I'm the one who was 'staggered' when I read today's newsletter.
If the EDS test is correct, and there's no reason to think otherwise, then, except for a measurement error, the previous XRF test would have been altered by some other agent(s) or factor(s).
Firstly, common 1010 steel, which is low-alloy and very soft carbon (class A or Adx ('mild steel') according to the 1920 Houille Blanche classification, would have only 0.30/to.60% manganese as a common element with the artifact. If we disregard traces of phosphorus and sulfur, which give an idea of the steel's purity, then yes, we have a very common steel.
This wouldn't be such bad news, since what I immediately found of the current French version of the '1010' (Arcelor/Mittal) gives us a composition similar to that of the 1920 Class A - 'Houille Blanche' type:
C: 0.08/0.013
Mn: 0.30/0.60
S: 0.035
P: 0.025
https://sections.arcelormittal.com/catalogue/B50/FRThe question of silicon remains. I can't explain the very high levels of this element.
From my casual eye, I'd say that only a few factors explain a transformation of the artifact:
- high heat; intense cold;
- exposure to the environment or to a persistent element in that environment;
- the passage of time leading to chemical transformations?
This steel was most probably in common use in France in the 1920s.
Among the types of use, La 'Houille Blanche' specifies that type A 'extra-soft' is used in particular for “cold-formed sheets and parts
hammered'. Apparently, this is also the case for welded parts.