While both cortical & cancellous screws are used in orthopedic fractures fixation, the region of use for both of them are so different:

First we need to take a look at the bone structure:

Compact bone is the harder outer shell of the bone while cancellous bone is the inner porous, less dense layers of the bone

So the both screws are made of Titanium (Or sometimes Stainless Steel) and both are available with locking or non locking options but the main diffenrence is the design and the region of use.

Cortical Screws has a fine pitch and are designed to anchor in cortical bone

Cancellous Screws has a coarse pitch and are designed to anchor in medullary bone