To create the chipped metal, I used a mask and ZAdd/ZSub with the Inflate brush in places on the surface.
To add grooves to the metal, I used the Slash 3 brush and some alphas. I used alpha 58 the most.
One part that was difficult to make was the hexagonal arms. First I mapped the arm. Then I did a pattern in Photoshop and loaded it into ZBrush as an alpha. Next I converted the alpha to a mask and increased the Inflate value. The studs I put in one by one, with the Inflate, DragDot and Alpha 14.
I've created a video to show this workflow better here.