Choosing Between SUS304 And SUS316L For Machined Parts
Where the extra cost of SUS316L is justified, and where SUS304 is the sensible answer.
The Practical Difference
SUS316L contains molybdenum, which makes it markedly more resistant to chlorides. That covers coastal air, de-icing salt, and most cleaning chemicals. SUS304 handles ordinary indoor and sheltered outdoor conditions perfectly well and costs less.
Threaded Stainless Fitting With Flange
How They Behave On The Machine
Both work-harden, which is why stainless parts are cut with dedicated tooling and different speeds from free-cutting steel. The low-carbon L grade is slightly gummier. In practice this affects cycle time and therefore price, not whether the part can be made.
- Expect a longer cycle than free-cutting steel
- Sharp tooling matters more than on carbon steel
- Interrupted cuts are harder on tool life
What Passivation Does And Does Not Do
Passivation removes free iron left on the surface by machining and lets the chromium oxide layer reform evenly. It is not a coating and it adds no thickness worth measuring. It will not rescue the wrong grade in the wrong environment.
A Simple Decision Rule
If the part will meet salt, chlorides or repeated chemical cleaning, specify SUS316L. If it lives in a dry cabinet, SUS304 is enough. If the part is handled daily, choose stainless over plated steel regardless of grade, because plating wears through at exactly the points fingers touch.
What To Put On The Drawing
Name the grade, state whether certificates are required, and say whether passivation is needed. Those three lines remove most of the back and forth from a stainless enquiry.
More Guides
Why Slender Parts Are Machined On Swiss-Type Lathes
What a guide bushing actually does, and why a long thin shaft behaves differently on a sliding-head lathe.
What To Check Before Importing Machined Parts From China
How to separate a machine shop from a trading company, and how to structure a first order so it proves something.
Reader Questions
Do you keep both grades in stock?
SUS304 and SUS316L are both grades we run on current production parts. Material is bought per order against the drawing, with certificates when they are requested.
Is SUS316L always better?
It is more corrosion resistant, not better in every sense. It costs more and machines slower. For a part inside a dry enclosure, paying for it buys nothing.
Can you passivate?
Through a qualified local processor, managed by us, with the certificate included in the shipment.
Not Sure Which Grade Your Part Needs
Describe where the part lives and what cleans it. We will recommend a grade and tell you what the difference costs on your quantity.