REX 734 (UNS S31675) is a nitrogen-strengthened austenitic stainless steel developed specifically for orthopedic and surgical implants under ASTM F1586 and ISO 5832-9. It's often described by its composition shorthand — 21Cr-10Ni-3Mn-2.5Mo — a chemistry built around a much higher nitrogen content than a standard implant-grade austenitic like 316LVM. That nitrogen addition, combined with chromium, nickel, and molybdenum levels well above 316L, pushes mechanical strength roughly 50-75% above conventional implant stainless while keeping the fully austenitic, ferrite-free microstructure that biomedical devices require for consistent corrosion behavior and complete non-magnetic response (a requirement for patients undergoing MRI imaging).

REX 734 bar stock is typically produced by electroslag remelting (ESR), a secondary refining process that removes inclusions and tightens compositional control far beyond what standard melting achieves. That level of micro-cleanliness matters directly for implant performance: fewer inclusions means fewer crack-initiation sites under the cyclic loading a hip stem or fracture fixation plate sees in service. The combination of high strength, excellent pitting and crevice corrosion resistance in physiological (chloride-rich) environments, and superior fatigue performance is why REX 734 has become a standard material for forged monoblock hip stems, bone screws, and other load-bearing surgical implants where 316LVM doesn't offer enough strength margin.

REX 734 shares the fundamental character of every nitrogen-strengthened austenitic stainless: a fully austenitic microstructure that cannot be hardened by heat treatment, low thermal conductivity that concentrates heat directly at the cutting edge, and a strong tendency to work-harden under a rubbing or dull tool. The elevated nitrogen content that gives REX 734 its implant-grade strength also raises cutting forces well above what a shop sees on 316L, and the higher molybdenum and chromium content compared with a standard austenitic adds further abrasive load on the insert edge.

Where REX 734 differs from a galling-resistant grade like Nitronic 60 is in surface finish and dimensional expectations rather than raw cutting difficulty — implant components typically require tight tolerances and excellent surface integrity, since surface defects can become fatigue crack initiation sites in a load-bearing device. That makes consistent, chatter-free cutting conditions as important as the speeds and feeds themselves. Sharp, positive-rake carbide that shears rather than rubs is essential to avoid work-hardening the surface and to protect finish quality; feed rates need to stay high enough and consistent enough to always cut beneath the hardened layer left by the prior pass. A wear-resistant coated grade, rigid workholding, and generous coolant are the baseline for holding both tool life and the finish quality implant work demands.