A patina formed on steel does help to prevent rust from forming on a steel blade. While they are both forms of oxidation, rust will eat into the edge and cause damage to the metal, whereas a patina will form a sort of finished seal that can prevent corrosion and future rust damage.

Is patina like rust?

"Rust is one form of patina. ... "Rust is an iron oxide usually red in color and usually on iron only, while tarnish is a thin layer and is often black or grey and it's on many different metals."

Should I force a patina on my knife?

Your carbon-steel knife's patina not only looks great, but is protective too. ... We found that if a knife developed a light charcoal-gray patina naturally over time, it was less likely to rust if left wet. To put this protection in place quickly, some manufacturers suggest forcing a patina to develop on the blade.