CA6NM is classed as a corrosion resisting material. However, unlike CF8M or 316 stainless it will rust. The following should be useful in deciphering cast stainless steel grades. There is a diagram in ASTM A781 that helps with this. The C in the grade designation indicates that it is corrosion resisting, A indicates a martensitic structure, 6 indicates Carbon content of 0.06 max and the NM indicate special elements, in this case nickel and molybdenum. In terms of corrosion resistance it is similar to CA15 or 410 material.
Martensitic stainless steels with this level of chrome are barely over the required level to be called a "stainless steel". This has 13% chrome, whereas you must have over 10.5-11% to develop a passive chrome-oxide layer typical of stainless steel. If you are talking about being defined as "CRA", you must look at the definition (CRA definition is different in API 6A versus NACE MR0175 for example).
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