Both surgeons and metallurgy industry technicians use stainless steel tools. However, while most people believe that these differ in shape and function only, the truth is very different — surgical steel and stainless steel aren’t the same things.

Since most people confuse one with the other, we’ll discuss the differences between surgical stainless steel vs general-use stainless steel. We’ll dive deeper into what those differences are exactly and how the chemical composition of stainless steel affects its corrosion resistance.

Surgical Steel vs. Stainless Steel

Unfortunately, the lack of official definitions and clarifications has led to a misconception that surgical steel and stainless steel are the same — they’re not. While it’s true that both are corrosion-resistant, surgical steel is a type of stainless steel suitable for medical applications. In other words, all surgical steel is stainless steel, but not all stainless steel is surgical steel.

So, to better understand the difference between the two, we have to discuss what exactly stainless steel is. Steel is a metal alloy made of iron, which has horrible mechanical properties — it’s soft and corrodes rapidly — with added carbon, which improves its strength and fracture resistance.

However, adding carbon does nothing to stop corrosion, so other chemical elements are added to enrich the properties of steel. This includes chromium, which bonds with low-carbon steel and reacts with oxygen from the atmosphere to form a stable oxide bond that helps prevent staining and further oxidation, creating stainless steel.

However, stainless steel also includes other elements, like molybdenum and nickel, all of which lend their desirable properties to the steel they enrich. This is what the biggest differences come down to, since there’s a variety of grades of stainless steel that vary based on their chemical composition.

Is Surgical Steel the Same as Stainless Steel?

If medical-grade stainless steel ever had a formal definition, it would sound something like this: surgical steel is a form of stainless steel with exceptionally high levels of corrosion resistance. This is achieved by adding more chromium to the steel, which enhances its corrosion resistance properties, making it suitable for biomedical applications and surgical instruments.

Surgical stainless steel typically contains anywhere between 18% and 20% Chromium but no less than 13% and usually not more than 30%. For comparison, typical general-use stainless steel only has 10.5% Chromium content. Surgical steel also contains higher contents of molybdenum, which reduces corrosion.

Adding nickel to the austenitic stainless steel reduces the steel’s brittleness while also providing much stronger high-temperature strength than other steel alloys. However, it also negatively affects the hypoallergenic properties of stainless steel since it can trigger an immune response within the patient’s body, leading to infections.

Thus, most surgical steel that’s used to make surgical instruments and other medicinal equipment contains nickel. However, orthopedic implants, bone fixtures, dental implants, etc., are exclusively made of stainless steel types that contain very little nickel — if any.

The effects of nickel are best seen with jewelry. Jewelers often mix pure gold with copper, nickel, zinc, and other metals to increase the base metal’s tensile strength. Typical 14-carat gold contains between 58.3% and 58.5% gold and approximately 8% nickel — which is enough to cause allergic contact dermatitis in people with sensitive skin.

That’s why stainless steel that’s designed for implants can’t contain nickel. In fact, there are great non-metal options now, which now include medical-grade plastics.

Key Differences

Designation	Chemical Composition (Major elements only)
SAE	EN	C, ≤	Mn, ≤	P, ≤	S, ≤	Si, ≤	Cr	Ni	Mo	N, ≤	Other Elements
304	1.4301	0.08	2.00	0.045	0.03	1	18.0-20.0	8.0-11.0	-	-	-
316	1.4401	0.08	2.00	0.045	0.03	1	16.0-18.0	10.0-14.0	2.00-3.00	-	-
316L	1.4404	0.03	2.00	0.045	0.03	1	16.0-18.0	10.0-14.0	2.00-3.00	-	-
420	1.4021	0.15, ≥	1.00	0.04	0.03	1	12.0-14.0	-	-	-	-
440B	1.4112	0.75-0.95	1.00	0.04	0.03	1	16.0-18.0	-	≤0.75	-	-
440C	1.4125	0.95-1.20	1.00	0.04	0.03	1	16.0-18.0	-	≤0.75	-	-
630	1.4542	0.07	1	0.04	0.03	1	15.5-17.5	3.0-5.0	-	-	3.0-5.0 Cu; 0.15-0.45 Nb

 

Other Properties

Surgical steel has numerous properties which make it suitable for biomedical applications:

Doesn’t Stain

Surgical steel is a form of stainless steel, and as the name implies, they belong to a group of steels that are less likely to rust. That doesn’t mean that they don’t stain, rust, or degrade over time, including surgical steel. However, due to higher chromium content, surgical steel is a lot more durable compared to stainless steel. Adequate cleaning will prolong the lifespan of your surgical equipment by reducing spotting and pitting.

Doesn’t Rust

As previously explained, the chromium within the steel produces an oxide bond that coats the surgical steel with a thin oxide film. This film prevents further oxidation, and unlike most steel types, which oxidize when scratched, surgical steel doesn’t oxidize since the oxidization layer heals, further protecting the steel.

Self-Healing

The self-healing qualities of surgical steel are essential for medical applications. This is especially true for steels with higher chromium content, as these tend to be somewhat harder compared to those with lower concentrations of chromium.

Micro-cracks in the surface of steel can serve as a bacterial haven. Any fissures using surgical steel will seal themselves before germs can establish a foothold. This, together with ongoing sterilization, aids in maintaining surgical steel in a sanitary state for use in medicine.

Magnetic Properties

Several surgical steel grades are magnetic. The chemical makeup of the steel dictates whether or not it is magnetic. Surgical steel becomes magnetic when ferrite is present in high quantities. Additionally, due to the high iron content, heat-treated surgical steel that has been added for increased durability is frequently magnetic.

But surgical steel containing nickel and chromium in particularly high concentrations—around 30%—is more likely to be non-magnetic.

Which Stainless Steel Grade is Best Used for Medical Instruments?

Whether a particular grade of steel is suitable for equipment or details greatly depends on the chemical composition of the steel, and everything previously mentioned applies. If you want to learn more about surgical steel and different stainless steel grades used for biomedical purposes, please refer to our guide called Surgical Steel: What is it?

Summary

After thoroughly discussing the main differences between stainless and surgical steel, we can conclude that surgical steel owes its fantastic properties to the higher chromium concentration and generally lower nickel concentrations compared to typical stainless steel.

To learn more about stainless and surgical steel, please visit Reid Supply — one of North America’s largest parts and components suppliers — and refer to their Engineer Resource Guides or some of their guides on Surgical and Stainless steel.