I’m looking for a fantasy series (at least 2 books) I read in the mid-80s. Most of it was set on a world without metal, so they had found other ways to make weapons. A second world, with metal, tries to take it over. I remember two main characters -brothers- on the first world, one becomes a ruler and the other is trying to learn about the second world.
Could it be Raymond Feist's Magician series / Riftwar saga?
I’m looking for a fantasy series (at least 2 books) I read in the mid-80s.
Check: Magician came out in 1982, and the series (with subsequent series, spin-offs and prequels) is over 20 books long.
Most of it was set on a world without metal, so they had found other ways to make weapons.
Most of the second half of the first book is situated on Kelewan, where metals are scarce and precious. Laminated wood is used instead to craft swords and armor.
A second world, with metal, tries to take it over.
You might have it the wrong way around: The world our protagonists start on - Midkemia - is rich in metals, and it is this world that is invaded by Kelewan through several magical portals between worlds.
I remember two main characters -brothers- on the first world, one becomes a ruler and the other is trying to learn about the second world.
Kinda strokes with Magician: Pug is adopted by Tomas' parents. Pug learns the Kelewan ways of magic after being captured on his home world Midkemia (in an attempt to close the primary portal) and sent to do slave labor. When his aptitude for magic is detected, he gets sent off to a huge magics academy, and eventually becomes a politically relevant figure on Kelewan.
Meanwhile, Tomas is transformed into something that could kindly be called a Dragonborn and marries into the Elvish Royal family - Just one of those weeks, amirite?
Does this match the stories you're looking for?
This actually reminds me of Bob Shaw's Land and Overland books (The Ragged Astronauts, The Wooden Spaceships, and The Fugitive Worlds). The story starts on Land, a world with little metal (though they have brakka wood which is nearly as hard and strong), where two natural chemicals, pikon and halvell ("orange and purple") are hypergolic when brought into contact -- they're used as fuel for jet engines that propel the balloons that are the highest advance of transportation.
Unfortunately, it turns out that either harvesting or use of pikon and halvell promotes a floating menace -- the incredibly toxic ptertha, which explode at a touch and whose residue leads to pterhacosis, a fatal affliction.
With ptertha growing more and more common, Land is becoming uninhabitable, so the decision is made to flee -- to Overland, the "moon" in Land's sky, orbiting close enough that both are tide locked and joined by a "neck" of thin atmosphere which, in the first novel, is found to be traversible by a suitably designed balloon.