Semi stainless steel question?

A

AshesFall

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Jul 16, 2019
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Just out of random curiosity.

Exactly how many semi stainless steels are out there?

I can only think of D2 and 3V off the top of my head.
 
There is no definition for semi stainless so hard to say.

Zwear/PD1/CruWear would be in the same class as 3V. A8mod, etc.

Some consider A8, A2, M4, etc semi stainless too.

Then there is ZDP-189 that is not truly stainless, or XHP, but then there is no real definition for stainless either, so bottom line, hard to say.
 
ace said:
but then there is no real definition for stainless either, so bottom line, hard to say.
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I believe there is fairly broad agreement that stainless steel is about +11% chromium and <1.2% carbon by alloy mass. I say 'fairly' because I've also seen 12% chromium and 13% chromium, and definitions that disregard carbon percentage.

Of course that's not to say that those steels are automatically more resistant to oxidation than steels that do not meet that definition, as if I recall correctly a stainless blade that has been heat treated such that much of the chromium has formed carbides will be less stain resistant, since free chromium in solution is what contributes to the stain resistance.
 
madcap_magician said:
since free chromium in solution is what contributes to the stain resistance.
Click to expand...

Right, that's where it is at, in general. Agree on the broad agreement of 12-13%, but not a definition and bunch that seem to meet this requirement and not be stainless in the broad understanding of stainless, ZDP-189 for example. Semi stainless is even harder, not even a broad agreement of what that is. Something between stainless and non-stainless. So let's say less stainless than 440A (considered stainless by most I assume) and more corrosion resistant than 1095 (considered non-stainless by most). Is A2 semi? Is M4? Do you have to get to the level of 3V or Z-wear?
 
I have some laminated blades with 420 bread and ZDP-189 bologna. The bread rusts more than the bologna in my experience. 420 is supposed to be highly resistant to corrosion. D-2 turns to red dust in my pocket in the summer.
 
I'm interested in a semi-stainless version of 13c26.
- not powder metallurgy
- tough
- The other properties are better to account for less corrosion resistance.
- It would be nice to see 13c26 steels data with 1%-12% chromium in 1% increments.
 
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I have a Hinderer Full Track with a working finish in S35VN that has rust spots. I don't get why because I live in an area where nothing really rusts. It seems semi stainless to me. I know the working finish does not help either.
 
A lot of tool steels like 3V, M4, D2 would fall into that category. I've never had a problem with rust with those steels.
 
Using the molar % instead of mass % would make it easier to see which steel is more stainless than the other. It is no easy way to accurate explain, as there are also many variation of thing, but I will give my general understanding.

Chromium carbide is Cr(3)C(2) (3 Cr moles for 2 Carbon moles), so the mole amount of Carbon has to be less than 2/3 that of Cr to have some "free" Cr. Then the "free" chromium has to be at a certain amount to a steel to be more stainless, say about 10% give or take molar %, as most of the "stainless" has in common.

The use of other kind of carbide effect the corrosion resistance as well, like:
Molybdenum carbide (MoC, 1 Molybdenum for 1 carbon, or Mo(2)C, 2 Molybdenum for 1 carbon)
Vanadium carbide (VC, 1 vanadium for 1 carbon)
Tungsten carbide (WC, 1 tungsten for 1 carbon)

For the moment, XHP main ingredients are carbon and chrome. It has the same amount of chromium as 440 series, but it is taken by the high amount of carbon. With the low leftover Cr, XHP is no where near near as stainless as many lower chromium steels.

S90V has higher carbon than XHP, nearly twice the carbon mass %, and chromium only at 12% (vs XHP's 17%), yet it is much more rust resistance, because it has a lot of Vanadium.
The molar % of carbon and vanadium in S90V is almost 1 to 1. As most carbon bids to vanadium, the effect of Carbon on the Cr content is less dramatic, therefore a lot of free Cr for rust resistance.

Cru-wear, again, lower chromium, but it has a multitude of heavy carbide former, therefore once again enough "free" Cr to be "semi-stainless".
 
By the percentage of chromium definition, magnacut barely if at all makes the cut as a stainless steel, which makes no sense because actually it is almost saltwater level stainless. So I think it is better to use actual performance of heat-treated steel rather than the chemical makeup of the steel.
Larrin says that XHP which he rates as 6.5 corrosion resistance on the scale of 1 to 10 shouldn't be considered stainless. So for him on his own scale the cutoff must of 7 out of 10. The label of stainless it seems is subjective even though performance is objective. XHP is more stain resistant according to his tests than any of the high alloy "semi-stainless" steels such as 3v and cru wear.
I believe that Nathan Carrothers claims that his heat treatment makes 3v more stain resistant than the typical industry heat treatment. So maybe it would register as a 6 if tested by Larrin with that heat treatment, instead of 5.5.. Just idle speculation but interesting because I think most people would see XHP as a stainless and 3v as a non-stainless when they might be very close in performance depending on heat treatment.
 
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Deino said:
Using the molar % instead of mass % would make it easier to see which steel is more stainless than the other. It is no easy way to accurate explain, as there are also many variation of thing, but I will give my general understanding.

Chromium carbide is Cr(3)C(2) (3 Cr moles for 2 Carbon moles), so the mole amount of Carbon has to be less than 2/3 that of Cr to have some "free" Cr. Then the "free" chromium has to be at a certain amount to a steel to be more stainless, say about 10% give or take molar %, as most of the "stainless" has in common.

The use of other kind of carbide effect the corrosion resistance as well, like:
Molybdenum carbide (MoC, 1 Molybdenum for 1 carbon, or Mo(2)C, 2 Molybdenum for 1 carbon)
Vanadium carbide (VC, 1 vanadium for 1 carbon)
Tungsten carbide (WC, 1 tungsten for 1 carbon)

For the moment, XHP main ingredients are carbon and chrome. It has the same amount of chromium as 440 series, but it is taken by the high amount of carbon. With the low leftover Cr, XHP is no where near near as stainless as many lower chromium steels.

S90V has higher carbon than XHP, nearly twice the carbon mass %, and chromium only at 12% (vs XHP's 17%), yet it is much more rust resistance, because it has a lot of Vanadium.
The molar % of carbon and vanadium in S90V is almost 1 to 1. As most carbon bids to vanadium, the effect of Carbon on the Cr content is less dramatic, therefore a lot of free Cr for rust resistance.

Cru-wear, again, lower chromium, but it has a multitude of heavy carbide former, therefore once again enough "free" Cr to be "semi-stainless".
Click to expand...
There are several chromium carbides, the most notorious of which is Cr23C6. The Cr3C2 version isn’t normally found in stainless knife steels as far as I know.

There isn’t a defined % of Cr to identify stainless steels, let alone semi-stainless steels. There is a drastic decrease in corrosion rate starting at about 10.5% and going to about 13%. The rate further decreases above that. It is further complicated by everything else in the mix. The 10.5% is generally the start of stainless steel but that’s in the low carbon structural steels. High carbon bonds with the Cr and removes it from the corrosion equation.

There are atomic % charts for steels but they are not commonly used and are difficult to find for specific steels. I don’t know that they are any more useful than the wt % diagrams.
 
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