Hey Trooper
I've worked with both S30V & S35VN. S35VN is
my preferred choice considering the 2 you mentioned, both in performance & upkeep for the user in the field.
Like every blade steel we use, correct grind/edge geometry, combined with proper thermal cycles & heat treat technique is imperative in bringing out the full potential of this material. And for that matter, every other piece of blade stock we use.
Like S30V
don't skip the cryo. Although there may be a lot of misinformation on the web regarding cryo, one aspect that's not in dispute is it's ability to transform retained austenite (in steels that are prone to develop it) to untempered martensite.
Per Verhoeven, when using high alloy air harden steels, to help reduce retained austenite
:
- avoid the higher
Data Sheet listed austenitizing temperatures.
For S35VN HT in my shop
. I use the
mean temperature of 1950*F.
- Avoid excessive soak times (for 3/16" stock I soak 20 min at temp)
- Use interrupted oil quench vs. plate or positive pressure air quench (I oil quench the blade to just <1000*F then positive pressure air quench using a cold air gun to ~ 100-150*F)
- Following the quench,
move directly to cryo. Don't allow the blade to rest at room temperature for even 5 minutes.
Don't snap temper or "1st cycle" temper prior to cryo. Pre-cryo tempering or "setting the blade down for the night after quench" will most likely result in some stabilizing of the retained austenite. Personally, I always keep the HT cycle moving forward. Again, per Verhoeven, austenite that has been allowed to stabilize can make conversion to martensite very difficult.
If moving from quench directly to cryo concerns you, to decrease the
potential risk of fracturing or micro-cracks resulting from going directly to cryo from quench, you can reduce the temp more slowly by placing the blade
above the LN prior to full immersion. FWIW, in my first experiments using D2, I did it both ways. After examining samples using fluorescent dye penetration inspection and later, SEM inspection, and finding not a single micro-crack or fracture (as in none) I now go directly to a slow full immersion in the LN following the quench.
As is standard practice,
all cold treatments (LN, Dry Ice + Acetone, etc.) should always be followed by tempering. In the case of CPM S35VN I use (3) 2 hr. cycles at 475*F. I quench in water between each cycle (right out of the tempering oven) so that I can go
immediately back in for the next cycle.
The end result of the above mentioned procedure for S35VN,
in my shop, results in a final HRC of ~60, + or - a point
I always try to give credit to those who paved the way before me, and in the case of Heat Treat, that would be Kevin Cashen. Speaking of custom knife making, Kevin has been a
Tour de Force in regards to teaching proper heat treat technique and listing of resources on the subject.
The best hes passed on have been:
"Steel Metallurgy for the Non-Metallurgist" by John D. Verhoeven , call # TN705 .V45 2007
Fundamentals of Physical Metallurgy by John D. Verhoeven, call # TN690 . V46 1975
Tool Steel Simplified by Frank Palmer, George V. Luerssen, Joseph S. Pendleton Jr. 1978 (sorry, no # for this one)
My final thanks in regards to my
extremely anal Heat Treat Procedures go to Nathan Carothers (at BF we know him as Nathan the Machinist). His ongoing experiments with D2 steel (among others) and his findings related to edge retention and stability following cryo was impossible to ignore, (for me anyway), and the final nudge I needed to pursue further knowledge regarding the subject. Thanks Buddy :thumbup:
Theres my experience with S35VN Trooper. Sorry for the long winded response I hope it helps you :thumbup:
