Steels for surgical instruments

In order to guarantee corrosion resistance, only steels which are stainless through and through may be used for manufacture of surgical instruments. By stainless steels are meant steels containing percentages of carbon, chromium, molybdenum and nickel. There are two main kinds of stainless steel:

1. Martensitic stainless steel
2. Austenitic stainless steel

1. Martensitic stainless steel

These are quenched, magnetic steels.

They include:

Carbon: from 0.10 to 1%

      Gives hardness and tensile strength

      Lowers the corrosion resistance

Chromium: from 12 to 14%

      Essential alloying element

      Gives corrosion resistance

Molybdenum: from 0.20 to 1%

      Helps to preserve the cutting edge

      Gives corrosion resistance and impact strength

      Cannot be used for pressure force instruments, as it makes them brittle

2. Austenitic stainless steel

These are non-quenched, non-magnetic steels.

They include:

Chromium: from 16 to 20%

      Essential alloying element

      Gives corrosion resistance

Molybdenum: from 2 to 3%

      Gives corrosion and impact strength

Nickel: from 8 to 12%

Based on this classification, we can define the types of steel in relation to the instruments which they are used to make.

Families of products

1 - Pressure force instruments and springs: martensitic steel

  1. -      Haemostatic forceps
  2. -      Dissecting forceps
  3. -      Gripping forceps
  4. -      Surgical towel clamp
  5. -      Needle-holding forceps
  6. -      Threading forceps
  7. -      Clamping forceps

The steel used must be springy and have high impact strength.

Carbon gives hardness, while chromium gives resistance to oxidation; the proportions have to be very exact.

Instruments made of these steels have to undergo complex, precise heat treatment in order to be of good quality. The aim of this heat treatment is to rearrange the molecules in order to harden the steel; otherwise the instruments will bend the first time they are used.

Instruments made of these steels must be carefully polished; the quality of the polishing determines the maximum resistance to corrosion.

2 - Instruments that cut by shearing: martensitic steel

  1. -      Scissors
  2. -      Curettes
  3. -      Raspatories
  4. -      Gouge shears
  5. -      Cutting forceps

The steel used has a higher percentage of carbon than in the pressure force instruments, in order to give greater cutting hardness.

The percentage of chromium is the same to give corrosion resistance, while incorporation of molybdenum makes up the balance.

3 - Instruments that cut by percussion: martensitic steel

  1. -      Chisel shears
  2. -      Osteotomes
  3. -      Gouges

The heat treatment and polishing for the cutting part are the same as for instruments that cut by shearing, while for the non-cutting part they are the same as for pressure force instruments.

4 - Static function instruments: martensitic or austenitic steel

  1. -      Autostatic (i.e. locking) retractors
  2. -      Long-handled retractors
  3. -      Valves
  4. -      Speculums
  5. -      Dilators

5 - Miscellaneous instruments

  1. -      Metal box
  2. -      Obstetrical hook
  3. -      Manual drill
    -      Etc.