A possibility of high strength + high toughness hardened steel?

[BluntCut MetalWorks]

6 months ago, I set goal to make a chopper with ~0.02" behind the edge thickness and 62rc.

Efficiency is the key reason for having a blade with high strength + high toughness + thin geometry. Goal is to have a high work_done/energy_input performance ratio.

http://www.bladeforums.com/forums/s...-arms-exercise?highlight=bluntcut+chopper+fun

Well, now I have a ht formula for low Cr carbon steels met such goal.

*Note: my videos are usually long and possibly boring *

June 12 2015 - I demo a small 61.5rc 52100 chopper with very thin edge - https://youtu.be/dFBM__wPCs8

Today July 11 2015 - video of a 10.5" blade (16" OAL) 62rc W2 chopper with 0.02" edge thick chopping pine log with full of pin knots. Successfully passed all tests.
https://youtu.be/X0jh0zPz7ao

To me, this is exciting because I have evidences contradicting the commonly accepted notion that high hardness is mutually exclusive to high toughness in hardened steels.

Thanks for reading/watching/comments.

Thoughts?

 

[Shorttime]

Ed Fowler has been working with 52100 for a while, now.

Search using his name, and his website should be easy to find.

 

[BluntCut MetalWorks]

Thanks, I am well familiar/aware with Ed Fowler's works on 52100 grain refinement. Please post links of his high strength(including hardness) + high toughness large knives - my google_fu need helps.

Ed Fowler has been working with 52100 for a while, now.

Search using his name, and his website should be easy to find.

 

[Insipid Moniker]

Not to offend, but I don't think it really contradicts the conventional wisdom, more that it demonstrates that high hardness steel can be still be tough enough. I'm beginning to develop the opinion that toughness is greatly overvalued in the current market and cutting efficiency and cutting geometry is significantly undervalued.

 

[BluntCut MetalWorks]

You are right about geometry is more critical than toughness (possibly over-rated). However can't have thin geometry when there isn't enough steel volume to provide sufficient strength + toughness to withstand high impact. Most steels toughness drop dramatically (square or cubic but not exponential) start right around 60+rc. So at 62rc hardness and low toughness, in order to withstand chopping pin knots pine, geometry need to drastically thicken to something 50% or 100% thicker than my 0.02 edge thick chopper. Well a thicker edge would certain will degrade chopping performance. Now if hardness keep at sub 60rc, then edge has less strength, so edge still need to be thicker to have enough UTS to withstand this scenario lateral damaging force. Yet, another way of lowering the chopping performance...

Let me rephrase, conventional wisdom - hardened steel can't have both high hardness & high toughness, is it THE law of physics or merely limitation of our metallurgy skills?

Not to offend, but I don't think it really contradicts the conventional wisdom, more that it demonstrates that high hardness steel can be still be tough enough. I'm beginning to develop the opinion that toughness is greatly overvalued in the current market and cutting efficiency and cutting geometry is significantly undervalued.

 

[The Mastiff]

It's relative. How tough do you need to consider it a tough, hard use knife? Steels like Vascowear/Cruwear/CPM Cruwear, PD#1, Z wear , M2, M3, M3-2, CPM M4, are pretty tough steels and can be used at rc 62-63 without losing too much toughness especially if heat treated for toughness and not max wear. 4V, Vandis 4E, etc. same thing. I have a 4V knife at rc 63 that isn't all that different from the one I have at rc 60. ( note: I haven't pounded either to the point of damage and don't intend to). I keep the edges thick enough with enough steel in the edge to do what I want yet still have great cutting potential.

Thin edges can be over rated IMO. They are fun at times for some things but I can have an edge angle of 40 degrees inclusive and still dry shave easily.

I have a Gerber Sportsman 2 "V steel" ( vascowear) which came out of the box at 50 degrees inclusive yet it shaved hair without pulling or scratching. The edges were straight and finished with a nice buffing from the factory ( circa 1984 production). On the other hand I've had knives at 30 degrees inclusive that couldn't shave.

As far as toughness goes CPM Cruwear, PD#1, and Z wear and CPM M4 steel aren't that much less tough at rc 62-63 than 3V is at rc60. They can do whatever I require of them. I have Axes and Mauls or saws or pry bars for tougher jobs.

joe

 

[Insipid Moniker]

It's relative. How tough do you need to consider it a tough, hard use knife? Steels like Vascowear/Cruwear/CPM Cruwear, PD#1, Z wear , M2, M3, M3-2, CPM M4, are pretty tough steels and can be used at rc 62-63 without losing too much toughness especially if heat treated for toughness and not max wear. 4V, Vandis 4E, etc. same thing. I have a 4V knife at rc 63 that isn't all that different from the one I have at rc 60. ( note: I haven't pounded either to the point of damage and don't intend to). I keep the edges thick enough with enough steel in the edge to do what I want yet still have great cutting potential.

Thin edges can be over rated IMO. They are fun at times for some things but I can have an edge angle of 40 degrees inclusive and still dry shave easily.

I have a Gerber Sportsman 2 "V steel" ( vascowear) which came out of the box at 50 degrees inclusive yet it shaved hair without pulling or scratching. The edges were straight and finished with a nice buffing from the factory ( circa 1984 production). On the other hand I've had knives at 30 degrees inclusive that couldn't shave.

As far as toughness goes CPM Cruwear, PD#1, and Z wear and CPM M4 steel aren't that much less tough at rc 62-63 than 3V is at rc60. They can do whatever I require of them. I have Axes and Mauls or saws or pry bars for tougher jobs.

joe

Personally, when talking about a thin edge or cutting geometry the measurement I'm more interested in than edge angle is thickness behind the edge.

 

[Insipid Moniker]

You are right about geometry is more critical than toughness (possibly over-rated). However can't have thin geometry when there isn't enough steel volume to provide sufficient strength + toughness to withstand high impact. Most steels toughness drop dramatically (square or cubic but not exponential) start right around 60+rc. So at 62rc hardness and low toughness, in order to withstand chopping pin knots pine, geometry need to drastically thicken to something 50% or 100% thicker than my 0.02 edge thick chopper. Well a thicker edge would certain will degrade chopping performance. Now if hardness keep at sub 60rc, then edge has less strength, so edge still need to be thicker to have enough UTS to withstand this scenario lateral damaging force. Yet, another way of lowering the chopping performance...

Let me rephrase, conventional wisdom - hardened steel can't have both high hardness & high toughness, is it THE law of physics or merely limitation of our metallurgy skills?

That's somewhat beyond me, but it's an interesting question. I've always heard that the properties are, by definition, inversely proportionate, but I don't know enough to say that for sure.

 

[Twindog]

Toughness and strength are, as a general matter, mutually exclusive. But not always. In making a chopper, the key elements are blade/edge geometry, heat treat and steel alloy.

Blade/edge geometry is the key to how well a blade can cut efficiently, but heat treat and steel alloy are the keys to how aggressive you can be with blade/edge geometry. Heat treat is probably the most important because it allows high-performance geometry to be supported by the steel alloy.

It's nice to see someone bring out the potential in W2. A few years ago, I bought a custom bowie in W2 that I planned to use as a chopper. A few test whacks into clear, straight-grained Douglas fir caused damage with every chop. The geometry of that blade was obtuse and not sharp at all. But the heat treat was so bad that the blade could not stand up to even gentle, non-abusive chopping.

On the other hand, I have a 6-inch fixed blade in M4 hardened to 64 Rc, that chopped that same round of Doug fir easily with no edge damage.

Bluntcut understands heat treat. And that is an under-appreciated skill, even here on the forum.

 

[Chris "Anagarika"]

Toughness and strength are, as a general matter, mutually exclusive. But not always. In making a chopper, the key elements are blade/edge geometry, heat treat and steel alloy.

Blade/edge geometry is the key to how well a blade can cut efficiently, but heat treat and steel alloy are the keys to how aggressive you can be with blade/edge geometry. Heat treat is probably the most important because it allows high-performance geometry to be supported by the steel alloy.

It's nice to see someone bring out the potential in W2. A few years ago, I bought a custom bowie in W2 that I planned to use as a chopper. A few test whacks into clear, straight-grained Douglas fir caused damage with every chop. The geometry of that blade was obtuse and not sharp at all. But the heat treat was so bad that the blade could not stand up to even gentle, non-abusive chopping.

On the other hand, I have a 6-inch fixed blade in M4 hardened to 64 Rc, that chopped that same round of Doug fir easily with no edge damage.

Bluntcut understands heat treat. And that is an under-appreciated skill, even here on the forum.

I can't say it any better. :thumbup:

 

[BluntCut MetalWorks]

A good ht for toughness often goes along with low strength (hardness is a majority composite indicator). So thickness behind the edge need to be sufficient to withstand damaging force, especially lateral kind.

Good point about bevel angle, Joe! going from 15dps to 20dps while keeping the same bevel face length, only change edge triangular cross section by 30.7%. http://ostermiller.org/calc/triangle.html - just plug in angle 30 or 40 and 10 in 2 sides, calculate the base.
There are so many variables in cutting interaction between edge bevel vs material + forces, this 30.7% could very much be statistically insignificant. However quantitatively it has significant, especially when talking about high performance while keeping everything else equal.

Calculating at toughness & strength by volume in this case (edge bevel angle and edge shoulder thickness):
K1: 20dps, 2mm
K2: 10dps, 1mm (just halves both figures)

If both K1 & K2 are right about the threshold of failure for certain difficult task in same optimal identical laboratory-environment. Both passed but can't take additional load. It's reasonably to say in geometrically term that K2 is 1/8 volume of K1, thereby deductively K2 is up to 8 times in combine of tough+strong per given tasks.

For occasional wear (Minimal in weight bearing activities of equipment over time, e.g. carry on long trek) and a few chops here/there, efficiency is clearly a nice-to-have. But if this tool is being use extensively in swing/chop for hrs/work-day, efficiency gets translate into productivity.

It's relative. How tough do you need to consider it a tough, hard use knife? Steels like Vascowear/Cruwear/CPM Cruwear, PD#1, Z wear , M2, M3, M3-2, CPM M4, are pretty tough steels and can be used at rc 62-63 without losing too much toughness especially if heat treated for toughness and not max wear. 4V, Vandis 4E, etc. same thing. I have a 4V knife at rc 63 that isn't all that different from the one I have at rc 60. ( note: I haven't pounded either to the point of damage and don't intend to). I keep the edges thick enough with enough steel in the edge to do what I want yet still have great cutting potential.

Thin edges can be over rated IMO. They are fun at times for some things but I can have an edge angle of 40 degrees inclusive and still dry shave easily.

I have a Gerber Sportsman 2 "V steel" ( vascowear) which came out of the box at 50 degrees inclusive yet it shaved hair without pulling or scratching. The edges were straight and finished with a nice buffing from the factory ( circa 1984 production). On the other hand I've had knives at 30 degrees inclusive that couldn't shave.

As far as toughness goes CPM Cruwear, PD#1, and Z wear and CPM M4 steel aren't that much less tough at rc 62-63 than 3V is at rc60. They can do whatever I require of them. I have Axes and Mauls or saws or pry bars for tougher jobs.

joe

 

[BluntCut MetalWorks]

* I am not a metallurgist but scientifically competent *

Inversely proportion on toughness vs strength mostly hold true when grain size > 2um and lattice cohesion+coherent. It's not really about grain size but what in grain boundary (GB). GB is a weak link where fracture initiate and propagate. GB porosity also a factor. Matrix cohesion is how tightly the steel lattice packed. Matrix coherent is how lattice aligned - a low mismatch angle intergrain and martensite type & orientation. So/IMO that 'inverse proportion' based on our in-ability of getting smaller grain (ok, for hardened martensitic steels).

I haven't test to my latest ht blades to failure point. Just make this accomplished goal as a new baseline. I saw early indication that currently blades edge failure mode is rippling or rolling, so there is some room to push for higher hardness and or use even thinner edge bevel shoulder.

That's somewhat beyond me, but it's an interesting question. I've always heard that the properties are, by definition, inversely proportionate, but I don't know enough to say that for sure.

 

[BluntCut MetalWorks]

Thanks Chris!

I can't say it any better. :thumbup:

Twindog - your kind words & input are very much appreciated.

My current ht process is for most of low Cr carbon steels: 5160; 10xx; 52100; Wx; O1; etc... Although, this ht work well for this wide range of steels. It's best result with ultra fine grain when steel has between 0.9% - 1.2%Carbon.

I am agreeing with you :thumbup: but like to add/augment:

Newton's 2nd & 3rd Laws : F=MA; equal and opposite force(EOF). In blade length, A (acceleration) is mostly R^2 (radius square) along with M (mass). So there is a large force different between 6" vs much heavier 10" blade. EOF is where edge & blade geometry & cutting material intertwined. A dull obtuse edge of thick blade rebouncing force propagating through your arm when chopping hard+tough material cross grain, EOF way to remind to avoid wasted energy in rebounce & obsorption. My chopper edge & blade geometry designed to cut as deeply as possible (for dried hardwoods) while maintain enough wedge & rebounce to prevent excess blade binding to material.

Toughness and strength are, as a general matter, mutually exclusive. But not always. In making a chopper, the key elements are blade/edge geometry, heat treat and steel alloy.

Blade/edge geometry is the key to how well a blade can cut efficiently, but heat treat and steel alloy are the keys to how aggressive you can be with blade/edge geometry. Heat treat is probably the most important because it allows high-performance geometry to be supported by the steel alloy.

It's nice to see someone bring out the potential in W2. A few years ago, I bought a custom bowie in W2 that I planned to use as a chopper. A few test whacks into clear, straight-grained Douglas fir caused damage with every chop. The geometry of that blade was obtuse and not sharp at all. But the heat treat was so bad that the blade could not stand up to even gentle, non-abusive chopping.

On the other hand, I have a 6-inch fixed blade in M4 hardened to 64 Rc, that chopped that same round of Doug fir easily with no edge damage.

Bluntcut understands heat treat. And that is an under-appreciated skill, even here on the forum.

 

[mete]

Get some CPM-3V and chop away !

 

[BluntCut MetalWorks]

Thanks for the suggestion, Robert/mete!

I've a question. First, my 59.5rc 80CrV2 (0.81%C) chopper with 0.022" behind 15dps edge thickness failed at almost cross grain chop against seasoned pin-knotted pine log. Do you think CPM-3V (0.8%C) at 62rc; 0.02" behind 15dps edge thick would successfully pass this chopping test? From Crucible site 62rc 3V impact toughness at 40 ft-lbs, I didn't find fracture toughness #. Fracture toughness maybe a bit more crucial than impact toughness in this case/test.

Also I would love to hear 3V large chopper users chime in with experiences or take on whether 3V at 62rc would survive this chopping test with quite a bit damaging lateral force.

Just to be clear. Both W2(0.93%C) and 52100(0.94%C) have higher carbide volume than 80CrV2(0.81%C) and CPM-3V(0.8%C). Although 3V has lower carbide volume, it has higher wear resistant than other listed steels. Further more, low Carbon percent is intrinsically tougher than steels with high carbon. Is that truth or just because we accepted so?

Get some CPM-3V and chop away !

 

[BluntCut MetalWorks]

I think 80CrV2 CharpyC falls within a narrow range of 3V - hopefully that is not a too far fetch projection. It's far cheaper for me to make another or two 80CrV2 chopper than worry about a 3V chopper with 2 halves after some test. Most likely 80CrV2 carbide size is smaller than 3V, toughness #s should be higher when grain size is the same.

So my ht version 1.0 80CrV2 chopper at 59.5rc; 0.022" edge thick - CharpyC (CC) ~60 ft.lbs. End up with large rippled edge after the test. For this pin-knotted pine chop test, obviously the combination of edge strength+tougness was less than the test load. So with added strength at 62rc but reduce toughness to 40 ft.lbs (33% less), would this combination pass the test?

My guess is No, I expect it to fail when edge thickness is less than a generous 0.03" at this hardness.

Using my latest ht, I can make 5160 or 80CrV2 tougher & stronger but it will not be as good as 52100/W2/(wimpy tough 1095)/high-carbon-low-Cr-steels. When grain size is near or below 1 micron, toughness & strength high value curves won't drastically diverge to near orthogonal until 64rc or so. My ht works well for steels with composition with less than 2.5%X. Where X is combination of Cr+other alloying elements.

btw - Infi is similar to 3V, except it only has 0.61% of Carbon+Nitrogen. Extra toughness probably will extend the Young Modulus of fracture some but strength is more important in resist edge from being steer away by pin knot. Once small part of the edge steers past a few degrees of the apex line, reaching edge failure point is very rapid after that. Lowering edge bevel angle could reduce steering but proportionally lower the impact & lateral capacity of the edge.

From your assessment/POV... is combination of high strength + high toughness hardened steel possible?

 

[Boris74]

Thanks for the suggestion, Robert/mete!

I've a question. First, my 59.5rc 80CrV2 (0.81%C) chopper with 0.022" behind 15dps edge thickness failed at almost cross grain chop against seasoned pin-knotted pine log. Do you think CPM-3V (0.8%C) at 62rc; 0.02" behind 15dps edge thick would successfully pass this chopping test? From Crucible site 62rc 3V impact toughness at 40 ft-lbs, I didn't find fracture toughness #. Fracture toughness maybe a bit more crucial than impact toughness in this case/test.

Also I would love to hear 3V large chopper users chime in with experiences or take on whether 3V at 62rc would survive this chopping test with quite a bit damaging lateral force.

I got put on blast for saying 80crv2 doesn't hold up well for the heavy duty tasks a bit back. Thank you for putting some science behind my observations and experiences.

 

[gadgetgeek]

Not that I'm an expert in anything, but I would think that the more efficient the cutting edge, the less overall strain on the blade. I don't know how much of a difference it would make, but it stands to reason that all things being equal, reducing shock loads improves overall performance. I would also think that you would also have some different results looking at point or distributed loads, and geometry would play into that. Cool stuff. I think that for the longest time we haven't really known where some of the failure thresholds were, so as we learn more, things can be engineered to be more efficient.

 

[Sonnydaze]

Bluntcut...I enjoyed your thread. You've put a lot of thought into that chopper. The video demonstrates just how good that blade is.
Sonnydaze

 

[bdmicarta]

will extend the Young Modulus of fracture some

I'm not sure what you are saying but "youngs modulus" and "fracture" are 2 separate things that don't go together. "Youngs modulus", also called "modulus of elasticity", is the measure of the stiffness of a material, in other words the slope of the stress strain curve in the elastic region. "fracture" occurs after the material reaches yield and hopefully elongates some. A more ductile material will elongate more before fracture. I think what you meant to say is "extend the plastic region".

is combination of high strength + high toughness hardened steel possible?

I think it might be possible. We have a lot to learn about metallurgy.