Nitronic 60 (UNS S21800, also sold as Alloy 218) is a nitrogen-strengthened austenitic stainless steel developed to solve a failure mode ordinary 300-series stainless handles poorly: galling. Wherever two stainless surfaces slide, rotate, or thread against each other under load — valve stems against packing, pump shafts against bushings, high-preload fasteners — standard 304 or 316 tends to seize and tear at the contact surface. Nitronic 60 resists that by combining roughly 4% silicon with 7-9% manganese in a chromium-nickel-nitrogen austenitic base, a chemistry specifically engineered to promote a hard, slip-resistant surface film at sliding contact points instead of the raw metal-to-metal adhesion that causes galling.

The nitrogen addition stabilizes the austenite phase and pushes mechanical strength to nearly double that of Type 316 in the annealed condition, while the alloy keeps reasonable general corrosion resistance and stays fully non-magnetic. That combination — high strength, galling and wear resistance from ambient to elevated temperature, and dependable corrosion performance — makes Nitronic 60 the default specification for valve stems and seats, pump shafts and sleeves, fasteners under high torque, and other sliding or rotating stainless-on-stainless contacts across chemical processing, power generation, and marine equipment.

Nitronic 60's entire design intent — resist galling and adhesive wear at a sliding contact — works directly against easy machining. The same silicon and manganese additions that give the alloy its slip-resistant surface chemistry also make it more abrasive on the cutting edge and more prone to work hardening under a dull or rubbing tool than standard 304 or 316. Published machinability data consistently puts practical machining rates for Nitronic 60 at roughly half those used for Type 304 — and that's on top of the already-conservative parameters 304 itself requires.

The alloy carries all the classic austenitic stainless problems — a fully austenitic microstructure that cannot be hardened by heat treatment, low thermal conductivity that concentrates heat right at the cutting edge, and a strong tendency to work-harden wherever a tool rubs instead of shears — but with roughly double 316's yield strength resisting the cut itself. Sharp, positive-rake carbide is essential to shear the material cleanly rather than push and rub it, since any hesitation invites the hardened skin that makes every subsequent pass progressively harder. Feed rates need to stay high enough and consistent enough to always cut beneath the work-hardened layer left by the previous pass.

A wear-resistant coated grade with a chipbreaker geometry built for tough stainless helps manage both the abrasive wear from the silicon content and the long, stringy chips typical of high-nickel austenitic alloys. Rigidity throughout the machine, toolholder, and workholding chain, generous coolant flow, and feeds and speeds noticeably more conservative than 316 are the baseline for consistent tool life on this grade.