Surgical stainless steel
From Wikipedia, the free encyclopedia
| Iron alloy phases |
|---|
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Austenite (γ-iron; hard) |
| Types of steel |
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Carbon steel (≤2.1% carbon; low alloy) |
| Other iron-based materials |
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Cast iron (>2.1% carbon) |
Surgical stainless steel is an alloy of iron, carbon, chromium (12–20%), molybdenum (0.2–3%), and nickel (8–12%).
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 maintaining 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, as a structural part of artificial heart valves, and other implants. 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.[citation needed]
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 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, 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.[1]
