Cyro treating 1095

J

Jack Henry

Joined
May 15, 2015
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hey guys so I statrted heat treating my own blades a while ago. And when i use 1095 i just cant seem to get complete formation of martinsite and ive tried many diffrent oils and water with brine for the quenc. i have also raised and lowered my temp but its still not getting what im after the steel is brittle but dosnt hold a good edge:( i have no idea why. I know people use dry ice treating on stainless annd i was wondering if this might help my problem with 1095. or if you have another solution i would love to hear it. Also if anyone could tell me what the deal is with being brittle but bad edge renetion that would be nice to know. Thanks in advance
 
If your 1095 is coming out "wrong" then theirs something else wrong entirely...Whats your HT regimen for 1095? Tell us that so we know were to start..
 
I will load the blades in my oven cold and let them come up to 1475. After a 10 minute soak I quench them. I usually quench up about an inch from the edge. Also I quench them in warm vehicle oil or salt water. After the quench they go right into the oven at 400 for 1 hour. Then I let it cool. After that I usually put it back in at 400 for an hour. That's my recipe for 1095
 
Cryo will do nothing to help 1095 harden. The Mf is around 200F. By the time it is at room temperature, it is completely hardened ( as much as it will be).

Look at the things that will affect a shallow hardening steel and make it less hard.

1) Quenchant. Motor oil will not quench 1095. It is a bad quenchant to start with, and far too slow for 1095. The best oil for shallow hardening steels id Parks #50 or a similar commercial quenchant. Second is probably 120F canola oil. Also, the quantity of quenchant is important. For a normal size blade, it takes a minimum of a gallon. For large blades, two or three gallons is better. The whole job of the quenchant is to remove the heat from the blade in a set time. If there isn't enough volume of oil, the blade gets surrounded by hot oil ... not what you want. For complete hardening, use a full quench ... straight in point first and move the blade back and forth in a cutting motion as well as up and down.

"Salt water" can be a lot of things. It should be a 7-10% solution of salt in water to make the brine for knife quenching. Put 3# of rock salt in five gallons of water and use that. A brine quench has to be a full quench straight in all at once.

2) Steel internal condition . The steel needs to be ready for hardening. The carbon and any alloying needs to be properly distributed and ready t convert to martensite. Do a series of thermal cycles prior to the final quench. Some steel comes so completely spheroidized from the supplier that it has to be taken above 1700F and cycled down to break it up and harden.


3) Temperature. Verify that your 1475°F is really 1475. Put some rock salt crystals on a piece of scrap steel in the oven and set to 1475°F. It should melt right at that point. Wait about 10 minutes, and if it is still solid, raise the oven 10°. The point where it melts ( after a 10 minute soak) is 1475F.

4) Steel. Just because it was a file doesn't make it 1095 ( e.g.). Know the source of your steel. If bought from a reputable supplier, it is most likely right. If sourced from "found steel" or a scrap yard, it may not be what you think. However, even the best suppliers get steel mixed up. Test a known sample that has worked well against the suspect steel if a problem persists no matter what you do.


5) The edge quench - Most likely problem. This may only partially harden the steel as well as when you pull it out of the quench, the hot spine may quickly pull the new martensite back into partial pearlite. I don't ever recommend an edge quench, but if you do one on a shallow hardening steel, after the first three seconds, fully immerse the entire blade and let drop below 900F before removing from the oil. Check quickly for warp, and return the blade to cool in the oil below 200F.
 
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You mentioned that you are putting your blades in cold. Do you mean that the oven is at heat and you are putting cold blades into a hot kiln... or that you are placing the blades into a cold kiln and letting them heat up together?

The kiln should be equalized at the target heat before putting your blades in. If not, you risk severe over-heating, which may also be the culprit.
 
So, putting your blades in a cold HT oven and letting them come up to temp with the oven is a no-no?
 
Not so much a no-no, as it is a bad idea. The temps may swing wildly as it starts heating, plus radiant energy may be high in the early heat stages. The blade may greatly exceed the target for a while, which could cause grain growth and more scale/decarb.

Either place the blades in an oven that has already reached the target and stabilized, or set a pre-heat step about 200F below the target and place the blades in then.
 
Depending on the source, the steel may be highly spheroidized, or worse in a lamellar annealed state. Refining the carbide distribution and grain structure/size through normalizing and thermal cycling will set up the steel for consistent, predictable results once you have your sequence worked out for this steel.
 
Willie71 said:
Depending on the source, the steel may be highly spheroidized, or worse in a lamellar annealed state. Refining the carbide distribution and grain structure/size through normalizing and thermal cycling will set up the steel for consistent, predictable results once you have your sequence worked out for this steel.
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Yes... this is also good practice.

With regard to the cold kiln scenario... I use a Sugar Creek Kiln with an Orton Auto-Fire Express controller and performed some tests to see how much the kiln over shot the mark on ramp-up. On FULL ramp-up speed it almost went 200F over the mark. Some makers do what Stacy explained and run a program that would ramp up short, then creep up to the target temp. I personally just let the kiln ramp up at FULL and put the blades in once it is at temp. I find it easier to judge soak times that way, too.
 
Would it make any sense to put a thin mild steel "shield" next to the elements to not have that radiant energy spike? I have tinfoil set up on my little tempering oven for the same reason.
 
Maelstrom78 said:
Would it make any sense to put a thin mild steel "shield" next to the elements to not have that radiant energy spike? I have tinfoil set up on my little tempering oven for the same reason.
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seems easier to simply preheat the oven and let it stabilize before putting the blade in.
 
Mine will overshoot at lower temps but at SS temps the temp is rising slowly enough that it can control it better. It will really overshoot at tempering temps. I just set it where I want it and put them in after it stabilizes.
 
What kind of oven do you have? I you reasonably certain you're getting to 1475F? I agree with the suggestions to let it come to temp first and equalize. If I'm planning on heat treating on a given day, I turn my ovens on as soon as I get into the shop and let them reach and hold temp for as long as possible.
Stacy's suggestions for 120F canola is good, and likely one of the best "home brew" alternatives to using a more expensive engineered quenchant. That said, if you have some extra funds you're willing to throw at this heat treat thing, give maxim oil a call and get yourself 5 gallons of Parks #50. It'll run about $120 to $130 IIRC.

Also, make sure you're not hesitating for too long in between removing the blades from the oven and plunging them into the quench. 1095 requires a little speed in this step, so that the temp doesn't drop too low.

When tempering, I assume you're seeing a fairly even straw color on the blades?
 
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