Surgical stainless steel

Surgical stainless steel

Surgical stainless steel is a specific type of stainless steel, used in medical applications, which includes alloying elements of: chromium, nickel and molybdenum.
The chromium gives the metal its scratch resistance and corrosion resistance. The nickel provides a smooth and polished finish. The molybdenum gives greater hardness and helps maintain a cutting edge.

Although there are myriad variations in the recipes, there are two main varieties of stainless steel: martensitic and austenitic; see the stainless steel article.
The word 'surgical' refers to the fact that these types of steel are well-suited for making surgical instruments: they are easy to clean and sterilize, strong, and corrosion-resistant. The nickel/chrome/molybdenum alloys are also used for orthopaedic implants as aids in bone repair, and as a structural part of artificial heart valves and other implants. However, immune system reaction to nickel is a potential complication. In some cases today titanium is used instead in procedures that require a metal implant which will be permanent. Titanium is a reactive metal, the surface of which quickly oxidizes on exposure to air, creating a microstructured stable oxide surface. This provides a surface into which bone can grow and adhere in orthopaedic implants but which is incorrodible after implant. Thus steel may be used for temporary implants and the more expensive titanium for permanent ones.

Most surgical equipment is made out of martensitic steel—it is much harder than austenitic steel, and easier to keep sharp. Depending on the type of equipment, the alloy recipe is varied slightly to get more sharpness or more strength.

Implants and equipment that are put under pressure (bone fixation screws, prostheses, body piercing jewelry) are made out of austenitic steel, often 316L and 316LVM compliant to ASTM F138[3], because it is less brittle.

316 surgical steel is used in the manufacture and handling of food and pharmaceutical products where it is often required in order to minimize metallic contamination. ASTM F138[3]-compliant steel is also used in the manufacture of body piercing jewellery[4] and body modification implants.