# Stainless Steel and Titanium



## McGizmo (Sep 14, 2006)

Hi guys,
I was about to place a post in a dealer's thread; subject being the sale of stainless steel bezels. I didn't want to side track the thread with a question on one of the sales points so I will bring it up here. I think the issue is moot in regards to the bezel rings any ways but in general, I am suspicious as to the veracity of a statement of one metal being harder than the other with no qualification of alloy or state of hardness (resulting from anealing or heat treatment). 

To quote:



> ... Keep in mind *Stainless Steel is actually HARDER than Ti*..


 
Bold emphasis mine.

EDIT: this quoted statement is no longer in place in the sales thread and we can move along...

Is this true regardless of alloy of Ti or stainless? I know that tensile and yield strengths can go either way depending on match up. I have work hardned stainless to the point it required a grinder to cut it (dull drill bits with heat generated as a result :green I know it _can_ be very hard.

17-4PH aside, it has been my experience that the harder and _stronger_ the stainless, the more prone to rust and corrosion it becomes (this is in comparison of alloys like the common 300 series). It has been my experience with both stainless steels and Ti alloys that the physical properties can range significantly as a function of alloy and heat treatment or state of aneal. I have not paid attention to the hardness of the various metals and in their various treated states.

Does the statement above hold true without qualification? If one is designing with a desire to maximize abraision resistance, will stainless fare better than Ti in all cases?

In my marine industry background, I have learned to prefer if not demand 316 over say 304 or 302 (typical 18-8 alloys) because of corrosion resistance considerations. The US Navy has done studies to the point of stating that 18-8 alloys should not be considered for use on naval vessels in general. 316 is inferrior to the 18-8's in terms of tensile and yield strengths but will weather much better and ultimately provide service when the stronger materials will fail due to corrosion. In the marine environment, stainless steel depends on an oxide film to protect it from attack of free clorine ions. If the stainless is scratched and its oxide film removed, in the absense of oxygen, it can suffer from accelerated crevice corrosion, or so I have been led to understand. The hardness of the metal will effect its propensity to scratches. On one hand, you want a hard metal to be less subject to scratching to avoid crevice corrosion but on the other hand, the stainless steels that are harder, to my knowledge, are more prone to corrosion due to oxidation (rust). :thinking: :shrug:

Well, at this point, I ramble! 

Any metal experts out there willing to comment on the hardness comparison?


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## Twellmann (Sep 14, 2006)

Try looking at http://www.matweb.com they have ALOT of different alloys of different metals and such listed. There is also a nice search function where you can sort by different properties eg. rockwell scale


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## McGizmo (Sep 14, 2006)

Twellman,
Thanks! I have run across matweb in google's in the past but not used them for such a search. In terms of Brinell hardness (what ever that is  ), I see that most of the 300 series of stainless steels are in the mid 100's range. Grade 5 Ti is in the mid 300's. Hardened stainless steels are also up in the 300's. As I suspected, the particular alloy and its treatment state is a significant factor, at least in terms of hardness in Brinell scale.


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## scott.cr (Sep 14, 2006)

Mid-300s Brinell ("HB") is the rough equivalent to 38 Rockwell "C" scale. This is probably on the soft side compared to knife steels, which are probably up in the 50s RC (500s HB).

In the higher hardness levels you might consider that toolpost grinder you've always wanted, but couldn't justify, for your lathe. ;-)


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## Calamityville_Horror (Sep 14, 2006)

My recollection (without looking anything up specifically):

Fully annealed grade 5 titanium will be harder than any annealed stainless steel, but some of the harder SS alloys should come close (420, 440). However, with both in their fully hardened states (via heat treating or cold working), stainless steel, and I think even mild steels, will be harder than titanium.

I would personally test material samples if a property was critical, but in general the above should be correct.


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## Loomy (Sep 14, 2006)

McGizmo said:


> In terms of Brinell hardness (what ever that is  ), I see that most of the 300 series of stainless steels are in the mid 100's range. Grade 5 Ti is in the mid 300's. Hardened stainless steels are also up in the 300's.



Brinell test: "_[size=-1]The smooth surface of the metal is subjected to indentation by a hardened steel ball under pressure or load. The diameter of the resultant indentation, in the metal surface, is measured by a special microscope and the Brinell hardness value read from a chart or calculated formula. [/size][size=-1]A material with a high Brinell number will have a higher surface hardness, and therefore resists wear better than a material with a lower Brinell number."[/size]_[size=-1]

I got that from typing "define: whatever" (without quotes) into google. So: http://www.google.ca/search?q=define%3A+Brinell+hardness Just for future reference 

For more on the different hardness scales, see: http://72.14.205.104/search?q=cache:VLkhf1AMjuUJ:www.ndt-ed.org/educationResources/CommunityCollege/Materials/Mechanical/Hardness.htm+hardness&hl=en&gl=ca&ct=clnk&cd=2

I've most commonly heard of the Rockwell test being used these days. BUT note this: _"_[/size]_The Vickers and Knoop *Hardness* Tests are a modification of the Brinell test and are used to measure the *hardness* of thin film coatings or the surface *hardness* of case-hardened parts. The measurements for hard coatings like TiN must be taken at very high magnification (i.e. 1000X), because the indents are so small."_

But while there may be two scales use for optimum testing of, say, a coated steel or titanium part, I think the Rockwell scale would cover both of them sufficiently if new tests were to be done, say for your own purposes. I say this because we already know the hardness of all these individual surfaces just by looking them up online. 

The only question is how they might work together, say on a flashlight body. For instance, you might want to know how well attached a given hard coating on a hard surface is. A poor anodization or coating job might flake off under pressure.

In the case of titanium alloys, I see that Matweb uses Rockwell C scale to measure titanium hardness. That works to compare with steel too. A brand of 6/4 is 32. CP grade 1 titanium is soft enough that it doesn't rank in the Rockwell C scale, and instead falls into the Rockwell B scale at around 70. For comparison purposes using a different scale, 6/4 has a Brinell rating of around 300, and CP grade 1 is around 120.

And just for fun, the hardest material cataloged by Matweb on the Rockwell C scale is this diamond-chrome composite coating: http://www.matweb.com/search/SpecificMaterial.asp?bassnum=NARMOL00 Which, you'll note, is not recommended for use on titanium or aluminum 

Matweb isn't designed to be user friendly, so for future reference here is how I found all of that information:

http://www.matweb.com/search/SearchProperty.asp -> Select Metal (or [size=-1]Nonferrous Metals, same thing for our purposes), then under Property select Rockwell C or whatever other scale you like. You can enter a value range to narrow down the search. (For easy absolute comparisons, Brinell, etc, would be easier, HOWEVER not all materials have ratings in all scales. The diamond composite coating for instance only has a Rockwell C rating.)[/size]
[size=-1]
I also used this: http://www.matweb.com/search/SearchSubcat.asp -> to search for Titanium under [/size][size=-1]Nonferrous Metals.

Now for more fun, I've searched for TiAlN. Found here: http://www.matweb.com/search/SpecificMaterial.asp?bassnum=BNTiA0

TiAlN has rating of 2800 on the Vickers hardness scale. For comparison purposes, 6/4 titanium has a rating of 318 on that same scale. Based on the units (kilograms per millimeter squared), I presume TiAlN withstood the force of a 1 mm diamond tip with 2800 kilograms pushing down on it.

For comparison purposes, this is using the Knoop hardness scale which they all have in common: (u represents the coefficient of friction, where 0 is perfectly slick)

[/size][size=-1]AlTiN: 4000, u: .45
CrN: 2200, u: .55
[/size][size=-1]TiAlN: 2500, u: .7[/size]
[size=-1]TiCn: 3000, u: .45[/size]
[size=-1]TiN: 2000, u: .65

The coefficient of friction is notable to me because I want good traction on something I hold in my hand. Simply put, the u number means that it takes that many newtons of force to move along that surface. So .7 is significantly less slick than .45. All else being equal, if I was building a flashlight, I would go with the rougher one[/size][size=-1] unless the slicker one felt good in person after a test run.

I was curious of PVD coatings work well on titanium, so I emailed a couple titanium works guys, and Mark from PVD-coatings.co.uk says that "[/size]You can get excellent adhesion to Ti [with PVD coatings like TiAlN], but I think the deposition temperature has to be lower than usual."[size=-1]

So yeah, hopefully that's fun or useful but always informative to someone! 


[/size]


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## cy (Sep 14, 2006)

ti is not on there, but may be useful as a reference


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## MSI (Sep 14, 2006)

Timken has some really hard tool steels, up to 63 HRC.

If you coat them, then corrosion resistance shouldn't be an issue. Take a look at XADC coating, makes TiN look fragile


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## 4sevens (Sep 14, 2006)

I just know PEU's bezels use 304 stainless 
They don't respond to magnets - which is quite curious to me...


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## blahblahblah (Sep 14, 2006)

I'm not a metals expert, but I am a hobbyist. I've only done welding and machining on a few 300 series stainless steels. I've researched various metals in the past. So, w/ my limited background, here's what I have to say.

It seems like you have a good grasp on SS vs Ti alloys. I can only add a couple minor points. 

You mentioned various PVD coatings. I use some drill bits and end mills with a TiAlN coating. These are AWESOME! I've got at least a couple thousand drill bits and end mills. Those TiAlN bits, although costly, are worth the investment. I believe I got them from MSC direct or some other tool catalog like that.

The other thing I'd like to mention is somewhat off topic. I've done some research into cryogenic freezing of metals. I was looking to freeze some automotive parts, but in my research I ran across several other applications of the tempering process. Since the metal grains realign into a more uniform crystal structure, wear is reduced. This is not the same as hardness, but somewhat similar in certain applications. Some examples of of this use: Cylinder sleeves, knife blades, brake rotors, etc. I doubt it is necessary in light applications unless you need to protect the threads from 100s or 100s of on/off cycles per day.

Gotta run, the wife is home and I forgot to do some "honey-do's".


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## McGizmo (Sep 14, 2006)

As Loomy pointed out, the coefficient of friction can vary with the metals and certainly with the surface finish of any material. I suggest this has its effect on abraision as well as does hardness of the material. If you look at teflon, for instance, you need to consider the physical property of _creep_; one that most of us are not real familiar with! :green:


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## PEU (Sep 14, 2006)

The bezels I made were made of Stainless Steel 304.

If you compare SS 304 with pure titanium (grade 2) its phisical characteristics are very similar, but if you compare SS 304 with grade 5 titanium (Ti 6Al4V), TI beats it in almost every aspect.

But we must compare (are we comparing?:green titanium and SS304 in it context, and our context here is bezels.

- If we want the bezel for looks, it doesn't matter if its TI or SS since both will shine after a short polish session.
- If we want the bezel for its tritium locators, well you need a bezel with tritium holes  
- If we want the bezels for striking things with them, there are some other factors that need to be considered, most important IMHO is which material is the flashlight holding the bezel.

a) If the flashlight is titanium, a softer bezel material like SS will deform faster thus somewhat protecting the threads that hold the bezel.

b) If the flashlight is aluminum, well, it doesnt matter if the bezel is TI or SS since both are far harder and stronger than ALU and if you strike something with this configuration hard enough the alu threads that hold the bezel will suffer for sure.


There are other uses for a crenelated bezel, but I think I addressed the most common ones


Whats better you ask me? I don't know... ask Don :nana:


Pablo


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## McGizmo (Sep 14, 2006)

Hi Pablo,
I didn't know _we_ were comparing anything. I do know 4sevens stated Stainless Steel is harder than Titanium and he joined this discussion with a comment that your rings are 304 and non magnetic. He has not supported his statement on hardness yet. In the context of bezels, I don't think it is significant, one way or another. 

I can pull a rubber bezel out of a tank of liquid nitrogen and claim it is harder than Ti or stainless steel. It would be a good idea if I qualify the conditions though and not let someone leave with the impression that rubber is harder than some metals! (BTW, this is pure speculation on my part and quite possibly false!!!)

Don't ask me what is better or not here! Beyond taking exception to what I perceived to be a false statement and seeking the truth here in the materials forum, I have no real interest or concern in the choice of Ti over stainless steel in bezel rings. I made my choice some time ago and am satisfied with the results.


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## McGizmo (Sep 15, 2006)

Hi guys,
For the sake of clarity, I won't edit out any of my posts here but the issue that brought this thread into being has been resolved. The title is broad in scope to the point of being almost pointless! It may serve as discussion of these metals further and in any direction one might be inclined to take it. On the otherhand, this thread can go to the dregs as the case might be. 

As a designer it really helps to have access to a number of materials so that one can select one best suited to the requirements as well as design goals. The matweb.com site is a great reference! (thanks!). What it doesn't tell you though is the relative costs of materials or their availabilities. The other thing is matching material physical requirements with demands placed on them by a design. This is an area I know enough about to know that I don't know diddley! I hope and expect that my designs are silly and over built to the point that the materials are never brought to their structural limits! :green: It really sucks when something breaks! I mean literally! 

I had a prototype of the HD idea that I knew had a thin wall section in the head. This prototype also had a cast urethane tail bumper and bezel bumper and it was fun to toss it down the street or up in the air to land on concrete. It was fun until the time I threw it into a wall and it came back in two pieces. 

Anyway, back to the topic, Uh, I have nothing further to add. :wave:


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## MoonRise (Sep 15, 2006)

Is stainless steel harder than titanium without qualification? No.

If you rephrase the question as -can- stainless steel be harder than titanium then the answer is YES. But you could also rephrase the question as can titanium be harder than stainless steel and the answer is also yes.

Confused? It all depends on the alloy and the heat treatment.

Generally titanium's strengths are that is relatively inert and corrosion resistant and can have a strength near that of most steels at a lighter weight. 

Steel's strengths are that there are hundreds of alloys that can vary in their properties. Those properties can be varying degrees of corrosion resistance, varying levels of strength (tensile, compressive, shear, fatigue, impact, etc), varying levels of machinability, varying levels of hardness, etc. There are generally correlations between some of the properties in that as you change the alloying elements and heat treatment to increase one property you will also increase -and- decrease other properties as well.

Titanium can max out in hardness near Rc 38 or so. Some stainless alloys (cutlery steel types) will go over Rc60 in the quenched state, and can still be Rc58-60 or so after tempering.

And the rubber plug chilled down to -196C by the liquid nitrogen may or may not be harder than metal, but it has definitely become much-much-much more BRITTLE when chilled to that temperature than it was at room temperature. Then again, an ordinary rose frozen to -196 in LN will also be so brittle that it will shatter if banged against something (like the desk).

If you want to look only at hardness, then the answer is that stainless steels can be harder than titanium.

Just remember that hardness of the metal is not the only property that can vary or is important. Others may include corrosion resistance, fatigue strength, impact strength, properties at high or low temperatures, machinability, weldability, price, etc.

Just like almost everything, it all comes down to looking at the needs and trade-offs.


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## AilSnail (Oct 31, 2006)

In Norwegian we have two different words for "less corrosive steel". The first is "rustfri". Literally translated "free of rust". It means, I have been told, that there is at least 12% chromium or something like that. In other words it doesn't have to be very rust resistant to be classified as R.
Then there is "syrefast" steel, literally "withstands acid" (origin similar to "stand fast"?) - and I haven't ever seen any such steel rust except in the welds. Is there a similar term in English - something meaning that it's "really stainless"?

Never seen a syrefast knife worth a poop. Rustfri knives can be ok.


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## highorder (Oct 31, 2006)

(edit I just realized this thread is a month old.








so much to add, and I missed the whole thread! you guys are a smart lot, drawing on diverse backgrounds and sources, ultimately comming up with all the answers you need, without the help of this machining instructor...

oh well, maybe next time I'll get to chime in!


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## TranquillityBase (Nov 1, 2006)

Has anybody considered 'depleted uranium' for a bezel ring material?


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## PEU (Nov 1, 2006)

Why not make them in Polonium You wont need tritium slots...




Pablo


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## MoonRise (Nov 2, 2006)

Ailsnail,

There are hundreds of different steel alloys, using all kinds of alloying metals and elements to vary the properties of the steel alloy. That is one of the strengths of steel alloys, they can be largely tailored to the desired properties needed or desired.

Stainless steels can vary a large amount in exactly how 'stainless' they are. Some grades/alloys are VERY stainless, and others are less stainless. Some alloys are more corrosion resistant than others to differing corrosive agents, like acids or alkalies or other chemicals.

Generally speaking, most of the time a steel alloy is classified as 'stainless steel' if the percentage of chromium is 13% or larger. In general, the more chromium in the alloy, the more 'stainless' to most things that the steel is. But also keep in mind that there are exceptions to the rules and also that the 13% cut-off point is not a go/no-go point for rust or staining, but that once the percentage of chromium in the steel alloy reaches 13% that the alloy will be generally 'stainless' to typical ordinary conditions. An example is the steel alloy D-2, used for tooling and some knife blades, which has 12% chromium and thus can't be called a "stainless steel", but which has enough chromium content in it to be pretty much semi-stainless in ordinary usage. A common stainless steel alloy used for stainless cookware and kitchen flatware might be 18-8, which has 18% chromium and is considered 'stainless' in ordinary usage. But even that alloy can stain, rust, or corrode in ordinary daily kitchen usage!

Stainless steels are just that, they stain LESS. Much less than a non-stainless steel. Even Rostfrei, rustfri, or syrefast -can- rust or corrode in the right/wrong conditions. The literal translation of "withstands acids" would be used in English as "acid resistant" in the description, but the most precise way to specify a steel is by the alloy designation and not the more general but vastly more imprecise terms of "tool steel", "high carbon steel", "low carbon steel", "stainless steel", "surgical steel", "high carbon stainless steel", or such.

Even within any of the above listed 'category' of steel, the material properties can vary greatly. 

And if you see the welds on some syrefast steel rusting, it is most likely because the wrong welding rod/wire/filler metal alloy was used for the base alloy and the environmental conditions.


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## Art Vandelay (Nov 2, 2006)

I don’t know anything about metal. I have read that knife blades are the only parts of knives that are hardly ever made of titanium. They say this because titanium is not hard enough and it will not hold an edge well. Does anybody know if this is true?


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## blahblahblah (Nov 2, 2006)

Art Vandelay said:


> I don’t know anything about metal. I have read that knife blades are the only parts of knives that are hardly ever made of titanium. They say this because titanium is not hard enough and it will not hold an edge well. Does anybody know if this is true?



That is true for the most part. There are some Beta titaniums that do hold an edge better than other grades. I have a couple titanium dive knives. I don't use them much for cutting, but they are there if NEEDED. I chose titanium for the corrosion resistance. There are occasions where I can not rinse my gear immmediately. A titanium dive knife is one thing less that I have to waste my bottled water on.


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## soapy (Nov 2, 2006)

Don't ever forget that steel is stronger than titanium, unless you are talking about weight-for-weight!

A 2cm diameter spur that can take 4 tonnes when made of stainless steel might need to be 3cm diameter if made of titanium, giving it double the volume of material. However, the titanium spur would still be lighter.

Don't forget, also, that tensile strength counts for a lot when threading things. You don't want the threads to deform under pressure. The depth and pitch you choose for steel might not be what is best for a switch to titanium, and vice versa. Unlikely to apply to a torch, though!

One big advantage with Ti is that once it is machined up, you can colour it by oxidation/nitriding, which also leaves a very, very hard corrosion and scratch resistant layer that is permanently and chemically bonded to the base material, very unlike something like powder coated steel.


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## blahblahblah (Nov 2, 2006)

soapy said:


> Don't ever forget that steel is stronger than titanium, unless you are talking about weight-for-weight!



Are you sure about that blanket statement?


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## xochi (Nov 24, 2006)

soapy said:


> One big advantage with Ti is that once it is machined up, you can colour it by oxidation/nitriding, which also leaves a very, very hard corrosion and scratch resistant layer that is permanently and chemically bonded to the base material, very unlike something like powder coated steel.



If the ti nitride coated drill bits are any indication these hard coatings are possible on steel as well. The easy and colorful anodize frequently seen on ti isn't very scuff or scratch resistant.

Also something to consider is that new "powdered metal" type technologies have changed the rules of metallurgy. Corrosion resistance /toughness/ hardness are no longer contrary aims and incredible steels have been appearing in knives. Both s30v and zdp-189 are amazing. I can't believe how well my sebbie holds an edge and even in the , sweaty salty environment of my summer dampened pocket I had no problems with rust with s30v. The ZDP189 kershaw I just received is nothing short of miraculous in terms of edge holding, this bugger stays sharp despite having a very thin edge. I've been shaving aluminum reflectors , cutting the outer jacket of high voltage cable and twist scapeing bamboo and the blade is still hair popping sharp. Weird stuff!

I think good times are ahead if this tech begins to be applied with other metals like ti and aluminum.


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## AilSnail (Nov 25, 2006)

Any idea what syrefast implies? I thought it implied a "trait", that it would not corrode under such and such circumstances - unlike the definition of rustfri/stainless, which only implies what it is made of.


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