I just discovered more information on Surgical Stainless Steel, so am editing this guide to reflect the new knowledge.

Most surgical equipment is made out of martensitic steel.

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 orthopedic implants as aids in bone repair, as a structural part of artificial heart valves, and other implants. Immune system reaction to nickel is a potential complication.

In most 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 orthopeadic implants but which is incorrodible after implant. Thus steel may be used for temporary implants and the more expensive titanium for permanent ones.

Martensitic stainless steels are not as corrosion resistant as the other two classes, but are extremely strong and tough as well as highly machineable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium (12-14%), molybdenum (0.2-1%), no nickel, and about 0.1-1% carbon (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic. It is also known as “series-00″ steel.

Type 316: The next most common; for food and surgical stainless steel uses; Alloy addition of molybdenum prevents specific forms of corrosion. Also known as “marine grade” stainless steel due to its increased ability to resist saltwater corrosion. SS316 is often used for building nuclear reprocessing plants. 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.

Type 410: Martensitic (high-strength iron/chromium).
Type 420: “Cutlery Grade” martensitic. Also known as “surgical steel”.