Hardness and abrasion capability

[miso2]

Hi all,

Recent discussions on the effectiveness of sharpening stones on high vanadium steels made me curious about the hardness and abrasion efficiency. I searched around the internet and found some numbers of common materials’ Knoop hardness as listed below. From this, it makes sense to me that one needs to use Diamond abrasives (or CBN) for steels containing a good mount of vanadium carbide (when polishing is desired). Also, for high hardness steels above 60 HRc, I would need at least an alumina ceramic stone, as tempered martensite is as hard as quartz, the main abrasive in natural stones.

As a disclaimer, I am no metallurgist. So, I would appreciate any inputs from metallurgist and sharpening specialists, as well as other sharpening enthusiasts, particularly whether this argument is reasonable and legit.


Miso


Material Hardness Table

Material                         Knoop        Comment

Glass                            530
Tempered martensite at HRc60     700          Value questionable
Quartz                           820          Silicone dioxide, Arkansas stone
Cementite                        1025         Iron carbide
Chromium oxide                  ~1200         Green compound (with alumina)
Zirconia                         1600         Zirconium dioxide
Zirconia toughened alumina       1700
Chromium carbide                 1735
Molybdenum carbide               1800
Tungsten carbide                 1880
Aluminum oxide                   2100         Alumina
Silicone carbide                 2480         Maybe harder due to hardness anisotropy
Vanadium carbide                 2660
Boron carbide                    2750
Cubic boron nitride              4500
Diamond                         >7000

(Vickers? hardness from Uddeholm)


Summary from the discussion below:
(1) Natural stones like Arkansas (quartz, silicate, or novaculite) may not be the first choice when sharpening high carbide volume steels.
(2) You can use any good ceramic stones (alumina and above) for a coarse finish above 10 micron or below #1,000 ANSI grit.
(3) You would need abrasives harder than carbides for finer finishes, if you want to save time and effort. For vanadium carbide steels, this would be cubic boron nitride or diamond. Alumina and silicon carbide can still work but not efficiently. This may also apply to strops.
(4) Alternatively, one can use diamond lapping films instead of stones for finer finishes.

 

[me2]

Just a few comments regarding the chart. Untempered martensite is typically harder than tempered. Arkansas stones will work on 1095, though the carbides in 1095 are cementite, though only 2-5 percent by volume and quite small. Coarse stones can ignore harder carbide as long as the volume isn't too high and the carbides are significantly smaller that the stone grit. Problems arise when trying to polish with to soft an abrasive that is similar in size to the carbides or when the carbide volume is to high.

 

[miso2]

Thanks for the comment, me2. Can you elaborate on the hardness of tempered martensite vs untempered? I understand that tempering reduces the overall hardness of steel for better toughness. But I do not know how to translate this to the hardness of martensite itself. Some sources say that the reduction of overall hardness comes from the conversion of some of martensites to softer structures.

The numbers I listed above for martensites are from separate sources. I have not found any reliable sources describing the hardness of tempered and untempered martensites in a coherent context, and therefore am having hard time to understand this.


Miso

 

[me2]

Ah yes I can see how that would be confusing. The hardness of untempered martensite depends primarily on the carbon content. Up to about 0.8% carbon, the hardness increases, after which it levels off and can even drop down due to retained austenite levels increasing. Tempered martensite can go up slightly, depending on the alloy in question and the overall carbon content and temperature involved. I get the point that hardened blades are similar in hardness to natural novaculite stones, or maybe harder. Also I'm only speaking of low alloy carbon steels. Lots of alloying makes it more complicated than it already is.

 

[samuraistuart]

Using the first google search for hardness equivalent charts I found, and assuming an as quenched hardness of 68 (not too uncommon), that is equivalent to 920 Knoop hardness, just under cementite hardness, but harder than Novaculite (Arkansas stones). Novaculite being approx 64HRC (820 Knoop). Very interesting.

 

[Jens Schuetz]

You can polish harder things using softer material. You just need a bit more of that material.
Paper can cut steel and water can cut stone.
Thus simply comparing the hardness might not give the whole picture.

 

[DeadboxHero]

I think the chart makes perfect since and that yes, you can have carbide tear out but its not a perfect one to one correspondence with abrasive grain hardness and Carbide hardness.

I think its overblown, I think that people struggle with angle consistancy and overpolishing and understanding the importance of proper edge finish for the job at hand more then carbide tearout, and that carbide tearout gets blamed.

Why? ive seen sharp edges from softer abrasives on high carbide volume steel, heck, Jim Ankerson uses only SiC stones and gets 1000's of cuts on 5/8 manila BAMF , Phil Wilson (who is the godfather of High Carbide PM steels)advocates sharpening with SiC and AO at low grit.

I also have friends that get consistent results with Alumina base polishing stones(3k-6k) on high carbide volume steels when they should not, but their execution with sharpening overcomes.

I tell them they need a harder abrasive but their edges tree tops hair so I shrug, if its working then who am I to say its not?

Real world evidence trumps techno babble

The Abrasive grain hardness or compressive strength is one of many factors not the sole factor

Besides nothing is a one to one transfer, if you rub something soft on something hard they both wear each other just at different rates sometimes the ratio is so big you don't notice.


if hardness was the only factor for everything then nothing would ever go dull unless it touched something harder, how cool would that be?

That's not the reality though, matter acting on matter they both wear each other to some degree.


This doesn't mean I'm going to sharpen on a Talc stone. Heck no, But it also doesn't mean I'm going to freak out and switch to only sharpening on diamond stones.

Not everything in the world is black and white and its difficult to discuss grey areas on a internet forum where everything has to be true or untrue or people's heads explode

I'm not going to get a degree in material science to discuss the physics, triobology and ceramics of abrasive stones and the metallurgy.

Don't have the time, Not my speed, I am a caveman, I do what works for me, and others should do what works for them.

Those hardness charts should be seen as a reference guide to seek out an efficient stone but not as the gospel.

In the end, Just stay away from Arkansas stones unless its part of your religion , in that case, then stay away from blasphemous high performace steels too hahaha

 

[FortyTwoBlades]

Hardness and abrasion resistance are not necessarily proportional to one another. Cast and wrought irons are notoriously difficult to abrade, but anvils made wholly of them dent and crumble rapidly. A good way to think of it is like stones in concrete. The cement is not very abrasion resistant, but the stones are, and they carry the brunt of the abrasive wear. You could replace all of the cement with chewing gum or silly putty and it would still be very abrasion resistant due to the stones in it rather than because of its macro-hardness. Steel is similar in this regard. Carbides greatly increase wear resistance in proportion to their hardness and proliferation in the steel, but that doesn't necessarily mean that a steel of a given RC is going to be as abrasion resistant as another steel at that same hardness. The composition plays a big role. Reduce how much stone is in that silly putty and/or increase the size of your abrasive and suddenly the wear dynamics are going to change.

 

[Securis]

I also have friends that get consistent results with Alumina base polishing stones(3k-6k) on high carbide volume steels when they should not, but their execution with sharpening overcomes.

I tell them they need a harder abrasive but their edges tree tops hair so I shrug, if its working then who am I to say its not?

I've seen a few video's where that was achieved. I'm curious to know what different types of methodologies they apply to attain such results, especially since they don't have to resort to diamond abrasives.

In the end, Just stay away from Arkansas stones unless its part of your religion , in that case, then stay away from blasphemous high performace steels too hahaha

I no joke lol'd at this.

 

[DeadboxHero]

I've seen a few video's where that was achieved. I'm curious to know what different types of methodologies they apply to attain such results, especially since they don't have to resort to diamond abrasives.



I no joke lol'd at this.

just like anything, Its just proper execution of the basic sharpening process, nothing special, just done consistently without errors.

Sometimes in sharpening there are small errors that add up if you don't hold your angle or use waayyy too much pressure, or if you don't fully deburr or deburr too aggressively.

its just skill not tools and its comes with practice.

its not some special tool, stone, steel, abrasive or gimmick, anyone can do it if the have the dexterity and understanding of how sharpening works.

If dexterity, disability or inpatients and interest is an issue then there is angle guided systems that lower the learning curve, but doesn't fully eliminate the need to understand the underlying process

don't get me wrong I want the right stone for the job to make my life better but that comes with a premium and will not make you a better sharpener. Yet I enjoy the process and results from exotic stones. What a hypocrite!

 

[miso2]

Thank you, guys, for the discussion. I know that the real-world sharpening is not this simple, but think that this can be a reference for beginners to choose their steels and sharpening stones.

I think the concrete analogy FortyTwoBlades gave is pretty intelligible.

When you grind this mixture of stones and cement with a soft file (but harder than cement), of which grit is bigger than or similar to the size of the stones, the presence of the stones may not matter to the result, in terms of morphology. When you try to refine the surface using a finer file (still softer than the stones), then the stones will appear as bumps and prevent the surface to be smooth. Of course, you can take time and spend a lot of replacement files to grind down the stones, but it won’t be efficient. Instead, you can use a file a lot harder than the stones and make the work more efficient.
(Note: The average size, size variation, and the total amount of stones in concrete would greatly affect the work and result, but this side is ignored here)

Alloys (steels) are like concrete in that they have hard non-iron carbides (stones) and softer iron-based structures (cement). One issue is that these carbides are much harder than natural stones and even many of ceramics. So if you want to grind them, you would want a sharpening stone (file) harder than them (or make a lot of and very consistent effort with a softer stone). Again, this won’t matter if all you need is a finish coarser than the size of carbides.


Summary:
(1) Natural stones like Arkansas (quartz or novaculite) may not be the first choice when sharpening current high hardness steels.
(2) You can use any good ceramic stones for a coarse finish above 10 micron or #1,000 ANSI grit.
(3) You would need abrasives harder than carbides for finer finishes, if you want to save time and effort. For vanadium carbide steels, this would be either cubic boron nitride or diamond.



Miso

 

[Wowbagger]

water can cut stone

Careful now . . . high pressure water cutting usually (always(?)) involves using grit mixed in with the water. Even a natural water course cutting the grand canyon etc is using grit traveling naturally in the stream.

 

[miso2]

Oh, I did not know that. According to Wiki, it seems like you have to have abrasives to cut stones and steels.
That was an eye opener for me. Thanks,


Miso

 

[Wowbagger]

I tell them they need a harder abrasive but their edges tree tops hair so I shrug, if its working then who am I to say its not?

Real world evidence trumps techno babble

I thought that too and couldn't understand what the big deal was sharpening S110V. I sharpened my Manix many, many times from toothy and polished and it went well and fairly fast. I was using the stock factory grind and then went a couple degrees steeper to get right on the edge.

Then . . . I had a BIG learning experience . . . I decided to cut the stock bevel back down to the edge entailing abrading the whole original sharpening bevel . . . only a millimeter and a half wide or so but . . . it took freekin' FOOOOOoooorrrrrrr EVVVVVvvvvver ! I was WEARING the 120 stone noticeably and polishing the heck out of the 220 stone and the rest of them . . . having to freshen them on my diamond plate over and over just to continue making some head way.

Yup . . . if I am going to do this again and not spend all morning doing it this boy needs to invest in some diamonds for his Edge Pro.

Why did it work in the first place while just "touching up" the very edge ? Force per square unit of area. I had VERY LITTLE area and the force applied, though not great at the ball end of the Edge Pro, was very significantly greater than I could apply once I got onto a relatively large bevel area.

if hardness was the only factor for everything then nothing would ever go dull unless it touched something harder, how cool would that be?

My "Little Monster" stays sharp for like EVER because I ONLY cut well washed produce and other clean food with it and I use a plastic cutting board that is very easy on edge tools.



It is the mineral "GRIT" imbedded in various materials, think wood with minerals sucked up with the water it drew in when living, that dulls my edges. The vegetables, what have you do not seem to have anywhere near as great of concentration of minerals as some of the exotic wood I work with hand tools : Especially teak but also bubbinga and some of the purple heart can be distressingly abrasive to edges depending on the source (and interestingly enough it smells like dirty feet while cutting it).

Just a reminder (not for you Dedbox Hero because you already know this I'm positive) but for the OP. Paper may be "abrasive" not because of the wood pulp etc but because of the contaminates in it. These contaminates "dirt" minerals are on that hardness chart and well up on the scale.

 

[FortyTwoBlades]

Remember, too, that dulling through abrasive wear is only one mechanism of dulling. Edges may also be blunted by rolling or fracturing. That's where the push/pull over geometry, steel, and heat treatment really comes into play. The thinner the geometry, the longer an edge will last when subjected to abrasive wear, but that thinner edged will also be more likely to roll or chip, and if you go thinner than a particular steel can hold you'll have a very unstable edge. It's the age-old battle between resiliency and efficiency.

 

[miso2]

To Wowbagger,
Right. I understand that it is the basis of us using leather and linen for stropping. If they do not have hard minerals at all, it might take a very long time to have any effect on steels.


To DeadboxHero,
I am not trying to ditch or ignore real-world evidence. I am just trying to understand them intelligibly. I guess I am a researcher not only as my occupation but also in heart. So, please forgive my techno-centered mind
You mentioned that an alumina-based stone can polish high carbide volume steels. Why? Was the carbide tungsten carbide, which is softer than alumina? Or was it really the technique to apply pressure to the edge properly and consistently to facilitate the abrasion? Or, was it because the stone actually contains other abrasives such as silicone carbide, like some of Shapton stones? I am not asking an answer, but this is my usual attitude toward a problem......


Miso

 

[bucketstove]

Hi,

Hi all,

Recent discussions on the effectiveness of sharpening stones on high vanadium steels made me curious about the hardness and abrasion efficiency. I searched around the internet and found some numbers of common materials’ Knoop hardness as listed below. From this, it makes sense to me that one needs to use Diamond abrasives (or CBN) for steels containing a good mount of vanadium carbide (when polishing is desired). Also, for high hardness steels above 60 HRc, I would need at least an alumina ceramic stone, as tempered martensite is as hard as quartz, the main abrasive in natural stones.

As a disclaimer, I am no metallurgist. So, I would appreciate any inputs from metallurgist and sharpening specialists, as well as other sharpening enthusiasts, particularly whether this argument is reasonable and legit.


Miso

Hi,
some updates and some references
Hardness Conversion of Metals

1) Standard Hardness Conversion for metals acc. ASTM E 140 - 97, September 1999, Conversion for Non-Austenitic Steels, Table 1. The accuracy of the conversion depends on the accuracy of the provided data and the resulting curve-fits.
2) Indentation hardness is not a single fundamental property but a combination of properties, and varies with the type of test. The modulus of elasticity and the depth of indentation influence conversions. Therefore separate conversion tables are neccessary for different materials.
3) Brinell Hardness numbers in parentheses are outsite the range (HB>630) This limit is set to avoid errors introduced by the deformation of the ball indenter itself.

Microhardness Test
Calculator for Conversion between Vickers Hardness Number and SI Units MPa and GPa

[table="width: 800"]
[tr]
[td]Material[/td]
[td]Knoop[/td]
[td]Comment[/td]
[/tr]
[tr]
[td]Untempered martensite[/td]
[td]300[/td]
[td][/td]
[/tr]
[tr]
[td]Glass[/td]
[td]530 or 49HRC[/td]
[td][/td]
[/tr]
[tr]
[td]Tempered martensite[/td]
[td]700 or 58HRC[/td]
[td]at HRc60[/td]
[/tr]
[tr]
[td]Quartz[/td]
[td]820 or or 800HV or 7.846GPA ~64.0HRC [/td]
[td]Silicone dioxide, Arkansas stone[/td]
[/tr]
[tr]
[td]Quartz corners[/td]
[td] ???1041HK/1086.5HK?? HKor 1181 HV / 1260 HV or 11.58 GPA / 12.21GPa or ~71HRC/~72HRC [/td]
[td]Silicone dioxide, Arkansas stone, anisotropy, the HK numbers iffy, not directly convertible from HV/GPa
[/td]
[/tr]
[tr]
[td]Cementite[/td]
[td]1025 or 73HRC[/td]
[td]Iron carbide[/td]
[/tr]
[tr]
[td]Chromium carbide[/td]
[td]1735 or 105HRC [/td]
[td][/td]
[/tr]
[tr]
[td]Molybdenum carbide[/td]
[td]1800 or 108HRC[/td]
[td][/td]
[/tr]
[tr]
[td]Tungsten carbide[/td]
[td]1880HK or 113HRC[/td]
[td][/td]
[/tr]
[tr]
[td]Aluminum oxide[/td]
[td]2100HK or 125HRC[/td]
[td](Alumina)[/td]
[/tr]
[tr]
[td]Silicone carbide[/td]
[td]2480HK or 148HRC [/td]
[td][/td]
[/tr]
[tr]
[td]Vanadium carbide[/td]
[td]2660 or 161HRC[/td]
[td][/td]
[/tr]
[tr]
[td]Boron carbide[/td]
[td]2750HK or 167HRC[/td]
[td][/td]
[/tr]

[tr]
[td]silicon carbide corners (anisotropy) [/td]
[td]2954/2917/2129/27555/2397/2755 HK or 182HRC [/td]
[td] KHN (100gf load) (kgf mm^-2) Microhardness anisotropy of silicon carbide | Philip Sargent - Academia.edu [/td]
[/tr]

[tr]
[td]Cubic boron nitride[/td]
[td]4500[/td]
[td][/td]
[/tr]
[tr]
[td]Diamond[/td]
[td]>7000[/td]
[td][/td]
[/tr]
[tr]
[td][/td]
[td][/td]
[td][/td]
[/tr]
[/table]

 

[Wowbagger]

the basis of us using leather and linen for stropping. If they do not have hard minerals at all, it might take a very long time to have any effect on steels.

Bare strop.
Oh now you've done it. Opened yet another proverbial can of worms.
Yes in an ideal world we have an edge WITH NO WIRE EDGE OR RAGGED APEX and want to just "abrade" that edge the lightest bit to make it beyond, beyond sharp . . . or at least take if from shaves or kind of shaves to "oh yah baby this easily shaves".

BUT
In the real world there is some wire edge or raggedness and PART of the reason the bare strop works is the cells or grain of the organic material (plant or animal) intertwines with the grabby/hooky steel garbage at the apex that is keeping the edge from being just two flat planes intersecting at infinity (or the opposite of infinity . . . nothingness) and when the garbage steel intertwines with the organic material it gets torn off the blade thus some what "improving" the apex.

Me . . . I would rather abrade this connection of the garbage to the apex until it can no longer adhere rather than tear it off while it is RELATIVELY thick and leaving behind a RELATIVELY thick divot where it comes off.

Compare this to the worlds sharpest edge : the edge left when a piece of glass is broken. If the grain of steel were as consistent as glass then maybe we could rip off that bur and leave a fantastically sharp apex but the matrix of steel is at least partially ductile (able to be bent back and forth in its plastic range) and still resist structural failure . . . try that with glass some time.

What I am saying is bare strops do not wear away steel so much as just snag garbage hangnails on the apex and rip them off at the quick. The second part of that is my OPINION perhaps the text in the link along with the photos proves me wrong. I have discussed this with razor aficionados (I'm not one) this is what they think/find to be true about bare strops.

Is that any way to treat a fine blade ? Maybe.
But intellectually . . . I still hate it.

 

[miso2]

bucketstove,

Thank you for the additional information to this. The hardness conversion is very useful.

You also added the hardness anisotropy of a silicone carbide alpha-crystal. Are you implying that silicone carbide can beat vanadium carbide depending on how they interact? If so, it makes me wonder whether we should expect some hardness anisotropy in other carbide crystals, alumina, and quartz.


Miso

 

[miso2]

Wowbagger,

I had no intension of opening that can!

I agree in part with that bare strops remove weakened metal at the apex. But I think images ScienceofSharp provides show that they can also abrade metal to some extent. Also, I have read somewhere that linens and leathers do contain some hard minerals like silica. To be honest, I cannot find any reliable sources to back this up, though.


Miso