The Collaborative International Dictionary of English v.0.48:

Ni-hard \Ni-hard\, Ni-hard iron \Ni-hard iron\n.
   Cast iron to which nickel has been added to make it resist
   abrasion.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

Ni-hard
    n 1: cast iron to which nickel has been added to make it resist
         abrasion [syn: Ni-hard, Ni-hard iron]