A Primer on Surgical Stainless Steel
Sponsored by:
LEARNING OBJECTIVES:
1. Present background information about surgical stainless steel.
CIS
2. Explain the three major types of stainless steel and discuss common types of corrosion.
3. Describe the mechanical, magnetic, and cryogenic characteristics of stainless steel.
4. Review steps in the fabrication of stainless steel instruments and note important
material selection concerns.
5. Summarize concerns important in caring for stainless steel instruments.
CIS Self-Study
Lesson Plan
LESSON NO. CIS 215
CRCST
(Instrument Continuing Education-ICE)
Lesson Author
Yaffa Raz, RN, BA
Central Service Sterile
Distribution Manager
Lady Davis Carmel
Medical Center
Haifa, Israel
Instrument Continuing Education (ICE) lessons
provide members with ongoing education in the
complex and ever-changing area of surgical instrument care and handling. These lessons are designed
for CIS technicians, but can be of value to any CRCST
technician who works with surgical instrumentation.
You can use these lessons as an in-service with
your staff, or visit www.iahcsmm.org for online
grading at a nominal fee: $5 per lesson, or
bundled packages of 6 lessons for $25 (save $5)
or 12 lessons for $50 (save $10).
Each lesson plan graded online with a passing score
of 70% or higher is worth one point (contact hour).
You can use these points toward either your recertification of CRCST (12 points) or CIS (6 points).
Mailed submissions to IAHCSMM will not be
graded and will not be granted a point value
(paper/pencil grading of the ICE Lesson Plans
is not available through IAHCSMM or Purdue
University; IAHCSMM accepts only online
subscriptions).
Surgical instruments are manufactured in response to the need for an ever-increasing variety of
devices required by surgeons. Designs are interpreted by bioengineers, refined by instrument
makers, and adjusted to address constraints imposed by the materials used, along with
their costs and fabrication methods. Surgical instrument manufacturing is a tradition passed
through generations and involves time-consuming manual labor. Choosing the right instrument
material is an important issue for the manufacturer, and reprocessing surgical instruments
requires special considerations for Certified Instrument Specialist (CIS) technicians. Stainless
steel is used to construct many instruments, and those with background information about
this material will understand the “whys behind the hows” of many processing requirements.
Stainless steel is the most common alloy
(a mixture or solid solution of two or more
metals) used for surgical instruments. Alloys are
used for manufacturing surgical instruments
because they have specific properties that
make them more useful than pure metals.
There are several types of stainless steel alloys
and understanding their characteristics is
critical to determine how they can be used.
Historical Overview
Stainless Steel and Corrosion
There are three main types of stainless steel
• Austenitic – Austenitic steels are alloys
containing chromium and nickel (and
sometimes manganese and nitrogen). The
most familiar stainless steel is Type 304,
sometimes called T304. The high chromium
content of austenitic stainless steel enables
it to resist oxidation (scaling) and corrosion,
and makes it more malleable and workable.
Stainless steel was introduced commercially by
Brearley of Sheffield in 1912 and was used for
rifling (spiral grooves) in gun barrels. The alloy
contained 13% chromium, 1% nickel and
0.2% carbon, and would now be classified
as a “low” alloy stainless steel. Shortly
thereafter (1916), Mayer and Company was
commissioned to make otolaryngological
instruments (those used for ear, nose, throat,
and head/neck procedures), which appear to
be the first non-rusting steel instruments.
• Ferritic – Ferritic steels contain ferrite, iron
and chromium. They are less ductile (able to
be molded or shaped) than austenitic steels
and cannot be hardened by heat.
Despite corrosion resistance, strength
and suitability for thermal hardening and
tempering, “low” alloy stainless steel provides
an inferior cutting edge and requires constant
sharpening. Also, when low-grade stainless
steel is in temporary contact with human and
other fluids, it can corrode. This promoted the
development of “high” alloy (Martensitic and
Austenitic) steels that are extremely inert within
the body and can also be used to manufacture
certain implants.
Resistance to corrosion is the primary reason
stainless steels are used to manufacture medical
instruments. However, they may corrode, and
care is needed to select a grade suitable for
a specific application. Corrosion can cause
a variety of problems, including perforation
(pitting), loss of strength, degradation of
appearance, and deposits of scale or rust that
can contaminate the material being handled.
• Martensitic – Martensitic steels contain
a small amount of carbon and they can
be tempered, hardened and sharpened.
Martensite gives steel great hardness, but it
also reduces its toughness and makes the
steel brittle. This type of stainless steel is used
when sharp cutting edges are required.
Some types of stainless steel corrosion are
caused by users:
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CIS Self-Study Lesson Plan
• General corrosion – This is a uniform
removal of material and is usually caused by
a reaction to strong acid.
• Pitting corrosion – Under certain
conditions, especially those involving high
concentrations of chlorides, moderately
high temperatures, and intensified by a
low pH, localized corrosion that creates
perforations can occur. Once a pit forms,
it often continues to grow—even if the
surrounding steel is still untouched.
ability of the material to resist distortion over
a long term).
Pitting can continue even if surrounding
steel is untouched.
• Crevice corrosion – The corrosion resistance
of stainless steel depends on a protective
oxide layer on its surface; however, this
sometimes breaks down (often when
instruments are improperly designed).
Crevice corrosion is a severe form of
pitting that occurs at significantly lower
temperatures than pitting corrosion.
• Friction – Friction (rubbing of one object’s
surface against that of another) occurs in
articulated surgical instruments. Material
fatigue can occur resulting in metal wear,
cracks and breakage. Proper instrument
lubrication may reduce friction.
• Stress corrosion – Cracking can occur from
the combined influence of tensile stress
(that caused by stretching or straining the
metal) and a corrosive environment. The
most damaging environment is a solution of
chlorides and high levels of salts in water.
Corrosion is accelerated because of the
pressure applied.
• Sulphide stress corrosion cracking (SSC)
— Stainless steel alloys can react with
hydrogen sulfide when in contact with high
sulfur materials and form metal sulfides and
elementary atomic hydrogen. These, in turn,
can diffuse into the stainless steel matrix
and cause cracking.
High stress and poor lubrication can damage
instruments.
Galling resistance is an important property of
stainless steel instruments, especially those
made from two parts that are in relative motion
(like scissors). When in use under sufficient
load, an instrument’s protective oxide layer
is disrupted which permits metal-to-metal
contact. Under high stress and poor lubrication
conditions, stronger bonds may form over a
large surface area and create galling symptoms,
including fractures, alignment problems,
scratches, and metal particles.
Magnetic permeability relates to the ability of
a material to carry magnetism, indicated by
the degree to which it is attracted to a magnet.
All stainless steels—except the austenitic
group—are strongly attracted to a magnet.
Some procedures such as magnetic resonance
imaging (MRI) interventions require nonmagnetic surgical instruments, so material
selection for these interventions is crucial.
Austenitic stainless steels also possess a unique
combination of properties that makes them
useful at cryogenic (very low) temperatures.
These steels have low temperature tensile
strengths that reduce strains and ruptures,
while their toughness is only slightly degraded.
This property is useful for surgical interventions
that use low-temperature action on the tissue
being dissected and for the forging stage of
instrument manufacturing.
Tensile stress and a corrosive environment
can create cracks.
Instrument Fabrication
Contact corrosion is a third example of a
manufacturing defect. It occurs when small
particles of foreign matter (especially carbon
steel) remain on a stainless steel surface. They
are likely to be quickly corroded away, but in
severe cases a pit may also form in the stainless
steel.
A major advantage of stainless steels and the
austenitic grades, in particular, is their ability to
be fabricated by all the standard manufacturing
techniques. The common austenitic grades
can be folded, bent, cold- and hot-forged,
deep drawn, spun, and roll-formed. The first
(forming) stage of instrument manufacture
may be done manually or mechanically.
Other types of corrosion may result from
manufacturing defects. For example,
intergranular corrosion is a form of relatively
rapid and localized corrosion. It is caused
by a defect in the stainless steel that allows
carbide particles to form. These deplete the
surrounding metal of chromium and reduce its
corrosion resistance.
Stainless steel has special mechanical
features. For example, it is strong and hard
so it can absorb energy without breaking. As
noted above, austenitic stainless steels are
exceptionally ductile.
Corrosion is an electrochemical process
that involves the flow of electric current,
and galvanic corrosion can occur from the
contact of dissimilar metals in an electrolyte
(a substance capable of conducting electric
current). This can be prevented by avoiding
mixed metal fabrications or by coating or
insulation.
Stainless steels have a high temperature
resistance. The high chromium content that
is so beneficial to the wet corrosion resistance
of these metals also contributes to their
high temperature strength and resistance to
scaling at elevated temperatures. The high
temperature strength of materials is generally
expressed in terms of “creep strength” (the
Characteristics of Stainless Steel
The weld ability of various grades of stainless
steels varies considerably. Nearly all can be
welded, and the austenitic grades are some of
the most readily welded of all metals. Examples
of welded instruments include Frazier suction
tips, Deaver retractors with formed handles,
and some orthopedic reamers. Inspection of all
welded points is essential to ensure the weld
is intact to prevent instrument failure during a
surgical procedure.
During the manufacturing process, stainless
steels are often heat-treated by methods that
depend upon the type of stainless steel and the
reason for the treatment. Annealing (to make
IAHCSMM
CIS Self-Study Lesson Plan
the stainless steel less brittle), hardening and
stress-relieving restore desirable features such
as corrosion resistance and ductility to metal
that were altered by fabrication. Note: while
austenitic stainless steels cannot be hardened
by thermal treatments, they do harden rapidly
by cooling to sub-zero temperatures.
The desirable corrosion-resistant surfaces of
stainless steel surgical instruments can only
be achieved if proper cleaning and finishing
operations are carried out after the fabrication
process is completed. The presence of any iron,
cast iron, mild steel, carbon steel, or low alloy
steel particles on the surface of stainless steel
will promote pitting corrosion at the points
where the “free” iron and stainless steel
meet. This potentially serious (and certainly
unsightly) problem most often occurs from
the contamination caused by scraping the
instrument with carbon steel tools or fixtures,
or from grinding and polishing tools.
The author wishes to acknowledge and thank
Zamal Jackobson, Aesculap, Israel, for use of
the lesson photos.
Instrument Care
References
Proper care and handling is essential for the
satisfactory performance of surgical instruments.
Water used for reprocessing is one of the most
important concerns in preventing instrument
damage. Natural water contains different kinds
of salts that, at higher temperatures, are not
soluble in water and tend to form a hard scale.
Tap (treated) water may contain chlorides that
Kirkup, J. From flint to stainless steel: observations
on surgical instrument composition. Annals of
the Royal College of Surgeons of England, v. 75,
365-374. 1993.
Lesson Author
Yaffa Raz, RN, BA
Central Service Sterile Distribution
Manager
Lady Davis Carmel Medical Center
Proper material selection is critical for the most
cost-effective instruments. The material must
perform as intended, and it must also be one
that can be fabricated economically.
Long, slender instruments, such as drivers
or arthroscopic instruments, will likely have
high demands placed on them. Increased
strength and toughness are necessary, and
some alloys provide the required hardness and
resulting edge retention. Cutting and shaping
instruments, such as shavers and samplers
(biopsy punches/forceps or rongeurs), require
Pagounis, E. and Lindroos, V. Processing and
Properties of Particulate Reinforced Steel Matrix
Composites. Materials Science & Engineering,
246, No. 1-2, pp.221-234, 1998.
CIS Self-Study Lesson Plans
Material Selection for Surgical
Instruments
Some instruments, such as trocars, that are not
subjected to high stress or loads, and are not
used for cutting or shaping, can be made from
a basic stainless steel. Many newer instruments,
however, require that the selected material
provide strength and wear resistance.
Technical Handbook of Stainless Steels. The Atlas
Specialty Metals, www.atlasmetals.com.au.
To learn more about instrument cleaning,
decontaminating and disinfecting procedures,
see the International Association of Healthcare
Central Service Materiel Management’s Central
Service Technical Manual, Seventh Edition, 2007
(Chapters 9 and 10).
Passivation creates a protective film on the
surface of steel. This process involves the
removal of free iron by immersing the steel
in an oxidant such as nitric acid or citric acid
solution.
Historically, enhanced-strength stainless steel
(type 304) has been used for the tubular
components of dental and surgical instruments.
This alloy has worked well for instruments
designed for use in confined spaces; however,
it has some drawbacks that limit its usefulness.
These include loss of strength during welding
and poor edge retention, wear resistance and
galling resistance.
Endnote
a hard alloy with good edge retention. The
wear and galling resistance of some alloys best
ensure the smooth operation of parts that move
in relation to one another.
The pH of water used for reprocessing is an
important concern.
can cause serious corrosion. The pH level of
water is also a concern. Acid or base water may
influence the properties of cleaning agents, and
corrosion may result from instrument exposure
to acid or basic water. Therefore, a neutral pH
is recommended for cleaning and rinsing of
surgical instruments.
Conclusion
Modern stainless steel alloys allow the
manufacture of surgical instruments that can
ideally perform tasks required by surgeons;
however, these devices can be damaged if
they are not handled correctly. CIS technicians
who understand the basics of surgical steels
can apply this knowledge to help ensure that
processing procedures prolong rather than
decrease the useful life of the instruments for
which they are responsible.
Technical Editor
Carla McDermott, RN, ACE
Education Specialist
Morton Plant Mease Healthcare
Dunedin, FL
Series Writer/Editor
Jack D. Ninemeier, Ph.D.
Michigan State University
East Lansing, MI
Lesson Reviewer
Mary Olivera, MS, CRCST, CHL, FCS
Independent Consultant
Newburgh, NY
IAHCSMM is looking for volunteers to write or
contribute information for our CIS Self-Study
Lessons. Doing so is a great way to contribute
to your own professional development, to your
association, and to your Central Service peers.
Our team will provide guidelines and help you
with the lesson to assure it will be an enjoyable
process. For more information, please contact
Elizabeth Berrios (elizabeth@iahcsmm.org).
CHL
CIS Self-Study Lesson Plan Quiz
(Instrument Continuing Education-ICE)
Lesson No. CIS 215: A Primer on Surgical Stainless Steel
CIS
Questions (circle correct answer):
1.
“Low” alloy stainless steel ________
corrosion resistant:
a.is
CRCST
b. is not
2.
Which type of stainless steel should
be used when sharp cutting edges
are necessary?
a.Ferritic
b.Austenitic
c.Martensitic
d. Type 304
3.
Which is a severe form of
pitting corrosion?
a. General corrosion
b. Stress corrosion
c. Crevice corrosion
d. Sulfide stress corrosion cracking
4.
Which type of corrosion results from a manufacturing fault?
a. Stress corrosion
b. Galvanic corrosion
c. Crevice corrosion
d. Contact corrosion
5.
Which causes general corrosion
of instruments?
a. Use under high temperatures
b. A manufacturing design problem
c. Exposure to high levels of salt in water
d. Reaction to strong acid
11.Passivation:
6.
The ability of stainless steel to
resist oxidation depends upon its
________ content.
a.nickel
b.magnesium
c.nitrogen
d.chromium
7.
Which stainless steel is not strongly attracted to a magnet?
a.Austenitic
b.Ferritic
c.Martensitic
d. All stainless steels are attracted to magnets
8.
Which stainless steel is most useful at cryogenic temperatures?
a. makes stainless steel sharp
b. allows stainless steel to resist cracks
c. provides a protective film on stainless
steel surfaces
d. all of the above
a.Martensitic
b.Ferritic
c.Austenitic
d. No stainless steel performs well at cryogenic temperatures
9.
The process of annealing makes
stainless steel:
a.hard
b.sharp
c. erosion resistant
d. less brittle
a.gains
b.loses
13. Most new instruments are made from
basic stainless steel.
a.True
b.False
14. Which instruments require good
edge retention?
a.Trocars
b.Shavers
c.Samplers
d. “B” and “C” above
e. All the above
15. Corrosion may result from an instrument’s
exposure to ________ water.
10. The presence of low alloy steel particles on the surface of stainless steel
________ corrosion.
12. Type 304 stainless steel ________
strength during welding.
a.acid
b.base
c. both of the above
d. neither of the above
Sponsored by:
a.promotes
b.hinders
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