Your SFM and feed is low for carbide. Usually, when I'm using carbide inserts, I like to see straw-colored chips come off the workpiece. I'd increase the RPM a bit, and maybe increase the feed to 0.005 I/R for the feed. Sometimes, increasing the feed on those carbide inserts helps the finish. If you were cutting with a HSS tool, those numbers you have might be pretty good. Carbide is "hungry" - it needs to be loaded up to get the best results.

As everyone else has noted, 1018 just doesn't give you a nice, smooth finish when machining without some work. It's bottom-of-the-heap steel. Stressproof/1144 machines much better, 1215 better yet, 1117 and 12L14 best of all. 4140 cho-moly machines nicely. 4340 machines like a dream, and is extremely strong (about triple the yield strength of 4140).

For 1018, one of the things that improves the situation is to use high-sulphur cutting oil. NB I said "improves" - not magically turns things into bright, smooth polished surfaces.