Others will be along to share their wisdom (and I'm waiting to read it) but...
...1018 steel doesn't mill or turn very well, in my experience. The surface tears instead of cuts and it creates a nasty finish.
I'd bet there isn't much you could have done to improve it without carefully choosing the inserts and even then, I doubt it would have improved much.
By comparison, I've turned some grades of leaded steel and stainless steel that were absolutely gorgeous with the same inserts and speeds/feeds.