It's forever! If you make a part from it, it will shine with a little polishing.....and no need to paint it!
Hard on cutting tools and tricky to machine. Some alloys, like 304 and 316 polish up nice. Specialized high strength alloys are available for critical fasteners but they are more expensive, harder to machine and may be slightly magnetic. Magnetic stainless steel has higher proportion of iron in the mix. While it will not rust away in anyone's life time it will, with time and exposure, haze over.
In metalurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is a steel alloy with a minimum of 10.5% chromium content by mass. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required. Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface.... You trying to fix some trim? or whats up?
The five families. Austenitic, ferritic, martensitic, duplex and precipitation hardening stainless steel. For shiny bits on your car you'll be using austenitic. Google is your freind for its properties.
The 300 series alloys will have a very light magnetic attraction, but it won't snap to it like ferrous steel. I've been working with stainless steel for so long, it does machine pretty easily with the proper speeds and feeds, chip load, etc. 300 series is not heat treatable, 400 series is. Alloys like 410 and 420 used to be popular for molds. I see a lot of 416 used in commercial and military electrical motor housings. This alloy machines very well. I'd stay alway from the PH (precipitation hardening) series for general fabrication. That gains its strength through heat treatment. Plus its not as available as anything in the 300 or 400 series.
There are 26 "Crucible Types" of stainless steel ranging from 302SS to 446SS. Some of it is pretty exotic and very expensive. Stuff we would never use in car applications but fascinating to read about. I read an article about jet engine exhaust manifolds fabricated from 321SS that were subjected to thousands of cherry red heat and cool cycles during testing with zero failures. Amazing stuff!
Not much like auto trim, but I used to use a lot of heavier stainless in the hog barn due to corrosion issues. If you have to drill it, I found zirconium nitride coated bits worked the best. I still keep a set beside the drill press because they keep their edge much longer than most bits.
We do quite a bit of stainless work in our shop, nothing exotic, but it's laying around so we've used it for almost everything over the years. Saves the bullshit of powder coating small items, and even if you don't polish it up ,it still looks OK. Have a HD 3 phase buffer for the fancier items.( I brought it home to keep the mess out of the shop, and do that near the bushes out in the driveway.) Way cheaper than chrome, which seems to rust up in two of three years anyway, and it's free. once you get setup for it stainless is a great way to go.
I use whatever is left over from paying-customer's jobs. So I have a lot of 416 and 303/304 rounds, some 302 sheet, plate and bar. Nastier than 303/304 but the price is right. Structurally as good as mild CRS or HRS.
Just make sure you don,t use 300 series fasteners for high tension aplications as they tend to stretch, always use ARP stainless fasteners if you need to tension them, IE exhaust manifold bolts etc. As others have said, hard to machine as 304 and 316 tend to work harden when machined, and use good quality tool steel taps for threading as the cheap ones will not last long .
I think most 18-8 (303/304 alloy) stainless fasteners have a tensile strength of 75ksi. Really not suitable for high strength applications. I had one run of parts for a customer that were cast 316, one of the worst things I have ever machined with all the hard spots in them. Even 303 will work harden, but I'll take that over CRS 1018 for general machining. The 316 castings, the only thing that held up were TiN coated 135* split point drills and TiN coated taps.
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