Avoiding Rust on 410 Stainless Steel

B

BILLH007

#1
Some medical one time use surgical devices use 410 stainless vs. 300 series stainless. Using 410 is important for tensile strength and hardness compared to 304.

My client is tied up in knots because a few cosmetic blemishes of apparent surface rust discolorations on their product.

The steel went through cleaning, brushing, alkalia soak and passivating process with Nitric (4) ASTM treatment. After sitting on shelf less than 2 weeks, it started to develop discoloration spots with rust like color. Not streaky but like tiny drops or sprinkles.

Since the device will not be used for surgery more than 1 hour/not implantable and with iron stain only on surface, I can't really see what the screaming is about.

In designs, has anyone else seen this in a device and was there a resolving action?
 
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Golfman25

Trusted Information Resource
#2
Might be worth a try to pack them in rust preventative paper. See what happens. You may need to oil them, but that could cause some usage issues. Good luck.
 

Big Jim

Super Moderator
#3
Some medical one time use surgical devicess use 410 stainless vs. 300 series stainless. Using 410 is important for tensile strength and hardness compared to 304.

My client is tied up in knots because a few cosmetic blemishes of apparent surface rust discolorations on their product.

Tje steel went through cleaning, brushing, alkalia soak and passivating process with Nitric (4) ASTM treament. Afte sitting on shelf less than 2 week stated to develop discoloration spots with rust like color. Not streaky but like tiny drops or sprinkles.

Since device will not be ued for surgery more thn 1 hour/not implantable and with iron stain only on surface I can't realy see what the screaming is about.


In Designs Has anyone else seen this in a device and was there a resolving action?
It sounds like something didn't happen properly with the passivation process. That's what passivation is supposed to do, remove any surface iron that can rust. You may want to get some samples and take them to whoever did the passivation to see what went wrong.
 

Jim Wynne

Staff member
Admin
#6
I agree with Jim that the passivation process is a suspect. Passivation may look simple - provided good care and practices are observed. The following write up is quite informative and includes some 'dos and don'ts': How To Passivate Stainless Steel Parts
That's a good article. I've attached another one that also discusses testing for compliant passivation.
 

Attachments

A

arios

#7
One basic compliance reminder, If you are planning to change, introduce or bring new chemical agents to your process may I advice you to communicate these to your customer in advance. Since it is for a medical device application the change may have a potential impact on bio compatibility (depending on how invasive the device is) and may also require validation.

Take a look at 21.CFR 820.50(b) and 21.820.70(b) and (h) :read:

http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=820
 

Wes Bucey

Quite Involved in Discussions
#8
From a different angle:
The spotty nature of the discoloration usually indicates free iron deposits on the surface of the metal. Does the metal forming process (machining? turning?) use HSS tooling versus carbide or ceramic tooling? The tool, itself, can embed iron deposits in the surface of the part to an extent normal cleaning and passivating do not remove them. Has this been a continuing problem since the part began to be produced or has something new in the process occurred just before this condition began to be observed? In over ten years of running all grades of SS through our machining, we never encountered a problem with coolant-borne contamination which could not be resolved by close attention to cleaning before passivating, but learned to use only carbide or ceramic tooling to eliminate tooling caused contamination.

Since the issue is important enough to cause consternation, why not spend a few dollars and take the products exhibiting this condition to a metallurgical lab to get a definitive readout of exactly what the discoloration is. With that info in hand, the metallurgist can most likely suggest the cause and subsequent cure.
(The article Harry provided mentions an author from Carpenter. I bought all my stainless from them and found them to be a good source for metallugical advice.)

FWIW:
Based on the information provided in this thread, I agree the most likely cause is something to do with the passivation process. My suspicions lean toward contaminated acid bath. Likely cause of contamination is inadequate cleaning of parts (yours or someone else's) before passivating. Has the racking procedure changed? Is there good circulation of acid bath around every surface of the part?

There is an outside chance the particular batch of steel may not meet the original composition standard for 410 stainless, thus making a standard acid bath and temperature inadequate.
 

Michael Malis

Quite Involved in Discussions
#9
I am in agreement with all above, however there is another angle.

410 SS is less corrosion resistant than the austenitic grades and "must be hardened for maximum heat and corrosion resistance. Due to the hardening capabilities of this steel, other properties and the resulting performance of this material are somewhat compromised."

This does not sound like material that should be use as a surgical blade...
How about 316 SS?
 
B

BILLH007

#10
MM: Just to clarify the 410 SS is not being used as blade material.
If I was designing this product it would be with 304 SS for this application but someone thought better many years ago.
Since I am not in a position to redesign (for now). I would like to avoid going down that road (for now).
 
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