Please explain me semi-stainless

[Jovidah]

I want to dispute this, (not you so much you @Jovidah) I see it stated frequently.

In my mind carbide type, size, volume, and steel hardness are what determine sharpenability. To say that semi-stainlesses feel like carbons makes very little sense to me because there are stainless steels with equivalent carbide type and lesser carbide volume to which no such subjective properties are attributed.

For instance take A2/SKD12, which is widely revered and touted as toothy and carbon like and etc

A2 has 6% CrC, and no iron carbide.....which is the same amount as AEB-L, a full stainless. In fact the carbide size in AEB-L is smaller and more uniform than A2, and so of the two, AEB-L should feel closer to a carbon steel.

https://i2.wp.com/knifesteelnerds.com/wp-content/uploads/2019/05/A2-cropped-scaled.jpg?resize=768,582&ssl=1

https://i0.wp.com/knifesteelnerds.com/wp-content/uploads/2019/05/1000X-AEB-L.jpg?w=750&ssl=1


Another instance of this is with CPM-D2/D2/SKD11.

D2 has approximately 15% CrC and wear resistance far exceeding any carbon steel. 440C, a steel with some infamy in our circles for being miserable to sharpen and having mediocre edge retention has only 12% CrC.

https://i1.wp.com/knifesteelnerds.c...2019/07/steel-carbide-volumes.jpg?w=527&ssl=1

And then there's Zwear with a mix of CrVC and MC carbide which makes it more closely related to S30V and S35VN in terms of carbide type and volume than any carbon steel.

So based on that I chalk up "carbon-like" sharpening characteristics to the placebo effect.

"Semi-stainless" is a reference to corrosion resistance. Which will be greater than that of a carbon steel and lesser than that of a fully stainless steel. It has no relation to, and no basis (as far as I can see) for being a reference to sharpening characteristics at all.

I probably should have specified more (typing on a phone was good for brevity but not for accuracy).
My statement was made entirely based on whatever unstated steel is in JCK's Carbonext series, of which I own multiple knives that have been used long-term.

When I say 'sharpening characteristics like carbon' I mean that it sharpens a bit faster and with less effort than the variety of stainless steels I have, and is more in line with the carbon steels I have (which are probably all on the more low-alloy side). For me 'ease of sharpening' mostly comes down to 'time spent sharpening'.

I won't claim to know the specifical mechanics at play (and it's hard to guess since I don't know the steel composition), but the experience is consistent and long-term enough that I would dare to rule out bias. The steel itself is probably on the simpler side of things, with a stated HRC of around 60...
Who knows the entire thing could simply come down to abrasion resistance. Still, if I could only have 1 knife steel I'd rather have that Carbonext stuff than <insert Hitachi part of rainbow here> from <insert Japanese geriatric grandmaster here>.

 

[Blank Blades.]

No metallurgist here. As far as my understanding goes, a steel is considered stainless if there's a fair amount of free chromium, i.e. not bound into carbides, forming a thin layer of Cr2O3. How does it work with semi-stainless? My guess would be all chromium is bound. What does confer the relative resistance to corrosion?

To actually talk about this part.

A steel that has all its chromium bound in carbines wouldn't be semistainless at that point its just a carbon steel imo, or idk if you want to split hairs maybe an alloy steel (like aogami, or apex ultra).

Semistainless steels are going to have more chromium in solution than carbon, but not as much as stainless. So like someone mentioned here, 4v. A2, and d2. They all have some amount of chromium in solution.

To me I think semistainless tool steels are about as optimal as you can get currently. At least for the most part. Since for a stainless to be stainless, it needs chromium in solution, which ends up limiting the hardness because of retained austenite. So even if I take aeb-l and heat treat up to 64-65. Even reaching the max hrc It can potentially more or less act in use like it is actually softer, because of that.

Of course not all stainless steels are the exact same. Some can potentially get to around 64 without having too much retained austenite, but I'm already getting too far off topic.

Back to semistainless. To me. These are the best combination of characteristics. Corrosion resistant enough to not need constant cleaning in use, generally better edge retention than carbon steels, potentially sharpen really well (this is subjective of course), and for people that care about patina some will show a patina over time.

 

[Benuser]

To actually talk about this part.

A steel that has all its chromium bound in carbines wouldn't be semistainless at that point its just a carbon steel imo, or idk if you want to split hairs maybe an alloy steel (like aogami, or apex ultra).

Semistainless steels are going to have more chromium in solution than carbon, but not as much as stainless. So like someone mentioned here, 4v. A2, and d2. They all have some amount of chromium in solution.

To me I think semistainless tool steels are about as optimal as you can get currently. At least for the most part. Since for a stainless to be stainless, it needs chromium in solution, which ends up limiting the hardness because of retained austenite. So even if I take aeb-l and heat treat up to 64-65. Even reaching the max hrc It can potentially more or less act in use like it is actually softer, because of that.

Of course not all stainless steels are the exact same. Some can potentially get to around 64 without having too much retained austenite, but I'm already getting too far off topic.

Back to semistainless. To me. These are the best combination of characteristics. Corrosion resistant enough to not need constant cleaning in use, generally better edge retention than carbon steels, potentially sharpen really well (this is subjective of course), and for people that care about patina some will show a patina over time.

Thanks!