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Surgical Stainless steel


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Greetings everyone, 

Its been some time for me to visit the forum. I have an interesting case for a job I was hired to do. 

The client requires forged surgical tools to be made. The only supply I have here is 316 stainless steel and I hope this is suitable for the project. 

My only concern is whether the antibacterial properties of the Stainless will change in the process of forging. Do you know if this is the case? 

If yes, what methods must be used after finishing a surgical scalpel for instance to return it to its non porous nature? 

Furthermore, which method is best to use for forging? A coal forge? or A gas forge? I believe it is the gas better but still I would like to hear your thoughts. 

Thank you for your time in advance.!!! 

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Thank  you for the quick reply Steve. Ok i will look for 440. Do you know though about its molecular structure and how it changes during forging? Specificly if it will be antibacterial after forging? How to polish it? 

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As far as I am aware, while stainless steel is often used for health care tools and surfaces, it is NOT inherently anti-bacterial, before or after forging.  It's surface is relatively inert due to the chromium oxide coatings that develop, limiting rusting, but while that surface can be easily cleaned it does not prevent organic growth like silver and copper are reported to do.  

What you may be referring to is the problem that some stainless steels exhibit once forged; where they lose their chromium oxide layer due to the excessive heat.  If I were making surgical instruments I would bring the surface to a high polish with successively fine abrasives, then investigate "passivation" (an acid based electropolishing operation).

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Agreed; stainless steel is not inherently antibacterial, but once polished and passivated, it is very easy to sterilize.

4 hours ago, santisandreas said:

Do you know though about its molecular structure and how it changes during forging?

Strictly speaking, steel doesn't have a molecular structure, as it is an alloy, not a compound. However, there's some good information about the metallurgy of 440 stainless steel here: https://matmatch.com/learn/material/440c-stainless-steel

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Chrome plating is used on surgical instruments, but (A) can't be used on the blade of a scalpel (as it interferes with sharpening) and (B) involves some pretty seriously nasty chemicals and processes that are best left to the professionals.

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I believe India and Pakistan produce most of the small surgical tools such as hemostats and forceps and such. If one looks at them they look hand forged or at least hand finished from stain-less. I think there is a standard as to what alloys are used. 
now things like scalpels use replaceable blades, tho some look like roast carving knives…

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I have attempted today to derust some screws I had Lying around with Hydrochloric Acid and then quench them into a Soda solution with water to neutralize the acid. This leaves a sort of grey finish. I wiped it and then left it as such. But I am worried that if they are not coated with paint or atleast oil they will begin to rust very fast. 

Does this apply to Stainless steel as well? 

In the case of stainless what must I do after the Passivation procedure to protect the piece from rust etc...?

 

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Passivating stainless steel exposes more chrome on the surface of the steel. The chrome reacts very quickly with oxygen in the air to form a protective layer preventing the iron from oxidation. You can polish it up after passivation, just don’t use any buffing material that was used on regular steel previously, it will basically negate the passivation process by depositing iron back on the surface. (All, if I’ve missed anything here, please add more information or corrections…) I personally have never neutralized a stainless steel part after passivation, just rinsed really well. I can’t see it hurting anything and could help…

Keep it fun, 

David

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The passivation process helps protects the piece from rust.  It removes iron from the surface of the piece and allows the chromium oxide layer to form.  Although it is not a guarantee that rust cannot form, it significantly reduces the chance of rusting.  It is stain-less, not stain-free after all.

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I personally wouldn't use HCl.  It might be ok, but one of the problems that occurs in stainless steel is stress corrosion cracking.  The presence of chlorides can make this worse.  For small blades and a single passivation cycle it might not matter at all.  I usually see it with tertiary or quaternary amine chlorides being transported in stainless tanks followed by a substandard washing and drying afterwards.

You can dilute most common acids easily using water, so saying one is stronger than another doesn't really mean anything unless you know the concentrations.  Just remember to add the acid to the water, not the other way around to reduce the risk of getting splashed.

If you're curious if it will work for you then just test a small piece to see how it reacts.  Remember, if you want stainless steel to retain its corrosion resistance never use abrasives, wire wheels, buffing wheels, etc. that were previously used for non-stainless steel.

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We use citric acid at work to passivate stainless (in food and beverage so everything is stainless) very easy to find as it is a common food ingredient. We buy big bags of it but I believe small quantities can be had locally from your favorite bulk kitchen type store. We mix to about a 10% strength. Polish first, then passivate, then rinse with water. 

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