Materials Glossary
Austenitic stainless steel is the 300-series family — 304, 316, and their relatives — that stays non-magnetic and corrosion-resistant at room temperature because of the nickel locked into its structure. It's the most common stainless steel in the world, and also one of the most misunderstood at the machine: it isn't hard, but it is gummy, and that difference is exactly what trips people up.
Austenitic stainless steels are the 300-series grades — 304 and 316 are the two you'll see most — typically alloyed with roughly 16–25% chromium plus enough nickel (and sometimes nitrogen) to hold the iron in its face-centered cubic (FCC) "austenite" structure at room temperature, instead of letting it revert to the magnetic body-centered structure ordinary steel prefers. That's why these grades read as non-magnetic or only faintly magnetic, and it's also why the nickel content is a real cost driver — it's doing structural work, not just sitting in the mix. 316 builds on 304 by adding molybdenum, which improves resistance to pitting and chloride attack, at the cost of being noticeably tougher to cut.
Unlike the 400-series martensitic grades, austenitic stainless cannot be hardened by quenching and tempering — its FCC structure simply doesn't transform into martensite the way carbon or martensitic stainless steels do. The only way to increase its strength and hardness is cold work: rolling, drawing, or otherwise deforming it below its softening temperature. That's a genuine advantage for forming and welding, but it's also the root of its reputation at the machine.
Austenitic stainless steel has a high work-hardening rate — the act of cutting it hardens the surface layer left behind, so a dull edge or a light pass can leave metal that's noticeably harder than what the tool just cut through. Combined with its ductility, this produces built-up edge: material welds onto the cutting edge, tears away, and takes some of the edge with it. The fix is sharp, positive-rake tooling, steady chip loads that avoid rubbing, and enough coolant to carry heat away rather than let it soak into the part. For high-volume work where machinability matters more than ultimate corrosion resistance, free-machining grades like 303 add sulfur to break chips cleanly and cut work-hardening tendencies substantially.