1095 Heat Treat Question

B

Brian West

Member
I did some research and followed the heat treating advice of Kevin....mostly. Where I strayed was with the quenching medium. I understand 1095 requires a fast quenchant like brine or Parks 50. I only have medium oil (canola) so that is what I used. Based on my qualitative observations after quenched it was not quite as hard as it could have been. No surprise right.

So my question is, what HRC should I expect having used the following heat treating recipe with the medium oil.

Stress Relieving at 1200F for 10min
Hardening at 1475F for 10min
Quenched in 5gal of canola at 130F for 7seconds moving up and down (200F when pulled out). Maybe 1sec between oven and oil.
Knocked off scale
Tempered in oven at 400F twice at 2hrs, water quenched after each
Med. straw color when finished, no warps

Had I used the appropriate quenchant, I would have expected 66 HRC as quenched and 62-63 after tempering. Do I have a useable blade? It sure took a sharp edge. Thoughts? Going forward, I will use brine and take the chance or just change steel.

Thanks!
 
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Some folks say they get better results with 1095 and canola by bumping up the hardening temp., a little, around 1550, but not over about 1600.

Your blade is probably usable, but there's always room for improvement, right?
 
So I have answered some of my questions by reading the "Last question for a while" thread. Great info in there. Let me qualify my question a bit more. The blade was 90% ground when heat treated so the edge was ~0.020 thick and the spine was 3/16in thick. If I understand the other thread correctly, I should have been at 65ish at the edge and 64ish at the spine. Am I correct on that?

Second, when tempering, does the act of tempering have a net effect or a gross effect on the final number. Meaning, does tempering at X temp reduce it by Y HRC regardless of starting HRC or does it bring it down to the advertised range regardless of starting number? As I type this, I suspect it is neither and probably a sliding scale of some sort.

In the end, if I was at HRC 65 as quenched and tempered @ 400F would I lose the same 1 point of HRC after tempering or a bit more?

Sorry for my rambling, but this is absolutely fascinating to me and trying to learn without being too much of a pain. If I am asking ridiculous questions, I apologize in advance.

Thanks guys.
 
Thanks One for the fast reply. A question for you. As I understand it, temperature has a greater affect on grain growth then time. Will I be getting into trouble by going over 1475? Would I adjust my soak time at 1550F?
 
Temps., and times: When you change one you usually need to change the other since the two are intertwined.

Grain size can be a factor. If the grain is abnormally small, it can be more difficult to harden. So, whether or not a little grain growth would be a good thing or a bad thing really depends on what the grain size is going into the quench cycle.

Geometry,... edge to spine thickness can also be a factor. For a medium/fast oil on 1095 I think it's a good idea to keep the cross section under 3/16 max. Personally I try to keep it under 1/8 with canola, the exceptions being edge quenched blades, quench lines, hamons etc., which you can go thicker on because you aren't quenching through the spine anyway.

Hardening temps., anywhere between about 1450 to 1600 should be within acceptable standards for 1095, depending on the variables.
 
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Brian West said:
I did some research and followed the heat treating advice of Kevin....mostly. Where I strayed was with the quenching medium. I understand 1095 requires a fast quenchant like brine or Parks 50. I only have medium oil (canola) so that is what I used. Based on my qualitative observations after quenched it was not quite as hard as it could have been. No surprise right.

So my question is, what HRC should I expect having used the following heat treating recipe with the medium oil.

Stress Relieving at 1200F for 10min
Hardening at 1475F for 10min
Quenched in 5gal of canola at 130F for 7seconds moving up and down (200F when pulled out). Maybe 1sec between oven and oil.
Knocked off scale
Tempered in oven at 400F twice at 2hrs, water quenched after each
Med. straw color when finished, no warps

Had I used the appropriate quenchant, I would have expected 66 HRC as quenched and 62-63 after tempering. Do I have a useable blade? It sure took a sharp edge. Thoughts? Going forward, I will use brine and take the chance or just change steel.

Thanks!
Click to expand...
1200F would not be a normalizing heat, at best it would be a stress reliving heat. For proper normalization you must exceed the recrystallization temperature and for a thorough job you would also need to be above the upper critical temp, (Accm) for 1095, which puts you at around 1550F to 1600F, this will prepare the carbide for subsequent treatments and could be followed up with a heat to 1475F -1500F with an air cool for further refinement.

The hardening temp and time are good.

The quench should be sufficient (depending on the thickness of the steel).

How did you determine your hardness? When did you determine it, before or after the tempering?

I cannot tell you what you will get for Rockwell with a given quenchant without actually being part of the process as any number of variables could be affecting the results, all I can say is that I have no problem achieving 66HRC in 1095 thickness up to an beyond ¼” with a fast quench oil. I see no reason as to why the 130F canola should not at least make 65HRC in thickness up to 3/16”.

If the hardness truly is lacking at the edge I would suspect your pre-treatments may have contributed to further carbide separation and interfered with proper solution, or you could be dealing with decarb issues.

Heating 1095 over 1500F will result in increasingly lower hardness and other issues due to retained austenite.
 
I had added the 1200F stress relieving cycle from my O1 recipe. Thanks for the correction on normalization. I was confusing the two because of sequence in reading other recommendations.

The only way I have to determine hardness is "skating" a file over the knife (qualitative at best). Before tempering, on the spine it didn't necessarily grab, but it didn't fly across it either as when I have hardened O1. I wonder if this was just the decarb layer as you suggested? The blade did require significant cleaning.

If I am understanding you correctly, my stress relief (at best) cycle of 1200F really should have been a true normalization cycle as you suggested. This makes sense because I had a heck of a time drilling holes as received from the supplier.

I have read your suggestions about 52100 from the supplier needing an initial normalization at 1650F (then air cooled) before hardening. Other then the temp being different, is this the same dynamic as you describe here for 1095? Meaning you have to prepare the steel for proper hardening procedure as the supplier has put the steel in a state that is best for their machining process but not necessarily for our hardening process? Maybe I am reading too much into this.

Looks like I need to get a Rockwell tester in the future. There is just no way to know what I have without it. Coming from a process oriented manufacturing career, it drives me nuts not knowing. Wonder if I can make one....I digress.

All in all, I have ended up with what I believe to be a useable blade. It takes a superior edge; we shall see how it holds it. The education has been the real benefit. Can't wait to try again.

Thanks One and Kevin!
 
A 1200F stress relieve is not out of line or detrimental at all if done at the correct time and for the correct reasons. The idea is to annihilate the strain energy systems that may have been created in heavy machining. But you would get into trouble if you confused it with normalization which is a much higher temperature treatment that will not only annihilate strain effects but will also recrystallize and dissolve carbide groupings, compared to mere stress relieving it is the full nine yards. What stress relieving does not deal with is carbide refinement, at normalizing temperatures carbides are broken down at stress relieving temperatures carbides gather more carbon, and if you do it a bit longer or a bit warmer it is called “spheroidizing”.


Unless you have the most optimal quenching conditions you should not expect to achieve the same maximum hardness at the spine that you will at the edge with 1095. I would be disappointed if the file bit a little on an O-1 spine but I would actually expect it a bit on a 1095 spine. It is not absolutely necessary to own a Rockwell tester, it is just necessary to know what it is you are testing for. The file will give you exactly what you need to know of you are only looking for scratch type hardness, it just won’t tell you much about penetrative hardness; just as a Rockwell tester won’t tell you much about scratch hardness or abrasion resistance.
Yes this is the same dynamic as with 52100 as they are both hypereutectoid steels, just this is much less extreme since iron carbide such as in 1095 is much more easy to dissolve than chromium carbide, such as in the 52100.
 
The thicker the spine the more likely to see some drop off in hardness with 1095. The thinner, the less likely to see any drop off in hardness. With most knives getting the edge section fully hardened is the main thing. However, a severe drop off in hardness could be a problem, depending on the overall geometry and what the blade is called upon to do.

With differentially hardened blades, I think it's a good idea (in many cases) to beef up the spine thickness for strength, which makes them a bit of a paradox.
 
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