Advantages of a higher Rockwell hardened blade?

Steel130

Steel130

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Sep 17, 2010
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Hey guys I was just curious. Say you have two knives of the exact same steel. One is hardened to 62 RC and the other blade is hardened to 58 RC. What are that advantages and disadvantages of steel that is harder? I heard that a higher RC holds an edge longer but takes longer to sharpen, But does it also increase brittleness? And if so why? Thanks in advance, I am trying to get on the more metallurgic side of blades.
 
The advantages of higher hardness is just that: they are harder and more resistant to deformation. Lower hardnesses correlate to a decrease in resistance to deformation, but there is also generally an increase in malleability.

Take candy as an analogy. Some candies are very hard, like toffee or brittles (peanut brittle), and can become sharp enough to actually cut you, yet they will shatter if dropped or snap if placed under enough pressure. Other candies, like caramel for example, are much more malleable, and while you won't be able to cut yourself with it, you won't be able to shatter or chip it either.

Steel is the same way. Certain formulas and ingredient ratios, just like different candy recipes, will create a steel that can be hardened to different HRC values with better results than other forumlas.
 
So I have a custom fixed blade in CPM154 and it is hardened to 62RC so in theory it is going to stay sharper longer yet it is more prone to chipping then say the same blade hardened to 58RC right?
 
Steel130 said:
So I have a custom fixed blade in CPM154 and it is hardened to 62RC so in theory it is going to stay sharper longer yet it is more prone to chipping then say the same blade hardened to 58RC right?
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Actually I happen to have 154CM at 62HRC, which originally was 60-ish. Increase in edge holding is very considerable. On top of that, one of the underused aspect of super hard blades is their ability to hold very thin edges. Depending on the steel and RC anywhere from 5-12 per side angle edges. Typically factory edges are 20 per side and more... Increase in cutting ability is just huge.

As for the chipping, yes, soft blade will deform, hard steel will chip, however also worth noticing, that soft steel will deform much easier than hard steel chips, given the same edge angles.
A while back I did Super Hard vs. Soft Edges testing, just to understand brittleness issue, and it's not that severe(in fact nothing has chipped) as one might think based on all the brittle hard knives stories ;)
 
Generally this is true. Some alloys can have greater toughnesses at weird HRC values, but in general the lower it is, the tougher and more malleable the steel.
 
Theres a ying and yang when it comes to hardness. Generally speaking the higher the hardness the better the edge retention. The lower the hardness the better the toughness (resistance to cracking, breaking, chipping).

So...
High RC = Generally means better edge retention.
Low RC = Generally better toughness.

But I'll throw another wrench into this:
One steel may be much better at toughness compared to another steel, and the same goes for edge retention. Take for example 3V vs. S90V...

3V at 62rc will have good edge retention, but relative to S90V its edge retention isn't even in the same ballpark. But 3V has unbelievable toughness. Its almost literally unbreakable. You can drop it tip first into concrete, it will cut into concrete and not even have scratch (theres a story somewhere in one of the theads).

S90V at 62rc will hold an incredible edge. Its insane trying to dull it, and when you do its very difficult to sharpen. But the toughness of S90V (especially at high RC) is horrible. Its relatively fragile.
 
Cool thanks guys. I was going to say my custom has a 30 degree inclusive angle and for a 15 degree edge it seems to hold a very sharp edge for awhile. I cut a whole bag of unwashed potatoes up with it and it is still very sharp. However it seems like most of my blades lose that hair whittling ability after cutting through a few zip ties and stuff.
 
To directly answer the question, higher hardness blades will hold a very sharp edge for longer. They will in theory take longer to sharpen, which is not the same as difficult to sharpen. However, in practice, the list of variables in sharpening time is long and the wear resistance of the steel is only one of them. If you have the wrong hardness, not necessarily too high, just wrong, then sharpening can be nearly impossible. The edge can chip on the stone as you make a pass.

The relationship between hardness and toughness and edge holding is a fairly complicated one. Steels like the 154CM you mentioned have more than one way to reach the same hardness level. In the relatively low tempering temperature range of the most common knife steels, the relationship between hardness and toughness is not direct, i.e. one goes up, the other may go up too.

Be sure to read gator's thread linked above. It shows some of the misunderstandings about very hard edges very clearly. As a knife knut, you just haven't lived until you've batoned a knife into a piece of wood using a hammer, knowing you shouldn't be able to because the knife's hardness is above 64 HRc. Like he also mentioned, softer edges are weaker and will bend rather than chip, but if it takes 5 times the force to make a chip than it does to deform a soft edge, is that what you really want? That is up to you and what you're cutting.
 
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There is a balance that has to met between hardness and blade/edge strength and that is assuming a good HT and tempering process.

S30V at 50 HRC that rolles and loses it's edge or at 65 HRC that the edge falls apart or just chips away in use won't do people any good.
 
steel130, when you come down we'll do some experimenting with some hard and soft steel. that might help you to understand a little better.
 
jaymeister99 said:
3V at 62rc will have good edge retention, but relative to S90V its edge retention isn't even in the same ballpark. But 3V has unbelievable toughness. Its almost literally unbreakable. You can drop it tip first into concrete, it will cut into concrete and not even have scratch (theres a story somewhere in one of the theads).
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IMO, a better comparison at 62 would be 3V vs CPM-M4. At 62, M4 is slightly underhardened, while 3V is well past a toughness peak at 58. If they are both at 62, then 3V loses half its toughness compared to peak values, and M4 is then about equal to it. Plus M4 is also about three times more wear resistant.

Conversely, 58 is within the recommended working range of S90V, so you have complete opposites in toughness/wear resistance at the same recommended hardness for 3V and S90V.

In either case, it is really alloy dependent, and also whether or not a secondary hardening from high temper is possible or used.
 
Cynic , the word you want is tough rather than malleable. Malleable - the ability to be hammered .Gold is IIRC the most malleable ,therefore can be hammered extremely thin as in gold foil.

Some of the 'super steels' can be tough and wear resistant at high hardness .One that I have is Fallkniven 's SGPS that has those fine qualities !
 
Cynic2701 said:
The advantages of higher hardness is just that: they are harder and more resistant to deformation. Lower hardnesses correlate to a decrease in resistance to deformation, but there is also generally an increase in malleability.

Take candy as an analogy. Some candies are very hard, like toffee or brittles (peanut brittle), and can become sharp enough to actually cut you, yet they will shatter if dropped or snap if placed under enough pressure. Other candies, like caramel for example, are much more malleable, and while you won't be able to cut yourself with it, you won't be able to shatter or chip it either.

Steel is the same way. Certain formulas and ingredient ratios, just like different candy recipes, will create a steel that can be hardened to different HRC values with better results than other forumlas.
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Very well put
 
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