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303 stainless shafts never rusted before, now they do

Recently we found a serious rust on our stainless steel shaft 303. This shaft is inserted to the rubber and given heat treatment 260C. But the funny thing is, we always doing this also before but we didn't found any rust. Does different batch of this stainless steel can give different properties. If yes, what can we do to check it. Thanks a bunch

Hobbies - Batam, Riau, Indonesia

You are a person with a mighty strange hobby, Evita. If you would be a little more forthright about who you are and what you are making you could probably get more help.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Yes, there can be significant differences between lots from the same MFG and between MFG's. My nickel goes to the suffix letters are not the same. Most shops use 303 that has a suffix like Se and etc. They are loosely called free cutting SS. Most machine shops could not tell you what it was, i.e., it was "303 SS" when in reality it was 303Xx which is far from being the same.

James Watts
- Navarre, Florida

This is quite typical for 303 stainless steel, which is a high sulfur free machining grade. You may be having a sulfide problem and not a rusting problem at all. Sulfides will bloom to the surface when exposed to moisture and look very similar to rust. Try soaking the part in 10% NaOH overnight and see if it goes away. If it does go away it is sulfides, not rust.

There are a number of variations of 303 stainless steel. Standard 303 and especially 303S will give you these problems for sure with some lots.

lee kremer
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Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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Evita, do you use the same tools or technique on inserting the shaft as before. I have found quite similar problem when the austenitic stainless steel come in contact with carbon steel material. It was due to the oxide film damaged.

Ahmad Muchsin
- Palembang - Indonesia

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