It is easy enough to create a raster or bitmap image to greyscale, but what if you want a vector image greyscale try using these steps.
1.     From the Edit menu, select Find and Replace > Replace Objects
2.    Select “Replace a color model or palette”
3.    Leave all settings here as is, with the exception of “Replace with the color model” and select Greyscale from the dropdown (note: this page works on fills and outlines separately)
4.    Click Finish
5.    Click Replace All
6.    Repeat steps 1-4 for the outlines

Tip provided by Roger Wambolt, CorelDRAW team.