Why not stainless steel?

[NewBie]

GregW, thats a pretty nice looking light, stainless can be as hard to machine as Ti, depending on the alloy.

When you say Stainless Steel holds up better, are you talking more scratch resistant, more impact resistant, or the threads hold up to wear better- in your experience?


While we are on the subject of Stainless Steel, Titantium, and Aluminum, here is some old information I put together:

So, Titanium has twice the weight as compared to aluminum (someone mentioned that Stainless was 3x earlier in this thread). For some, weight is important. So that is definitely something to consider, especially with small lights that folks EDC, which use very light weight Lithium cells.

6AL-4V has a lot of alloy material in it which preclude it from being classified as Ultra Corrosion resistant, but is still considered corrosion resistant. With six percent aluminum in it, it does help to lighten the load a little down to 0.16 lbs per sq. in., from 0.19 lbs per sq. in. 6063-T6, a highly common aerospace grade alumium comes in at 0.0975 lbs per sq. in.

Besides being a poor conductor of heat (6AL-4V has over thirty times the thermal resistance of 6063), Titanium also has nearly twice the electrical resistance of Aluminum.

Some are not familiar with what T6 in aluminum alloy is. Basically it is a tempering that greatly increases the hardness of the material. Many flashlights are made from much softer aluminums, as it is cheaper to machine.

So, what does the T6 tempering do for a person? Lots of things, one one big one is the surface hardenss, which helps a lot to reduce scratching, wear in the threads, impact resistance, and such- it is unfortunate that you rarely find 6063-T6 used in flashlights:

Hardness, Brinell 73
Hardness, Knoop 96
Hardness, Vickers 83

Lets compare that with pure Titanium:
Hardness, Brinell 70
Hardness, Vickers 60

However, you can alloy Titanium with some select materials if you really want to increase the surface hardness.
Here is a rather hard Titanium that isn't very common, and is used for things like jet engine nozzels, Ti6Al2Sn4Zr2Mo, Ti-6242, Ti-6-2-4-2, UNS R54620
Hardness, Brinell 318
Hardness, Knoop 346
Hardness, Vickers 333

You can also anneal Titanium 6AL-4V to help it too, but it increases cost:
Hardness, Brinell 334
Hardness, Knoop 363
Hardness, Vickers 349

6AL-4V is also able to be heat treated.


Machinability:
"As a family, titanium and its alloys have developed a mystique as a nightmare to machine. This is simply not the case. Experienced operators have compared its characteristics to those found in 316 stainless steel. Recommended practice includes high coolant flow (to offset the material's low thermal conductivity), slow speeds and relatively high feed rates (high feed rates reduces the machining time). Tooling should be tungsten carbide designations C1-C4 or cobalt type high speed tools."
(this is directly out of the Ti manufacturer's datasheet, and I spoke last month with some aerospace machinists, who concurred, but added that proper setup is important)


One of the really nice things about Titanium is it usually springs back into shape after it is deformed. Once it is deformed too far, it can be a real bummer to get back into shape, unless you heat it up, as it wants to retain it's newly "set" shape.

Now, one can Type III, Hard Anodize the flashlight to give it a rather durable surface. Unfortunately, if the alloy used is just regular 6061 or 6063, it is much softer underneath, and the Type III Hard Anodize isn't going to help you out much during impacts. But if you go with a Tempered Aluminum, things hold up a lot better.

An example is regularr 6063, non-tempered:
Hardness, Brinell 25

That is a substantially softer aluminum.


Now, you can also go with aluminum that has even "better" tempering, such as 6063-T835, but it costs a little more, but give the HA III coating a much firmer base which helps it hold up to more types of abuse better:
Hardness, Brinell 105
Hardness, Knoop 130
Hardness, Vickers 118


GregW, have you fiddled at all with Titanium hard coats, to reduce the fine scratching that occurs with use over time? Especially in your case, where the light appears to be designed for keychain use.

 

[Stingray]

Thanks for all that info Newbie, that's good to know.

What annoys me about expensive aluminum pocket lights is that the HA3 coating comes off at the sharp corners and the knurling so easily, and the lights often dent when dropped. If the lights didn't cost $100 - $300, I wouldn't really care that much.

Stainless lights can be carried in a pocket with keys, knives, coins and other pocket items, dropped on the floor etc., and still retain their original appearance over time, as this inexpensive Walgreens pill container I have has done.

Greg, that Exolion SS looks like a really nice light.

 

[bfg9000]

Just this year I was wondering why stainless stamped thermoses and cups can be sold at the dollar store but nobody mass produces stainless flashlights (yes some have stainless trim but are plastic underneath).

The main advantages include being really cheap in quantity because it needs only stamping and swaging like metal flashlights of old rather than labor-intensive machining operations. Plus the bare brushed finish is very durable but even if scratched, a brillo pad can make it look like new again.

 

[gregw]

GregW, thats a pretty nice looking light, stainless can be as hard to machine as Ti, depending on the alloy.

When you say Stainless Steel holds up better, are you talking more scratch resistant, more impact resistant, or the threads hold up to wear better- in your experience?

I've had a prototype Exolion SS on my keychain for about 6 months now. Comparing the surface scratches on it to my Exolion Ti (6Al-4V) prototype, which had less keychain time, the Exolion SS shows less scratches. Could this be attributed to the surface of Stainless Steel being more "slippery"? The threads were already smoother than the Exolion Ti originally, and after having been worked in for 6 months, is just about perfect.

GregW, have you fiddled at all with Titanium hard coats, to reduce the fine scratching that occurs with use over time? Especially in your case, where the light appears to be designed for keychain use.

I haven't tried hard coating Ti since I like the colour of the material as it is.. Another thing about not doing a coating is that you can polish out the fine scratches should it really bother you since it is just a bare material.

 

[NewBie]

Great, thanks for the info Greg!

 

[buddyrohr]

It's the same reason John DeLorean went out of business. Remember the stainless steel automotive beauty known as The DeLorean? It went the way of the Edsel.

once you get this sucker up to 86 miles per hour youre gonna see some serious #$&!

 

[Ladd]

Is this what you had in mind?

Go the the large auction site and search on stainless flashlight.
This one and many more will pop up.

The Convoy S7 is a stainless copy of the well-thought-of Convoy S2. It is nicely made, but heavy.

In the custom arena, TnC makes SS lights. See the custom makers section of CPF. RMSK sells them.
They are absolutely top-notch.

 

[Nicrod]

Nice pic Ladd,

Just noticed this thread is from 2007

 

[DIWdiver]

No, it's from 2004. ;-)

 

[jason 77]

once you get this sucker up to 86 miles per hour youre gonna see some serious #$&!

It's 88 miles per hour not 86......

 

[jonathanluu2]

While we're raising the dead, I wanted to point out:

• Stainless steel is more dense, but also stronger/harder [than aluminum], in equal magnitudes. Therefore, a well made stainless steel light should weight the same amount as an equivalent titanium or aluminum light by using thinner walls.
• Stainless steel does have less thermal conductivity compared to aluminum, but is comparable to, or better than titanium alloy. However, you can still find many (bright and functional) custom Ti lights.
• Stainless is more expensive and harder to machine than aluminum, but is again comparable to Titanium, if not less finicky. You will also find more options as far as billet/tube-stock options for Stainless than titanium.

Bottom line, I would say SS is the odd man out. Its not cheap so it wont make it into economical market, but it doesn't have the allure of titanium to show up in more expensive lights.

 

[Energie]

... I would say SS is the odd man out....

 

[DIWdiver]

Stainless steel is more dense, but also stronger/harder, in equal magnitudes. Therefore, a well made stainless steel light should weight the same amount as an equivalent titanium or aluminum light by using thinner walls.

I beg to differ. Unless you can point to a specific stainless that has much better properties than common 300 and 400 series alloys.

The most common titanium alloy, Ti6Al4V (grade 5) has a minimum yield strength of 827 MPa and Rockwell C hardness of 33.

Some high strength steels have yield strength of 1650 and even much higher, as well as far greater hardness. But they are not stainless, and I doubt anyone would try to machine them into a flashlight.

304 (18/8) and 316 stainless in full hard condition have a minimum yield strength of 759 MPa and Rockwell C hardness of 24 (min).

Some 400 series steels have hardness of >90RC, but no higher yield strength, even in full hard condition, which few people could machine.

On top of that, even if you did find a stainless with yield strength of 1650 MPa or more, comparable or better hardness, and still machinable, you have to remember that the bending strength of a thin structure is proportional to the square of the thickness. So a tube of the same inner diameter and weight would still be twice as resistant to dents if made from Ti6Al4V.

But I'm perfectly happy with unanodized 6061-T651, so who am I to talk.

 

[jonathanluu2]

Let me edit my other post to clarify that SS is harder than ALUMINUM. You're in the same ballpark with the proper steel grade (410 comes to mind) and Ti alloy selection. You are right that the more common 300 steels tend to be sub-par compared to the grade 5 Ti alloy; however they are also more machinable and economical.

Not trying to get into a SS vs. Ti argument here, as there are many pros/cons and probably plenty of folks here armed and ready with justification for each.

 

[lucca brassi]

SS rust in contact with ordinary steel sooner or later .