I hope y'all will forgive me for the length of this post...
I am reluctant to weigh into this topic again, as I don't want to be misunderstood again as being opposed to 3V being used in a folder. To be clear, I like 3V and 4V and I'm also the type that would buy a Spyderco 3V folder just because I'm a steel geek and the novelty of it would be worth the cost to me. I know there are better choices that would do everything a 3V folder can do and more, but I'm not opposed to the idea of a 3V folder being made.
That said, in these conversations about "tough steel" I see a lot of anecdotal information being shared and I just want to add a little more testing-based data to the conversation so that my friends here at the Spyderco Forum can be as informed as possible. The reason this is important is because the degree to which steel composition specifically affects blade toughness performance properties is smaller than many people imagine and in fact, only a small portion of the actual result the person experiences. Heat treat and geometry have so much impact on the actual result or experience that those two variables can out-weigh differences provided by steel chemistry entirely. Steel composition has a far greater impact on wear resistance and corrosion resistance.
So, I thought sharing some of tests I do might be helpful for understanding how much or how little it really matters if the blade is 3V, 4V, Cruwear, or even S35VN for that matter.
When I make a knife from a given steel I do a variety of heat treating tests, rope cutting tests, chopping tests and when I'm done with the "normal" testing I move on to extreme abusive testing...mostly to satisfy my curiosity. But, I also do the extreme abuse for whatever interesting information might come from it. I think some of the results I've seen in testing Cruwear, CPM4V and S35VN might be interesting to many of you.
Please understand that abusive tests are not meant to mimic real-life use, but rather to see where the limits and boundaries are. Chopping a nail in half is not something that anyone should ever remotely consider doing with a knife. It also doesn't begin to tell us all that we need to know to fully understand a blade's edge stability. Among other things, a nail chop does provide some useful data for those concerned about hitting a staple in cardboard or other accidental impact with hard objects, which is the type of occurrence often referred to in these tough steel conversations. Mostly, I'm showing these tests here because they illustrate the tremendous role of heat treat and more importantly, geometry in a knife's performance.
In these first photos you'll see 2 test samples of Cruwear.
One was heat treated at 1850F and one at 1950F. Both were plate quenched, cryo'd in liquid nitrogen and triple tempered at 980F.
Target hardness of the 1850F sample was HRC 60 and the 1950F was HRC 63.
I ground the 2 samples to basically identical angles and thicknesses (total variance of .001"). I ground them very thin at first. One is .011" behind the edge and the other is .012".
Then, I used a hard rubber hammer and pounded them through a nail. As you can see from the half-moon chunks of steel missing, the thin edge geometry could not handle that type of abuse...understandably.
Next, I re-ground the Cruwear samples to be .025" behind the edge and re-tested.
I had to take pics a various angles just so I could see the edge damage in a picture.
After changing only the geometry, both knives chopped the nail in half with barely an edge roll.
I also put those samples through a bend/break test. Just sharing for the heck of it..
The two bent to within 1 degree of one another before breaking and the softer of the 2 held a lot more bend than the harder sample.
Then, just for my friends here at the forum I decided to put one of my 4V camp knife prototypes through the same test for comparison sake. I had ground that knife down to what I thought was thinner than it should be for a camp knife but I wanted to test the boundaries of 4V. I'm glad I did this test because it helped me dial in the exact blade thickness and edge shoulder thickness I will use on this type/size 4V blade in the future. For reference, the 4V here was HRC62.
I chopped 2 nails with this blade and the first one (in the belly of the blade) resulted in a small chip, while the second one (further down the blade) resulted in more of a roll.
The 4V at .015" did considerably better than the Cruwear at .012" and almost as well as Cruwear at .025", but not quite. Of course, since the 4V and Cruwear samples are not identical we cannot make direct comparisons. Interesting nonetheless that the 4V blade did so well with such a thin edge.
Last, I thought you all might appreciate having a steel that more people are familiar with to compare. Fortunately (or unfortunately), when you make knives there are always blades around the shop that are FUBAR so I grabbed one such blade in S35VN and took pics of the same tests with it as well. This blade was heat treated, cryo'd and double tempered and has a hardness of HRC 59/60. The blade has a spine thickness of .125" and it is about .0148" behind the shoulder.
I put the nail on the flat steel surface on one of my vises this time. I chopped 2 nails in half with this blade. The first time, the 2 pieces of nail went flying across my shop in 2 different directions...never to be found again :rolleyes: . But, you can see the mark the first nail left in the S35VN blade..
I taped the nail down before I chopped the second nail. You can also see the line in the steel surface where the blade cut into my vise.
You can see that the S35VN blade actually performed better in this torture test than the 4V or the Cruwear blades. I am not saying that these tests provide all the information needed or even a complete picture of the performance capabilities of these steels. I am certainly not saying S35VN is tougher than the other 2. I am showing however, that test results show heat treat and geometry have the capability to override the differences in steel composition every time. And, that the differences in toughness-related performance as it relates strictly to steel composition is relatively minor in the end. Ultimately when it comes to actual toughness of any particular knife blade, steel composition is only one small factor.
I am definitely a fan of "tough steels". I choose to use V4E, CPM4V, CPMCruwear and 52100 for specific designs, and they're all tough steels that have their strengths and weaknesses. I also use CPM154, S35VN, Vanax, LC200N, CPM20CV and M390 for other designs because they are also tough steels that have their strengths and weaknesses. The intended use of the particular design combined with wear resistance, corrosion resistance and the subtle differences in steel properties is how I decide which one to use. However, with appropriate manipulation of the geometry and the heat treat every one of those steels can be made to perform exceedingly well in any application.
I hope some of you find any of this useful or helpful. Thanks for reading :) .
Chad
:spyder: Spyderco fan and collector since 1991. :spyder:
Father of 2, nature explorer, custom knife maker.
@ckc_knifemaker on Instagram.