Interesting video… do you destress your edge?

[Cliff Stamp]

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 2×4’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.

[Blunt Cut]

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 😀

[Cliff Stamp]

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.

[Blunt Cut]

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.

[Leo James Mitchell]

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

[Josh]

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…

[Leo James Mitchell]

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

[wickededge]

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?

-Clay

[Josh]

Some things you could probably pull right off of cliff’s website (if he was fine with that)

http://www.cliffstamp.com/knives/articles/index.html

[Leo James Mitchell]

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

[Cliff Stamp]

In general what I post is meant to be shared, I have an academic background, I would just appreciate a reference to the original source material.

In regards to HT, etc. it is a really large and expansive issue, there are entire books wrote on it (many). I would not have a problem looking at wiki articles.

If anyone wants a decent background and has the time/inclination, then Verhoeven’s metallurgy book is very nice as it is made specifically for knife makers.

[Leo James Mitchell]

” I would not have a problem looking at Wiki articles.” Cliff

That is good to hear Cliff. It is quite clear that you have an academic background,so we need your skills to help add commentary to threads that are put in the Wiki to help clarify any arcane and abstruse references that would help us all to understand things clearly.
Someone will no doubt be in touch with you about this. You will not be alone nor will there be tsunamis of extra time expected for your part.Just some general comments to extract what is important from threads going into the Wiki in your area of expertise.
Having said all of that, I suspect Clay will be on to you as well as others to discuss how you might be able to help.

Leo

[Geocyclist]

First of all thanks to Cliff for all you input here. :cheer:

I did this for the first time today, destressed a S30V Benchmade mini Ritter grip. Normally the idea of destressing a nice edge would make me shutter. Plus the fact that it will take more time to get it sharp again. This blade was dull enough that I figured it couldn’t get any worse.

I used a broken ceramic stick to destress. I started of with 600 diamonds, which I think I would have needed anyway without destressing given the dullness of this knife. The end result was amazing, definitely sharper that the initial edge. And I don’t think it added much more sharpening time.

I think I will do this in the future when ever I have to “resharpen” where use of diamond stones is required. I have been able to “touch up” edges in with just ceramics and get good results if I didn’t let the knife get too dull.

[Cliff Stamp]

The thing that puts most people off is actually cutting into the stone which sets off abuse flags. However all you are removing is damaged steel which you would not want to form an edge on anyway as it is severely weak and brittle.

You can see this on a macroscopic scale if you just take a spoon and bend it back and forth until it breaks. Now look at the area right next to the break. It will be obvious that the damage extends beyond the immediate break.

Similar with a knife, the damage from blunting is beyond the immediate and if you keep forming an edge into this damaged material you will often never see the actual ability of the steel.

[Leo James Mitchell]

A very clear and concise answer Cliff. I winced the first time I tried this, but you are right…my next edge was the best yet.

Leo

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