S30V vs M390 Toughness?

What kind of underwear does Granny wear? Depends! :D

Glad to see everything got smoothed out because I ended up learning a few things. Thanks to all who contributed. :thumbup:
 
I have never seen 3V chip from a single impact, even on steel. It will deform for sure, but I've not seen it chip. Then again, I don't make "fine" edges. Sharp edges but not thin, fine edges.

So which is tougher? S30V or M390? It depends.
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Wild ass guess, M390, but "it depends". :)

Here is a photo of a test done on S30V and another steel that is particularly noted for its toughness. Same test, same impact on the same target for both steels. S30V chipped, the other was deformed. Same damage to both. Picture a scale, extreme brittleness on one end and extreme weakness on the other. The ideal blade steel will fall exactly in the middle; it won't chip, it won't deform. There is no such steel, but some come close.

busse.jpg

Here's another photo. Two steels, the bottom one is 154CM, the top one is a steel that scored high on CATRA and had great Charpy marks, but... Both were hammered through a nail with as close to the same impact force as I could achieve. See what happened to the high scoring steel? The company had high hopes for this in the knife world, but decided to look elsewhere for a market. Numbers...

plastic.jpg

Edited to clarify. "Bottom one" meaning the one underneath - top edge in the photo. Sorry.
 
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On the finer/thinner edges that I usually like to deal with it seems that a combination of high compression strength (Higher RC Hardness) and high wear resistance works better than the so called tougher steels that are in the lower hardness ranges (Lower Compression Strength). I generally see less edge damage in my testing overall and that's just cutting.....
 
Ankerson said:
On the finer/thinner edges that I usually like to deal with it seems that a combination of high compression strength (Higher RC Hardness) and high wear resistance works better than the so called tougher steels that are in the lower hardness ranges (Lower Compression Strength). I generally see less edge damage in my testing overall and that's just cutting.....
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Cutting what? This is essential.
 
It depends....

On what you're cutting and how. For slicing things, no doubt. For encountering nails, maybe not so much. :)

Edited to add, yeah what he said... :)
 
Jerry Hossom said:
It depends....

On what you're cutting and how. For slicing things, no doubt. For encountering nails, maybe not so much. :)

Edited to add, yeah what he said... :)
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Metal and a thin knife edge isn't going to be a good thing. :D

I try and stay away from hard metal.....
 
Ankerson said:
On the finer/thinner edges that I usually like to deal with it seems that a combination of high compression strength (Higher RC Hardness) and high wear resistance works better than the so called tougher steels that are in the lower hardness ranges (Lower Compression Strength). I generally see less edge damage in my testing overall and that's just cutting.....
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Ankerson said:
Mostly rope and cardboard in testing.... (Controlled)

Not concrete, rocks or steel I-Beams....
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And what do you mean by 'edge damage' exactly? That is, blunting in what way? Abrasion, impaction etc.
 
ClipPointed said:
And what do you mean by 'edge damage' exactly? That is, blunting in what way? Abrasion, impaction etc.
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Impact has nothing to do with it.....

It's slow deformation from pressure and the steels get to a certain point and either can't snap back into place (Rolling/blunting) or they chip out (Micro Chipping).

The higher the Compression strength the longer the edge will go before it starts to deform, combine that with high wear resistance and they can go for a long time....

That's from my own testing using proper cutting technique.... Very little side loading.....

85 LBS of Charpy Impact isn't going to do one much good when the hardness is low and the edges are thin when cutting/slicing abrasive media.....
 
Ankerson said:
Impact has nothing to do with it.....

It's slow deformation from pressure and the steels get to a certain point and either can't snap back into place (Rolling/blunting) or they chip out (Micro Chipping).

The higher the Compression strength the longer the edge will go before it starts to deform, combine that with high wear resistance and they can go for a long time....

That's from my own testing using proper cutting technique.... Very little side loading.....
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Right - so then assuming that I'm understanding you properly:

'High RC hardness blades with high wear resistance show less damage than lower RC hardness blades with high toughness cutting abrasive media (rope, cardboard).'

That's just trivial? Nobody denies this?
 
darrin sanders said:
What kind of underwear does Granny wear? Depends! :D

Glad to see everything got smoothed out because I ended up learning a few things. Thanks to all who contributed. :thumbup:
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That makes 2 of us Darrin. ;)
Thanks to Jerry and Jim for posting what you did, it's always nice to read new to me info.
 
ClipPointed said:
Right - so then assuming that I'm understanding you properly:

'High RC hardness blades with high wear resistance show less damage than lower RC hardness blades with high toughness cutting abrasive media (rope, cardboard).'

That's just trivial? Nobody denies this?
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There are some..... Believe me.....

That speaking in general terms though as it depends is always a factor....
 
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Anyway, can anyone think of a cutlery application where the original thread question is relevant?

That is, on what type of knife and doing/cutting what would you need to know if either S30V or M390 is tougher.

It just seems to me if you are going with either S30V or M390, toughness considerations need not apply in the first place.
 
ClipPointed said:
Anyway, can anyone think of a cutlery application where the original thread question is relevant?

That is, on what type of knife and doing/cutting what would you need to know if either S30V or M390 is tougher.

It just seems to me if you are going with either S30V or M390, toughness considerations need not apply in the first place.
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It really isn't..... Not really, but it depends on the intended use of the blades, geometry etc....

Strictly cutting, no... Not usually.....
 
ClipPointed said:
That pretty funny. And sad.
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Not always as there are two sides to every conversations. Some sides are supported by peared reviewed metallurgical studies that some on forums neglect to mention because it does not support their standpoint.

Anycase, in my experience, I like low alloy steels at low edge angles (because it cuts better) at high HRC.

12C27/AEB-L or 14C28N at HRC of 62-63 functions a lot differently than a Mora, SAK, razor blade or Kershaw Blur.

The reason for my liking in these steels is beacuse I work where I cut a lot of dirty material and side loading happens when you have to get the job done quickly. This cutting blunts any type of steel and I do not want to remove chips at the end of the day out of my edge.
 
I find it funny that when discussions come up about sharpness, most people don't take their edges to atom splitting sharpness for EDC use for various reasons. However, in some steel discussions where micrographs and charts are brought in, somehow 15 dps angles won't make the cut. :D
 
Thanks a bunch chiral.grolim... this has been very informative. I tend to question every thing (which gets annoying I'm sure) but I learn more this way. Crucible responded with in a few hours to my email which really surprised me I was going to give them at least a few days before sending another email. They have impressed me for sure. I was wondering why some of you were posting at so early in the morning as well I figured odd job hours or insomnia lol so the answer to the OP question is...... a big dirty depends.
Ankerson said:
From my own testing of a variety of knives in various steels I believe that it's more the slow loading that causes the edges to have issues more so than impact when cutting .... Can be micro chipping, rolling and flattening.....

In use the edge is going to flex back and forth kinda like bending a metal coat hanger back and forth until it breaks.

That's were proper cutting technique really comes into play as in keeping the spine behind the edge when cutting to reduce as much side loading as possible, especially with thin grinds and edge geometry.

Now with choppers impact does have more relevance.
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chiral.grolim said:
To shinyedges, Yes, it's like grains of wood ... except many MANY times smaller and also stronger, and again the PM process greatly reduces (but doesn't eliminate) the directionality of the grains.. is that even a word? Anyway, as Ankerson and Jerry have both noted, most edge damage isn't even caused by impacts, it is caused just as you describe, by cutting into hard materials or encountering slow-load lateral stress on the edge (google 'edge flex test'). When you split a piece of wood, for example, the grains of wood place lateral loads on the edge which can flex it out of alignment. If the edge is too soft, it will permanently deform (squash, roll/bend) which cold-works the edge to higher hardness and a thinner, more fragile geometry that can crack. If the edge is too thin and too brittle, it will resist bending but may fracture readily. If you cut into something hard, the edge will squash or try to bend around the object or may crack - same thing. This is all slow-loading, no impact-toughness value need be consulted.

Once a crack or other stress-riser (as Jerry described) is present, this focal point can lead to further crack-propogation... all in the absence of an impact. Now while some call this "toughness" it is important to qualify it as "fracture toughness" as a corollary of strength - i.e. the ability of a material to resist crack propagation, often discussed as "edge stability" in regard to knives) and not "impact toughness" (the ability of a material to resist crack formation, especially at a focal point, upon a sudden impact which can carry the crack to full failure).

As you've hit upon and Ankerson has been trying to put forward, impact toughness is not the most important property of knife steel because it isn't the most common method of failure. Even chopping wood, the wood is usually soft enough that it slows the impact force to a compression force relating to strength rather than toughness.

But if you are unlucky enough (as I have been) to encounter an embedded spike or lock-staple or nail/screw/etc. on a strike, THAT is impact force and even my GSO-10 in CPM-3V suffered a major chip from than encounter! But I may have you note that the chip was much wider than it was deep. Can you tell me why?
In case not, it's because the longitudinal toughness was sufficiently high as a thickness a little back from the edge that the crack couldn't propagate any deeper but it could propagate transverse along what little grain CPM-3V has to follow. Now if the transverse toughness had been higher, certainly the chip would have been smaller, but the chip would still be present because the threshold of longitudinal toughness was exceeded.

Anyway, you seem to have the right idea, I've learned somethings about S30V's origins that I didn't know before (and continue to be impressed about how responsive Crucible is to e-mails, this is the 3rd time I've read of quick replies from them to forumites :thumbup:), but the question I have is why oh why were both myself and Ankerson posting to this thread so late into the night? ;)

Sorry for another wall of text :o Listen to Jerry and Ankerson - impact toughness is important, but not that important for knives. Use the values as a guide, but make sure you are comparing the same values for each steel (i.e. transverse or longitudinal but don't mix-and-match). In the end, the best test is how the knife blade actually performs in use, not what value a generic test-specimen gives. SOOO many other variables for knife edges. :thumbup::thumbup:
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