The clearest definition of "special steel" I've found is at
https://www.voestalpine.com/blog/en/innovation-technology/what-is-special-steel/"When Steel Becomes Special
As so often in life, when it comes to special steel it is the intrinsic values that count. Including those which are absent. What makes these steel grades special is their purity. That means an exceptionally low sulfur and phosphorus content: no more than 0.025%, or 25 parts in a thousand. That is comparable to two tiny pinches of salt in a liter of water, which is why extreme precision is required to achieve the chemical compositions of special steel grades. It is the same level of precision as demanded in their subsequent processing.
The exceptional properties of special steel, such as resistance to corrosion and heat, strength, wear resistance, workability, and polishability, all depend on its composition and the care with which it is produced. This is where special additives, so-called alloys, come into play. The manufacturers’ “recipe books” include a variety of ingredients:
• Chrome: for resistance to corrosion and heat
• Tungsten and cobalt: increase wear resistance which is important for milling tools and drills
• Chrome and nickel: increase weld strength
• Molybdenum: increases heat resistance and makes steel rust-proof
• Titanium, niobium: creates resistance to intergranular corrosion
• Manganese: increases tensile strength"
We have 15 XRF scans of various points on the exterior surface of our cylindrical artifact, 4 done in September 2021 and 11 done in November 2021. As expected, in all scans, iron (FE) was greater than 90%.
• The cobalt, titanium, and lead detected are almost certainly attributable to the bluish-gray paint and are not almost certainly part of the steel alloy.
• The most common probably-alloyed element (found in 12 of the 15 scans) was manganese. The percentage of manganese was quite consistent, from a low of 0.262% to a high of 0.580%. The average was 0.458.
• The second most common probably-alloyed element was molybdenum (found in 7 of the 15 scans). The readings measured from a low of 0.015% to a high of 0.087% percentage, except for one reading of 0.683%. If we throw out the anomaly we get an average of 0.0325.
• In third place was chromium (found in 6 out 15 scans) from a high of 0.238% to a low of 0.096 for an average of 0.129.
• Silicon came in fourth (4 out of 15 scans) with readings of 3.507, 3.151, 3.010, and an anomalous 0.864.
• Zinc was found in 3 readings but the amounts are all over the shop: 2.425%, 1.303%, and 0.494%
• Vanadium was also present in 3 scans, more consistent: 0.118%, 0.059%, and 0.058%
• Inconsistent traces of copper and tin showed up in 2 scans and there was bit of phosphorus in 1 scan. I think those can be dismissed as environmental contaminants.
The steel in this artifact fits the above definition of "special steel". The steels shown in the “Houille Blanche” article are quite different, but neither does it fit the definition of 12L14 in
https://www.eatonsteel.com/12l14-cold-rolled-steel-bar.html"12L14 is a standard resulfurized and rephosphorized carbon steel. Lead is also added in order to increase machinability, and it also means it can be bent, riveted, or crimped. However, this extra ductility and machinability do mean that 12L14 is slightly weaker than comparable carbon steel alloys." There is no sulfur and no meaningful phosphorus in the artifact. Also, there seems to be no such thing as 12L14 sheet. It's generally used for plating.
As you say, "special steel" seems to have been a catch-all name. I think we have a piece of "special steel" and it should be possible to research its virtues, which may point us to where it came from.