Shear values for stainless nails?
jimblodgett
| Posted in Construction Techniques on
Anyone ever look into the shear values for stainless framing nails?
In general, is stainless softer or harder than other steel? Seems to me, whenever I try to cut a sheet of it, it’s hard. But then I’ve heard that stainless is softer than steel.
Can someone straighten me out?
Replies
I don't have the answer your looking for but there are many different grades of stainless steel and then among those they can have diferent hardness. Stainles Steel is a broad general term so what you experience in one form may not be true in another.
And in some cases stainless will rust and be not so stainless at all but has enough nickel content to fall into the category.
Edit: not nickle, it's chromium as later pointed out.
Edited 8/21/2008 4:14 pm ET by john7g
I can add to your confusion.
Ductility and Mallebility enter into the math as well as hardness.
It may seem soft, but it can be a real pain to drill ( say try drilling a storm window frame screw head for an ez-out type extractor, damm near impossible) due to some crazy formula.
As far a shear, I see more bending w/SS than other nails. So I'd say it is good as far as snapping, cuz it generally won't unless work hardened.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations
For framing, I'm pretty sure that the strength of the nails never comes into play. It's the density of the wood that matters. I've heard it referred to as "dowel bearing strength".
Well, maybe I need a little context to make my question clearer.
Like you, Boss, when I started using fasteners to hold boards together, we used nails. Commons for certain applications, brites for others. And I think alot of why we used one guage or the other had to do with shear and pull out values.
Actually, same goes today with nailing schedules, size of nails, and you're right, species of wood.
But at some point along came drywall screws and they were used for applications they shouldn't have been used for, because they are (I think) drop forged so they have zero shear value. Of course, we all know there are lots of people still today using them in shear applications, not malliciously, but probably because they don't know any better (do I get credit for not saying "out of ignorance"?).
So the root of my question is, we are using stainless nails in more and more applications. The change accellerated by the switch to ACQ lumber. And I'm wondering if all us seat of the pants engineers are asking for trouble simply using stainless in the same manner we've always used hot dipped galvys and I just thought I'd throw it open for discussion.
I'm trying to remember some of the math involved in figuring connections. I'll take a crack at it, but some of this may be off. Take a nail connecting a pair of 2X boards together. Let's say the nail is .15" in diameter. (Just to pick a number)Let's say the lumber has a value for compression perpendicular to the grain of 500 PSI. (Picking an easy number to work with)I believe you can only count 12 times the diameter of the nail in order to find the dowel bearing strength. So 12 times .15" equals 1.8". Take 1.8" times the .15" diameter, and you get .27 square inches of dowel bearing area. Multiply .27 times the 500 PSI value of the lumber, and the nail only has to hold 135# to max out the lumber. No way is that gonna be more than any nail can handle..When you talk about using drywall screws in shear applications, the shank diameter is often very small. I think that's more of a problem than the strength of the screw, and for the same reason.
What you didn't like my answer?
I will try again.
A stainless nail will have a higher shear value than a common, sinker, or galvy as stainless is a harder steel than the mild (low carbon) steel commonly used in regular nails.
There, is that better?
Also I agree with boss, it is the wood that is the critical factor in determining the shear value in the application.
I cannot see any circumstance where the seat of the pants engineering will get you into trouble by swapping stainless for mild steel coated or uncoated.
It may be remotely possible that some earthquake resistance value is less with the harder more brittle stainless, but i think the wood will fail before the nail breaks, so again a moot point.
>A stainless nail will have a higher shear value than a common, sinker, or galvy as stainless is a harder steel than the mild (low carbon) steel commonly used in regular nails.<
are you sure about that? Which alloy are they making it out of and what hardness are they taking it to? I know I've gotten some cheap chinese stainless (as advertised) cable fittings & chain links from the BBs and they twisted ap[a]rt in my hands (tools). Lot's softer than what I was expecting, also weaker.
Edited 8/21/2008 4:39 pm ET by john7g
Well it all depends on what else is in the recipe, if you start with bad steel (lots of contaminants in the alloy) then you will have both bad carbon steel and bad stainless steel.
Again, steel is an alloy of iron and carbon with trace amounts of other elements. Stainless steel is by definition is 12% chromium, and adding chromium to the alloy recipe produces similar results as higher carbon in the alloy recipe such as harder and stronger while less ductile. I am sure about that.
God only knows what was in those cheap chinese tools, probably not enough metal in there to rust which is why they were calling it stainless.
you're only addressing the alloy and not the hardness. Take 301 stainless for instance. It can be had in annealed, 1/4 or 1/2 hard. Closer to Full (1) the harder it is to drill. Work a piece that's annealed and send to heat treat and it comes back looking something close to what you wanted, hopefully it isn't too warped from what you started with. I've worked all hardnesses mentioned.
So, you gotta know the hardness as well as which alloy that's being used.
Read a little closer, it wasn't tools, it was cable hardware (clamps) and chain hardware (threaded slip links) and not tools.
cheers
My bad, I re-read and you did say the hardware twisted apart in your tools, not that the tools fell apart.
Now speaking of annealed, or 1/4 or 1/2 hard I do not know how it can be had in nails, or exactly what those terms refer to but I do know you can change the molecular structure of a steel by heat treatment, and I don't think they are doing any heat treating on nails.
Also there is as you speak of, work hardening. Although I doubt if that is ever done to nails, I really don't know. I bet they would be expensive if they were.
Hardness the way you describe I understand as a combination of "working" and heat tempering which will change molecular structure but not elemental or chemical composition of the alloy's, and is possible to do that with a wide range of different composition steels.
I stand by original statement that stainless nails will have a higher shear value than mild carbon steel nails with any coating just because the stainless that they use for nails is by chemical composition a harder stronger steel, but you are absolutely right in that the metal can be worked and heat treated to be much stronger (or weaker if you screw it up) than in its starting state.
Do you know if stainless nails are heat treated or worked in any way? I am just guessing but I would guess not just because of cost, I would also guess if they did work or treat the stainless it would be then still stronger?
I am also curious as to what caused the failure of the hardware you describe, what could they possibly have done to it to make it crumble like that?
No, I liked your answer a lot. Very thourough and easy to understand. Thank you.
Fact is, I was typing my answer to Boss this morning and it takes me a while to compose my thoughts, much less find the appropriate keys, proofread and post.
So I think maybe you posted while I was writing.
Of course, that still doesn't make it gospel, just because you wrote it, right?
I am pretty sure of the content of the message, of course it was explained in laymans terms. It can get very complicated, but I think it was correct.
I am however not an expert, and was just joking with you about not liking my answer (trying to keep a boring subject fun). I am sure there will be lots of folks in here who know more about metallurgy than I do.
That's one of the great things about this forum, many heads put together adds greatly to the body of knowledge. I was hoping that others would add to and possibly correct or more precisely define what I describe.
"A stainless nail will have a higher shear value than a common, sinker, or galvy as stainless is a harder steel than the mild (low carbon) steel commonly used in regular nails."You really can't make a blanket statement like that. Some SST alloys are weaker than mild steel. The yield strength for steel can range from 30,000 PSI to over 180,000 PSI, and most nails are made from alloys in the lower end of that range. On the stainless side, the yield strength ranges from 20,000 PSI (304 & 316 alloys) to 300,000 PSI for the hardened, 440C alloy used in ball bearings.For a given diameter, the 316 SST nails sold for use with ACQ lumber are probably weaker than a common nail drawn from 1018 low carbon steel. You can always make up for the lower strength of SST by using a larger diameter nail.
Edited 8/22/2008 1:20 pm ET by TJK
That matches my real-world experience of bending about every third SS nail I drive, not being able to get a side grip on them with a hammer claw, and stripping the heads of SS screws.
Like Boss said though, it's usually the end-grain compression strength of the wood that's the limiting factor when determining shear values for assemblies.
Thank you, that was the information I was hoping for. I didn't just make the blanket statement however, it was in context of a discussion going in the thread. Adding chromium (to make it stainless) makes it stronger.
Now a question, It was my understanding (and I posted this in the thread) that adding chromium to the alloy to make a steel stainless has a similar effect as raising the carbon level in a given steel alloy "recipe", it will be stronger and harder, but less ductile.
The question part comes in here, how is it that mild steel has a yield strength of 30,000 and up, and yet some stailnless will have a lower yield strength?
Doesn't steel have to start out as a certain percentage of iron and carbon creating a certain grade of steel?
Don't you create "stainless" steel, and a stronger harder alloy by adding chromium to the given recipe?
Doesn't that end up with the stainless having higher yield strength?
This thinking was the basis for my statement that stainless is stronger, I was unaware that some stainless had lower yield strength than mild (low carbon) steel. I didn't realize it was possible.
What would be the elemental make up of such a low yield stainless steel? My understanding is take a given yield strength of stainless and remove the chromium (thereby rendering it common mild steel) and you will have a lower yield strength mild steel.
I would appreciate your explanation of the relationship.
hmflic
don't focus solely on the alloy of the metal. You're missing out on the processes after the alloy has been mixed, the rolling process after the pour and any heat treatments (easily done) that may occur. 301 stainless in the annealed form is softer than 2024 T3 AL. Stainless that's easier to work than AL? yep. But the SS needs a heat treat before being put into use in that example.
I understand working and heat treating can change the properties of a metal, but we were talking nails, I posted that I didn't think nails were worked or heat treated.
Annealed is super slow cooling which will soften, resulting in a Pearlite microstructure, a faster cooling a Banite. Fast quench results in martensitic microstrucutre, which then needs to be re-heated to about 600-700 degrees and then air cooled to be tempered Martensite, for swordmaking etc.
I've been looking around and I've only found allusions to heat treat of the alloys used for the nails but nothing definitevely stating that the nails are indeed heat treated.
The recipe for 316 SST (best corrosion resistance) is: Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S304 SST is:Fe, <0.08% C, 17.5-20% Cr, 8-11% Ni, <2% Mn, <1% Si, <0.045% P, <0.03% SCommon 1018 steel is:Fe, 0.15-0.20% C, 0.60-0.90% Mn, <0.04% P, <0.05% S Chromium and Nickel in various amounts give SST its corrosion resistant properties. Strength in steel comes from adding Molybdenum, Cobalt and Vanadium. More Carbon allows hardening.
Steel is an alloy of iron and carbon, with trace amounts of other elements. Generally the more carbon the stronger the steel, but with more strength comes less ductility.
Stainless by definition is at least 12% chromium, so you are adding that element to the alloy of iron and carbon. Chromium provides corrosion resistance and hardness, generally similar to higher carbon content, so in laymans terms you may correctly look at it that way.
So a stainless nail would be harder and stronger (direct relationship between hardness and strength) than a mild carbon steel nail. It would also be less ductile, more likely to break than bend, but would probably break at a higher tensile strength, which I think makes it a higher shear value as shear measures the ultimate tensile strength of the cross section of a nail.
It can get a lot more complicated and detailed than that, and I am sure there are lots who know more but I think my simplified understanding and explanation is correct.
Probably more info than you need but interesting non the less.
http://en.wikipedia.org/wiki/Stainless_steel
yep, lots of info there. didn't mention nails though....
I wonder now just what categorie SS nails would be in?
http://www.manasquanfasteners.com/faqs