While my setting has magic, the material world acts the same way as ours. Only reason why I am mentioning magic in my question is because I'm explaining why I need to satisfy such an odd set of requirements.
In my setting, most civilizations consist entirely of magic-users. This however has a drawback, as magic users have negative reaction to iron, and mere presence of larger-than-grain-of-sand-sized piece of metallic(non-compound) iron or steel within 3-5 m distance causes them headaches, which only can eventually even kill the person. This led to ironwork becoming road not taken(except for occasional use in torture and such).
However, assuming existence of non-magic or almost non-magic civilizations which later wish to interact and even trade with these civilizations, there might be need for me to make steel exportable comodity to magic civilizations. With that comes one solution for - iron alloys.
My question is: which metalic or non-metalic element should I introduce into my iron/steel alloys to neutralize its magician torturing effect, to satisfy following set of conditions?
These are things that such an ingredient has to satisfy:
In concentration within 1-2%, it doesn't impede qualities of steel for production of things such as steam engines, guns, etc. That probably means the addition can't have too drastic effect when combined with other alloying ingredients, as I don't want them to impede development of my magic civilization.
The alloying ingredient can't be naturally present in most iron ores(duh), to ensure that no magic civilization can accidentally discover workable iron before non-magic civilization comes into play.
It's artificial addition into the iron shouldn't require 20th century technology. Ideally it should be something that can be sucessfully introduced into the cast iron.
Rather than just one ingredient, if needed, I can perhaps justify two or three different ingredients that might neutralize anti-magician effect of iron. This shall however only apply if restricting it to single ingredient would lead to too much restriction on steel alloy materials as my society develops. (That is, if no single ingredient can be mixed into iron/steel alloys without it causing large barrier in 20th century tech tree.)
TL;DR: What do I mix into my iron, steel and steel alloys at around 1% which isn't naturally occuring in early produced iron and which doesn't really affect qualities of steel and steel alloys.