Once again Cliff your deep knowledge of steels is much appreciated. My favourite steels for super easy and super sharp edges is Sandvik 12C27 and 13C27. My French folders from Chambriard use the 13C27 razor steel and the edges obtainable with little sweat on those blades are most satisfying. My Helle Temagami knife uses a triple laminate steel with 12C27 at the apex point. Love these very sharp knives.
Once again thanks for the stimulating comments.
Cheers
Leo
I generally recommend anyone who wants to learn/understanding sharpening get at least one steel which is easy to sharpen simply to see what should be the ideal process. Everything you have listed are examples of that as they are all razor blade steels and when hardened properly they are ideal as they have :
-excellent grindability
-trivial ease of sharpening
In general there is rarely even an issue with burr formation/removal. While difficult to obtain, if you really want to see something special try to find :
-AEB-L at 62/64 HRC
-1095 at 65/67 HRC
-SuperBlue at 65/67 HRC
-M2 at 64/65 HRC
These steels are so strong that the edge will form very crisp very easily. However the HT is critical and if it isn’t done well then you will likely hate it.
I have a knife from Joe Calton in full hard 1095 which I expect to perform well from a very quick inspection of it. Even with the edge set on a semi-coarse Norton diamond :
-it shaves with no pressure felt on the skin
-true/90 push cuts newsprint at 3/4" from the point of hold
As boxed it is one of the sharpest knives I have seen in a long time.
I have an ESEE Laser Strike knife of 1095 steel but I don’t know the hardness. I do know it sharpens up beautifully but with more effort necessary than for either of the Sandvik steels. Do you know the ESEE knives at all…they are all 1095 carbon steel.
Leo
Yes, I have a number of them.
They set the hardness at 55-57 HRC so while the steel will grind easily, there are likely to be some issues with edge crispness / burr formation if you are trying to achieve a very high sharpness.
Of course they are promoted for very heavy use and thus the tempering is going to be high, above 450 F to ensure they are outside of the embrittlement range and thus the mid-range hardness.
They are quite durable though and resist fracture strongly.
Thanks very much Cliff! That is exactly what I wanted to know. You are a genuine huge nugget of knowledge that all of us are going to appreciate. I suspect we will be wanting information on steels like this in our Wiki and we will be getting to that fairly soon I hope. Your encyclopedic knowledge will be useful here.
Very best regards
Leo
Cliff,
Thanks for jumping on to the conversation and adding your knowledge. I’m really glad you did.
–Clay
for the hardness numbers to be as high as this, these steels should be almost untempered, this is very close to “as quenched” hardness figures for given types of steels. Will it be useful for anything more than paper cutting, wouldn’t it be too brittle?
I have knives in all of those steels and more, the 1095 is actually above the as-quenched hardness due to the strong carbide precipitation it has due to the super saturation of martensite.
In general no, they are not so limited - but again, they have to be done right. Here is just one example of a 1095 paring knife being used in non-paring knife work :
and why not :
and :
It has a micro-bevel normally, 10-12 dps, usually a very high finishing grit (high for me), which is 4k+ waterstone or similar.
Again though, and I can’t stress this enough - if the HT isn’t there the steel will be horrible as there are many ways to get hardness but only one right way :
-presoak
-soak at the minimum time/temperature to put 0.6% carbon in solution (CRITICAL)
-quench immediately
-cryo immediately
-snap temper
-water quench
repeat cryo until cost is a factor, water quench after the snap temper, then final temper around 350 F give or take (M2 is a HSS so it tempers hot).
The first part is critical, if you soak too long more than 0.6% carbon goes into solution, plate martensite forms instead of lathe, the steel becomes very brittle, it becomes hard to remove retained austenite, etc. .
This is an example of a full hard 1095 blade :
This is Calton’s paring knife :
-0.055" stock
-ffg (hint of convex, you can’t see it but you can mic it)
-edge is micro-bevel only, not visible
-norton diamond, worn/fine
Here is a really horrible picture which I used to think were ok before I started looking at Clay’s pictures :
The scope I am using has a horrible issues with depth of field and reflection hence coarse edges look very blobby, but in any case you can see the very small bevel, this is at 50X linear magnification.
Here is the edge after sixty 2" slices on that rope, note no chips/rolls, just light wear. The initial performance was :
-6 to 7 lbs
after 60 cuts it was in the plateau and was :
-11 to 12 lbs
If those numbers don’t impress you, just try to cut a piece of 3/8" hemp with a 2" draw with less than 6 lbs of vertical force.
In any case, this rope is fairly demanding on edges, more so than most kitchen use anyway and similar to cardboard and other utility work and it does nothing significant to the edge.
The edge only reflects light in one small section of edge which was the peak force position during the slices.
It looks deadly sharp the thinness of the taper to the edge is what makes the knife practically sharp high levels of polishing does not necessarily make a sharp knife especially if there are appreciable shoulders on the edge of the final bevel .
I alway s think that big shoulders are like air brakes on a wing the leading edge if fine for cutting processed foods like thin sliced ham or cheese but if the blade it to really cut it needs to have no real shoulders then the knife will cut deep which is what is needed for preparing real food.
That paring knife looks and sounds awesome!
Yeah, there is no real transition in this knife that you can see, it is full flat with a hint of a convex taper to true zero and then there is a micro-bevel applied. It was hand sharpened by the maker hence you can see multiple layers of scratch patterns.
With the destressing, some people get really focused on wasting the metal and are opposed to doing the initial cuts into the stone because it grinds off steel which could have been used. The problem is though is that steel is in a very stressed state and is thus very weak and it also is going to be carbide depleted due to tear out and fracture. If you form an edge on that then the edge retention and durability will suffer.
To me this is self-defeating because which would you rather use :
-a knife in 154CM, S30V, m390 etc. where the edge is always stressed
-a knife in 420J2 where the edge is always formed on clean steel
The first knife will actually have less edge retention/durability than the second one so what exactly did you pay more money for that “upgrade” steel if sharpening it properly wears it out too fast for you and to compensate you have to leave the steel weakened so the performance is lower than if you went for a lower cost steel in the first place?
For me one of the most dramatic experiments was one I did on a Battle Mistress were Busse asked me how many 2x4’s worth of wood could I chop before sharpening (if I stropped). I cut over a 1000 with no real problems but suddenly the edge started to take visible damage on the wood which it had not in years of previous use. I then repeated this (more than once) and sharpened the knife instead of stropping and the damage never happened again.
Even with a lot of sharpening, as long as you are not spastic about it, a knife will last a long time. If you are using a system like Clay’s where you can exactly set bevels and minimize over grinding then I really see it as a moot point. For me accidental damage is what limits the lifetime of the knife, never sharpening.
I have knives which are literally generations old and still used. I sharpened a knife for a friend recently which was given to her from her grandfather and he got it from his parents and it wasn’t new to them. She won’t use it out and neither will her children.
Remember when you destress the edge it is only going to be about 50 microns wide as you just want to be able to see it. Depending on angle, this means that 20 full sharpenings will remove a mm of metal from the width of a blade. For kitchen knives for friends I sharpen them at most twice a year, this means in 10 years they have lost 1 mm of metal from the width. Most people lose knives before they actually wear them out.
Cliff - beside sharpening, are you making knives too? Glad to see Joe’s paring knife received high remark from you. I didn’t know he utilized cryogenic (liquid nitrogen involved) with his ht. Maybe you should mention for grain refinement - iirc Joe always mentioned thermal cycling prior to hardening sequence. Also Cryo part of ht wouldn’t has significant benefit to alloy steels.
I am not a metallurgist & confused on how carbide precipitated when your stated soak aim for 0.6% C in solution. Mostly martensite is carbon rich, when carbon leak/migration from matrix to form carbide by precipitation would soften the matrix. Hence wear resistance go up (due to carbides) but will be at the cost matrix hardness (RC). The only scenario I see where one can get harder rc than at quench by having excess retain austenite at quench and then gain extra hardness from cryo lowering RA %.
I enjoy tinker/mangling steels. A friend just filled my 20L dewar for free, in the name of eta carbide science 
That HT I described isn’t what Joe uses, it is a very basic and general procedure. Roman Landes was the first person I saw really talk about this in a specific way in detail on the whole process and map out a HT for steels which is then adapted to the specific nature of the steel in question.
There are a few stages of tempering,they also over lap, but basically a few critical points :
-250 C and below, precipitation of α-iron carbide
-between 200 and 300°C, decomposition of retained austenite
These actually strengthen the steel which is why 1095 will actually improve in the yield point from the as-quenched state and then starts to decrease as the other parts of tempering start to set in (martensite loses the quasi-stable tetragonal state, the carbides spheroidize, etc.) .
This is why 350 F is a nice tempering point because it gets the benefits of both the high strength stages and the high toughness stages so it has a higher yield and much higher UTS point than the as quenched state. You only get a better combination when you go above the 500F embrittlement zone (which is where ESEE uses hence they are so tough).
300 F is the max yield point, but the UTS point is very low so I do not see that being a decent choice as the edge is likely to be too brittle.
The torsional stress/strain graphs show this very clearly. But again, the HT is critical, if you over soak, if you pause before quenching, if you wait after quenching before tempering - then running 65/67 HRC is not going to be very forgiving.
No I don’t make knives, I enjoy using them, but would not enjoy sitting at a grinder and hogging material off, maybe later in life.
Thanks Cliff!
I mostly concentrate my tinkering around with 52100 steel (except only a few knives with high alloys m4, 3v, k390, s90v, etc..). No 1095 yet, so I will keep your 1095 ht params in mind and possible add a tiny harmon.
I have to say that this has to be the most edifying discussion.I could have given out thank you’s and karma points all over the place and in fact I did! Never to date have I come across posts that were , to me at least, as exciting as some good novels. Each comment by the various posters was thoughtful and clear, plus I could feel my brain filling up with new thoughts about steels and sharpening.
Very gratifying guys! All of the contributors have done excellently. I might be criticized as being gushy, but what the heck! A big heart felt thank you to all. More please! :cheer:
Best to all
Leo
I definitely agree Leo!
So Cliff, this is the question that probably doesn’t have an answer…
If a given knife is damaged by the initial sharpening in the factory (such as your brothers grip), couldn’t you just overly cut the edge off to remove all of the damage in one go vs it taking several sharpenings? I suppose it would depend on how deep the damage is…
Maybe others will feel the same, but I think this is the kind of post that could well be added to the Wiki when it finally peters out.
I also think someone with knowledge like Cliff for one, could add an overarching summation of the thread to make it clear to people researching steels for example.
What are other people’s thoughts? Clay? Cliff?Mark? Razorsedge? and anyone else?
Leo
This is a great idea Leo. I’d love to have some of this info consolidated onto the wiki. Between some of the guys here, like Phil, Lagrangian, Cliff and others, we have quite a range of high level knowledge. Perhaps we can think about sections on the wiki where their knowledge can really shine and be readily accessible.
Cliff, would you be willing to do as Leo suggests - sum up your thoughts in a consolidated way so we can add them to our wiki? Perhaps a quick section on HT and another on edge stresses?
Some things you could probably pull right off of cliff’s website (if he was fine with that)
That is true, but perhaps someone who is articulate in the area of both metallurgy and sharpening in all its aspects would be the ideal to do something like this. As well as Cliff, yourself and the several mentioned above by Clay might put together the blog/wiki note more intelligently so that it makes sense even to me…I have to admit as I read, what I was reading was not the easiest going when dealing with the metallurgical terms et al. To pick out the really germane points would probably be done better by someone who knows exactly what is written and then to convey those points in a way that is easily absorbed let’s say even by old brains like mine that are not as sharp as they used to be. 
LOL!
Leo