I'm trying to put something together and need some strong bolts/nuts. I was looking at the titanium stuff in a grade 5 but I cannot for the life of me find the specs on it to compare to steel grading. I was wondering if anybody had tensile and yield strength and had experience with titanium bolts/nuts?

 

those bolts are rated grade 5 because the tensile strength of titanuim sucks.it breaks way to easy. just get some grade 8 bolts and call it a day.if grade 8 bolts aren't stong enuff at the bolt size your using then increase the bolt size,or if you cant increase bolt diameter then go to another technique like welding. pics of what your doing or more informatin would be helpful.


Modified by rob... at 8:32 AM 10/14/2007

 

Yeah, the only reason for Ti bolts is weight savings. If you can't get a regular bolt to be strong enough in your application then you need to rethink things.

 

A trick that we use is to weld a grade 8 nut to the end of 4130 tubing, then tap the 4130 tube. This is however still used as a weight savings trick only.

 

I can use grade 8 steel, I was just looking for a lighter solution for it. I guess I'll just grab some grade 8 bolts and call it a day.

 

Titanium has a much better weight/strength ratio but its not stronger than steel, no material is. matweb.com is a good site for material properties. and be careful where you get your "grade 8" bolts. some are cheaply made from china and their strength can be decieving. get a mil-spec fastener if you really need good quality stuff.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by paulzy &raquo;</TD></TR><TR><TD CLASS="quote">I'm trying to put something together and need some strong bolts/nuts. I was looking at the titanium stuff in a grade 5 but I cannot for the life of me find the specs on it to compare to steel grading. I was wondering if anybody had tensile and yield strength and had experience with titanium bolts/nuts?</TD></TR></TABLE>

The grade 5 titanium refers to the SAE bolt strength grade. for reference

min UTS (ultimate tensile strength) grade 5 sae bolt 120,000 PSI HRC (Hardness Rockwell C scale) 23
min UTS (ultimate tensile strength) grade 8 SAE bolt 150,000 PSI HRC (Hardness Rockwell C scale) 32

Further more the type of material has no bearing on the grading. a steel bolt or titanium bolt graded the same will have the same UTS. Its merely a measuring scale.

Heat treatments can change the strength and UTS of the material drastically. For example Grade 5 titanium can be heat treated to exceed 165,000 PSI UTS. ALso the oxygen content can be slightly altered to further increase the strength.

Omnipower makes a fair amount of bolts and nuts and other parts from titanium. Titanium tends to have a bad rep only because people generally use the wrong grade for their applications resulting in a failure.

Titanium alloy can have a strength range from 90,000 psi to 240,000+ psi depending on what grade you use. Also contrary to what some may think titanium is superior to steel in many ways including strength. The only disadvantage it really has is cost, and even that should be lower as its the 9th most abundant element in the earths crust. The high cost is due to a few reasons, low demand, expensive to refine, and limited number of refiners/producers.

 

Wow I don't really know where to start clarifying the misleading arguments you presented trying to sell parts through your company so I'll just post some facts.
It's a good thing you're not trying to sell anything, because you're not a sponsor.

The application of titianium has to be pretty selective. If this guy was looking to use Ti bolts for an exhaust manifold, for example, that would be a very bad choice because of titaniums oxygen embrittlement at elevated temperature. (heat + oxygen = titanium becomes brittle). It has very good evelated temperature strength properties relative to the other lightweight engineering metals like aluminum or magnesium (or even including steel depending on the alloy) but that doesn't last terribly long compared to redily available alternative metals in any environment with oxygen. If he was bolting together dissimilar metals Ti's relative nobility to the common engineering metals would cause galvanic corrosion in the presence of almost any electrolyte. (the threads would slowly dissolve if there's liquid around.)

Those kinds of reasons are why, for example, Ti retainers crack. Surface embrittlement can lead to crack propogation, and in an alloy that tends to have fairly regular hexagonal grain structure, like Ti, the crack propogation can lead to some really awesome looking catostrophic failures.

The UTS of almost any metal can be dramatically improved by heat treating or alloying. If that was the only number anyone looked at everything would be made of SiC in compression for it's 425+ksi yield strength.

4140 can be treated well above 250 KSI, but with all the heat treatment processes the improvement in strength is at a cost of ductility. It's no good to have fasteners that are phenomally strong, but break every time you try to torque them down because they have so little ductility.

In the event an alloy of Ti starts to fail because of overloading, the stronger alloys have pretty low elongation to failure relative to high strength engineering steels. You'd be looking at 8% to failure instead of more like 20%. Failure mode and effects analysis is a pretty hot topic in any liabilaty concerned industry, so depending on the application that can be an important point.

Titanium and it's alloys also have pretty poor resistance to abrasion. So for example if you used a Ti bolt in an application like a suspension pickup or a swaybar link and things around it were a little bound under load it would start grinding away the Ti pretty quickly. Which is alot of fun because Titanium fines are flamable/slighltly explosive.

Titainum is a very cool metal, it has a lot of uses. It has good strength at high temp, it is lightweight for how strong it is, etc. But it's not for everything.

So basically, you have to be very careful when selecting titanium for your application, and there a litany of reasons steel is the predominant fastener choice.

Peace,
--Niles

 

very good post niles, its scary that people think there are no considerations other than tensile strength in design.

 

look at NAS or AN bolts for you application. it is better to design bolts in tension, but thats not always possible. there are special shear bolts that meet those standards. these bolts are stronger than grade 8. if you want to save weight, then you can use a stronger bolt in a smaller size.
good luck

 

Actually, when it comes to cars in general, there are hundreds of places to save weight before you should even consider doing it with changing fastener specs.

 

i didnt know he was even doing this for a car.