I play a world for 70 hours now and just started a steel outpost, but can't find the steel recipe. Do I need to unlock more research to be able to smelt steel? I only have green science currently.

Well....
1: You need a big-furnance to smelt, no assembler (just to make sure)
2:research steel smelting in the researchtree
3: if its still not there, type "/c for i, player in ipairs(game.players) do player.force.reset_recipes() end" in the console

I have steel smelting and try using a big furnace, that's why it's wierd.
Will this disable achievements?

Turns out it does. I think I'll just build a normal smelting setup, for the time being. I also tried reinstalling the mod, didn't help. I can only smelt iron, copper and stone bricks.