# SS vs Ti



## aljsk8 (Sep 23, 2008)

i want to know properties of 316L stainless steel vs 6/4 Ti

im not interested in any advantage due to titanium being stronger
if the peices were the same weight

im interested in thickness

eg) 25mm dia tube 2mm thick wall 1 in SS 1 in Ti

add weights until one fails - which would it be?

im not looking for a complex list of properties

just a comparisson of strength and resistance to scratching
but without including weight or any thermal properties

would also be interested in life expectancy of the materials
like the 2mm x 25mm tubes mentioned - would they both still be around in 100 / 500 / 1000 years? if so which one wins

finally which is easier to machine Ti or SS

thanks

Alex


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## light man (Sep 23, 2008)

no comment


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## AvidHiker (Sep 23, 2008)

I'm no expert on machining, but have always heard that titanium is one of the most difficult materials to machine - hence the high cost and scarcity of machined titanium.

In terms of abrasion/scratch resistance, that probably isn't dramatically different between the two and is probably more a function of surface finish than anything else. The right surface finish can minimize the appearance of fine scratches.

In terms of environmental resistance, I don't think anything can approach the inertness of titanium. I believe that there are a number of common corrosive environments where titanium is far superior to stainless. Of course, it all depends on the exact environment.


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## precisionworks (Sep 23, 2008)

316L is the low carbon (weldable) version of 316, and both have identical corrosion resistance. 316 is considered to be suitable for some marine applications such as boat rails and hardware, which are exposed to salt spray. 316 performs without evidence of corrosion in the 100-hour, 5% salt spray test (ASTM B117). Stainless is often used for medical implants that will not stay in the body.

Ti 6-4 (Grade 5) has high toughness, high strength and exceptional corrosion resistance. Titanium is currently used for submarine ball valves, fire pumps, industrial heat exchangers, hull material for deep sea submersibles, water jet propulsion systems, and shipboard cooling and piping systems. Ti is used for medical implants that are permanent.



Tensile strength of 316 is 72 ksi, versus Ti at 130 ksi - titanium is nearly twice as strong. (Tensile Strength - aka Compressive Yield Strength - is the maximum load a sample will carry before breaking, with the load gradually increased until the breaking point. Measured in either psi or ksi.)

As far as machinability, SAE 1212 = 100%.

Type 316 stainless = 45% 

Ti 6-4 = 22%

The machinabilily rating means that you could run 1212 @ 200 sfpm, 316 @ 90 sfpm, and Ti 6-4 at 44 sfpm. In relative terms, the same job in Ti will require double the machine time as a 316 part. Add to that the low elastic modulus of titanium, which permits greater deflection of the workpiece - requiring a rigid machine setup, sharp tooling, flood coolant to handle the heat, etc. Part of the high cost of any Ti product is the material, part is the machine time.


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## aljsk8 (Sep 24, 2008)

precisionworks

very useful info

basicly then the ti is superior in every way
i could have sworn that steel was stronger than Ti

i thought it was just that you could make a thicker peice
so then for the same weight it is stronger

why do Ti bike wheel spokes snap a lot easier than SS ones?
im talking same thickness?

thanks for the info

Alex


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## precisionworks (Sep 24, 2008)

> ... steel was stronger than Ti


Some steels are ... generally higher carbon steels & alloyed steels, many of which are above 130 ksi. Two problems with steel that isn't stainless - it rusts in a heartbeat, and it weighs nearly twice as much as Ti. If you look at Ti bicycle frames as an example, the makers usually go with a slightly thicker or larger tube (sometimes both) to end up with a frame equal to steel in strength & stiffness - and it still weighs 30% to 40% less.



> why do Ti bike wheel spokes snap a lot easier than SS


Customers often want the lightest wheel possible, whether for a road bike or an off road bike. To achieve that, the builder uses fewer spokes (which increases the load per spoke) and shorter spokes, like a radial pattern - which subjects each spoke to tremendous loading on bumps or rough trails. I've never seen any studies that show Ti spokes to be less strong or less durable than stainless, and I used to ride quite a few miles - about 5000 per year. I have seen 250 pound riders on 19mm rims, and it's not surprising that they break spokes on a regular basis.



> basically then the ti is superior in every way


The biggest drawback to Ti is the cost of admission - roughly double that of aluminum. Some makers, like Enrique Muyshondt, offer identical lights in both Al & Ti. The new Aeon hardcoat aluminum is $199, while the Ti Aeon is $399.


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## aljsk8 (Sep 24, 2008)

very useful info

personaly in a flashlight i like the extra weight of stainless steel over aluminium and its good to know its easier to machine

but i might have to try titanum one day

thanks

Alex


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## AvidHiker (Sep 24, 2008)

No doubt others may have more useful input, but coming from a materials science background, I can tell you that when designing for a particular application, there is A LOT more to it than simple comparisons of typical mechanical properties (no offense to precisionworks intended, just a general statement). A "figures of merit" approach to material selection is often used and can be quite an undertaking as it takes into account numerous properties of interest (tensile strength is just one of many).

An relatively simple example of what is typically done can be seen in this material selection analysis.

For one, if my memory serves (sorry, its been a long time since metallurgy classes and I'm not currently a metallurgist), the fracture toughness of your common grade 5 Ti is not terribly good, and many other ferrous (and even some non ferrous) alloys can be far superior. A bicycle spoke has a lot of stresses on it and is probably sensitive to impact damage and defects (or even design features) which generate stress concentrations - in this case, I could see how fracture toughness might play a major role. Further, workability/formability constraints are numerous with titanium alloys, so the ideal forming process can't always be used, which can result in the situation you described with spokes. An "adequate" part for a particular application might be possible, but limitations in workability might leave you with an inferior part when compared with the state of the art in steel spokes. Of course, these drawbacks are acceptable to some who are looking to shave every ounce off their rides and are willing to pay a premium for such components (kind of ironic, isn't it?). Did you happen to see the French guy (going for a speed record I think) do a face plant on his fancy composite ride (it fell apart) after having just ridden the same hill with his conventional bike?

Oh, just thought of another example - ever wonder why its almost impossible to find titanium carabiners (I've only ever seen one, and I think its intended for marine use more than anything else). Take a look at FAQ #5.

Just my attempt to give you a better appreciation of the complexities of material selection. Hope it make some sense.


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## precisionworks (Sep 24, 2008)

> the complexities of material selection.


+1

Evey part made by man or machine, including those that went to the Moon, involve setting priorities & matching those with suitable materials & manufacturing methods.

I didn't mean to imply, by my limited answers, that Ti is better than Alloy XYZ. I would like to see a Ti/Carbon Composite design - Ti for the head, carbon for the battery tube. Some of the 'flat' designs (like the Spy 007) could be made mostly from carbon, but probably wouldn't have the curb appeal of an all Ti design.


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## PhotonFanatic (Sep 24, 2008)

And when it comes to flashlights and LEDs, one definitely needs to consider thermal transfer, and neither SS or Ti is stellar in that department.

My approach when using Ti is to at least put a nice copper heat sink in the head for some thermal absorption, but that negates the lightweightness of the Ti, doesn't it?

Everything is a compromise, or so it seems.


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## precisionworks (Sep 24, 2008)

Ti seems to find some uses because of the lighter weight - bicycles, aerospace, etc. In other designs, like lights, toughness & corrosion resistance make Ti the material of choice. I'd have no problem with a copper heat spreader in a Ti light, even at a small weight penalty.

I'm not sure what McGizmo uses, but my Mac's P7 has the LED thermal bonded to a large aluminum disc. That light will run at full power til the battery dies, and just get warm


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## McGizmo (Sep 25, 2008)

AvidHiker said:


> .....
> 
> Oh, just thought of another example - ever wonder why its almost impossible to find titanium carabiners (I've only ever seen one, and I think its intended for marine use more than anything else). Take a look at FAQ #5.
> 
> .......



I looked at FAQ#5 and agree with what was said but they did not mention forging the part. A properly forged Ti biner will do well in comparison to other materials as long as you are willing to ignore the cost. 

Ti has been around a long time but only recently has it been introduced as a solution in many of the forms it can now be found in.



> would also be interested in life expectancy of the materials
> like the 2mm x 25mm tubes mentioned - would they both still be around in 100 / 500 / 1000 years? if so which one wins
> 
> finally which is easier to machine Ti or SS


316 is excellent in corrosion resistance in most environments but it can be eaten away in some. In marine applications and any other saltwater environments, oxygen deprivation can induce crevice corrosion in 316. This is typically in places you can't visually inspect and the results can be disastrous! I believe chlorine radicals are the culprit but don't remember the details.

I read a number of years ago that there is one of the Egyptian ruins that needs desperately to be reinforced with a bunch of rod. I believe some rebar or similar was used early last century and it is now rusting away. Whoever it was responsible felt that there was only one more time and shot at reinforcing the sandstone or what ever it is and they felt the only material that would hold up indefinitely was Ti. The decision at the time was to hold off until they could afford to do it with Ti. I have no idea if anything was ever done.


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## paulr (Sep 25, 2008)

Anything known about the toxicity of ti? With all this stuff about chemicals leaching from plastic water bottles (including the epoxy coating in aluminum Sigg bottles), I was thinking of getting a Wiggy's stainless steel bottle. But titanium would be pretty interesting too. It's used in camping cookware and tableware already...


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## easilyled (Sep 25, 2008)

paulr said:


> Anything known about the toxicity of ti? With all this stuff about chemicals leaching from plastic water bottles (including the epoxy coating in aluminum Sigg bottles), I was thinking of getting a Wiggy's stainless steel bottle. But titanium would be pretty interesting too. It's used in camping cookware and tableware already...



I don't know anything about the toxicity of Ti but since its used in Dental Implants and as Prostheses for joints and stabilizers in the rest of the body,
I'm guessing that it can't be very toxic.


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## AvidHiker (Sep 25, 2008)

McGizmo said:


> I looked at FAQ#5 and agree with what was said but they did not mention forging the part. A properly forged Ti biner will do well in comparison to other materials as long as you are willing to ignore the cost.


 
Ah, nice to get some feedback from one of the foremost titanium experts around here! Agreed, forging would seem a logical alternative and in many cases is the only method capable of achieving truly optimal mechanical properties as it offers a means of controlling grain structure, among other benefits. As they mentioned the relatively low cost of quality Al biners, might the cost of a forged titanium part be so sky high that they're not considering it?



paulr said:


> Anything known about the toxicity of ti? With all this stuff about chemicals leaching from plastic water bottles (including the epoxy coating in aluminum Sigg bottles), I was thinking of getting a Wiggy's stainless steel bottle. But titanium would be pretty interesting too. It's used in camping cookware and tableware already...


 
My understanding is that its quite non-toxic. The only thing which would "leach" would probably be titanium dioxide, which is only a respiratory hazard (as a powder) and hasn't been found to have any toxcicity when ingested (oddly enough, I recently read about someone eating a pound of the stuff with no ill effects). Now, of course, the alloying elements may be a source of toxins so I guess my statement only really applies to commercially pure Ti, but I doubt that in the doses possible there's anything to be concerned about. I've heard some claims regarding dangers of cooking with stainless steel as some of the alloying elements there, such as chromium, are toxic (but also present in relatively high percentages in the alloy). Not sure if there is any evidence to support such claims.


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