AM-350 (UNS S35000, AISI 633) is a semi-austenitic precipitation-hardening stainless steel with roughly 16.5% chromium, 4.3% nickel, and 2.8% molybdenum, along with a nitrogen addition that helps stabilize its structure. "Semi-austenitic" describes the way this alloy behaves through processing: it solidifies and can be worked in a soft, formable austenitic condition, then is converted to a strong martensitic structure through a conditioning treatment (sub-zero cooling or a warm/cold working step) followed by an aging cycle that precipitates strengthening phases. That two-stage transformation is what lets AM-350 combine good formability as-supplied with high strength and hardness once fully heat treated.

AM-350 is a long-standing aerospace alloy, used in gas turbine compressor blades, discs, and shafts, edge-welded bellows, precision seals and couplings, and other components in high-vacuum and semiconductor processing equipment that need a combination of strength and corrosion resistance approaching that of the austenitic 300-series grades. Because the final martensitic transformation and aging happen after most of the shaping is done, AM-350 is normally machined in its annealed, semi-austenitic condition, before the conditioning and aging treatments raise its hardness and cutting forces substantially.

In its annealed, semi-austenitic condition, AM-350 machines in the same general territory as other chromium-nickel-molybdenum stainless grades: gummy chip flow, a tendency to work-harden if the tool rubs instead of shearing, and low thermal conductivity that concentrates heat at the cutting edge instead of carrying it away in the chip. The molybdenum content pushes cutting forces and abrasive wear a step above straight chromium-nickel grades like 304, closer to what you'd expect from 316.

Sharp, positive-rake tooling and consistent feed rates that cut beneath the previous pass's work-hardened layer are the fundamentals here, same as any austenitic or semi-austenitic stainless. Coolant matters more than it does on carbon or low-alloy steel because of the poor thermal conductivity. Once AM-350 is conditioned and aged to its final martensitic, high-strength state, cutting forces and tool wear increase substantially — finish machining and most stock removal should be planned for the annealed condition wherever the process allows it.

Values are for the annealed, semi-austenitic condition. Assume favorable conditions: a well-matched insert grade, rigid tool and workpiece clamping, good raw material quality, short tool overhang, and adequate coolant. Reduce speeds significantly for conditioned/aged material.

Turning

Parting / Grooving

Milling