Understanding Surgical Stainless Steel
These days surgical Instruments are made from a variety of materials including composites, plastics, titanium, and (the more traditional;) stainless steel. Typically two types of stainless steel series are most commonly used for instruments manufacturing.
- 300 series (Austenitic) stainless steel, and
- 400 series (Martensitic) stainless steel.
The Austenitic steel cannot be hardened through heat treatment. The 304 grade is the typical grade used for surgical instruments and is suited for items which require some malleability, that is, they can be pressed or formed into another shape without breaking the metal. Cannulas, retractors, probes, mallets, and spreaders are amongst some of the instruments that are traditionally manufactured through this series of steel.
The Martensitic steel are low carbon steel that can be hardened and tempered through heat treatment process. Due to the strength achieveable through hardening process, this series of steel is more suitable for instruments that require strength and tough cutting edges. Bone cutters, clamps, forceps, needle holders, and chisels are some of the instruments that are traditionally manufactured through the 410/420 grade of this series of steel.
Even though the stainless steel is generally corrosion resistant, it does not mean that rust and corrosion cannot occur on it. Perhaps a better term that could reduce this misconception is using ‘stain-resistant’ not ‘stainless or stain-free’. This is because there are many things that may cause corrosion on stainless steel. These things include high acid, or alkaline concentrated detergent, friction with other non-corrosion resistant metals (during manufacturing or afterwards), defects in steel, lubrication electrolytes, conditions involving high chlorides and other factors. Having said this, corrosion can be prevented through proper material and tools selection, manufacturing care and processes like passivation, and proper care and handling in the hospitals before and after each use.