The Collaborative International Dictionary of English v.0.48:

Manganese steel \Man`ga*nese" steel\
   Cast steel containing a considerable percentage (10-14) of
   manganese, which makes it very hard and tough and highly
   resistant to wear. See Alloy steel, above.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

manganese steel
    n 1: a steel with a relatively large component (10-14%) of
         manganese; highly resistant to wear and shock [syn:
         manganese steel, austenitic manganese steel]