Stainless Steel tools have corrosion resistant steels. “Corrosion-resistant”, does not mean “rust-free forever” and a certain amount of care is needed to maintain the tools’ original corrosion –resistant layer. Passivation of stainless steel is a process used that produces a passive (i.e., non –reactive) oxide surface layer which protects the steel against corrosion. Old instruments with carbon, chrome, and nickel plating can rust when the plating wears off exposing the steel underneath. You should read and follow the Care Instructions for maximum performance and extension of use. Back to Top
Stainless steel is a low carbon steel which contains chromium at 10% or more by weight. It is this addition of chromium that gives the steel its corrosion resistant properties. The chromium content of the steel allows the formation of an invisible chromium-oxide film on its surface. If oxygen is present, even in small quantities, this film self-repairs if damaged mechanically or chemically. Corrosion resistance of stainless steel is enhanced by increased chromium content and the addition of other elements such as molybdenum, nickel, and nitrogen.
The three main classifications of stainless steel are identified by the alloying elements which form their microstructure. Austenitic steels have austenite (face centered cubic crystal) as their primary phase. These are alloys containing chromium and a major proportion of nickel. Austenitic steels are not thermally hardenable but have excellent corrosion resistance. Ferritic steels have ferrite (body centered cubic crystals) as their main phase. These steels have a low carbon content and contain chromium as the main alloying element. Usually between 13% and 17%. Ferritic steel is less ductile than austenitic steel and is not thermally hardenable. Martensitic steels are low carbon steels typically containing 12% chromium, a moderate level of carbon, and very low levels of nickel. Martenitic steels are distinguished from other stainless steels in their ability to achieve high hardness by a heat treatment that products martensite (a supersaturated solid solution of iron characterized by a needle-like microstructure)
410 Stainless Steel is a Martensitic alloy similar to 405 but with a higher carbon content and no aluminum. It is this increase in carbon and absence of aluminum that improve the mechanical properties and strength of 410 by making it hardenable steel to regular carbon and alloy steels.
Carbon 0.15% max. Manganese 1.00% max Phosphorus 0.040 % max
Sulfur 0.030%max Silicon 1.00%max Chromium 11.5/13.50%
420 stainless steel is a Martensitic alloy that is strengthened by the addition of carbon at a 0.15% minimum (0.30% nominal) compared to the 0.15% maximum for type 410. Along with carbon, chromium content is also slightly increased to offset the tendency of the higher carbon content to lower the alloy’s resistance to corrosion. In the hardened and tempered condition, the alloy’s yield strengths are substantially greater than type 410. Type 420 is used for such applications as surgical and dental instruments, cutlery, scissors, valves, and ball bearings.
Carbon 0.15% max. Manganese 1.00% max Phosphorus 0.040 % max
Sulfur 0.030%max Silicon 1.00%max Chromium 12.00/14.00%
is a thermally hardenable, martensitic stainless steel alloy combining corrosion-resistant properties with maximum hardness. Both carbon (0.95% - 1.2%) and chromium (16-18%) contents are increased substantially to impart hardness. While it is the strongest of all stainless steel alloy, its high carbon content reduces its corrosion resistance.
Carbon 0.95/1.20%. Manganese 1.00% max Phosphorus 0.040 % max
Sulfur 0.030%max Silicon 1.00%max Chromium 16.00/18.00%
Molybdenum 0.75% max
Stainless steel is a metal which resists rust, can be ground to a fine point, and retains a sharp edge. Its composition can be altered to enhance certain qualities. For example, a manufacturer can make a scissor of stainless steel with carbon to create a harder cutting edge on a scissor. It is the Carbon in the stainless steel that makes the scissor stronger but the Carbon can cause the instrument to rust and corrode. All stainless steel can stain, pit, and rust if not cared for properly.
When manufacturing a stainless steel instrument it is subject to a passivation and polishing process in order to make the steel as stainless as possible. Passivation and Polishing eliminates the carbon molecules form the instrument surface. This forms a layer which acts as a corrosive resistant seal. Passivation is a chemical process that removes carbon molecules from the surface of the instrument. This chemical process can also occur through repeated exposure to oxidizing agents in chemicals, soaps, and the atmosphere
Polishing is a process used to achieve a smooth surface on the instrument. It is extremely important to polish an instrument because the passivation process leaves microscopic pits where the carbon molecules were removed. Polishing also builds a layer of chromium oxide on the surface of the instrument. Through regular handling and sterilization the layer of chromium oxide will build up and protect the instrument from corrosion. In some circumstances, that is why you will notice older instruments less corrosive than new ones. The newer instruments have not had the time to build up the chromium oxide layer. However, improper cleaning and sterilization can cause the layer of chromium oxide to disappear or become damaged thus increasing the possibility of corrosion. That is why it is so important to properly clean, sterilize, and store your instruments. For proper cleaning, sterilizing, and storage of surgical instruments please consult our web site under Rinse, Cleaning and Sterilizing. Back to Top
Tools are shipped in non-sterile condition and should be cleaned and sterilized before and after use. Distilled water is recommended for cleaning and rinsing as tap water may contain minerals which can stain or discolor the steel. If using tap water you should dry immediately to avoid staining.
Do not use high concentration bleach which may cause pitting, or abrasive cleaners which may scratch and remove the passive surface layer. Tools should be arranged by metal type to avoid galvanic corrosion (due to contact of different metals) and stainless steel tools should never be stored with carbon steel tools to avoid ferrous contamination (the transfer of ferrous particles).
Use of distilled water and a neutral pH cleaning solution is recommended for all these procedures.
Immediately after use, rinse instruments under warm (not hot) water. It may be helpful to use a nylon toothbrush to rinse the lock boxes and joints of the instrument. Be sure to remove all grime, grease and dirt.
You should clean instruments immediately after rinsing,
Do not place dissimilar metals (stainless, copper, chrome plated etc.) together.
- Use stiff plastic cleaning brushes (nylon etc.).
Do not use steel wool or wire brushes except specially recommended stainless steel wire brushes for instruments such as bone files, or on stained areas in knurled handles.
- Use only neutral pH (7) detergents. If not rinsed off properly after cleaning, low pH detergents will breakdown the stainless protective surface and cause black staining.
- High pH detergent will cause surface deposit of brown stain (this deposit may look like rust) which will also interfere with smooth operation of the instrument.
- Brush delicate instruments carefully and, if possible, handle them totally separate from general instruments.
- Make sure all instrument surfaces are visibly clean and free from stains and dirt.
This is a good time to inspect each instrument for proper function and condition.
- Check the following:
Scissor blades glide smoothly from open to closed (they must not be loose when in closed position). Test scissors by cutting into thin gauze. Three quarters of the length of the blade should cut all the way to the scissor tips, and not hang up.
- Blades of all cutting edges should be sharp and undamaged.
- After manually scrubbing instruments, rinse them thoroughly under running water (distilled water is best). While rinsing, open and close scissors and other hinged instruments to make sure the hinge areas are rinsed out, as well as the outside of the instruments.
If the instruments are to be stored, let them air dry and store them in a clean and dry environment.
If instruments are to be reused or autoclaved:
Lubricate all instruments which have any metal to metal action such as scissors, nippers and other such instruments. Lubricants such as instrument milk are best. Do not use WD-40 oil or other industrial lubricants.
Use disposable paper or plastic pouches to sterilize individual instruments. Make sure you use a wide enough pouch (4” or wider) for instruments with hinges and locks so the instrument can be sterilized in the open and unlocked position.
If you are autoclaving instrument sets unlock all instruments and sterilize them in an open position. Place heavy instruments at the bottom of the set (when two layers are required).
Never lock an instrument during autoclaving. It will not be sterile as the steam cannot reach the metal to metal surfaces. The instrument might develop cracks in hinged areas caused by the heat expansion during the autoclave cycle.
Do not overload the autoclave chamber. Pockets may form that do not permit steam penetration. Place a towel on bottom of pan to absorb excess moisture during autoclaving. This will reduce the chance of getting “wet packs”. Make sure the towels used in sterilization of the instruments have no detergent residue and are neutral pH(7) if immersed in water. The residue of the high-pH (9-13) detergents used by some laundries to clean the towels could cause stains on some instruments.
CAUTION: At the end of the autoclave cycle- before the drying cycle- unlock the autoclave door and open it more than a crack about ¾”. Then run the dry cycle for the period recommended by the autoclave manufacturer. If the autoclave door is opened fully before the drying cycle, cold room air will rush into the chamber, causing condensation on the instruments. This will result in water stains on the instruments and cause “wet packs”.
Roll-packs should never be used in an autoclave.
If you have unusual staining on your instruments during rinsing, cleaning or autoclaving contact us or look in our web site under staining.
Important: For instruments with tungsten carbide inserts, tips or blades we do not recommend use of solutions containing Benzyl Ammonium Chloride. This will destroy the tungsten carbide inserts. Back to Top
Stains can either be plated or deposited on the surface of an instrument. Stains are discoloration of metal by material being just added to the surface of the metal. Stains are often mistaken for rust- an actual change to the metal material. A brown/orange color stain is the most common and is often mistaken for rust.
The brown/orange color stain is usually a phosphate deposit on the instrument. Phosphate can come from traces of minerals in the autoclave water source, a dirty autoclave, high alkaline or acidic detergents, surgical wrappings, and dried blood or tissue. Hot steam in the autoclave deposits the phosphate and produces the stain on the instrument’s surface. Remove this type of stain from the instrument by rubbing with a pencil eraser (rust cannot be removed by an eraser).
A brown/orange stain or a blue-black stain can occur from plating during the cleaning or autoclaving process. Through electrolysis when dissimilar metals touch while being autoclaved, ultrasonically cleaned, or sometimes even stored together, plated stains actually bond the stain material to the instrument metal. They do not often change the metal-material except for the discoloration. These stains are very difficult to remove and will probably need refinishing.
Acid Reaction Stains
Black stains are usually due to an acid reaction. An acidic detergent deposit left on the instrument during autoclaving might cause a black stain. Always use neutral pH detergents and distilled water in your rinsing, cleaning or autoclave process.
Excessive Heat Stains
Multi-colored stains or chromium oxide stains result from excessive heat. These rainbow colored stains indicate the instrument may have lost some of its original hardness after being heated. Cutting edges loose their sharpness quickly when hardness is reduced. Flash flame decontamination (an instrument is decontaminated by inserting it into a flame for a few seconds) changes the molecular structure of most material adversely, shortening the useful life of instruments. Consider another method of decontamination where lower heat levels can be applied to keep your instruments useful for many more years
Pitting can occur on a instrument when it is improperly autoclaved or cleaned.
When an instrument is autoclaved using a solution containing chloride or an acid based detergent it can cause pitting. Hydrochloric acid forms in the solution removing the protective chromium oxide layer of the stainless steel. The acid can then attack the unprotected steel and cause pitting. Avoid the problem of pitting by using only pH neutral (7.0) detergents and making sure all instruments placed in the autoclave are thoroughly rinsed before being put in the autoclave.
Pitting can also occur if dissimilar metals come in contact with each other in an ultrasonic cleaner or autoclave. Electrolysis from dissimilar metals touching in a solution (the steam in the autoclave acts as a conductive solution that allows electrolysis) transfers metal molecules from one instrument to the other, leaving pits in one instrument. Avoid having any instruments touching during autoclaving, cleaning or storage to eliminate pitting.
True rust on a quality stainless steel instrument is very rare. Rusting can be caused by the chromium oxide layer on the instrument coming in contact with very caustic chemicals over a long period of time.
Stainless steel may rust if the surface has not been passivated (processed to create a thin oxidation layer) or finished properly. Old instruments with carbon, chrome, and nickel plating can rust when the plating wears off exposing the steel underneath. What is often thought to be rust is actually mineral deposits resulting from improper cleaning or autoclaving procedures. Rubbing the instrument with a pencil eraser will remove mineral deposits but will not remove rust. Back to Top
Lubrication is the most important action you can take to extend the life of your instruments. The use of a surgical instrument lubricant, known as "milk" because of the white coloring caused by the emulsion in water, will prevent spotting from mineral deposits left behind by water after cleaning. Corrosion can also be prevented by the application of lubricant. Corrosion starts in the pores of the metal and is often related to improper cleaning. With proper handling and lubrication the surface of your stainless steel instruments will develop a thin hard coating, similar to oxidation, which will help prevent damage from corrosion. Known as the passivation layer, it makes the instrument more resistant to staining and rusting.
In addition to stain and corrosion protection, lubrication reduces friction at the joints, keeping the action of the instrument light, delicate and smooth and extending the life of the instrument by reducing wear. Back to Top
When storing instruments it is recommended that they never be stacked or piled together. This may cause physical or other damage to instruments, including even the larger ones. Instrument edges, points and finish are best protected by individually laying them in a storage container. It is most important that this area be a dry cabinet or drawer. The use of drying agents such as silica packets or even an open box of baking powder will aid in controlling moisture.
When storing instruments re-using the tip guard included with many instruments may reduce damage to instrument tips. As a reminder, do not autoclave an instrument with the tip guard on the instrument. The tip guard might retain moisture that could cause staining, or the tip may not be sufficiently sterilized.
The use of disposable instrument pouches is an excellent way to store and autoclave instruments. The pouches keep the instruments from touching each other and the sterilized indicator strip will insure the instruments are ready for use after autoclaving.
Make sure all instruments are properly cleaned, sterilized, and lubricated before storing. This is the best way to prevent water spotting, staining, and more serious damage to instruments. Back to Top