Difficulty with S35VN heat treat. Frustrating

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godogs57

Joined
Apr 16, 2004
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My second batch of S35VN has pretty much turned out like my first. Not hardening sufficiently. CPM154 is my primary steel and I have zero issues with my ht process, getting 60.5-61.0 every time. Figured I’d try the 35 and see what happens.

Both times my process has been: 1950 @ 30 minutes, aluminum plate quench and get into liquid N @ under ten minutes for two hours. Temper twice @ 400 degrees/2 hours. My hardness tester says 54-55 on the blades at the conclusion. I cant really point my finger at the oven….perfect results on other steels. Hardness tester? Test blocks say it’s on with my new diamond indenter. Made a test knife to see if it was my imagination and the diamond sharpener is just eating up the blade….it’s indeed soft. A shaving edge has proven to be impossible. Six blades trashed this time.

Pulling my hair out over this. I’ve never done this before but with my blades, could I anneal them and start the ht process over? Suggestions for next time? Thanks in advance guys.
 
godogs57 said:
My second batch of S35VN has pretty much turned out like my first. Not hardening sufficiently. CPM154 is my primary steel and I have zero issues with my ht process, getting 60.5-61.0 every time. Figured I’d try the 35 and see what happens.

Both times my process has been: 1950 @ 30 minutes, aluminum plate quench and get into liquid N @ under ten minutes for two hours. Temper twice @ 400 degrees/2 hours. My hardness tester says 54-55 on the blades at the conclusion. I cant really point my finger at the oven….perfect results on other steels. Hardness tester? Test blocks say it’s on with my new diamond indenter. Made a test knife to see if it was my imagination and the diamond sharpener is just eating up the blade….it’s indeed soft. A shaving edge has proven to be impossible. Six blades trashed this time.

Pulling my hair out over this. I’ve never done this before but with my blades, could I anneal them and start the ht process over? Suggestions for next time? Thanks in advance guys.
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maybe this would help you
knifesteelnerds.com

S35VN Steel - Properties and How to Heat Treat - Knife Steel Nerds

Information on how S35VN compares with other knife steels and how to best heat treat it for optimal hardness and toughness.
knifesteelnerds.com knifesteelnerds.com
 
Maybe not enough time at temperature? Do you put the blade in at temp? Let the oven settle for a while? How do you do the time?

Assuming you are hardness testing clean, non decarbed steel.

Just some thoughts. I’m interested to hear what the experts say. When it calls for 30 minutes I either give it another 5 minutes at least, or start the time when the oven gets back to temp.
 
godogs57 said:
My second batch of S35VN has pretty much turned out like my first. Not hardening sufficiently. CPM154 is my primary steel and I have zero issues with my ht process, getting 60.5-61.0 every time. Figured I’d try the 35 and see what happens.

Both times my process has been: 1950 @ 30 minutes, aluminum plate quench and get into liquid N @ under ten minutes for two hours. Temper twice @ 400 degrees/2 hours. My hardness tester says 54-55 on the blades at the conclusion. I cant really point my finger at the oven….perfect results on other steels. Hardness tester? Test blocks say it’s on with my new diamond indenter. Made a test knife to see if it was my imagination and the diamond sharpener is just eating up the blade….it’s indeed soft. A shaving edge has proven to be impossible. Six blades trashed this time.

Pulling my hair out over this. I’ve never done this before but with my blades, could I anneal them and start the ht process over? Suggestions for next time? Thanks in advance guys.
Click to expand...

I don t know if this make any difference but from Larrin article .... I heat treated a range of S35VN specimens using a 30 minute austenitize for 1925 and 1950°F, and 15 minutes for higher temperatures. The samples were then plate quenched, given a cryo treatment in liquid nitrogen, and then tempered twice for 2 hours each time

Crucible words.............A freezing treatment may be used between the first and second tempers
 
One thing that you could to trouble shoot your problem is to double check the thermocouple on your kiln.
I bought a second thermocouple to double check mine when I was having difficulty hardening W2. I drilled a hole in the door large enough for the second thermocouple and found a difference of 70 degrees. In heat treating a number of coupons I found that the results were much better using the second (new) thermocouple.
If yours is off by enough degrees CPM154 may harden and S35VN may not.
 
Natlek said:
I don t know if this make any difference but from Larrin article .... I heat treated a range of S35VN specimens using a 30 minute austenitize for 1925 and 1950°F, and 15 minutes for higher temperatures. The samples were then plate quenched, given a cryo treatment in liquid nitrogen, and then tempered twice for 2 hours each time

Crucible words.............A freezing treatment may be used between the first and second tempers
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Expression for freezing between tempers is secondary cryo ...and they may be or not ;)
And Larrin's recommendation is
Therefore I recommend heat treating S35VN by austenitizing for 15 minutes at 2025°F, plate quenching, a liquid nitrogen treatment for at least 30 minutes, and tempering between 300 and 400°F twice for 2 hours.
Optimum heat treatment was found to be 2025°F for 15 minutes with a cryo treatment and tempering between 300 and 400°F.

And now what is interesting to me .... higher austenitizing temp.:)
and let’s just say it’s much more dubious to me in his tests and HT
European steels that seem to deliberately want to ignore or has no interest in deriving HT in the same variables😁
https://knifesteelnerds.com/2020/05/01/testing-the-edge-retention-of-48-knife-steels/
:cool:in this world it's all about interest isn't it;)
 
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godogs57 said:
Thanks for the suggestions. Can I anneal and start over?
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I don't know about SV35, but HOSS (Larrin's Dad) who is considered the real guru on AEB-L has said that 12 hours in an oven at 1350°F (4 hrs at 1375°F will also works). It doesn't need slow cooling, air cooling is just fine per Hoss. I would think SV35 might work also - worth a try rather than throw those blades away. I would consider wrapping in SS foil for the anneal even though it's not that hot.
 
Larrin said:
You should try grinding both sides flat and testing hardness again. And make sure all the decarb is gone.
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I just picked up some s35vn as well, and your advice was;
2025 15 minutes
freeze if possible, (I'll use my freezer)
2, 2 hour tempers at 400

sound about right for a burly, choppery kind of knife?
 
Lorien said:
I just picked up some s35vn as well, and your advice was;
2025 15 minutes
freeze if possible, (I'll use my freezer)
2, 2 hour tempers at 400

sound about right for a burly, choppery kind of knife?
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I don’t remember saying freeze if possible. The 2025F recommendation is for cryo.
 
Larrin said:
I don’t remember saying freeze if possible. The 2025F recommendation is for cryo.
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not verbatim!
I can only bring the steel down to about zero, should the protocol I posted be adjusted? I usually stick em in the freezer for an hour after quenching, but I've only ever used A2.

The thickness is about 3/16" by 2" wide and the blade will be around 9" long, flat ground with a convex shoulder. I'd like it to be hard enough to be tough, it's for trail blazing

I certainly have no expectation for an answer, but if you decide to provide one I would be most grateful:thumbsup:
 
Try dry ice if you can't do LN. I have found that higher austenitization has improved hardness.

Comment: Let's all be honest, few people used temperatures above 1950°F before reading Larrin's test results. Now, most serious smiths are using temps like 2025° and 2050° for the newer steels. The improved results show how much potential we didn't reach. Back then Rc 59 was considered a hard blade. Now, it is common to make a Rc64 kitchen knife.

Second comment: Cryo with LN and sub-zero treatments in Dry Ice used to be considered optional. They are really a requirement for the newer high alloy steels.
 
Lorien said:
not verbatim!
I can only bring the steel down to about zero, should the protocol I posted be adjusted? I usually stick em in the freezer for an hour after quenching, but I've only ever used A2.

The thickness is about 3/16" by 2" wide and the blade will be around 9" long, flat ground with a convex shoulder. I'd like it to be hard enough to be tough, it's for trail blazing

I certainly have no expectation for an answer, but if you decide to provide one I would be most grateful:thumbsup:
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Yes when a temperature is optimal for cryo it won‘t be the same without cryo. 2025F would lead to too much retained austenite.
 
Larrin said:
Yes when a temperature is optimal for cryo it won‘t be the same without cryo. 2025F would lead to too much retained austenite.
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In the absence of cryo with LN is there a temperature range that would be suitable ? Dry ice is not sold here, getting LN is iffy now for me. Freezer might have to suffice. Trying to see what options I have.
 
godogs57 said:
In the absence of cryo with LN is there a temperature range that would be suitable ? Dry ice is not sold here, getting LN is iffy now for me. Freezer might have to suffice. Trying to see what options I have.
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With a hardness tester you can figure it out on your own easily. Just do coupons in 25F increments, quench them and put them in the freezer after. Measure the hardness of the coupons and see where the hardness is maximum.
 
Larrin said:
Yes when a temperature is optimal for cryo it won‘t be the same without cryo. 2025F would lead to too much retained austenite.
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:thumbsup:I think I'm starting to figure a little bit of this stuff out. In no small part due the information you've disseminated
 
Larrin said:
Yes when a temperature is optimal for cryo it won‘t be the same without cryo. 2025F would lead to too much retained austenite.
Click to expand...
so, I've read Dr. Larrin Larrin 's book 14 times- studying every word and even the punctuation in order to unravel the mystery of how to get some performance out of my S35VN without sub zero quenching. Hour after hour I devoted to the pursuit of understanding everything there is to know! But, alas, I realized my intellect is not well suited to metallurgy and I'd go so far as to say that my brain might have too much retained austenite...but lo and behold! The answer is there, if only one learns to read between the lines and divine the truth and I found it I tell you! I FOUND IT!

in the appendix. Who knew?
 
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