Stainless Steel Grades

[st@rk]

Looking mainly at fasteners and have bought A2 and A4 (catering quality I believe?) grade up until now, but looking at genuine Jubilee hose clips and they come in three grades: 18/8, 304 and 316.

Can anyone explain in simple terms the grading system for stainless?

Thanks!

 

[rlitman]

18/8, 304, and 316 are designations of steel alloys.
18/8 is essentially synonymous with 304. It is an austenitic stainless steel (generally non-magnetic), and is pretty general purpose go-to stainless.
316 has a higher chromium content than 304, and is considered marine grade. It is more rust resistant in corrosive environments.

What are you doing with these?

 

[st@rk]

They're for water hoses on a car.

The engine is subject to plenty salt on the roads and I want them to stay fresh as cheap fasteners corrode at a ridiculous rate here.

It also means that whenever I'm working on the car all the new fasteners come off easy and only take a quick rinse with parts cleaner and they're sparkling clean again rather than corrosion setting in and causing problems.

Another question - a lot of automotive bolts are grade 8.8 but some higher tensile bolts are 10.8. How would I compare stainless grades against these?

I think I need to do some reading on metal grades - anyone know of good books on the subject?

 

[bsaint]

316 will last longer than the car.

 

[racingtadpole]

Be wary of using stainless fasteners in critical applications like steering and suspension. Stainless has less iron in it which is why it doesnt rust, but removing the iron means it becomes more brittle.

Carol Smith's Engineer to Win and Build to Win books both discuss fasteners in detail. As does his Nuts, Bolts, Fasteners and Plumbing book.

 

[shocwav3]

Be wary of using stainless fasteners in critical applications like steering and suspension. Stainless has less iron in it which is why it doesnt rust, but removing the iron means it becomes more brittle.

Carol Smith's Engineer to Win and Build to Win books both discuss fasteners in detail. As does his Nuts, Bolts, Fasteners and Plumbing book.

Zinc coated grade 8's are my go to for critical applications, much tougher. .500 bolt has a tensile strength of something like 220,00 psi vs. stainless coming in around 125,000.

I think stainless hardware is used many times assuming they are stronger than alloyed steel, but its a common miss-conception. I do like them in corrosive environments like the OP is looking for.

 

[retrobuilder]

Stainless does not mean rust proof. If you see 400 series like 416 expect some oxide coloring and spotting. The higher chromium alloys makes it harder and stiffer to bend.

Low 300 series is generally suitable for many applications. Grades also vary in designation if cast, forged vs sheet/plate.

 

[welder4956]

There is some really good (and correct) info on stainless steels on the Nickel Development Institute website (www.nidi.org). 18-8, 304 and 316 are all "austenitic" steels, which means their microstructure is austenite and have excellent ductility. 316 has molybdenum added for pitting resistance and better elevated temperature mechanical properties. I would recommend 316 for bolting for your application (a.k.a. Grade B8M).

 

[theoldwizard1]

Be wary of using stainless fasteners in critical applications like steering and suspension. Stainless has less iron in it which is why it doesnt rust, but removing the iron means it becomes more brittle.

I don't think "brittle" is the proper term, but as shocwav3 pointed out, they have a much lower tensile strength.



It has been way to long since I have studied mechanic of materials, but isn't a brittle material one that fracture very close to its yield point (a very short amount of plastic deformation) ?

 

[st@rk]

racingtadpole - Thanks, I've bought Carol Smith's Nuts, Bolts, Fasteners and Plumbing book but only 1/4 way through it. Think I'll get the other two as they're very popular.

shocwav3 - when you say Grade 8's do you mean 8.0 (like typical 8.8's) or 0.8? As you mention .500's which I would take as you meaning 0.5 - is this Grade 5 and 10.8's being 'Grade 10' ? And retrobuilder mentions '400 series' and 416 - are these 0.400 & 0.416 so 'Grade 4' ???

I'm really confused as to the ratings and terminology - especially as some grades are listed as A2 and A4 etc rather than numerical figures.

I did wonder at the strength of stainless steel - I had heard it wasnt suitable for suspension etc so wanted to clue myself up more before replacing those types of fasteners.

 

[racingtadpole]

I don't think "brittle" is the proper term, but as shocwav3 pointed out, they have a much lower tensile strength.



It has been way to long since I have studied mechanic of materials, but isn't a brittle material one that fracture very close to its yield point (a very short amount of plastic deformation) ?

Does it show that Im not an engineer.. Everyone seems to know what Im jibbering on about though..

I believe the technically correct expression centres around ductility.
And the laymans term is along the lines of it'll break at the first decent pothole...

 

[racingtadpole]

racingtadpole - Thanks, I've bought Carol Smith's Nuts, Bolts, Fasteners and Plumbing book but only 1/4 way through it. Think I'll get the other two as they're very popular.

shocwav3 - when you say Grade 8's Grade 5 and 8 are imperial standard do you mean 8.0 (like typical 8.8'smetric standard) or 0.8? As you mention .500's 1/2" diameter which I would take as you meaning 0.5 - is this Grade 5 and 10.8's being 'Grade 10' ? And retrobuilder mentions '400 series' and 416 - are these 0.400 & 0.416 so 'Grade 4' ???The 300 and 400 series reffered to are alloy grades no direct reference to tensile strength

I'm really confused as to the ratings and terminology - especially as some grades are listed as A2 and A4 etc rather than numerical figures.

I did wonder at the strength of stainless steel - I had heard it wasnt suitable for suspension etc so wanted to clue myself up more before replacing those types of fasteners.

Clear as mud

 

[rlitman]

They're for water hoses on a car.

The engine is subject to plenty salt on the roads and I want them to stay fresh as cheap fasteners corrode at a ridiculous rate here.

304 is just fine around road salt. It will outlive anything else in the engine bay.
316 is unnecessary outside of a marine environment. Do you trailer a boat to the ocean on a weekly+ basis?

For hose clamps, you must look at the entire clamp. Many clamps will have a stainless saddle, but not a stainless screw or band, or whatever.
The good ones will say ALL 300 stainless or something to that effect. At Home Depot for example, you MUST pick through the hose clamp bin to get to the good ones. All the ones that are the same size are all the same price, but some are good, and some are ****.

I suggest you look at Breeze Constant Torque clamps. That's the very best.
The thermal expansion and contraction of heater hoses does not work well with ordinary hose clamps. That's why most vehicles now use spring clamps out of the factory. Hose clamps have a constant circumference. In order to accommodate for the hose expanding and contracting without leaking, they must be over tightened, which causes cold-flow and damage to the hose.
The Breeze clamps are spring loaded to keep a constant tension under thermal cycling, and they have an inner band that not only prevents extrusion of the hoses through the slots (which is a BIG problem with premium silicone hoses), but also guarantees 360 degree clamping (so there is no leakage under the saddle). There's a reason they're the choice for aircraft and commercial vehicles.

 

[shocwav3]

racingtadpole - Thanks, I've bought Carol Smith's Nuts, Bolts, Fasteners and Plumbing book but only 1/4 way through it. Think I'll get the other two as they're very popular.

shocwav3 - when you say Grade 8's do you mean 8.0 (like typical 8.8's) or 0.8? As you mention .500's which I would take as you meaning 0.5 - is this Grade 5 and 10.8's being 'Grade 10' ? And retrobuilder mentions '400 series' and 416 - are these 0.400 & 0.416 so 'Grade 4' ???

I'm really confused as to the ratings and terminology - especially as some grades are listed as A2 and A4 etc rather than numerical figures.

I did wonder at the strength of stainless steel - I had heard it wasnt suitable for suspension etc so wanted to clue myself up more before replacing those types of fasteners.

By .500 I meant a 1/2 bolt. Grade 2, 5 and 8 are ratings for hardware in the US, not to be confused with metric rating system.(8.8 in metric is more like grade 5 here in the US) Take a look at this link, it should clear it up a bit.

http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

4 series is a specific composition of stainless.

Ferrite, martensite, austenite, bainite are grain structures developed during different cooling stages of the heat treating process in steels which make up a lot of their characteristics, along with alloying elements....but I might be going off track a bit.

Take a look at the link above and it should give you a clear idea of the different fastener ratings and their applications.

 

[HDawg 440]

I'm a mechanical engineer by degree. I mostly work in electronic controls but I have actually looked into this in detail, since I have a weekend racer car and a daily driver here in Ohio.

I frequently use A2 stainless fasteners for exhaust parts, brackets, underbody panels, and similar. Basically, non-structural, low-stress stuff. I wouldn't use stainless hardware on any suspension or driveline parts. Or brake parts, with one exception: the screw or bolt that secures the brake rotor to the hub (it's just there to keep the rotor in place until you bolt it to the hub with the four, five, or six bolts or nuts that hold the wheel on).

Grade 8.8, 10.9, and 12.9 fasteners are used frequently for driveline and suspension parts, and for a reason. They're much stronger than stainless, so they can provide a higher clamping force for a given size of fastener. This lets the vehicle manufacturers shave weight out of the car by using a high-strength, low-weight fastener. Substitute a different grade of fastener at your own peril.

For when I want things to come apart later, I use Loctite Nickel Anti-seize (awesome stuff, by the way) along with a locking nut and/or washer. Then I will spray the external surfaces of the fasteners with either Transtar Amber, or CRC Heavy Duty Corrosion Inhibitor. These are not good solutions for a show car, because the corrosion inhibitor sprays and grease attract dirt and look, well, dirty. But for a daily driver, they really work.


Chris