420V

B

Burke

Joined
Feb 25, 1999
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It seems like Spyderco is leading the changeover from standard steels to the CPM ones. Is there any chance of using 420V, which sounds like it would make a better knife steel than 440V? Why did Spyderco originally use 440V, and not 420V? I am assuming it had something to do with the machinability of the two steels.
 
OK, I may be wrong here, and I'll wait for corrections. According to the CPM folks, 420V has more 'wear resistance' (durability) than 440V, but 440V has more 'toughness' (strength). CPM3V and CPM9V beat them in both categories. 440V is made with aluminum oxide whereas 420V is made with vanadium carbide. Note, though, that all wear resistance and toughness data are nominally relative at RC 58-61.

After a certain point, Wear Resistance and Toughness are negatively correlated. In other words, the more you have of one quality, the less you have of the other.

Both are tough to work with and require significantly more expensive materials (or more of the same) to sharpen, sand, polish, etc.

420V's edge retention gets a slight nod over 440V, but Military users have found it difficult to remove its edge even with rugged use in the field against a variety of materials.

Burke, I assume it may not only be the machinability, but the cost issue. How much do you want your knives to cost, and is that difference worth 'significantly' more to you? Note the word 'signficantly.'

Given the chemical properties and density of CPM steel, I'll take any of them. For more info on this, check out:

http://www.crucibleservice.com/cscd/crucpm.htm

Since I'm not fully informed, I'll wait for for those who know more on this subject. Perhaps Ed or Tom?
 
Kysa - Gteat info, thanx. We are also still testing 420V as to production requirements and ultimate performance. 440V has been an enlightening experience. Blazing trails is fun, but tough and expensive. We cannot use the same grinding wheels for all steels.

Special wheels must be developed which takes time. It took us almost 2 years to develop the wheels for production grinding of 440V. Those that follow have an easier time. And even with the specially developed wheels, it still grinds considerably slower than say ATS. Also, we found that ideal rockwells for 440V are not as recommended. Again, more tesing and refinement.
sal

 
Kysa, according to the spec. sheets from CPM, here are some specifics on both steels tempered to a RC of 55:

420V 22 30/35
440V 18 15/25

The first number is the impact toughness in ft-lbs, and the second the wear resistance. As you can see, 420 V is superior in both respects and has twice the corrosion resistance of 440V as well.

I can see no reason to use 440V over 420V for the ELU.

-Cliff
 
Thanks for the info, Cliff. Are those specifications listed on their website somewhere? I'm eager to learn more.

The only problem is that I wouldn't want a knife that had an RC-55, ESPECIALLY if it's CPM steel! That may skew their results for those two particular tests. A more realistic RC would be slightly higher, toward 61. If you could find 'those' specs, it would provide us with a more valid assessment as users.

If you're wanting to continue to up the ante, then go straight to 3V or even 9V, but good luck finding a knife company that could reasonably afford the retooling required for the grinding wheels required to generate all the blades for all the ELU. I'd agree with Kevin at CPM that 440V is a very 'high-end' compromise for knife steel.
 
Cliff - thanx. I imagine we'll make something out of 420V next year. We did make a batch of "Q's" for Crucible that have the blade lazer cut out to say CPM420V and they're made out of 420V. Intreresting project, it was.

Kysa - at 61 they crack when dropped. 55 seems to give us the best strength and edge retention.
sal
 
Kysa, no. They are on the full spec sheets which are not available, I don't know why. I got a copy off the good doctor (WW) and I am sure he would be happy to send them to you. As for the RC, here are the stats on D2 for comparasion (at 59 RC) :

Toughness : 22, Wear Resistance Abrasive : 3/4

420V at 55 RC has as much toughness as the D2 and greatly improved abrasion resistance.

As you increase the RC on the CPM steels you lose toughness quickly and gain abrasion resistance very slowly. Most people I know are heat treating at what would be soft RC's for other steels.

As for 3V, I am getting a custom blade made out of it so I should be able to see if it lives up to its specs.

CPM3V (58 RC) : Impact Toughness : 85, Wear Resistance Adhesive 6.

Comparing this to the D2 it has greatly increased toughness while still significantly better abrasion resistance.

-Cliff
 
Thanks Cliff (and Sal) - I appreciate you doing the research footwork for me!
 
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