M 204 is a specialty cast cobalt-base alloy closely related to M 203, covered elsewhere in this reference library, sharing the same general nickel-tungsten-chromium alloying pattern but with a higher cobalt fraction and no measurable iron content in the available source data. Cobalt is clearly the dominant single element (~43%), well ahead of nickel (~24.5%).

Transparency note: we were unable to independently verify a current ASTM/AMS/DIN/UNS cross-reference for the M 204 trade name in public sources, and the prior version of this page had no equivalent-standards data at all - the "Equivalent International Designations" table was completely empty, with no data and no comment placeholder, unlike every other material handled in this batch. We have kept that section omitted here rather than invent a cross-reference. Notably, this is also the only one of the eight alloys in this batch whose old page had no machinability description block at all (not even an incorrect one), so there is no prior "nickel-based" claim to correct here - but based on the composition data, M 204 should still be classified as cobalt-base, not nickel-base, for machining purposes.

Given its composition profile, M 204 should be treated as a cobalt-base cast alloy with a substantial carbide-forming tungsten addition, calling for the same conservative machining approach used for other cast cobalt superalloys in this family.

M 204's composition - cobalt-dominant with a significant tungsten addition and a substantial nickel fraction - points to a solid-solution and carbide-strengthened cast structure similar in behavior to other cast cobalt-nickel-tungsten alloys in this family. Expect abrasive tool wear from tungsten-rich carbide phases and sustained retained hardness at elevated temperature, meaning the cutting edge does not get relief from thermal softening even at higher cutting speeds.

As with related cobalt-base alloys, expect rapid work hardening under cutting force - light, hesitant, or interrupted cuts leave a hardened surface that is measurably harder to machine on the following pass. Maintaining steady, adequate chip load throughout the cut is essential.

Because published machining data specific to M 204 is limited, start at the conservative end of the recommended speed range, use sharp positive-rake ground carbide inserts, rigid low-deflection setups, and generous, consistent coolant delivery, and monitor flank wear closely on initial cuts before committing to a production speed and feed.