Cobalt Special Steel

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Nemo

Nemo

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I'm interested to know how this steel performs.

Superficially it is similar to VG10, with a bit more Cr, Mo and Co. It also has a bit of W:

http://zknives.com/knives/steels/steelgraph.php?nm=VG-10,Cobalt Special&ni=4001,6664&hrn=1&gm=0
Has anyone used it? How does it perform in terms of sharpening, deburring, edge retention, edge stability, etc?

Edited to add: I realise that HT is probably super important with this type of steel, so it might be good to say whose (which smith) knife you tried.
 
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It's an odd choice for knives, cobalt is normally added for working hardness at high temperature in tool steels. That being said I've never seen another good explanation for what properties cobalt adds to a steel. Maybe @Larrin can comment.

It only has a small nickel addition but in my experience nickel alloyed steels are tough but incredibly painful to deburr.
 
Larrin did do an article on Co in VG10. IIRC, the conclusion was that the main benefit was that it could take a high temperature process to apply a coating.
 
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Would the added Co boot also mean the steel is less likely to loose its temper when grinding?
 
I have a Yu Kurosaki Raijin Nakiri. The edge retention is comparable to a better VG10 one. Definitely not bad in that regard. With Kurosaki's grind the edge feels a bit more brittle overall. It has kind of a glassy feeling and you will notice immediately when you begin to torque it and correct it. Not my favourite to sharpen and feels slightly different than VG10 though but not super terrible, but prefer SG2. Never had any problem with chipping or micrchipping but nicked a tiny bit of the heel, barely visible though. Definitely had to get used to it while sharpening with burring and deburring, had to check with my fingers several time but once used to it not super terrible. Overall okay stainless steel but favour SG2.
 
JayS20 said:
I have a Yu Kurosaki Raijin Nakiri. The edge retention is comparable to a better VG10 one. Definitely not bad in that regard. With Kurosaki's grind the edge feels a bit more brittle overall. It has kind of a glassy feeling and you will notice immediately when you begin to torque it and correct it. Not my favourite to sharpen and feels slightly different than VG10 though but not super terrible, but prefer SG2. Never had any problem with chipping or micrchipping but nicked a tiny bit of the heel, barely visible though. Definitely had to get used to it while sharpening with burring and deburring, had to check with my fingers several time but once used to it not super terrible. Overall okay stainless steel but favour SG2.
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Thanks for the insight and comparison with SG2 as a baseline!
 
I don’t know why they like cobalt so much. There isn’t much reason for it to be in VG-10 either. I covered it here: Why There is Cobalt in VG-10 - Knife Steel Nerds

The higher Cr in the Special would give somewhat enhanced wear resistance but toughness would also be reduced relative to VG10. I would personally prefer VG10 or move into a powder metallurgy steel if I wanted more wear resistance.
 
I asked a Takefu blacksmith that uses it.

Edited response - cobalt special is the best for balance of corrosion resistance, wear resistance, grindability, workability.
 
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JoBone said:
I asked a Takefu blacksmith that uses it.

Edited response - cobalt special is the best for balance of corrosion resistance, wear resistance, grindability, workability.
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Interesting to have the knife-maker's perspective on it. As an end user, the corrosion resistance and wear resistance is what would matter to me (assuming that the maker can make an equally good grind on it). Anyone have an opinion on how the Cobalt SS Raijin line would compare with VG-10 Fujin, both from Kurosaki? That seems like a fair comparison holding most other factors constant.
 
Don't really understand why Kurosaki's Raijin line is more expensive than his R2 lines if CSS is the easier steel to work...
 
Nemo said:
Don't really understand why Kurosaki's Raijin line is more expensive than his R2 lines if CSS is the easier steel to work...
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He did not state that it was easier. Also, it may not equate to less time or lower cost of materials. From my understanding, there is more time at the forge with his raijin line than the R2.

I should have a 210 raijin coming in alongside one of the new Makoto’s VG10, I’m curious how the grinds compare.
 
Cobalt is added to steel to improve hardness at high temperatures. High speed steel with added cobalt remains hard at red heat and is commonly used in machine tools like drills and lathe tools. The purpose of cobalt in a knife steel supposedly reduces wear by reducing adhesive wear on the edge. This is when the edge becomes welded to the substrate while its cutting it and some of the welded edge stick to the substrate and is torn out of the blade. Its rather doubtful the edge can become welded to tomatoes or chicken when cutting them. Sounds a bit like marketing to me.
 
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