Types of Stainless Steel used in Medical Instruments

Stainless Steel used in Instruments and wearable metal objects.

Stainless Steel is a generic term commonly used to describe a group of
Iron-based alloys which exhibit a phenomenal resistance to rusting or corrosion
because of it’s Chromium content. Chromium has been added in small amounts to
strengthen Steel since the Famous Eads Bridge spanned the Mississippi River at
St. Louis, Missouri, in 1872. But it was only discovered in the present century
that when Iron was alloyed with Chromium in excess of 10%, and Carbon held
suitably low, it was effectively rustproof. The term “Stainless” was
first used to describe steel cutlery that was produced in Sheffield England in
C.1916. In 1913 316L stainless Steel was first patented, In 1926 a Stainless
Steel composed of 18% Chromium and 8% Nickel was developed, however this steel
still had problems with corrosion resistance. This problem was solved by the
addition of 2-4% Molybdenum.
Stainless Steels can be broken down into three main types:


Ferritic alloys are obtained when Chromium is added to Iron to develop
corrosion resistance without steel-type hardening. ferritic alloys are mainly
used for construction, and for use in automobiles.


Martensitic alloys result when Chromium is added to steels with carefully
chosen Carbon contents, they range from the least expensive and most widely
used 410 grade, to 440-C grade which is used for knives and surgical tools due
to it’s great hardness.


Nickel is the next most important alloying element, the most famous alloy being
“18-8″ containing 18% Chromium and 8% Nickel. Unlike the atomic
structure of ferritic or Martensitic Steels, Austenic Steel has a face-centred
cubic form made stable by the presence of Nickel. This gives the Austenitic
Steels unique properties of workability, toughness, and corrosion resistance.
The Austenitic grades of Steel are the most highly prised for these properties,
and also the most expensive.


Some reports in Body Piercing literature state that there is no such thing as
“Surgical” Steel, However, there is a certain grade of steel which is
used for implantation into the body, or “Surgical” purposes. So we
can therefore use the term “Surgical Steel” even though that’s not
the exact scientific terminology, it’s easier to use that term than to try to
get the public used to all the other more complex classifications used for it.

316L is the most useful for body piercing jewellery, as it is fairly strong,
easy to work with, and will not lose it’s corrosion resistance during
manufacture Type 316L (L = Low Carbon at 0.03%) 316LVM (Low carbon Vacuum
Manufacture), and 317 are the only steels classified for use for surgical


Because there are so many different alloys of steel available on the market,
industry groups i.e. SAE (Society of Automotive Engineers) and AISI (American
Iron & Steel Institute) have devised a numbering system, 316L is the old
version, the new version is 30316L, and this has been superceded by the Unified
Numbering System (UNI) which is S31603. But the old version has become almost a
generic term and is still recognized by most manufacturers and body piercers,
and I will therefore use it here. There are various standards applying to
Stainless Steels throughout the world, and several different classifications
are used to designate “Surgical”Steel. The most common are listed

Manufacturer’s Codes
30316L 926L 3R60
National Codes
British German Japanese United States
new type W.No DIN JIS UNS.No ASTM/AISI type
316S11 1.4404 X2CrNiMo17 13 2 SU316L S31603 316L

There are very specific guidelines for the production of “Surgical”
Steel, the one used for the purposes of this article are the American Society
for Testing & Materials (ASTM) standards, specifically ASTM F138 (1982)
Standard Specification, Stainless Steel Bar and Wire for Surgical Implants
(Special Quality).

The term Stainless Steel is a misnomer, these steels are subject to staining
and corrosion, although at much lower rates than standard steel. A Chromium
content in excess of 10.5% is what makes steel so called “Stainless”.
The oxidization of this Chromium content upon exposure to air causes very thin film
of Chromium Di-Oxide to form on the surface of the steel. The Film of Chromium
Di-Oxide is extremely thin, passive, continuous, tenacious, stable and
self-repairable. It renders the surface inert to many chemical reactions and
therefore passive, thereby giving stainless steel it’s phenomenal built in
corrosion resistance, especially in organic environments like the internal
Human body. The Molybdenum confers a special resistance to pitting corrosion.

The exact Metallic composition of 316L by Heat analysis is:
Chromium 17.00%
Nickel 12.00%
Molybdenum 2.25% Maximum
Manganese 2.00% Maximum
Silicon 0.75% Maximum
Copper 0.50% Maximum
Nitrogen 0.10% Maximum
Carbon 0.03% Maximum
Phosphorus 0.025% Maximum
Sulphur 0.010% Maximum
Iron 65.345%*

*Approximately the remaining balance

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Surgical Instruments Passivation – Rust Prevention

How Instruments are made resistant to rusting and reacting with acidic elements during the operation.

The removal of exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination but will not significantly affect the stainless steel itself”

In addition, it also describes passivation as “the chemical treatment of a stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film.”

In layman’s terms, the passivation process removes “free iron” contamination left behind
on the surface of the stainless steel as a result of machining and fabricating processes.
These contaminants are potential corrosion sites which, if not removed, result in premature corrosion and ultimately result in deterioration of the component. In addition, the PASSIVATION OF STAINLESS STEEL passivation process facilitates the formation of a very thin, transparent oxide film, which protects the stainless steel from “selective” oxidation (corrosion).

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Surgical/Dental Instruments Manufacturing Steps

Instruments Manufacturing Steps – Dental Forceps Blog

Instruments Manufacturing Steps

1. Steel
The quality of steel is very important in the production of quality instruments. The best you select the best you produce. In order to ensure the finest of quality steel, we have imported or best quality local steel as required by valued customers.

2. Forging
Forging is a process of cutting shaped raw instruments with the help of dyes and hammers. Here, the skilled hands give life to the metal and give it the rudimentary shape that will go through series of complicated processes.

3. Forging Inspection
At this stage, forged tools are checked to ensure no piece contains any cracks or is reshaped beyond acceptable limits. Checking the quality of raw instruments for: -
a. Shape fault
b. Broken

4. Machining
In this process forging is cut or shaped by machines i.e. cutting sharp edges and raw material in the shape. Here instruments are given their shape through grinding and hammers. For this purpose, extremely skilled labor is required and this process is carried out by instrument specialists only.

5. Milling
Drilling of holes in the instruments where required for screws. Different kids of screwing machines are used and instruments are made pairs here. Instruments with even the slightest difference in whole positions will suffer otherwise.

6. Inspection
At this stage, all the instruments are inspected not only for machining and milling, but for every process they’ve been through. It’s the stage where only best instruments are selected and instruments with tiny holes and manufacturing faults are again sorted out.

7. Filling
At this stage the steel is not too hard so filling is used to shape the instruments in the exact shape they are required to be. The workers match the shape exactly with the samples provided at this stage. So the instruments get most of their shapes at this stage.

8. Filling Inspection
After filling the inspection is made and measurements and shapes are checked according to samples.

9. Binding and Temper
At this step the instruments are bound in groups of 12 pieces. Then they put them in temper machine, which is filled with a particular material. Here instruments are tempered and its ensured that every instrument get equal heat and treatment so a consistent quality would achieve.

10. Snaffing Fitting
For scissors and forceps they are in two pieces so they are joined in this process with screw. Forceps (Tweezers) are joined before and their joint is leveled with a machine by burning the raw material on the joint. At the same stage, instruments are filled to eliminate welding suspensions.

11. Plant or Heat Treatment
In this process the instruments are dipped in a material by hanging for five minutes to harden the material.

12. Polishing

Instruments are polished at this stage. Till this point at manufacturing stage, all the necessary shaping is done. Polishing makes every millimeter of instrument clear and any instrument with hidden defects are revealed could be sorted out.

13. Q. A Inspection 2%
2% of each lot of instruments is checked by executives and then go the further processing. In inspection they see each and every part and defective parts are marked with red marker and if rejected send to polishing again.

14. Ultrasonic Cleaning
In this process the instruments are dipped in two materials for cleaning the polish raw thing on it. 1 min. for first material and then for half min. for other material. Ultrasonic cleaning cleans any polishing material stuck and leaves the instrument crystal clear.

15. Lubrication
All the instruments involving screws are lubricated at this step. Lubricating the instruments moveable portions facilitates the instrument movement.

16. Tuck checking
In this process workers check the cuts and all other things just by viewing the instruments individually.

17. Etching
Putting each instrument on stamp pad and burning process to put stamp on each instrument. This stamping procedure is done through electronic etching machines that make the stamp reliable and even sustainable under high boiling temperatures when instruments are sterilized.

18. Cleaning and Checking
Instruments are cleaned and checked again one by one. Again it’s the checking for operation, measurements, polish and usability.

19. Q. A Inspection 4 %
4% of the instruments are inspection by Q. A. Directors. Samples for inspection are taken randomly and are observed to every bit of detail. Even the slightest difference from acceptable standards could result in rejection of whole lot.

20. Packing
Packing in boxes each contains 100 pieces. 10 Boxes in a Carton. Here instruments are packed with respect to sizes and types. Instruments boxes are properly labeled and stored in proper storing environment.

21. Labeling
Labels are put in this process.

22. Storage
Storage by lot and order number

23. Delivery

These processes are also included as required.

* Passivation
* Boil Test
* Gold plating in different manner.
* Copper Sulphate test.

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