The logic behind SAE Steel Nomenclature. 1

[Arshad Ahamed]

Hi Everyone,

This is my first thread/query here at eng-tips.com.

I was recently having a discussion with my manager about materials (especially SS and Duplex SS). We were talking about grades and the inherent strengths and weaknesses of different grades. I was then asked of the logical reason behind naming the different grades as they are - ex., if 304 implies 18/8 then 321 and 310 should also imply something derived from the base.

The reason behind this query is simple - if the logic behind nomenclature is known, then it would be easier to identify the composition/characteristics (I find myself frequenting the mini-chart pitting one grade against the other often).

Thanks and Regards.

 

[AidanMc]

I think the Wikipedia article covers the SAE naming conventions pretty well. Sadly the stainless steel conventions have less information in them then the alloy steel ones.

Aidan McAllister
Metallurgical Engineer

 

I don't have any issue with 3 digit alloy designations that contain few indicators of alloy type or even class. In the case of 304 vs 310, the only thing linking the two names is that they are 300 series, or austenitic stainless steels. More than that you will need to look up and learn.

But 304, 316, 2205 are learned pretty quickly, whereas 44Cr3Ni5Mo3Nb2 is eminently forgettable and needs recalculation by your brain every time you encounter it. Studies have shown the human brain cannot handle more than 6 or 7 objects or characters in one bunch, so the European style is highly error-prone. They don't exactly roll off the tongue either!
As much as it pains me to say it, the Yanks have it over the Europeans when it comes to alloy naming.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

All alloys have a UNS number (Universal Numbering System) that is linked to a specific chemistry.
These are all one letter followed by 5 numbers, quite manageable.
These are what are used in American specifications.
The Europeans agreed to use them (in exchange for some other concessions) but never have implemented it.
These are what we use for alloy identification in our documentation.
The traditional numbers really don't mean anything, other than the general alloy type, 400 vs 200 vs 300 series.
The key information is often in the letters that follow, L for low C (though sometimes S is also low C), N for nitrogen modified, M for added moly, and so on. This helps distinguish the sub-grades, but each of these has a unique suffix on the UNS (S30400 vs S30403)
The duplex are all CrNi content labeled, as are many of the PH grades.
Then you get into proprietary alloys that have names, that once you know them you understand (AL-6XN, Custom 455, 1925hMo).



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P.E. Metallurgy, Plymouth Tube

 

[bobjustbob]

Probably due to my time in the foundry, but I prefer the method of describing the cast grades.

CF8 for example is the cast equivalent to 304. C meaning its a corrosion resistant grade. F describing the Ni/Cr content. 8 telling the carbon content (.08% max). M telling us it has Mo added.
CF3 is 304L same as above with .03% max C
CF8M is 316, same as CF8 with Mo added
CF8C is 347, CF8 with Cb (or Nb) added
CG8M is 317, it is a bit more Cr/Ni and Mo than the CF8M.

CD3MN is 2205. So its corrosion resistant with less Ni/Cr content with Mo and Nitrogen added.
CD3MWCuN is the UNS J93380. Corrosion resistant with similar Ni/Cr content to CD3MN with Mo, W, Cu and N added.

 

[MagBen]

Some basics:
200 series covers austenitic SS with Cr, Ni, Mn, N as the main alloying elements
300 primarily for austenitic with Cr, Ni as main alloy elements, although it has been used to designate duplex
400 for martensitic and ferritic SS with Cr as main alloying element.
600 for high-temperature high strength both non SS and SS, including PH SS. for instance 630 is PH 17-4.
304 and 316 tells nothing difference, except that the first digit 3 means they are austenitic SS.
While 2205 and 2507 tell you the composition difference: 2205 has 22% Cr, 5% Ni, 2507 is a super-duplex with 25% Cr, 7% Ni.