UNS S31675 High Nitrogen Steel Round Bar, Rods & Bars

Product Description

UNS S31675 High Nitrogen Stainless Steel Round Bars, Rods, and Bars

UNS S31675—internationally specified under ASTM F1586, ISO 5832-9, and European standard DIN Werkstoff Nr. 1.4472 (X2CrNiMoN21-16-5-4), and known commercially by trade names such as Rex 734 and UGIPURE 4472—is a high-purity, fully austenitic stainless steel manufactured via vacuum-arc remelting or electroslag remelt processes. Designed primarily for orthopaedic implants, surgical instruments, and high-fatigue engineering components, it relies on a deliberate solid-solution nitrogen addition of 0.25 to 0.50 percent. This nitrogen enrichment provides substantially higher yield strength, enhanced fatigue resistance, and superior resistance to localized pitting and crevice corrosion compared to conventional implant-grade stainless steels like 316L.

Standards and Specifications

Governing specifications include UNS S31675, ASTM F1586 for wrought nitrogen-strengthened stainless steel bar and wire for surgical implants, ISO 5832-9 for surgical implants, and DIN Werkstoff Nr. 1.4472.

Chemical Composition Limits

The chemical baseline requires 19.50 to 22.00 percent chromium, 9.00 to 11.00 percent nickel, 2.00 to 3.00 percent molybdenum, 2.00 to 4.25 percent manganese, 0.25 to 0.50 percent nitrogen, and 0.25 to 0.80 percent niobium. Maximum impurity thresholds are set at 0.030 percent carbon, 0.75 percent silicon, 0.025 percent phosphorus, 0.010 percent sulfur, and 0.25 percent copper, with iron forming the balance.

Physical Properties

UNS S31675 exhibits a density of 7.88 grams per cubic centimeter (0.285 pounds per cubic inch) and a tension elastic modulus of 200 gigapascals. Its calculated Pitting Resistance Equivalent Number ranges between 33.0 and 38.0. Due to its balanced austenitic structure, the alloy maintains a magnetic permeability below 1.005, remaining non-magnetic even after extensive cold deformation.

Mechanical Properties

Mechanical requirements vary based on product form and processing condition.

In the solution-annealed state, round bars specify a minimum tensile strength of 740 megapascals (107 ksi), a minimum 0.2 percent yield strength of 430 megapascals (62 ksi), a minimum elongation of 35 percent, and a hardness between 200 and 250 Brinell.

In the cold-worked high-strength condition used for fixation devices, minimum tensile strength increases to 1000 megapascals (145 ksi), minimum yield strength increases to 750 megapascals (109 ksi), minimum elongation is 10 to 15 percent, and hardness reaches 30 to 38 Rockwell C.