I know, proposed a lot times, but i think w12 deserves this mechanic.
Just tried to consider - what's the point of making steel for now? It doesnt have any sink mechanic/other high demand usage, just some few recipes you can reach by 1 run of your steel crucibles, and next run of your steel factory will be required only when you will reach higher quality metal/brick/etc.
So idea is quite simple - allow craft metal gear/weapon/tools from any metal (with some restrictions ofcourse, we dont need tin breastplate), which will affect stats of the result.
Tools: Tools will be more efficient, if made with better mettal, e.g. Cast Iron < Bronze < Wrought Iron < Steel
Weapon: There should be few recipes with different armor penetration, base dmg and other stats, which can be crafted from "any hard metal", same as tools, material will determine damage stats of weapon.
Armory: Same as weapon, different recipes with different advantages, can be crafted with any hard/soft metal, where metal type determine armor/agi debuff
Main question - what for? Just to make steel an ultimate material, needed for all end technologies.