Does surface finish affect steels strength properties? If so, how does strength increase or decrease with the type of surface finish applied?
Finishing operations on steel will not affect the harness significantly.
Roughing operation on steel, however, do increase its hardness.
The more the machining deforms the surface of steel the harder it becomes.
Here is a research article on, Effects of Milling Condition on the Surface Integrity of Hot Forged Steel
Shot peening improves the fatigue life , mostly used for steel springs. It does not change the bulk strength much . Shot peening is also used for aluminum. A very smooth ,polished surface can also improve "strength" in VERY highly stressed high strength steels ( this is likely of little use in ordinary applications ; I measured the effect in hydrogen stress cracking coupons stressed nearly to yield.). Generally steels are so tough that surface finish does not have a large affect.