Quote Originally Posted by Greywander View Post
By this logic, one would think that steel would be even more effective, since it is more "refined" than iron.
Logically, yes, particularly since modern steel has a higher iron content than the kind of iron people were using when those myths were being created. Whether that actually holds, though, depends on the setting. In some, like in many urban fantasy series, most notably the Dresden Files, steel is just as effective against iron-vulnerable creatures as iron is; this is usually the case for settings where humanity is dominant, faeries and other iron-vulnerable creatures are in decline, and the fact that everything from cars to manhole covers to houses to skyscrapers are full of iron and steel is used to explain their decline. This tends to work out narratively because it makes the creatures in question very resistant to "civilian"-level weapons like punches, wooden bats, and the like, so authors can put in scenes about having to go for a fireplace poker or crowbar or something.

In other settings, like most fantasy series and RPGs, most notable D&D, iron and steel weapons are ubiquitous so authors and developers have to come up with some way to set iron apart to justify still needing special weapons to combat the fey. In more historical settings, steel weapons would be much less pure than iron weapons (2-5% carbon content plus a bunch of trace minerals, compared to ~0.2% carbon content for wrought iron), so it's the purity of the iron that matters. In more fantastic settings, "cold iron" is often given some special definition (iron that has never been heated because heating ruins its magical properties, a particular alloy of iron with different alchemical properties than steel, etc.) to justify the need for iron over steel, hence why so many people are confused about what exactly "cold iron" means.

Although steel, simply by virtue of its hardness and lightness, might correspond better to fantasy metals like mithril or adamantine. Steel probably seemed pretty mythical to the people who first developed it, and more so to the people it was used against. It would be interesting to see a setting where, for example, the secret to making steel is a closely guarded one, and so steel weapons and armor are comparable to or even count as magical gear.
Indeed. Several stories and settings that mix sci-fi and fantasy (or attempt to retrofit fantasy stuff into real world history) say that adamantine or other super-hard materials are Damascus steel or the like, mithril or other super-light materials are aluminum or titanium, and so forth to give them a veneer of realism.