Best Knife Steel?

Thanx, Marcinek- but it's got nothing to do with smartness... I'm a mechanical engineer, so I should know that stuff (or at least be vaguely well informed). BTW, I just fiddled a bit to make this graph (just for the sake of curiosity):

Xt5pbhM.jpg
 
Wolf_HR said:
Thanx, Marcinek- but it's got nothing to do with smartness... I'm a mechanical engineer, so I should know that stuff (or at least be vaguely well informed). BTW, I just fiddled a bit to make this graph (just for the sake of curiosity):

Xt5pbhM.jpg
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What exactly is "strength"? You mean toughness?

Hardness is not proportional to toughness.
 
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No, strength and toughness are unrelated properties... To explain this graph, left scale is strength in MPa. To illustrate strength, 'normal' mild steel is 380MPa (if you have a rod of this steel 1mm x 1mm square cross section, you'll have to hang 38 kg weight on it before it breaks*). ZDP-189 in my Endura is I believe hardened to 65 HRC, at which hardness it has approximate strength of 2800MPa (meaning the same rod would break lifting a 280 kg weight).

* US unit of strength is psi- in the first case a 1inx1in rod would break under 55000 pound load, and ZDP-189 at 65HRC under 400000 pound load.
 
Wolf_HR said:
No, strength and toughness are unrelated properties... To explain this graph, left scale is strength in MPa. To illustrate strength, 'normal' mild steel is 380MPa (if you have a rod of this steel 1mm x 1mm square cross section, you'll have to hang 38 kg weight on it before it breaks*). ZDP-189 in my Endura is I believe hardened to 65 HRC, at which hardness it has approximate strength of 2800MPa (meaning the same rod would break lifting a 280 kg weight).

* US unit of strength is psi- in the first case a 1inx1in rod would break under 55000 pound load, and ZDP-189 at 65HRC under 400000 pound load.
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That still isn't relevant, steel type "x" hardened at 60 hrc will not necessairly perform like steel type "y" at 60 hrc. You should go back and read the link I posted from crucible (aka the guys making your blade steel)...
 
Of course they will not 'perform' the same- otherwise there would be no need for different alloys. But 'performance' does not depend solely on strength of material, or hardness, or wear resistance, or toughness, or corosion resistance, &c. Most of those properties are not even directly related (I was speaking of two properties that are), and your link was nice but nothing I already didn't know. Besides, to show that with steel 'all things being equal' means nothing because they never are- from my own experience I can tell you that even the same alloy from different manufacturers behaves differently when machined (say, a standardized tool steel like O2 from Bohler or Metal Ravne)... the same applies to aluminium alloys. Besides, it's all 'a rule of thumb' with those kind of things- everybody will tell you that D2 is not stainless because it has 12% chromium, yet I would think in my experience is more stain resistant than a certain alloy with 20% chromium.
 
Wolf_HR said:
Of course they will not 'perform' the same- otherwise there would be no need for different alloys. But 'performance' does not depend solely on strength of material, or hardness, or wear resistance, or toughness, or corosion resistance, &c. Most of those properties are not even directly related (I was speaking of two properties that are), and your link was nice but nothing I already didn't know. Besides, to show that with steel 'all things being equal' means nothing because they never are- from my own experience I can tell you that even the same alloy from different manufacturers behaves differently when machined (say, a standardized tool steel like O2 from Bohler or Metal Ravne)... the same applies to aluminium alloys. Besides, it's all 'a rule of thumb' with those kind of things- everybody will tell you that D2 is not stainless because it has 12% chromium, yet I would think in my experience is more stain resistant than a certain alloy with 20% chromium.
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I completely agree with you, but I'm still having trouble understand how that chart has anything to do with knives. It basically says that hardness corresponds to strength, it doesn't. There are a lot of other things going on in a steel, like grain structure/size.

http://materion.com/~/media/Files/P... No 15 - Grain Size and Material Strength.pdf
 
Blues Bender said:
That still isn't relevant, steel type "x" hardened at 60 hrc will not necessairly perform like steel type "y" at 60 hrc. You should go back and read the link I posted from crucible (aka the guys making your blade steel)...
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He's got it right:

Strength and hardness are directly related. Strength is how much force it takes to get some sort of permanent deformation - whether that is bending or breaking. Harder steel resists deformation more than softer steel.

Toughness is a measure of plasticity - how much of an impact the steel can take without cracking.


A tire is not strong, but incredibly tough.



To the OP, if you want to talk cheap steel, then stuff like W2, O1 and 52100 can be made hard and still pretty tough. If you want to spend money, CPM 3V and 4V are very tough steels that hold a decent edge, and CPM M4 is a very high edge holding steel that is quite tough.

Most other steels are either going to be very wear resistant but not tough, really tough but not wear resistant, or just fall short of both toughness and edge holding compared to 3V, 4V and M4.


There are other steels out there that compare to those, like ZDP-189, that I just am not as familiar with. But I see the pinnacle steels as those that can do both very well.
 
RX-79G said:
He's got it right:

Strength and hardness are directly related. Strength is how much force it takes to get some sort of permanent deformation - whether that is bending or breaking. Harder steel resists deformation more than softer steel.

Toughness is a measure of plasticity - how much of an impact the steel can take without cracking.


A tire is not strong, but incredibly tough.
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Crucible defines resistance to bending as toughness. I feel like I'm repeating myself when all you have to do is read what I originally stated... There is not one standard toughness test, it's measured in different ways; again, read my link from crucible...
 
Blues Bender said:
Crucible defines resistance to bending as toughness. I feel like I'm repeating myself when all you have to do is read what I originally stated... There is not one standard toughness test, it's measured in different ways; again, read my link from crucible...
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Resistance to permanent bending is toughness, but the amount of force necessary to get to that point is defined by strength, which is hardness. To put it another way, toughness is what takes over after you hit the strength limit given by the hardness. Toughness is when you are in the plastic deformation range, but the amount of deformation is minimized.

So a non-tough steel would have the same yield strength, but would break when it goes past yield. The tough steel at the same hardness would go through yield, but the amount it would deform would be minimal - so little that it effectively hasn't deformed at all.

If two 55 Rc steel rods will support 2000 pounds, and at 2100 pounds one is broken and the other is bent a fraction of a degree, it is because the second one is tougher. Both yielded above 2000, but one used it's toughness to keep from fully failing.


Sorry to the engineers and everyone else if I'm making this muddier. This is how I keep the distinction in my head.
 
Blues Bender said:
Crucible defines resistance to bending as toughness. I feel like I'm repeating myself when all you have to do is read what I originally stated... There is not one standard toughness test, it's measured in different ways; again, read my link from crucible...
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Reading what was copied and pasted in a previous post in this thread, that is not what was said. This is what was posted earlier:
"Hardness is a measure of a steel’s resistance to deformation" and "Toughness ... is the relative resistance of a material to breakage". They said that toughness is resistance to breaking, not resistance to bending. Bending and breaking are 2 different things. Everybody has picked up a piece of wire and bent it, maybe a coathanger or a piece of copper wire. A coathanger will bend a lot and not break. It has low strength because it is fairly easy to bend but it has high toughness because you can bend it a lot and it doesn't break. The terminology is hard for the layman to understand and it is easy to get words mixed around. It is hard to explain simple engineering concepts such as stress in a way that people can understand. I've been dealing with stress calculations for 40 years but I can't give a simple sentence to explain what stress is and know that any reader will understand it.

Regarding hardness vs. strength- they are the same or are virtually the same. Steel strength is a measure of how much stress you can put on the steel before it permanently deforms or fractures. In other words you can hammer or bend on a piece of steel and it will return to its original shape without permanent deformation, up to a point. Beyond that you will leave a dent in the steel or it will be permanently bent or whatever. A stronger steel will go farther before this happens. Now consider how hardness is measured- the testing machine pushes on the steel with a point until it puts a dimple into the steel. So in the process of measuring hardness it is also directly measuring strength.

But back to the OP, any given steel alloy at any given heat treat level has a certain amount of hardness and a certain amount of toughness. There is a tradeoff between these 2 properties- change the alloy or the heat treat and you increase one of these qualities while decreasing the other, that is the tradeoff. Different alloys and different heat treat procedures will move the tradeoff point up and down the scale so that you can have more of one quality before you adversely affect the other. This is the eternal search for knife people.

The question of what is a hard and tough steel- by now it should have been proven that you can't have both. Pick which property is most important to you, which is why people were asking what the intended us is, then you can select a steel that is better suited for that use. When I see someone ask about tough and hard, I think of steels like A2 and 3V. Because the word "tough" is mentioned I think that property is important enough to pick a steel with good toughness.
 
From ASM international:

Properties of materials: more than physical and chemical

Strength

Strength is not a precisely defined mechanical property, as there are many
types of strength. Collectively, it means the ability of
a material to stand up
to forces being applied without it bending, breaking, shattering or deforming.
A strong material is one able to withstand large stresses before either
breaking or deforming. Some materials have different strengths according to
the nature of the stress applied. Concrete, for example, is strong under
compression but has relatively poor tensile strength

Toughness

A characteristic of a material that relates to its response to sudden blows or
shocks. Toughness can be expressed as the amount of energy required for
creating or propagating a crack. Closely related to resilience.

Google is your friend, there are standards for steels and fixed terminology. Preferably, use Google Scholar.
 
Blues Bender said:
This explains everything a lot better than I, or anyone else here can: http://www.crucibleservice.com/eselector/general/generalpart1.html

It mainly talks about tool steels, but the ideas expressed here are universal for all steels.

Just a few relevant paragraphs I randomly picked...

"Hardness is a measure of a steel’s resistance to deformation. Hardness in tool steels is most commonly measured using the Rockwell C test. Hardened cold work tool steels are generally about 58/64 HRC (hardness Rockwell C), depending on the grade. Most are typically about 60/62 HRC, although some are occasionally used up to about 66 HRC.

Toughness, as considered for tooling materials, is the relative resistance of a material to breakage, chipping, or cracking under impact or stress. Toughness may be thought of as the opposite of brittleness. Toughness testing is not as standardized as hardness testing. It may be difficult to correlate the results of different test methods. Common toughness tests include various impact tests and bend fracture tests.

Wear resistance is the ability of material to resist being abraded or eroded by contact with work material, other tools, or outside influences (scale, grit, etc.) Wear resistance is provided by both the hardness level and the chemistry of the tool. Wear tests are quite specific to the circumstances creating the wear and the application of the tool. Most wear tests involve creating a moving contact between the surface of a sample and some destructive medium. There are 2 basic types of wear damage in tools, abrasive and adhesive. Wear involving erosion or rounding of edges, as from scale or oxide, is called abrasive wear. Abrasive wear does not require high pressures. Abrasive wear testing may involve sand, sandpaper, or various slurries or powders. Wear from intimate contact between two relatively smooth surfaces, such as steel on steel, carbide on steel, etc., is called adhesive wear. Adhesive wear may involve actual tearing of the material at points of high pressure contact due to friction.

We often intuitively expect that a harder tool will resist wear better than a softer tool. However, different grades, used at the same hardness, provide varying wear resistance. For instance, O1, A2, D2, and M2 would be expected to show increasingly longer wear performance, even if all were used at 60 HRC. In fact, in some situations, lower hardness, high alloy grades may outwear higher hardness, lower alloy grades. Thus, factors other than hardness must contribute to wear properties.

[carbides]
Tool steels contain the element carbon, in levels from about 0.5% up to over 2%. The minimum level of about 0.5% is required to allow the steels to harden to the 60 HRC level during heat treating. The excess carbon above 0.5% plays little role in the hardening of the steels. Instead, it is intended to combine with other elements in the steel to form hard particles called carbides. Tool steels contain elements such as chromium, molybdenum, tungsten, and vanadium. These elements combine with the excess carbon to form chromium carbides, tungsten carbides, vanadium carbides, etc. These carbide particles are microscopic in size, and constitute from less than 5% to over 20% of the total volume of the microstructure of the steel. The actual hardness of individual carbide particles depends on their chemical composition. Chromium carbides are about 65/70 HRC, molybdenum and tungsten carbides are about 75 HRC, and vanadium carbides are 80/85 HRC.

These embedded carbide particles function like the cobblestones in a cobblestone street. They are harder than the steel matrix around them, and can help prevent the matrix from being worn away in service. The amount and type of carbide present in a particular grade of steel is largely responsible for differences in wear resistance. At similar hardnesses, steels with greater amounts of carbides or carbides of a higher hardness, will show better resistance to wear. This factor accounts for differences in wear resistance among, say, O1, A2, D2, and M4. Ideally, tool steels would contain as much carbide volume as needed for the desired wear performance. In fact “solid carbide” tooling is typically 85% or 90% tungsten carbide particles, in a matrix of 10% or 15% cobalt to hold them together. Chemically, the microscopic carbide particles in tool steels are similar to the carbide particles in solid carbide tools. However, very high amounts of carbide particles can lead to problems in grinding, or lower toughness. More comments on the effect of carbides on toughness and grindability are discussed in the following section: Effect of Steel Manufacturing on Properties.

Because of their high hardness, vanadium carbides are particularly beneficial for wear resistance. When present in significant amounts, vanadium carbides tend to dominate other types in affecting wear properties. For instance, M4 high speed steel’s chemical content is nearly identical to M2 high speed steel, except M4 contains 4% vanadium instead of 2%. Despite the high levels of molybdenum and tungsten carbides (about 6% tungsten, 5% molybdenum) in each grade, the small difference in vanadium content gives M4 nearly twice the wear life of M2 in many environments. In cold work tool steels, the carbide content in general, and to a limited extent the vanadium content in particular, may sometimes be used as a rough predictor of potential wear life.

Heat Treating Benefits of High Alloy Tool Steels
The heat treating process used to harden steels consists of heating them up to a high temperature (usually 1700/2200°F), then quenching to near room temperature, and finally reheating to some intermediate temperature for tempering (300/1100°F). A characteristic of low to medium alloy steels (A2, O1, D2) is that they soften from their maximum hardness somewhat during tempering. The amount of softening depends on the temperature exposure and the individual grade characteristics. To retain maximum hardness (over about 58 HRC), A2 and D2 are usually tempered around 400/500°F. Higher exposures result in lower hardness. A side benefit of high alloy content, typical of high speed steels, and most of the high wear resistance CPM steels, is that the tempering characteristics are changed because of the alloy content. They are tempered over 1000 F, yet retain their full hardness during this exposure."
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Thoughtful post, good on you Man! We we all new here once. Russ
 
I guess this is where I'm confused. While you guys are calling it strength, crucible clearly defines the same thing as toughness. Is a bend fracture test not considered bending? I'm not trying to argue, but I feel like there is a misunderstanding somewhere here.

They include impact and stress for defining toughness, does bending not stress steel?

"Properties of Tool Steels — Toughness

Toughness, as considered for tooling materials, is the relative resistance of a material to breakage, chipping, or cracking under impact or stress. Toughness may be thought of as the opposite of brittleness. Toughness testing is not as standardized as hardness testing. It may be difficult to correlate the results of different test methods. Common toughness tests include various impact tests and bend fracture tests.

In impact testing, a small sample is held in a fixture and fractured by a moving impacter, such as a calibrated weight on a pendulum. Toughness is reported as the amount of energy, usually measured in foot-pounds or joules, that the sample absorbs before it breaks. Brittle materials will absorb little energy before fracturing. In bend fracture testing, a fixtured sample is subjected to gradually increasing amounts of pressure, usually side or bending pressure, until it breaks."
 
Blues, it's no problem at all- a good starting point in any discussion is that everybody is 'on the same page' with terminology. Crucible definition is not 'happiest' wording, but I certainly am not liking it much because it's a bit iffy.

Strength and toughness can be likened to strength and stamina in humans. Say, you can lift a 500lb load and carry it for 5 yards. On the other hand, I can lift no more than 90lb, but can easily carry it for half a mile or up the 5 flights of stairs. What we can conclude is that you are definitely stronger than I am, but I have done more work (I had more stamina). The same is with steel- ability to withstand stress is is called strength, while toughness is the ability to absorb strain energy (impacts). Say, you take a strip of mild (tough) and hardened tool steel (hard, but not tough) and place it supported only on edges and put a weight in the middle. Hypothetically speaking, if mild steel supports 10lb load before breaking, stronger steel will support 60lbs before breaking. That is strength. But take a 3lb weight and drop it on those same pieces from 5ft height- mild steel will bend and deform but remain in one piece, while tool steel will shatter and fail. That is toughness.
 
I agree with your definitions, from an engineering point of view, I'm sure they are correct. I mentioned in a previous post about grain size, and how it affects a steels performance. If I'm understanding this correctly, hardness would not be the only thing corresponding to strength, regardless of hardness. Smaller grain size can increase a steels strength without increasing hardness, so hardness wouldn't necessairly predict the true strength. I feel like we're talking about the same thing, but defining it differently:D Could these engineering terms mean something entirely different in metallurgy? Crucible seems to define these thing differently, and that's what I'm confused by. Heck, they don't even mention the word strength throughout the entire article. The only hint I see pointing at strength, is in their explanation of toughness.
 
Yes, hardness is not the sole factor affecting the strength, but by far the most dominant. I would guesstimate that by increasing hardness on can trpile the strength, and refining grain can improve it measured in percent, or by order of magnitude less... The way I understand it that refining grain is fine tuning of 'performance'- one targets the desired hardness and then seeks to gain a 'few extra points' by refining the grain. Incidentally, I was under the impression that grain size even more improves the toughness (sort of double benefit, but less pronounced in the effect).
 
Hypothetically speaking, if mild steel supports 10lb load before breaking, stronger steel will support 60lbs before breaking. That is strength. But take a 3lb weight and drop it on those same pieces from 5ft height- mild steel will bend and deform but remain in one piece, while tool steel will shatter and fail. That is toughness./QUOTE]

Interesting discussion guys. I liked the way you explained that Wolf.
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Okay, anyone who has seen me on any of these threads like this knows I have a very perticular opinion on this topic, and I have a lot of stuff I could say here about all the different types of steels in different price ranges, for different types of use, on different types of knives, for different types of people.

But I am NOT going to say even a word of that, because, in reading through this thread, I noticed one really important thing:

THE OP HAS YET TO RESPOND TO ANYTHING SAID HERE OR TO EVEN MAKE A SECOND POST ON THIS THREAD

Because of this, we are probably talking around in circles, and really haven't gotten to the point he wanted to know about at all...so I'll wait.

Thought that was worth mentioning though.

Oh, and BluesBender, thanks for beating me to the punch with that information you posted. I almost went and got mysefl in this, but you did that for me, and then I noticed the issue above and managed to stay out of it for now ;)
 
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