304/316 Stainless Steel

Help me with some (possibly) misleading advertising material.

I’m thinking about buying some stainless steel mesh security/insect screens. There are basically two manufacturers here, one using 304 and one using 316 grade steel.

The 316 guys say “buy ours, they’re more rust resistant, particularly in coastal environments”.

My research suggests that to be correct, but I’m not in a coastal environment, so I don’t care.

The 304 guys say “buy ours, you only need 316 in coastal environments [agreed] and everywhere else 304 is better because it’s stronger”

My research suggests this is incorrect: that the physical characteristics of the two are near as dammit the same.

What say you?

You out there, Una?

Here is a Stainless Steel Selector Chart from a college texbook on material selection. It indicates that 316 vs. 304 is only for pitting resistance.

Now and then, in knife collecting magazines, we are reminded that stainless steel is not rustproof. It “stains less” than non-stainless steel. In Germany, it is often called “rostfrei,” which seems to promise more. Really hostile stuff, such as fish blood, will sometimes induce rust. I don’t know if acid rain, bird poop, or dog urine is nasty enough to do any harm.

Sorry, I can’t tell you the difference between 304 and 316.

I’m exercising my right to one bump. One of the dopers who knows this sort of stuff inside out has to be out there somewhere.

OK, I don’t have all of my engineering texts in front of me, but a quick look at Marks’ Standard Handbook for Mechanical Engineers would seem to indicate that 304 stainless is slightly stronger than 316 (85 ksi v. 80 ksi Ultimate Tensile Strength; 35 ksi v. 30 ksi Yield Strength). More importantly for your application, I think, is that 304 is slightly harder than 316 (Rockwell B80 v. B78). Generally, the harder the steel, the more difficult it is to cut it. Of course, this is all sort of generic data. These properties can be changed slightly depending on how the steel is processed.

Is there some kind of industry standard or testing standard for these types of screens? For example, are they required to meet a certain ASTM specification? A performance specification or test would be more meaningful than simply comparing the properties of the base material.

I won’t say that I know this stuff inside and out, but I have done a fair amount of work selecting steels.

Thanks all.

Both security screens meet the Australian Design Standard. I’m just trying to decide how to decide between them.

Oooh! Ooooh! Me! Me!

304 and 316 are both austenitic stainless steels, meaning that they are nominally non-magnetic. They offer good resistance against normal wet corrosion, but are vulnerable when contaminated by salt (actually all the halide ions cause problems, but chloride is the most commonly encountered.) Grade 316 contains molybdenum, which ups the resistance to chloride, but it can still be corroded by seawater in the right (wrong?) circumstances. Otherwise they are more or less interchangable.

If you’re not in a coastal enivronment, 304 will do and ought to be cheaper. From a strength point of view there’s practically nothing between them and both are fairly poor compared with even simple mild steels. Their strength and hardness vary somewhat depending upon the amount of strain-hardening they have been subjected to - the book figures can give a false impression.

From a machining view, 304 is easier to work with. Not that you are doing any of building, cutting, welding, bending, turning, milling etc.

From the purchasing point of view, I’ve bought thousands of pounds of each, 304 is more popular and cheaper.

[hijack]I am now… My web browsing here is very sporadic due to being increasingly sick, and “Una” doesn’t show up on a vanity search due to being 3 letters. I only do those once every week in any event. If anyone really wants to ask me a science/engineering question, or have me look it up in one of my books, please mail me. I’m happy to at least try to find an answer and make an effort, even if I don’t know off the top of my head.

However, there are scads and scads of smart, experienced, and knowledgeable people here that can help you out as well, if not quite a bit better, on science/engineering topics. The SDMB won’t miss me one bit when I go. Until someone asks about coal, I guess.

Sorry to hear you are ill, Una.