316 SS

[eyschulman]

Worried about Chinese 316 SS. Would good quality SS attract a magnet? What does it mean about the product if there is attraction?

[roverhi]

304 is usually slightly magnetic. 316 is often very slightly magnetic. The metal gets magnetized as it's worked and/or sheared. If it's anywhere near as magnetic as mild steel, run away.

What are you going to use the SS for. If you want very corrosion resistant common SS get 316L instead of plain 316. There are grades of stainless (are they called Duplex??) that are very very corrosion resistant. There was a thread about it on this site in the past week. If I had to do it over again would use that or Titanium.

[roverhi]

Here's the thread on Duplex SS:
http://www.cruisersforum.com/forums/...gs-121004.html

[Celestialsailor]

On things like chainplates or other very important fittings, use good quality SS. The was a guy on a Fantasia 35, some years back that lost his mast due to a Chinese SS tang bolt that snapped.

[Andrew Troup]

Hmmm - 316L (low carbon) is a great choice for any component which will be welded, but the corrosion resistance in the unwelded condition is indistinguishable from 316.

For more info on the respective merits, refer
Alloy 316/316L Technical Information

Don't use too strong a magnet for testing 300 series stainless alloys like 316: for instance, a rare earth magnet will attract them quite strongly, especially if they have been work hardened (which, to a degree, bright round bar is, having been cold-drawn down to diameter).

An old-fashioned red-painted small horseshoe magnet provides about the right amount of muscle.

[rw58ph]

The difference between SS 316 and 316L is 316 is active and 316L is passive. Passive has a protective film to prevent corrosion and active does not. On the galvanic table, rated 1 to 100, 316 is 67 and passive is 76. However when 316L is welded the film is broken/destroyed. Since it’s the weld that tend to corrode there really is not a big difference.

SS requires it to breath oxygen, so its not recommend for fuel tanks. SS is great for water tanks as long as the water is not stagnant. Also do NOT paint SS. Mild steal is still my choice for fuel tanks as the galvanic rating is 31 and aluminum is 10 to 20. Anyway make sure you use the right metal for the application.

[Cheechako]

300 Series SS can all get fairly magnetic fom cold work. If the bar stock for instance is cold rolled as a final pass, it will be quite magnetic. If you solution heat treat it after it will not be magnetic at all.
316L vs 316 has nothing to do with passivation, the L means low carbon. It's a tighter tolerance on the carbon content. Either can be passivated to help refine/protect the surface.

[Celestialsailor]

Originally Posted by Cheechako

300 Series SS can all get fairly magnetic fom cold work. If the bar stock for instance is cold rolled as a final pass, it will be quite magnetic. If you solution heat treat it after it will not be magnetic at all.
316L vs 316 has nothing to do with passivation, the L means low carbon. It's a tighter tolerance on the carbon content. Either can be passivated to help refine/protect the surface.

...and to add to that...
"The difference between 316 and 316L stainless steel is that 316L has a .03 max carbon and is good for welding whereas 316 has a mid range level of carbon.
316 and 316L are austenitic alloys, meaning that these stainless steel products gain corrosion resistance from use of a nonmagnetic solid solution of ferric carbide or carbon in iron in the manufacturing process.
In addition to chromium and nickel, these alloys contain molybdenum, which also makes them more corrosion resistant. Even greater corrosion resistance is delivered by 317L, in which molybdenum content increases to 3 to 4% from the 2 to 3% found in 316 and 316L".

[Andrew Troup]

I'm on Cheechako's team as far as L (low carbon) being an entirely separate issue from the active/passive states

Passivation strengthens and stabilises the naturally forming surface changes which maintain the stainless character of stainless steels, whether they be standard (eg 316) or low carbon (eg 316L).

Particularly in the absence of artificial passivation, it is possible for a single piece of austenitic stainless steel to develop some areas which are active while the remainder stays passive. This is bad news because the active areas will be attacked by galvanic corrosion from the much larger passive areas on THE SAME PIECE OF METAL.

It's a striking example of 'enemy within the gates' syndrome.

This is why even 316 and 316L, which are both highly resistant to pitting, are not suitable for prolonged immersion in standing or sheltered salt or brackish water, where there is insufficient oxygen to maintain the passive layer indefinitely.

[Celestialsailor]

Originally Posted by Andrew Troup

This is why even 316 and 316L, which are both highly resistant to pitting, are not suitable for prolonged immersion in standing or sheltered salt or brackish water, where there is insufficient oxygen to maintain the passive layer indefinitely.

So right...I always cringe when I see a bob-stay plate immersed on a boat to hear the owner say..."Oh it's SS, not to worry".