UNS S29108 Cr-Mn-N Steel Round Bar

Product Description

UNS S29108 (commonly recognized by its commercial brand name BioDur® 108) represents a premium, high-nitrogen, essentially nickel-free austenitic stainless steel. Standardized under medical and surgical specifications like ASTM F2229, it replaces nickel with exceptionally high levels of manganese and interstitial nitrogen to maintain a stable austenitic structure.

The primary engineering purpose of S29108 is to eliminate risk from nickel hypersensitivity or metal allergies while providing dramatically superior tensile, fatigue, and pitting resistance compared to conventional implant alloys like 316L (ASTM F138).

Chemical Composition (Mass Weight %)

To ensure dynamic microstructural cleanliness, grain refinement, and absolute stability, S29108 is typically processed using Electro-Slag Remelting (ESR) or Vacuum Degassing (VD) routes.

Key Technical Attributes

• Biocompatibility & EU MDR Compliance: Because it restricts Nickel and Cobalt to trace residual amounts ($\le 0.10\%$), components manufactured from S29108 circumvent strict European Medical Device Regulation (EU MDR) labeling requirements regarding potential CMR (carcinogenic, mutagenic, or reprotoxic) elements.

• Superlative Pitting Resistance: High Chromium and Molybdenum paired with structural Nitrogen yield a significantly elevated Pitting Resistance Equivalent Number (PREN) over standard 316L. It exhibits a critical crevice corrosion temperature of 10°C (per ASTM G48 Method D), whereas 316L drops below 0°C under identical parameters.

• Magnetic Footprint: S29108 is strictly non-magnetic and completely ferrite-free. It retains ultra-low magnetic permeability even when undergoing aggressive cold drawing or severe strain hardening.

Mechanical Properties (At Room Temperature)

Like most authentic austenitic grades, UNS S29108 cannot be hardened via heat treatment; it relies entirely on strain hardening (cold working). Thanks to interstitial nitrogen strengthening, its baseline annealed yield strength is nearly double that of typical 300-series stainless steels, and it maintains exceptional work-hardening rates.

The mechanical properties scale cleanly based on the percentage of cold work reduction:

Processing & Fabrication

• Machinability: High nitrogen levels coupled with high work-hardening rates make machining challenging. To mitigate immediate tool glazing, utilize rigid setups, sharp carbide tooling, heavy positive feeds, and specialized sulfurized cutting fluids.

• Finishing: Precision ground round bars are standard for surgical component lines. The material polishes efficiently to high mirror finishes necessary for medical insertion tools.

Target Applications

Due to its unique focus on high structural fatigue life and human tissue compatibility, UNS S29108 round bars are prominently deployed in:

• Orthopedic Implants: Bone screws, compression plates, intramedullary pins, and spinal fixation components.

• Prosthetic Hardware: Load-bearing joints and hip/knee reconstruction assemblies.

• Specialized Instrumentation: High-strength, non-magnetic surgical drills, dental tools, and diagnostic implements used near sensitive MRI environments.

• Hypoallergenic Consumer Goods: Luxury body jewelry, orthodontic braces, and premium watch components requiring absolute skin safety.