarb? i didn't want to use the stainless envelope thing because it will reduce cooling rates but with these slow cooling alloys maybe thats not so bad.
 
Don't sweat the time. When they say "Quench as quickly as possible" they are referring to the order of the process, not specifically to the speed of the process. The steel has a goodly time before it will reach the pearlite nose. Move efficiently, but safely. A stainless envelope is the best way to deal with decarb.

Remove the envelope from oven,
cut the packet open,
remove the blade,
quench in oil/air/salt/aluminum plates,
allow to cool to room temp,
snap temper,
cryo,
temper,
cool to room temp,
temper.
 
bladsmth said:
Don't sweat the time. When they say "Quench as quickly as possible" they are referring to the order of the process, not specifically to the speed of the process. The steel has a goodly time before it will reach the pearlite nose. Move efficiently, but safely. A stainless envelope is the best way to deal with decarb.

Remove the envelope from oven,
cut the packet open,
remove the blade,
quench in oil/air/salt/aluminum plates,
allow to cool to room temp,
snap temper,
cryo,
temper,
cool to room temp,
temper.
Click to expand...

thanks very much bladsmth.. w/o that snap temper i'd be snapping blades. i'll go up to 250F for about 30min on the M390 and Elmax snap, but that high temp K390 since it doesnt need cryo (or does it, even though the heat treat write up does not mention it) i dont need a snap temper. I will have HT results next week for these alloys and post results here.
 
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