ASTM F899 / UNS S46500 / Custom 465 Medical Stainless Steel

ASTM F899 specification covers the chemical requirements for wrought stainless steels used for the manufacture of surgical instruments. Custom 465 stainless steel is a high-strength, corrosion-resistant stainless steel that has become the go-to material for medical device manufacturers. Its unique combination of strength and corrosion resistance makes it ideal for medical applications.

 

Cold worked Custom 465 (UNS S46500) stainless steel, aged at 900ºF (482ºC), can provide maximum achievable tensile strengths approaching 300 ksi (2070 MPa) for parts with diameters less than 0.75 in. (20 mm). This capability has been useful for making surgical and dental instruments and needle wire for the medical industry.

 

General corrosion resistance of Custom 465 stainless approaches that of 304 stainless. In both the H950 and H1000 conditions, exposure to 5% neutral salt spray at 95ºF (35º C) (per ASTM B117) caused no rusting after over 2000 hours. Double-cantilever-beam tests conducted in 3.5% NaCl (pH 6) show Custom 465 stainless to possess inherently good resistance to stress corrosion cracking.

Its stress corrosion resistance, furthermore, improves with increasing aging temperature. It is comparable to that of 13Cr-8Ni stainless and Custom 455 stainless steels, but at significantly higher strength – and its resistance is superior to that of both when overaged to the same strength level.

 

Cold worked Custom 465 stainless , aged at 900ºF (482ºC), can provide maximum achievable tensile strengths approaching 300 ksi (2070 MPa) for parts with diameters less than 0.75 in. (20 mm). This capability has been useful for making surgical and dental instruments and needle wire for the medical industry. While the more conventional ferritic and martensitic stainless steels sufficed for a long time in making surgical instruments, that landscape has changed.

 

The evolution of new surgical techniques requires instruments of improved design that do not break, distort, or otherwise fail during surgery. Materials used for the instruments must be strong and tough. The combined high strength and toughness of Custom 465 stainless has allowed instruments to withstand higher operational torque loads during surgery. These properties have facilitated the design of longer and smaller cross-section instruments that are typically required for minimally invasive surgeries.

 

Superior fracture and impact toughness are also key properties of the alloy when it has been used for surgical tools. At comparable strength levels, Custom 465 has exhibited more than twice the impact resistance of either Custom 455 stainless or 17Cr-4Ni stainless, two alternative precipitation hardenable stainlesses used by the medical industry.

 

Instruments fabricated from Custom 465 stainless are autoclaveable and resistant to oxidation in a steam environment. The alloy also has been found to be resistant to cleaning and sterilizing solutions and to body fluids and is included in ASTM F899, which is the governing specification for Stainless Steels for Surgical Instruments.

 

Although not designed specifically for wear and edge retention applications, Custom 465 stainless has been used for instruments, such as scrapers, and cutters with superior results when compared to Custom 455 and 17-4. In addition to the alloy’s use for surgical tools, Custom 465 stainless has served well when used for suture needles due to its combination of high strength, ductility and corrosion resistance.