To have your model smoothed during rendering, simply go to> window> Rendering Editors> Mental Ray> Approximation Editor.

... And create a Subdivision.

Example:

Attached Thumbnails

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www.stevenegan-cgi.com

"Your weapons are no match for ours! People of Mars, surrender!"
"Um, this isn't Mars. This is Earth."
"Earth? Earth-with-nuclear-weapons Earth?"
"Yes."
[long pause] "Friend!!"