Another perspective on Steel composition

Gator97

Gator97

Joined
Apr 10, 2000
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Well, we all are used to usual steel composition charts, where elements are listed by element mass % in the alloy composition. This is how the Steel Composition comparison graph worked too.

Few days ago Cotdt proposed to add different viewing perspective to the graph builder. So, the credit goes to him for the idea.
Basically, just mass % doesn't tell the whole picture, and it is useful to see the numbers of atoms of each elements in the mix, since it is individual atoms that create the carbides and mass % is quite different from the percentage of the atoms in the alloy. So, 1% Carbon and 1% Tungsten are quite different number of atoms because of the different atomic mass.

Basically, I've added 2 more options to the graph. Atom Count and Molar Mass %. They both represent numbers of atoms in the alloy, once is simply gives the number of the element atoms in 1000 atoms of the alloy. Another is simply molar mass % for the alloy. Details on the molar mass can be found in Wikipedia, but it's a pretty simple concept. Inside the graph, from the settings many (More button) you can use Show Composition As: combo box to sleect the method, or use query parameter gm to select the mode, 0 for mass %, the usual, then 1 for atom counts and 2 for molar mass %.

I've looked at the familiar steels with new options and it is really interesting picture and for certain things it is quite telling.

Let's take ZDP-189. 20% Chrome, 3% C, and it's a lot less stain resistant than bunch of other steels with less Chromium. Take a look at this graph:ZDP-189 vs. 440A steel atom count comparison

For 1000 atoms of ZDP-189 alloy we have 385 atoms of Cr ad 250 atoms of C. For 1000 atoms of 440A we have 346 atoms of Cr and 62 atoms of C.
So, I'm not so sure how many atoms of C end up in the Chromium carbides, but as you can see the difference in the count of the Cr and C is significant for those alloys and 440A having a lot more free Cr is more stain resistant.

On the other hand, if you look at CPM S35VN steel composition atom counts, in 1000 atoms of that alloy we have 112 atoms of C and 5 atoms of Niobium. S35VN has 1.34% C and 0.50% Nb, less than 3x, but atom count is a little over 21x.

Niobium is considered to be one of those super additions to the steel, although I am not quite sure how 5 atoms of Niobium can so dramatically alter steel properties. I mean, obviously it is all not as simple as just comparing numbers of the atoms.

On the other hand, CPM S110V steel composition atom count shows 238 atom of Carbon with 38 atoms of Niobium. So whatever the Niobium effects are should be a lot more pronounced in there. Also, interestingly S110V has 233 atoms of C vs. 269 atoms of Cr. I.e. less even difference than in ZDP-189, but S110V is much more stain resistant, perhaps because of the 177 atoms of Vanadium in the same mix and bunch of other things.

Another interesting part is that whatever carbides I've looked up, each atom of Carbon binds to one or more other element, Cr3C2, Cr7C3, WC, Nb2C, VC, Mo2C and so on.
Not being a metallurgist I don't really understand when and how carbides form and if there are several alloying elements, e.g. niobium, tungsten, moly what forms carbides and what not. Or what percentage.

Well, I guess others with more knowledge in this area can comment on the rest, but it was quite interesting observing the relationships of the numbers of the atoms. Of course it is directly related to the element mass %, but the ratios are very different.
 
An interesting addition.
Humans tend list components of a formulation in wt %, because that is how we make them. But usually it's the volume% or molar% that controls the properties of a thing. So the expected performance of a formulation can be more easily predicted if one looks at these instead of the wt percent.

I'll have to look at it.

Thanks.
 
You're welcome.
Yeah, I think in many ways volume % is more telling. The thing is understanding how various elements for carbides in presence of each other is quite complicated, at least for me, with no education in metallurgy .
 
The carbide percentage is often used when comparing steels, I suppose for wear resistance and strength comparisons. That obviously doesn't tell the whole story as a steel with 9% carbide percentage with mainly chrome, moly and iron carbides will act totally differently from a knife steel with 9% of mainly the drunken, rowdy, criminaly oriented Vanadium carbides.

Some examples of common steel percentages:

CPM S30V 4% Vanadium + 10.5% chrome = 14.5% carbide fraction ( crucible website)
Rex M4 ( CPM) = 12.5%
S110V = 22%
S90V = 23% ( yet less wear resistance than
S110V)
S125V = 28%
MPL1 = 46%
440C = 12%
154cm = 17.5% (higher than S30V, but low/wear)
3V = 5% ( that's why it's so tough)
10V = 17.5 ( similar percentage to 154cm
but as the carbides are mostly
evil, devil worshipping
vanadium carbides the wear
resistance is not even close)
 
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So, basically you can add up all the carbide formers by mass to get carbide percentage? Actual Carbide percentage doesn't depend on HT and other factors?
 
Heh Larrin :) Good that you showed up.
Is there a formula or rule that tells us which carbides form first?
I.e. if we have let's say 100 atoms of C and 100 atoms of Cr with 100 atoms of V...
So, which ones will react with Carbon first?
Theoretically I want V carbides and leave Cr free for rust resistance.

I remember Butch saying once that Nb carbides form at lower temps compared to Vanadium.
 
Great idea, very informative- thanks for doing the work and posting!
 
Gator97 said:
Heh Larrin :) Good that you showed up.
Is there a formula or rule that tells us which carbides form first?
I.e. if we have let's say 100 atoms of C and 100 atoms of Cr with 100 atoms of V...
So, which ones will react with Carbon first?
Theoretically I want V carbides and leave Cr free for rust resistance.

I remember Butch saying once that Nb carbides form at lower temps compared to Vanadium.
Click to expand...
There isn't a formula, no. You can read about the reactivity of various metals with carbon though.
 
Thanks MVF.

Larrin, I was searching for last few hours on metal reactivity. Got very generic chart with few elements generally found in alloys, and another source had temps when carbides form for few metals, but no indication on what's more reactive.
I think it'd be useful if I could make a list of the element reactivity with Carbon, should help when looking at the steel composition.
Do you have any good source(s)?
 
Gator97 said:
Larrin, I was searching for last few hours on metal reactivity. Got very generic chart with few elements generally found in alloys, and another source had temps when carbides form for few metals, but no indication on what's more reactive.
I think it'd be useful if I could make a list of the element reactivity with Carbon, should help when looking at the steel composition.
Do you have any good source(s)?
Click to expand...
I don't know of one. A book on alloys in steel might be helpful. Maybe mete knows one.
 
In order of carbide forming tendencies least to greatest:

Ni
Si
Mn
Cr
Mo, W
V
Ti
Nb

There is a pretty steady increase in tendency except from Mn to Cr is a big jump and from Ti to Nb is a huge jump. Mo and W are about the same, V and Ti are close, and then comes Nb. All these are relative to iron. Mn doesn't have a native carbide, but is part of (Fe,Mn)3C cementite carbide. Nickel and Silicon essentially form no carbides, but can form other compounds or disolve in other compounds, if available. For instance, Ni will form Ni3Al if Al is available, and Si will form oxides and disolve in other oxides as well. Ref: Structure and Properties of Engineering Alloys 2nd Edition.
 
This is interesting, but is it fair to compare aerosolized (powdered) steels to other steels? Yes, I understand the ratios are still the same, but the crystalline structures are radically different (especially as regards Vanadium).
 
Samael said:
This is interesting, but is it fair to compare aerosolized (powdered) steels to other steels? Yes, I understand the ratios are still the same, but the crystalline structures are radically different (especially as regards Vanadium).
Click to expand...

Good point, that's why looking at a steel's composition requires some interpretation. The graph just tells you the relative compositions of the steel by atom. No one is comparing powder vs wrought versions of the steel.

Powder steels are easier to predict as they follow theory more closely. In a powdered steel the alloys are finer and more evenly spaced, so they dissolve more readily. You typically have more carbon dissolved in a CPM version so you end up with a little higher hardness than the wrought version of the steel, and strong carbide forming elements like Mo/W/V prevent Cr from forming carbides by taking up the carbon (as theory predicts). Thus CPM-D2 ends up with much more free Cr than D2, and is basically a stainless steel, which you can see by looking at the composition (same for CPM154). Whereas regular D2 is less corrosion resistant than what the composition implies. In this way powder steels are much easier to interpret by looking at the composition.
 
Thanks guys,

Didn't know Ni carbides existed at all :)

Hardheart, that's a lot of reading stuff, thanks tho.
 
So is there any correlation between the strength of the carbide forming tendency and the inherent hardness of the carbide formed. I heard that the Rc hardness of of VC was 82 and WC was 72 and that NbC was very hard. These seem to follow the tendency list as presented by me2.
 
Dunno yet :) I just printed out 300+ page book hardHeart linked and it'll take time to read through, and it'snot exactly "easy reading" either.

Other than that, I've heard Nb carbides were around 90HRC and form at lower temps than V carbides.


If someone has that info, i.e. Carbide forming temperature and their hardness (for the popular alloying metals) that'd help.
 
Really crazy technical information you got there, but it's pretty fascinating. Thanks for sharing a fresh take on percentages in steel composition! :cool::thumbup:
 
42Blades - Thanks.I'm trying to keep it easy to read/understand, not being metallurgist myself.

ME2, in your reactivity list, where does the Cobalt stand? I found Cobalt in another reactivity series chart, where it was between Ni and Cr. But I can't deduce where it will be in relation to Mn ans Si.

Ni
Co ???
Si
Mn
Cr
Mo, W
V
Ti
Nb

Also, I have carbide forming temperatures as following:
V - 1100 - 1200
Nb - 1300 - 1400
Cr - 1400 - 1800
Mo - 1200 - 1400
W - 1400 - 1600

Is that correct? I thought Nb carbides for at lower temperatures than V.
 
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