Preventing CPM S30V from chipping

flatgrinder

flatgrinder

Joined
Dec 20, 2005
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I just bought my second Spyderco Native in CPM S30V. (The first didn't have any problems).

I was cutting up some heavy cardboard boxes this morning (I didn't hit any staples) and then tried to slice some paper, immediately I noticed two very small chips in the blade as it wouldn't cut smoothly (it would snag on these chips and tear the paper).

I decided to submerge the handle portion in a cup of water (to protect the handle from heat) and used a propane torch to gently heat the blade. I heated it slowly until it turned a "straw" color and then let it return to room temp. I then resharpened it using the Sharpmaker at 30 degrees total (30 strokes with the medium coarse rods and 20 with the fine).

I went back to the same cardboard, cut twice as much as I did before and then tried the paper, it sliced it easily. It would also shave hairs very easily afterwards.

I'm not saying that this is a cure for everyone, but it worked for me.

Has anyone else tried this? It probably would have been better to remove the blade and temper it in an oven, but it's riveted onto the handle. Is the chipping generally related to the particle metallurgy technique or is it the result of heat treat? And if it is, perhaps the steel was not tempered at a high enough temperature? :confused:
 
Tweaking the heat treat of a knife blade using a propane torch is probably not something I would recommend.

A number of people have reported that their S30V chipping problem disappeared after sharpening the blade. At least one famous maker firmly believes that chipping is due to surface roughness rather than poor heat treat.
 
For my Native, a long-lasting, non-chipping edge was accomplished by thinning out the back-bevel until it was 0.008" thick at the shoulders (the hollow is now gone) and adding a polished edge around 40 included degrees (maybe a little thicker). Cuts like a demon because less of a back-bevel bunches up behind what's being cut and finally stays at barely armhair-shaving sharp instead of just below that level of sharpness when dulled.
 
flatgrinder said:
Is the chipping generally related to the particle metallurgy technique or is it the result of heat treat? And if it is, perhaps the steel was not tempered at a high enough temperature? :confused:
Click to expand...

It would be interesting to know what really happened to the steel after the torch treatment. Is the blade now softer on the Rockwell scale? If so; By how much? What about all the other variables; toughness, abrasion resistance, rust resistance, etc. How were they altered? Just rhetorical questions until someone decides to do tests.

At least we know the chipping problem is cured.

I am one of the many who has experienced chipping with S30V blades but I hesitate to torch them because of the unknowns. I thin down the edges of my blades somewhat, for more efficient cutting but would not want to go as far as Thom has because of fragility with very thin edge profiles.
 
There are three things that happened :

1) the temper was drawn
2) it was resharpened
3) different cardboard was cut

It is not known which one of these was the critical factor or if it was in fact a combination of all three. Multiple reports have noted that sharpening alone can decrease the frequency of chipping.

-Cliff
 
I don't know why, but I had a S30V Strider that was chipping so I took it and reprofiled the edge and fully convexed it to a zero edge which seemed to eliminate the chipping and also increased performance. I used it for cutting some very thick plastic straps and some pretty industrial looking zip ties which also made the original edge chip. The convexed one just slid through whatever I was cutting (even though I kept it razor sharp before) without any damage even though the edge was thinner.
 
I forgot to mention that I actually resharpened it with an Edge Pro to 25 degrees (total) about a week ago, (immediately after I bought it and noticed that it was chipping). But that didn't help, so I boxed it up -until deciding to tinker with it.

I resharpened it with the Sharpmaker before cutting the cardboard. After it chipped again, I did the temper thing, resharpened with the Sharpmaker and went back to the same cardboard (it was a pretty big box) and cut against the grain as I did before.

I'm not recommending that other people do this, it was just my observations if anyone is interested. I figured it's a $40 knife (from Walmart) so I didn't have much to lose and after reprofiling, it was still chipping, so why not experiment on it? I noticed from crucible's S30V datasheet that as long as I kept the tempering temp under 500 with S30V, it could work. I have a digital pyrometer... I could have put the probe on the blade for a more accurate tempering -but didn't, anyway I'm happy with it now. It's still cutting like a razor, and is now my EDC.

P.S. Some Simichrome and a buffing wheel takes off the oxide layer. Can't even tell it's been retempered.
 
If you sharpened it before, then that makes it unlikely that the sharpening did anything. The change in cardboard is also a small effect in total. Most likely the tempering was the major effect. It would be interesting to see the structure before and after.

-Cliff
 
I wish I rockwell tested it before and after. It would also have been interesting to see what the tempering temp was.
 
The Spyderco CPM S30V military model has been a good knife for me, but I never pry with the blade. Part of the joy of using this knife is that it features a very slim profile that cuts many materials with ease. The tip is almost fragile, and I would not suggest any rough treatment here. Again, as I mentioned before, any edge can and will chip if the edge is exceedingly thin. This knife is very thin at the edge and can chip if exposed to abuse despite a decent thickness in the spine.

A fillet knife works better when applied to fish, an axe chops better on a thickly built piece of oak. Also, I would shy away from any heat treating outside of the factory.
 
The above isn't about chopping oak, but cutting cardboard which should be in the range of use of any utility knife.

-Cliff
 
Cliff Stamp said:
Did you notice a different feel on the stone?

-Cliff
Click to expand...

Actually, it feels like the medium-coarse stones "bite" the steel better (if that makes any sense :confused: ). -Feels like it sharpens up easier. Before my personal tempering, it felt like I was trying to sharpen a piece of glass. It would get sharp, but not extremely sharp.

I like the edge a lot better now, before this I used to think "production" knives in S30V didn't take a good edge (I actually preferred 154CM), but now I'm very impressed. I've made a few kitchen knives from S30V and had Paul Bos heat treat them to HRC 59, these take a serious edge and keep on cutting.

I was almost at the the point where I was going to say screw CPM S30V, as the material is so expensive that factory knives are pricey and the edge sharpness and retention didn't impress me -and I would rather make my own knife out of D2. However, for $40 and a razor sharp blade that keeps on cutting, I'm very impressed with my Native now. :thumbup:

I'm not a metallurgist, but could it be that the combination of a hard blade (ie. HRC ~61+?) and a high percentage of carbon (over 1.2%) would result in a more brittle blade, hence the chipping? Maybe very high carbon stainless steels should be run at a lower hardness? -But why doesn't ZDP-189 chip? :confused:
 
A lot of people have made that statement about high hardness and chipping, and in this case it appears that softening the steel by drawing the temper did in fact solve the problem. However it isn't as much hardness alone but how that hardness is achieved. Many people are in fact tempering in the embrittlement zone, these steels should all be tempered low, or very high 980+ .

It is unfortunately that there is little actual sensible discussion of the reason for the problems from the makers and manufacturers of the steel. Most of what is retorted, especially from Crucible is nonsense and directly contradicts the origional promotion of the steel. I would like to see some actual micrographs of the problematic knives in question as they have been returned. Of course I don't really expect manufacturers to be so open and I expect spin on the results, I am not so naive to think otherwise.

I have had some really nice S30V blades and some really bad ones. Easy chipping on some blades, some chipped even when sharpening, edges not forming, etc. , replacements had the same problem.

What is really amusing is that the main promotion of that steel was "high toughness" and it chips on carbboard, corn stalks, plastics, and even sharpening stones. It failed frequently to be even a light use knife and was promoted for large tacticals.

-Cliff
-Cliff
 
Cliff Stamp said:
What is really amusing is that the main promotion of that steel was "high toughness" and it chips on carbboard, corn stalks, plastics, and even sharpening stones. It failed frequently to be even a light use knife and was promoted for large tacticals.
-Cliff
-Cliff
Click to expand...

I'm glad someone finds amusement in it. It should be a major embarrasment to Crucible.
 
Indeed. In fact what is even more amusing is the push on CPM154. This steel already existed pre-S30V as RWL34 by another manufacturer and S30V was promoted as a superior product.

-Cliff
 
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