Please explain me semi-stainless

[Benuser]

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?

 

[timebard]

Not a metallurgist either but as usual Larrin has a good explanation: https://knifesteelnerds.com/2019/01/14/which-knife-steels-have-the-best-corrosion-resistance/

 

[Redwax]

.

 

[Boynutman]

Interesting to read how HT can affect corrosion resistance.

 

[Jovidah]

Don't know how the mechanics work but in ny experience it does work as advertised. You get sharpening characteristics that ate very much like carbon, while being reactivity is a complete nonissue and stain resistance is quite decent - though you wouldn't mistake it for a full stainless, especially if you leave it dirty. Mine are very much 'in between'.
Wished there were more semistainless knives, IMO its the perfect compromise.

 

[Just a DK]

Don't know how the mechanics work but in ny experience it does work as advertised. You get sharpening characteristics that ate very much like carbon, while being reactivity is a complete nonissue and stain resistance is quite decent - though you wouldn't mistake it for a full stainless, especially if you leave it dirty. Mine are very much 'in between'.
Wished there were more semistainless knives, IMO its the perfect compromise.

Love me some of that A2.

But damn a lot of makers can do some beautiful stuff to carbon steel….

 

[Jovidah]

Love me some of that A2.

But damn a lot of makers can do some beautiful stuff to carbon steel….

Probably why it gets preference. Semi stainless looks more boring, won't get pretty patina or hamon. Doesn't help there's been a lot of BS glorification of carbon going around in the last decade.
And for normie knives it gets passed over because it won't survive a dishwasher.

 

[stringer]

The Western semi-stainless monosteel mid weight gyuto with welded bolster and black pakka scales is the Toyota Hilux of the chef knife world.

 

[MSicardCutlery]

You get sharpening characteristics that ate very much like carbon

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.c...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.

 

[nopomo]

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.

We don’t like to talk about retained austenite here but could that not also be relevant? What property is responsible for making steel feel “gummy” vs “crisp”?

 

[MSicardCutlery]

We don’t like to talk about retained austenite here but could that not also be relevant? What property is responsible for making steel feel “gummy” vs “crisp”?

Haha, I thought about that just after finished writing that. My guess would be that gumminess is mostly a consequence of low hardness though. Maybe retained austenite can be a problem in the same way, but I don't know. Excessive RA tends to go hand in hand with softness, so differentiating between the two probably isn't easy. The gummiest steels I've sharpened, 420, 440B, 440C were all in the 50's hrc.

 

[Cliff]

Very subjectively, AEBL feels to me like white no. 2 and SKD more like AS, at least in terms of toothiness.

 

[Barmoley]

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.c...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.

Thank you for saying this. This whole semi-stainless sharpens like carbon is nonsense. You could call 4v or 10v semi-stainless as their corrosion resistance can be better than a2 for example.

Or another claim that ginsanko sharpens like white2, but is stainless and holds a better edge. If anything AEB-L should be easier to sharpen and more like low alloy steels not AEB-H(ginsanko)

I just think that when people who mostly have experience with Japanese knives run into skd12/a2 or ginsanko they realize that these are not that difficult to sharpen with conventional stones. So the legend grows when in reality there is a huge world of semi-stainless steels that have very little commonality as well as stainless steels that should be easier to sharpen than ginsanko.

 

[MowgFace]

Stainless always feels a little “crunchy” on the stones in comparison to Carbon.

Semi-stainless is slightly less crunchy.

Sorry for the use of technical terms.

 

[ptolemy]

I think this topic is pretty interesting, because you can go into it feel wise, or science wise (i.e % of chromium), or something im between.

I look at it as something in the middle, not quite stainless but also not quite as crazy relative that will patina in 5 min of use. I.e somewhere in the middle that care has to be taken to use it.

 

[Barmoley]

I think this topic is pretty interesting, because you can go into it feel wise, or science wise (i.e % of chromium), or something im between.

I look at it as something in the middle, not quite stainless but also not quite as crazy relative that will patina in 5 min of use. I.e somewhere in the middle that care has to be taken to use it.

Reasonable as long as we remove sharpenability, edge holding, etc out of it.

Carbon- really dislike the name, they are all carbon - reactive
Semi-stainless — less reactive
Stainless — non reactive within reason

Of course each category has pretty wide ranges, but if we had to.

The whole feel on stones has so many variables to it including user’s experience and the stones that I don’t know if anything useful can be gained from it.

 

[Troopah_Knives]

Haha, I thought about that just after finished writing that. My guess would be that gumminess is mostly a consequence of low hardness though. Maybe retained austenite can be a problem in the same way, but I don't know. Excessive RA tends to go hand in hand with softness, so differentiating between the two probably isn't easy. The gummiest steels I've sharpened, 420, 440B, 440C were all in the 50's hrc.

Excessive RA is not necessarily correlated with hardness in that way. In my most recent article, I looked at an HT of Rex 121 which hit 70Rc and had 18% ish RA (fine but on the edge of what is acceptable). Excessive RA comes from austenitizing too hot. Which further complicates separating excessive RA from hardness for most people. (Unless you have an XRD in your basement )

Semi-stainless also doesn't necessarily have more RA than low alloy steels. It's more a function of how far you are pushing the HT. Generally harder HTs of the same steel have more RA because they use higher austenitization temps.

 

[blokey]

Thank you for saying this. This whole semi-stainless sharpens like carbon is nonsense. You could call 4v or 10v semi-stainless as their corrosion resistance can be better than a2 for example.

Or another claim that ginsanko sharpens like white2, but is stainless and holds a better edge. If anything AEB-L should be easier to sharpen and more like low alloy steels not AEB-H(ginsanko)

I just think that when people who mostly have experience with Japanese knives run into skd12/a2 or ginsanko they realize that these are not that difficult to sharpen with conventional stones. So the legend grows when in reality there is a huge world of semi-stainless steels that have very little commonality as well as stainless steels that should be easier to sharpen than ginsanko.

Ginsan is bit special tho, on paper they are similar to VG1, aus10 and AEB-H, but sharpen VG1 and Ginsan side by side is night and day, I don’t know why, maybe conventional melting has more variations, I will sent some sample to @Troopah_Knives once he has time. Also Moriya Munemitsu sharpens as easily as Ginga Aeb-l, despite larger carbide size

 

[blokey]

The Western semi-stainless monosteel mid weight gyuto with welded bolster and black pakka scales is the Toyota Hilux of the chef knife world.

Not welded bolster, but….

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.

TBH I think no one likes conventional D2/SLD either

 

[HolyDiverScallop]

Not welded bolster, but….
View attachment 318474


TBH I think no one likes conventional D2/SLD either

That is pretty as hell.

 

[blokey]

That is pretty as hell.

Courtesy of @Blank Blades.

 

[Barmoley]

Ginsan is bit special tho, on paper they are similar to VG1, aus10 and AEB-H, but sharpen VG1 and Ginsan side by side is night and day, I don’t know why, maybe conventional melting has more variations, I will sent some sample to @Troopah_Knives once he has time. Also Moriya Munemitsu sharpens as easily as Ginga Aeb-l, despite larger carbide size

I really hope you do and we can finally put this one to rest. I would guess that there is nothing special to the steel and it behaves the same as steels in its group (AEB-H)

 

[Blank Blades.]

Not welded bolster, but….
View attachment 318474


TBH I think no one likes conventional D2/SLD either

Could have soldered the bolster if you wanted.

 

[Blank Blades.]

Not welded bolster, but….
View attachment 318474


TBH I think no one likes conventional D2/SLD either

I think cpm d2 needs more praise.

The d2 name gets it lumped in with ingot d2 and I don't think that's fair.

I think if it was just a completely different name people would say they really like it, or at least give it a chance before judging it.

 

[Blank Blades.]

Excessive RA is not necessarily correlated with hardness in that way. In my most recent article, I looked at an HT of Rex 121 which hit 70Rc and had 18% ish RA (fine but on the edge of what is acceptable). Excessive RA comes from austenitizing too hot. Which further complicates separating excessive RA from hardness for most people. (Unless you have an XRD in your basement )

Semi-stainless also doesn't necessarily have more RA than low alloy steels. It's more a function of how far you are pushing the HT. Generally harder HTs of the same steel have more RA because they use higher austenitization temps.

Of course you can do a hardness austenitizing curve and make guesses based on the peak hardness, on what the level of RA might be.

 

[blokey]

Could have soldered the bolster if you wanted.

lol I’m fine with it, epoxy and rivet is more than strong enough

 

[blokey]

I think cpm d2 needs more praise.

The d2 name gets it lumped in with ingot d2 and I don't think that's fair.

I think if it was just a completely different name people would say they really like it, or at least give it a chance before judging it.

Yeah would love to try it later, I guess it’s just too much choice at it’s range

 

[Troopah_Knives]

Of course you can do a hardness austenitizing curve and make guesses based on the peak hardness, on what the level of RA might be.

My point is that given a hardness you cannot find the RA content.

 

[Blank Blades.]

My point is that given a hardness you cannot find the RA content.

Yeah, of course.

I mean, and if we are talking just knife users they won't be able to get any additional context from hardness.

But at least the knife makers can give a decent guess. If they have a general idea of what causes RA.

 

[Troopah_Knives]

Yeah, of course.

I mean, and if we are talking just knife users they won't be able to get any additional context from hardness.

But at least the knife makers can give a decent guess. If they have a general idea of what causes RA.

They know when they are approaching 20% RA but I don't think they know much else.