Nitro-V hardening

i4Marc

i4Marc

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Oct 19, 2011
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Is anyone else having trouble hardening Nitro-V?

I am using an Evenheat KH418 oven followed by 6061 aluminum quench plates (1.5"X8"X16.5") with compressed air then into dry ice/acetone bath. Foil wrapped blade. Hardness readings taken with Grizzly HR150A calibrated and reading dead on with test block. Blade dimensions not including tang are 10"L X 2.5"H X .1645"T

My previous attempt was pre-heat to 1550˚f for 20 min, ramp to 1850˚f for 5 min. (I had called Aldo for the latest HT recipe and this is what I was told.) this resulted in 59.5Hrc untempered.

I then made a new blank and went back to my log of past knives and used a recipe that had gotten me 63.5 untempered. This was pre-heat to 1600˚f for 20 min then ramp to 1950˚f for 30 min. This netted only 57.5 Hrc untempered.

Experiences/ideas?
 
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I have been doing grain refinement at 1700f for 20 minutes then plate quench. 1975f for 15 minutes then plate quench and dry ice. After the dry ice, testing with hardened files gives me somewhere around 65HRC. 65HRC is barely cutting into the steel. Definitely harder than the 60HRC file.
 
I'd be curious about your post-temper numbers. Based on the article https://knifesteelnerds.com/2019/03/04/all-about-aeb-l/ I would expect a rise in hardness after temper by 1-2 points. Still not what we are going for, but potentially informative. Relavant section is near the text "The hardness is increased by using low tempering temperatures" and an assumption that AEB-L is quite similar to Nitro-V.

That said, the difference of 6 points using the same process doesn't seem right. My initial debugging would be to assume a different batch of steel or a difference in your process. Was the hardness reading an average of multiple readings, or a single?
 
Using same ht on old & new supply batches of nitro-v recently. 1st batch(from a couple years ago) is 3-4rc higher than 2nd batch (bought few months ago). Based on my wag that 2nd batch could/maybe contained more nitrogen% and other alloys%, so I reduced 1975F aust soak time to 10-12 minutes for 2nd batch which then produced similar hrc as 1st batch ~ 64.5-65rc. ymmv.
 
FC,
Hardness readings were an average of 5 sample points.


Thanks bluntcut, I'll make a similar adjustment and check results.
 
btw - my ht, I put blades in a preheated/equalized 1975F oven, after temp stabilize back to 1975f (a few minutes, depend on # of blades) then start soak timer.
 
i4Marc said:
Is anyone else having trouble hardening Nitro-V?

I am using an Evenheat KH418 oven followed by 6061 aluminum quench plates (1.5"X8"X16.5") with compressed air then into dry ice/acetone bath. Foil wrapped blade. Hardness readings taken with Grizzly HR150A calibrated and reading dead on with test block. Blade dimensions not including tang are 10"L X 2.5"H X .1645"T

My previous attempt was pre-heat to 1550˚f for 20 min, ramp to 1850˚f for 5 min. (I had called Aldo for the latest HT recipe and this is what I was told.) this resulted in 59.5Hrc untempered.

I then made a new blank and went back to my log of past knives and used a recipe that had gotten me 63.5 untempered. This was pre-heat to 1600˚f for 20 min then ramp to 1950˚f for 30 min. This netted only 57.5 Hrc untempered.

Experiences/ideas?
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i4Marc, I apologize here, I know you’ve made lots of knives, it’s best to make sample coupons of a steel and find the peak hardness without cryo and then with cryo. You should start with 1925, 1950, 1975, and 2000 and maybe go to 2025 with cryo.

That will tell you a lot about the steel and your furnace.

This grade does not need a preheat soak nor does it need a long soak at full aus temp. It does need to go into sub-zero or cryo right after the quench and temper right after the cryo.

Hoss
 
bluntcut, thank you.


Thanks Hoss. No need for apologies. I appreciate the input. I generally do the coupons when working with a new steel or new batch. This is why I referred back to my notes in an effort to fix the problem, as I've had decent results with this steel prior. But I didn't realize this steel doesn't need a pre-heat. Thank you for the information. I'll do another run of coupons. Just out of curiosity, AEB-L needs a pre-heat? If so, what is it about the addition of Nitrogen and Vanadium that causes Nitro-V to NOT require the pre-heat?
 
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i4Marc said:
bluntcut,


Thanks Hoss. No need for apologies. I appreciate the input. I generally do the coupons when working with a new steel or new batch. This is why I referred back to my notes in an effort to fix the problem, as I've had decent results with this steel prior. But I didn't realize this steel doesn't need a pre-heat. Thank you for the information. I'll do another run of coupons. Just out of curiosity, AEB-L needs a pre-heat? If so, what is it about the addition of Nitrogen ad Vanadium that causes Nitro-V to NOT require the pre-heat?
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These steels have low carbide volumes and small carbides. Steels like 440c, D2, 154 cm, and on up have large carbides and higher carbide volumes which require more soak time to dissolve enough carbide to put enough carbon and chrome in solution for a good heat treat.

Preheating is used more for complex shapes in order to avoid stresses. Long straight blades usually heat evenly without trouble.

Hoss
 
I’ve been sending all of my blades to Buck knives for HT for a long time, I ask for 60-61 RC and I and my customers have never been disappointed by the edge retention, Hardness, etc , so I am
No help with your HT process.. —-1What I do ask and maybe can help is are you getting the Nitro V from the same supplier ? I’ve bought all of my AEB-L & Nitro V from The NJSB so I’m confident that I’m getting what I’m paying for...I think he was the only source at first, but I don’t know if others are selling it now? Best of Luck to you!
 
Hi Marc,
The other thing you could try is a pre-quench at 1750 X 10 min.
@Larrin did a great post on AEB-L and found that doing a pre-quench at 1750 X 10 min before Aus at 1975 then 30 min cryo gave about a 1 RC increase in hardness over no pre-quench.
Now I may be wrong to assume you can do the same with Nitro V but it may be worth a look.
 
Rhinoknives1 said:
I’ve been sending all of my blades to Buck knives for HT for a long time, I ask for 60-61 RC and I and my customers have never been disappointed by the edge retention, Hardness, etc , so I am
No help with your HT process.. —-1What I do ask and maybe can help is are you getting the Nitro V from the same supplier ? I’ve bought all of my AEB-L & Nitro V from The NJSB so I’m confident that I’m getting what I’m paying for...I think he was the only source at first, but I don’t know if others are selling it now? Best of Luck to you!
Click to expand...
Usaknifemaker is carrying it, but I believe he gets it from Aldo.
 
If i wanted to take another shot at the two blades I made with unsatisfactory results, what would the annealing process be for Nitro-V? Or would you suggest just making a fresh new blade?
 
Protect the blades with foil, heat to 1350’f for between 4-12 hours, longer will be softer. This is a subcritical anneal and is a good condition to re-harden from.

Hoss
 
Can a AeB-L OR Nitro V blade be successfully hardened without cryo or dry ice? I have access to neither where I live.
 
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