You should be able to run iron with no problem as long as you’re not using a ton of it. If you are going to run a lot, you should replace the stock nozzle with a hardened steel nozzle. They’re relatively cheap and easy to install.
The really abrasive filaments are the ones where the filler is hard and sharp / needle like. Carbon fiber, glow in the dark, and glass are the worst. I imagine hemp might be pretty bad as well, but haven’t used it.
After that, you have the fills that are harder than the brass nozzle, but not so sharp. Iron and steel are good examples of this. They will wear the nozzle, but more gradually.
Then you have the relatively soft fills. Wood, cork, etc. I don’t think you really see any significant wear from these.
Search for the the blog post at E3D’s website for when they launched the hardened steel nozzles. They posted cross sections of brass and hardened steel nozzles after printing with carbon fiber. It’s really fascinating to see how the nozzles worse. It was more like they were gouged out than eroded away.