Stainless Steel Grades and Finishes for Surgical Instruments

Catalogues describe instruments as “surgical grade stainless steel”, “German steel”, “TC” or “satin finish”, often without saying what those terms mean. This guide explains the main material families used for reusable surgical instruments, the finishes you will see listed, and what tungsten carbide inserts are. It sticks to what standards, reference works and manufacturers’ own documents state. For the exact material of a specific instrument, the manufacturer’s technical file or material certificate is the authority.

Why “stainless” is not one material

Stainless steel is a family of iron alloys that contain chromium. The chromium forms a thin oxide film on the surface that protects the metal from corrosion. Carbon, nickel and other elements are added in different amounts, and the mix decides how hard, tough, springy or corrosion resistant the steel is.

A lesson plan from the Healthcare Sterile Processing Association (HSPA), adapted from material by Aesculap, puts it plainly: stainless steel is not truly stainless. How easily an instrument stains depends on its composition and on how it is cleaned and rinsed.

In the US system, grades are identified by three-digit numbers issued by the American Iron and Steel Institute (AISI). In Europe, the same steels are named under EN 10088 with a chemical designation (such as X46Cr13) and a material number (such as 1.4034). Catalogues may use either system.

The standards behind instrument steels

Two standards are widely referred to:

• ISO 7153-1:2016 (Surgical instruments, Materials, Part 1: Metals) specifies metals commonly used for standard surgical instruments, including those for general surgery, orthopaedics and dentistry. It groups steels by typical use. The choice of grade also depends on the design and manufacturing route.
• ASTM F899 (Standard Specification for Wrought Stainless Steels for Surgical Instruments) covers the chemistry of wrought stainless steels for instruments. It groups them into austenitic (Class 3), martensitic (Class 4), precipitation-hardening (Class 5) and ferritic (Class 6) steels.

Large manufacturers write these standards into their supplier requirements. KLS Martin’s published delivery terms, for example, require approved materials under DIN EN ISO 7153-1 and hardness values taken from the drawing or, where none are given, from that standard.

Martensitic stainless steel (400 series)

Martensitic stainless steels are the main material for instruments that must hold an edge or keep their shape under load: scissors, scalpels, osteotomes, needle holder jaws, and the jaws of many forceps and clamps.

Their key property is that they can be hardened. They contain roughly 12 to 17 percent chromium with enough carbon to form a hard martensitic structure when the steel is heated and quenched. The steel is then tempered to reduce brittleness. They are ferromagnetic, so a magnet will stick to them.

The trade-off is corrosion resistance. Martensitic grades resist corrosion less well than austenitic grades, which is why careful cleaning, drying and correct water quality matter so much in reprocessing.

Common examples:

Grade	What the sources say
AISI 410	General-purpose martensitic grade, carbon 0.15% maximum.
AISI 420	Carbon 0.15% minimum, for greater strength. Often used for surgical cutting instruments.
X46Cr13 (1.4034)	About 0.46% carbon and 13% chromium. Treated as equivalent to AISI 420C. Can reach up to 56 HRC. Surgical instruments are among its listed uses.
AISI 440 series	Higher carbon. 440C contains 0.95 to 1.20% carbon and is the hardest of the series. Also used for cutting instruments.

Wikipedia’s article on surgical stainless steel names 420 and 440 as the grades often used for surgical cutting instruments, because they combine high hardness with acceptable corrosion resistance. It also notes that their corrosion resistance is lower than that of 316.

Austenitic stainless steel (300 series)

Austenitic grades such as 316 contain chromium and nickel. They resist corrosion better than martensitic grades, but they cannot be hardened by heat treatment in the same way, so they are not used for cutting edges.

The HSPA lesson notes that the 300 series is generally used for non-cutting instruments and devices that need strength, such as heavy retractors.

Because they contain nickel, nickel sensitivity is sometimes raised for steels that contact the body. Wikipedia’s article on surgical stainless steel notes that nickel-free, nitrogen-strengthened austenitic alloys exist for this reason.

Other steels and metals

Precipitation-hardening steels such as 17-4 are listed by ASTM F899 as a separate class. Wikipedia names 17-4 among the common “surgical steels” and says it is used for general surgical tools.

Titanium is listed among the metals used for surgical instruments. In unalloyed form it is as strong as some steels but less dense, and it is non-magnetic. Some patterns, such as Mayo scissors, are sold in both stainless steel and titanium, with the stainless steel versions noticeably cheaper. On our database you can filter for instruments listed in titanium or for stainless steel instruments.

Tungsten carbide inserts

Tungsten carbide is a very hard compound of tungsten and carbon. For tools it is made as a cemented carbide: tungsten carbide powder is mixed with a metal binder, usually cobalt, and sintered. Its hardness is comparable to corundum and approaches that of diamond.

In instruments, tungsten carbide is normally used as an insert. A small carbide piece is fixed into the jaw of a needle holder or forceps, or along the cutting edge of scissors, while the rest of the instrument stays stainless steel. The aim is a working surface that wears more slowly. Wikipedia notes that needle holder jaws are often reinforced with tungsten carbide inserts. Wikipedia’s tungsten carbide article notes that carbide instruments for open surgery, such as scissors and forceps, cost much more than stainless steel versions and need delicate handling.

Many makers give carbide instruments gold-coloured finger rings or handles, and catalogue numbers or names often carry a “TC” mark. This is a trade convention, not a standard requirement, and a gold handle tells you nothing about the quality of the insert. Check the catalogue entry, which should state “tungsten carbide” explicitly. You can browse instruments available with tungsten carbide in our database, including patterns such as the Mayo-Hegar needle holder.

Surface finishes

The finish is the final surface condition of the instrument. The HSPA lesson describes three types:

• Highly polished (mirror or bright): the most common finish. It is shiny and reflects light.
• Satin (matt): a non-reflective surface, chosen to reduce glare under operating lights.
• Ebony (black): a black finish that removes glare and is used in laser surgery.

Whatever the look, the surface has to be sound. KLS Martin’s supplier terms require surfaces free of pores, cracks, grooves and burrs, with roughness no higher than Ra 0.5. Pits and crevices trap soil and are where corrosion tends to start.

Passivation

After grinding and polishing, stainless steel instruments are usually passivated. The treatment removes free iron and other particles left from manufacturing and helps the protective chromium oxide layer form. The HSPA lesson describes dipping instruments in nitric acid. The ASTM A967 specification also covers citric acid and electrochemical methods. Wikipedia notes that passivation greatly improves the corrosion resistance of all stainless steels. The oxide layer thickens with age, and protecting it is the basis of instrument care. Our overview of how to read a surgical instrument catalogue shows where these details usually appear in product listings.

Questions to ask a supplier

• Which steel grade is used for each part, under which standard (ISO 7153-1, ASTM F899, EN 10088)?
• Can you provide a material test certificate (for example EN 10204 type 3.1)?
• What hardness range is specified for the jaws or blades, and how is it tested?
• Are tungsten carbide inserts used, and can they be replaced or re-tipped?
• Which finish is applied, and is the instrument passivated?

If you need help finding manufacturers that work with a particular material, our Looking for a Manufacturer? page explains how to send a request.

Sources

• HSPA: Spry, C. and Aesculap Inc., “Processing and Care of Surgical Instruments”, CIS Self-Study Lesson Plan CIS 294, Process, Nov/Dec 2022
• ISO 7153-1:2016 Surgical instruments: Materials, Part 1: Metals (catalogue entry)
• ASTM F899-23: Standard Specification for Wrought Stainless Steels for Surgical Instruments
• KLS Martin Group: Technical terms of delivery of surgical instruments
• Wikipedia: Surgical stainless steel
• Wikipedia: Martensitic stainless steel
• Wikipedia: X46Cr13
• Wikipedia: Tungsten carbide
• Wikipedia: Titanium
• Wikipedia: Needle holder
• Wikipedia: Mayo scissors
• ASTM A967/A967M-25: Chemical Passivation Treatments for Stainless Steel Parts (scope via SNV)