Is it usual for CPM-S30V to chip out at high grits?

S

Squashfan

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Jun 6, 2012
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I expected S30V to chip out during use but is it normal for it to chip out during sharpening??? I sharpened my Spyderco Military yesterday and when I got finished I looked at the edge. I had not cut anything yet and the edge was badly micro chipped out. I sharpened it on the Lansky system all the way up to 2000 grit after which I stropped with green compound on an an Lansky's leather hone. After that it received 2 pass per side on an other leather compound loaded with Flexcut Gold compound and a single pass per side on plain leather. I will guesstimate the edge angle is around 20 degrees per side. It is quite sharp though!

Thanks for the help.
 
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Check that your strops are not dirty is my first guess. Other then that the very apex could have been influenced by over heating while sharpening. This happens more then you think. Just keep sharpening for a while and see if it improves. You will have to remove what damaged metal there might be.
 
I have a couple s30v's from spyderco, Military and PM2, and I have not experienced chipping.
When you say high grits how high do you mean?

For my PM2 I go all the way up to 20,000 grit (0.5 micron abrasives from Suehiro Gokumyo),
and have not experienced chipping during sharpening. I have also sharpened on Japanese
naturals with dilution, and have not experience chipping. I have experienced consistent chipping while sharpening in only one situation (without tempering problem) and that's when I am sharpening ceramic knifes.

I'd be interested in hearing the resolution for your chipping problem. Keep us posted.
 
What was I thinking?! I didn't do this with the printer paper strop. I was green and gold compound on leather! It did notice that after the green it was almost tree topping sharp but after the gold it was *just* hair popping.

Never the less, the Millie is still extremely sharp it is just a toothy edge. I seem to remember that when I was using the fine diamond stone (600 grit) the edge looked funny. I decided that it would come out with the higher grits but I was obviously wrong.
I think I am going to carry the knife for a couple of weeks and when it starts to dull I will strop it on the printer paper strops.
 
S30V is known for it's 'toothiness' at the edge, due to the relatively large and abundant vanadium carbides in it (Crucible has published it's average carbide size at 2 - 4 microns, for the vanadium carbides). It can initially take a fine edge, but that goes away pretty quickly, as the carbides fracture out (maybe 'tear out' is more accurate) at the very edge. The edge that's left behind is less fine, but more durable in heavy use. Some of the 'experts' working with it seem to believe it performs better when finished to a relatively coarse grit (such as DMT's 600 mesh/25 micron). The more I mess with it, the more I'm inclined to agree. To some extent, that simplifies sharpening of it, because there's not much to be gained in going too high in polish.

I've generally noticed the same effect on every S30V blade I've sharpened. No matter how shaving-fine the edge initially is, immediately after sharpening, it always seems to settle back to something a little more coarse, when put to use. But that coarser edge is then a lot more durable, and will last a good while.


David
 
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I looked at the edge under magnification and it looks like there are 20-30 small chips per inch. I haven't actually counted but gives you an idea what is looks like under magnification. With the naked eye the edge the edge looks wavy. I don't really mind the toothy edge because the knife is sharp but I will keep this in mind when purchasing knives in future.
 
I sharpen my Paramilitary 2 to a pretty thin edge with the ultra-fine,(2000gr),stone on my Lansky. It will cut anything very smoothly and cleanly. I dont use it for hard use cutting so this is fine. The blade on the Para2 screams for a fine edge. I have no problems with chipping since I dont abuse it. One or twice I have dropped it and got a tiny chip from a rock. The chip is taken out very easilly. I leave the edge on my Mini Grip a little thicker to tackle rougher jobs. I frequently carry the both at the same time.
Dont know if that tells you anything but I tried.
Thanks
 
I will see what I can do tomorrow. I will have to charge my camera overnight because it is dead from my trip to Fall Creek Falls.
 
nope it's not normal, it should be smooth after sharpening and even after normal use you shouldnt be able to see/feel microchipping. go back to the last stone that produced a smooth edge with very light pressure until the apex feels smooth again then polish back checking the apex often.

i think marthinus is right the very edge probably gor overheated on the belts and you have to remove some steel to go back to normal. this happens sometimes.
 
I tried to get good pictures but my camera didn't cooperate. I had to shot through my jeweler's loop.

This is one of the best shots. The chips show up as the shiny, wavy part of the edge.
militaryedge003.jpg


militaryedge002.jpg


militaryedge001.jpg
 
Nice close ups.
I would try using it like that.
I would think it would perform well with those micro serrations.
 
Squashfan said:
I tried to get good pictures but my camera didn't cooperate. I had to shot through my jeweler's loop.

This is one of the best shots. The chips show up as the shiny, wavy part of the edge.
militaryedge003.jpg
Click to expand...

This happened to me too with a DMT Aligner kit. I surmised that I had too much flex in the system and wasn't hitting the edge cleanly. This was my fix and it did help a lot but YMMV.

AlignerClampFix_zps2677c373.jpg
 
singularity35 said:
This happened to me too with a DMT Aligner kit. I surmised that I had too much flex in the system and wasn't hitting the edge cleanly. This was my fix and it did help a lot but YMMV.

Pic removed for space conservation.
Click to expand...

Thanks for the complements on the photography. I am very pleased with how those shot came out.

I use my finger to hold the stone's rod in about the same place. I push the rod towards the handle. This was taught to me by the guy who recommended the Lansky.

I did remember this afternoon that I did something different. Most of the time I try to make 3-4 passes in a space roughly an inch long. When I sharpen this I did the normal 3-4 passes with the fine 600 grit stone and then switched to 1-2 passes per inch with the 1000 and 2000 grit ceramic hones. However, there is a big hole in that theory. I first noticed that the edge looked wrong when I was working with 600 grit stone.

All in all this has been a wonderful learning experience. When I started this thread, I was concerned that S30V would not take a polished edge. Having just discovered how to polish edges, this was of great concern. Side note: I love the polished edge on my Queen D2 Country Cousin. I keeps cutting and cutting and cutting...
 
Squashfan,

I just asked a custom knife maker about whether overheating during factory grind could result in chipping.
He said no. If they over ground to tempering temperature or higher, the metal would soften, preventing chipping rather than causing it. When it is held at that temperature for too long, then the metal could soften enough to lose the ability to hold edge. If you are thinking in the future about grinding away metal because you suspect over heatting problem, I think you don't have to.

Thanks and good luck.
 
This knife came to me as a user from the exchange. I don't think that damage to the steel is the problem but I thank you for that useful information.

Speaking of softening, I was using a benchgrinder for the first time to day and I can now say that I have experience with burned steel. It was super, super soft. I would just fall away from the hardened steel as it was sharpened.

I actually have a Kershaw Crown that flaked when I sharpened it. It was definitely not burned. It just happened as I used the fine hone. One of the flakes was almost a half an inch long and about an 8th of an inch wide.
 
From the picture I see left-over coarse grind marks and that shiny thing is the burr. Looks like you need to start over and spend more time on each stone.

The first picture also shows you did not bring the bevel slopes to a apex.
 
xuz said:
Squashfan,

I just asked a custom knife maker about whether overheating during factory grind could result in chipping.
He said no. If they over ground to tempering temperature or higher, the metal would soften, preventing chipping rather than causing it. When it is held at that temperature for too long, then the metal could soften enough to lose the ability to hold edge. If you are thinking in the future about grinding away metal because you suspect over heatting problem, I think you don't have to.

Thanks and good luck.
Click to expand...


I found the thread you started asking the question on another forum. I am not stating that you should grind off a large amount of steel on a $300 knife. It can take less then 1mm of steel removal to see improved results.

The steel will role rather then chip, however unless they dunk it into water thereby quenching the over heated part. This can result in embrittlement or microfracturing of the very apex. This is only one aspect.

I first became aware of overheating while grinding through CATRA having a machine to detect this. This is especially important for corrosion resistance.

http://www.catra.org/pages/products/kniveslevel1/bod.htm

This lead me to the following:

"A disadvantage of high-speed grinders is that the tool edge is heated up by the friction,
with the risk that the temper is drawn from the steel. The edge then loses its hardness and
the tool soon needs to be ground again.
You can reduce the risk of overheating by regularly placing the tool in water during the
grinding. However, it is very difficult to prevent the extreme edge from becoming too hot
as it is very thin and very sensitive to heat. It is very easy to reach 230° - 240°C which is
the annealing temperature for carbon steel. If the tip is overheated, the tool has to be re-
ground (without overheating!) until you reach material which has not been affected by the
heat."

http://www.rockler.com/faq/sharpening.pdf

Here are some further reading:

http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=391

http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=285

The problem with S30V is that when you lose the temper even without suddenly putting it in water, one can experience "carbide fallout". This looks similar to chipping and the second aspect.

To illustrate this have a look here:

http://www.hypefreeblades.com/files/schneiden.pdf

See the white carbides in S90V? Those are kept in place by the matrix, fine grain structure. If the steel is over heated in sharpening the matrix is influenced and they wont be able to keep the carbides in place, thereby the carbides will simply fall out, looking like a chip.

It seems Elmax is suffering lately the same fate S30V did when it was introduced.

[video]www.youtube.com/watch?v=Zz_vJCfmdYk[/video]

[video]www.youtube.com/watch?v=V2SQyF7sj9s[/video]

Back on topic. Jip, there is a burr. The burr could be from over stropping or not removing it as you progress to higher grits.

The following is how a burr looks under magnification:

Slide3_opt.jpeg


It is a strange thing. A burr can shave, feel extremely sharp, as soon as you cut and it folds over, your edge is gone and you have poor performance. It can also break off, leaving an edge jagged feeling like the edge chipped.
 
marthinus, thanks for the insightful remarks and informative links . (Also, it's good to see the member from the other forum here as well.)
I don't mean to hijack the thread, and maybe we should start another thread but here goes.

What exactly do people mean when they say the edge has lost or ruined temper.
I'm not a metalsmith, but my basic understanding is that metal goes through several steps. Forging, hardening, and tempering.
Followed by griding/sharpening, that hopefully, leaves the metal well enough alone.
There is only one step that makes a knife hard, the hardening step.
The metal is heated to high temp, where it favours BCC formation, then quenched quickly, forming martensites.
These high-strain, high-dislocation crystalline organization is what gives steel their hardness.
The high-strain state is prone to chipping and brittleness upon impact.
So to mitigate that, they introduce some controlled amount of heat, tempering.
This relaxes some of the structures in the martensite organization, introducing more toughness, at the cost of hardness.

Okay, so that's the limit of my metallurgy.
It seems to me introduction of heat through grinder, or any other means, should add (not lose) tempering - again, softening the metal and preventing chipping even further.
Am I wrong about this?
From physics of it, overheating should have a very characteristic consequence, softening of metal.
Therefore, ruined temper due to belt grind overheat should have one symptom only - a softer edge that doesn't get keen easily and loses edge quickly.
Further, s30V has annealing temp of 900 Celsius and austenitizing temp of 1100 Celsius, and is recommended to hold those temps for 2 hours.
http://www.trugrit.com/heat-treatment-cpm.htm
S30V, I suppose being a super steel of a sort, seems quite different from some other carbon steels in that respect.
I have my doubt that even a tired and distracted factory grinder will sustain that kind of heat for that period of time (or anything remotely close).

So, since the OP is specifically worried about chipping, I think I will stick to my gun and recommend no removal from the edge.
 
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