In Blender, select your object [object mode is fine] and you set the shading to "smooth" or "flat" depending on your object; in your case, you want flat. Blender's default smoothing angle is set to 180 I believe, which will give you, well, what you got! You can walk it down until things look right if you have an object that has curves and hard edges.

Note - this is a slightly older version of Blender, but things should still be largely the same.

As far as Poser/Octane, I've never used either, and that's where you'll probably have to address this, because that's where you're rendering ...

"OCTANE POSER PLUGIN USER GUIDE - 4.10

Smoothing In the Poser plugin for Octane you can use 2 different methods of smoothing: The Poser smoothing algorithm and the Octane algorithm. In most cases it will not make much difference, but sometimes Poser smoothing leaves artefacts when rendered in Octane. Octane smoothing however has a single smoothing angle for all geometry while you can specify a separate angle in for each mesh in Poser.

Unfortunately, you can only use one smoothing algorithm at a time. The Poser smoothing is turned on when the Smoothing Angle is set to 0 in the Setup Window. If you choose an angle (like 80 degrees), it will use Octane smoothing."

• Page 93 - OCTANE POSER PLUGIN USER GUIDE

Hopefully that at least starts you in the right direction?

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