# Tool steels and carbide pull-out



## Nemo (Dec 13, 2016)

We got talking about this in another thread and I wondered if the sharpening experts could shed some light.

My understanding is that steels with large carbides (?most tool steels) will need relitavely obtuse angles at the very edge (be it a microbevel or more obtuse primary bevels) or risk microchipping at the edge (because the large carbides get pulled out in use), thus reducing their otherwise substantial edge retention. 

Am I near or far from the mark in my understanding of carbide pull-out? Can some expert sharpeners shed some light? How do you sharpen tool/PM steels differently (or not differently).

Thanks for your opinions/ expertise.


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## Marek07 (Dec 13, 2016)

Can't offer an opinion here but look forward to reading any opinions/thought/expertise on the topic. Thanks for starting the new thread Nemo - I think I was in danger of hijacking the Tojiro PS thread.


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## malexthekid (Dec 13, 2016)

Not an expert, but from what I gather from reading information on here, carbide pullout isn't micro-chipping. Basically what it means is that when you are sharpening you have these larger, very hard pieces (the large carbides) that get pulled out, instead of worn away.


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## larrybard (Dec 13, 2016)

malexthekid said:


> Not an expert, but from what I gather from reading information on here, carbide pullout isn't micro-chipping. Basically what it means is that when you are sharpening you have these larger, very hard pieces (the large carbides) that get pulled out, instead of worn away.



But, as a practical matter, wouldn't they be much the same as far as effect on performance (and appearance)?


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## zitangy (Dec 13, 2016)

carbide pull out: So which tool steel and from which maker are you referring to?

from my limited experience, carbide pull out that i have seen are during my sharpening process when the angle is too low and thin behing the edge and especially when you have used a 200 grit stone and the striations are too deep and as you go along refining the edge on a higher grit stone, suddenly you see a void along the edge. Best to avoid anything lower than 400Grit adn if really need to use 200 grit... do not aim for the burr at this grit.

Both are imperfections along the edge.. however.. micro chips do happen when the edge cldnt take the stress because it is too thin and has met crossed the tolerence point resulting in a very clean break due to the high HRC in the tool steels. ON softer steel it tends to flex first , bend and then break and thus not a very clean break..
I hv not seen any carbide pull out on the regular tool steels 

rarely have i seen a few carbide pullouts on an edge. MIcro chips.... rarely in isolation and in carbide pull out steel you can never take it to an acute angle with a thin behind the edge...

carbide pull outs in my case normally happens during sharpening adn MIcro chips during use .. based on my limited experience

rgds
d


rgds
d


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## malexthekid (Dec 13, 2016)

larrybard said:


> But, as a practical matter, wouldn't they be much the same as far as effect on performance (and appearance)?



Probably... though they are different and caused by totally different processes.

I'll leave it to someone with better metallurgical knowledge to comment


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## Benuser (Dec 13, 2016)

I know the carbides breaking through only as a description of what happens with soft stainless (e.g. the Krupp 4116) when you overly polish the edge. The already soft matrix is weakened even more. This to explain the edge instability under high grits.
Let's say that in general you prefer to enhance a quality rather than to combat it. Why would you polish an edge of a coarserly grained steel? You will benefit more from applying a very light touch, just to abrade the burr.


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## Benuser (Dec 13, 2016)

But basically, keep them rough.


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## malexthekid (Dec 13, 2016)

Benuser said:


> But basically, keep them rough.



Essentially the largest carbide realistically governs how fine your edge can get.


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## Nemo (Dec 13, 2016)

Thanks for the responses. If I can summarise, it seems that carbide size governs the ability to refine the edge.

Does it have any role to play in governing how acute an angle the edge can sustain? If so, how? If not, what does (apart from hardness)?


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## malexthekid (Dec 13, 2016)

Nemo said:


> Thanks for the responses. If I can summarise, it seems that carbide size governs the ability to refine the edge.
> 
> Does it have any role to play in governing how acute an angle the edge can sustain? If so, how? If not, what does (apart from hardness)?



I would suggest yes but i dont know if it has any practical application... logic would tell me you cant get the steel thinner than the largest carbide size... though we are talking super small which probably means this isn't a practical constraint.

You should try do a google search of the forum for carbide discussions. Some of the makers and those with good metallurgical knowledge have written heaps on its formation, controlling ut, effects for knives etc.


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## Nemo (Dec 13, 2016)

Is there anything which limits the angle at the edge of high carbide steels such as SG2 (or did I somehow get completely the wrong idea about this)?


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## LifeByA1000Cuts (Dec 13, 2016)

@malexthekidd only if your abrasive is unable to grind the carbide into compliance ... or, if it is a soft bound/loose abrasive (slurry), the abrasive could end up compliant and grind out *between* the carbide teeth?


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## malexthekid (Dec 13, 2016)

LifeByA1000Cuts said:


> @malexthekidd only if your abrasive is unable to grind the carbide into compliance ... or, if it is a soft bound/loose abrasive (slurry), the abrasive could end up compliant and grind out *between* the carbide teeth?



My understanding is that grinding (or sharpening as we call it) doesn't break apart carbides but breaks the bond between carbides. Aka you are pulling out carbided but they are just extremely small....

But as I have stated that I just reiterating my interpretation of previous post, someone correct me.


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## Kippington (Dec 13, 2016)

malexthekid said:


> My understanding is that grinding (or sharpening as we call it) doesn't break apart carbides but breaks the bond between carbides. Aka you are pulling out carbided but they are just extremely small....



Yep they're small... Real small.
They would be difficult to spot without the help of something stronger then an optical microscope (unless the heat-treatment was completely bungled and the carbide growth had run away).







In any half decent knife the carbides are small enough that it has no major effect on the performance of kitchen knives. On other things such as razors it becomes more important to have a finer edge over the abrasion resistance that carbides can provide.

For some kitchen cutting tasks you may even find carbide roll-out to be desirable.


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## Benuser (Dec 13, 2016)

Enjoy shaving with SLD or 19C27!


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## Nemo (Dec 15, 2016)

OK so it sounds as though my concept of carbide pull-out was slightly off.

On a related question bought up in this thread, is the consensus that PM tool steels such as srs15, sg2/r2 and HAP40 can sustain angles at the very edge of 10-15 dps (I'm not talking about rough use here) or do they need a higher angle or a microbevel? Or is it different between these steels? How do ZDP189 and CowryX compare in this regard?


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## Benuser (Dec 15, 2016)

Only very limited experience here with advanced stainless. I though would end a R2 sharpening with micro-bevels. Keep them as thin as you like, but end very conservative. This steel is always -- at any angle -- toothy, so don't worry about performance.


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## Nemo (Dec 15, 2016)

Benuser said:


> Only very limited experience here with advanced stainless. I though would end a R2 sharpening with micro-bevels. Keep them as thin as you like, but end very conservative. This steel is always -- at any angle -- toothy, so don't worry about performance.



I must say that I had begun micro bevelling R2 without any obvious drop in performance. I was wondering whether this was overkill, but it sounds like it might be a good idea to continue. Thanks for your input.


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## Benuser (Dec 15, 2016)

I must admit my own reluctance to applying a micro-bevel with new blades -- simply because most get much better once you've abraded some steel that got fatigued by factory buffering. But in the case of R2 I believe you better do, indeed.


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## LifeByA1000Cuts (Dec 15, 2016)

I guess ANYTHING but great shirogami (or maybe some swedish steels too?) will not be up to non-gentle board use at 10dps? Or am I far off the mark there?


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## malexthekid (Dec 15, 2016)

LifeByA1000Cuts said:


> I guess ANYTHING but great shirogami (or maybe some swedish steels too?) will not be up to non-gentle board use at 10dps? Or am I far off the mark there?



I think off the mark totally... heaps of steels can just depends the HT etc.. also what is happening behind the edge can affect the how the edge performs.

As for micro bevels on R2.. i take mine quite low withour it and have no issue. Can't tell you what the angle is sorry, don't reallt measure it or care what the actual number is.


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## Nemo (Dec 15, 2016)

Thanks for the opinions... keep them coming.


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## bennyprofane (Dec 16, 2016)

I also havent used microbevels on my R2 and find them among my longest lasting edges. In regards to small angles, the Takamura R2 is shipped with a 9dps angle.


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## LifeByA1000Cuts (Dec 16, 2016)

@bennyprofane I still find exactly that combo - Takamura R2 with 9dps - isn't exactly board-proof ....


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## Benuser (Dec 16, 2016)

bennyprofane said:


> I also havent used microbevels on my R2 and find them among my longest lasting edges. In regards to small angles, the Takamura R2 is shipped with a 9dps angle.



A factory edge doesn't mean anything. See it as a kind of service to the customer there's any edge on it. A 9dps edge allows an easy sharpening, with a few strokes you can put your own edge on it.


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## LifeByA1000Cuts (Dec 16, 2016)

In which case, you have microbevelled it  Unless it's a few strokes with a very low grit stone ....


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## malexthekid (Dec 16, 2016)

LifeByA1000Cuts said:


> @bennyprofane I still find exactly that combo - Takamura R2 with 9dps - isn't exactly board-proof ....



I bang away on my Ryusen Blazen and Itou on my cutting board witj no dramas and the edges last easy.


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## Marcelo Amaral (Dec 20, 2016)

Some info related to carbide pull-out: http://www.hocktools.com/tech-info/o1-vs-a2.html


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## psfred (Dec 20, 2016)

Carbide pull-out is really only an issue in softer steels, about RC 60 or so I don't think the matrix is soft enough. 

Point is that the carbides are as hard or harder than most shapening stone abrasives, especially natural silicate stones, and the friction of dragging them through the stone particles can dislodge them from softer stainless steels, which also have VERY large carbides in terms of steel, although they are not visible to the eye. With electron microscope level magnification you can see the swiss cheese effect at the very apex, which makes it very vulnerable to deformation. 

Those large carbides give the steel very high abrasion resistance, and used properly those soft steel knives can stay working sharp quite well. I just don't particularly like that type of sharp, nor the need for the use of a steel constantly.

Edge retention in tool steels, and how fine an edge a steel will take depends on the alloy, the heat treatment, prior manufacturing (for fine or large carbides, etc) and use. A2, for instance, will NOT take the same edge a carbon steel tool will, but due to the relatively large carbides and the presence of vanadium and chromium carbides, which are harder than iron carbides, whatever edge you have will last about ten times as long. It's not a particularly good steel for kitchen knives, as it's more brittle than many other tool steels in thin cross section. This is why it's prone to microchipping.

Most of the knife steels are better than A2. Makes a very good bush knife though, with a more acute edge, with very good edge retention due to the carbides.

It's all a balancing act -- wear resistance vs hardness vs toughness vs fineness of edge, you have to decide what you want.

And, one should be quite careful of using coarse diamond hones on very hard steels. The diamond particles will not, as a rule, chip or deflect much, and can cause quite deep scratches under high local pressure -- they are a long way apart on a coarse hone, in terms of making an edge. It's quite possible to exceed the deformation limit of the steel at the very edge, resulting in both a deep scratch and a fracture at the bottom. This can then result in crack propagation in use, and microchipping between fractures. The harder the steel, the more likely this is to occur, and it's a problem in some well known VG-10 knives, probably because they are too hard for the angle of sharpening from the factory.

A2 and D2 were developed for things like stamping dies, lathe tools, and forming rollers where abrasion resistance is most important, and they are unlikely to have acute edges. Along with M2, M4, and M4+ they make very good power planer blades, and things like that with fairly obtuse edges (35 degrees) and light loading.

Peter


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## Nemo (Dec 20, 2016)

Thanks for that in depth answer Peter. From what you are saying, it sounds like it's not a major issue in PM steels like SG2, srs15, hap40 and zdp189?


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## LifeByA1000Cuts (Dec 21, 2016)

Isn't SKD-12, which seems to be successfully used in kitchen edges, an A2?


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## Nemo (Dec 21, 2016)

It does look quite similar on the zknives comparator. I have it in my Yoshikane, where it takes a reasonably fine edge which it holds a while. Having said that, HT is pretty important and Yoshikane's are (if I remember correctly) renowned as being very good for this steel.


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## foody518 (Dec 21, 2016)

LifeByA1000Cuts said:


> Isn't SKD-12, which seems to be successfully used in kitchen edges, an A2?



And I thought SLD (used in some semi stainless kitchen knives) and D2 were effectively the same thing


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## Kippington (Dec 21, 2016)

Nemo said:


> Thanks for that in depth answer Peter. From what you are saying, it sounds like it's not a major issue in PM steels like SG2, srs15, hap40 and zdp189?



Nah it isnt. Power steel practices were developed specifically to cram as much alloying into the steel as possible without allowing the time for large carbides to grow.
As mentioned before, maybe you'll notice it when shaving but you probably wont see any difference in the kitchen.


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## Nemo (Dec 21, 2016)

foody518 said:


> And I thought SLD (used in some semi stainless kitchen knives) and D2 were effectively the same thing



Once again, quite similar te each other on zknives.


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## Nemo (Dec 21, 2016)

Kippington said:


> Nah it isnt. Power steel practices were developed specifically to cram as much alloying into the steel as possible without allowing the time for large carbides to grow.
> As mentioned before, maybe you'll notice it when shaving but you probably wont see any difference in the kitchen.



Thanks Kippington, that makes sense and it kinda gels with the experience that people here have with sg2.


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