Hardness of Titanium

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npueppke
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Hardness of Titanium

Postby npueppke » Tue Dec 28, 2010 8:55 pm

I was reading an article today in Popular Science about a research lab/detector facility for "dark matter". They had to fit something very tightly inside of a titanium vessel, but couldn't because some welds were in the way, so he was describing the difficulty that they were having grinding away the titanium filler material with diamond bits because "titanium is harder than steel".

That can't possibly be true, if it were people would be using TI to make knife blades all over the place, right? I seem to recall hearing somewhere that TI was something like 40 RC. Not as soft as aluminum but certainly not as hard as steel.

It just struck me as kind of funny that they would comment about how titanium was difficult to grind because it is too hard.

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Postby Jordan » Tue Dec 28, 2010 9:02 pm

Probably depends on the alloy used. I think that the selling point of titanium is it's strength relative to it's weight. I remember reading somewhere that it is only about half again as dense as aircraft aluminum, but has more than twice the tensile strength.
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Postby SQSAR » Tue Dec 28, 2010 9:05 pm

Just thinking out loud here, and someone correct me if I'm wrong: But if you are grinding a non-ferrous metal with a diamond cutter, might the titanium be clogging up the cutter?

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Postby jzmtl » Tue Dec 28, 2010 9:07 pm

Titanium is harder to grind not because it's harder, but because it tend to gum up your grinding bit. It's probably what happened to that guy and he just thought it's because titanium is harder.

If he had used a carbide cutter it would've been like butter.

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Postby Dr. Snubnose » Tue Dec 28, 2010 9:07 pm

The most common grade, 6% Al- 4 V- balance Ti, a.k.a. 6-4, or Grade 5, won't hold an edge, even in the highest strength heat treatment. Even the beta titanium alloys, the highest strength ones, will only get to mid 40's on the Rockwell C hardness scale.

and yes the cutter might get clogged SQ.....Doc :D
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Postby Donut » Tue Dec 28, 2010 9:19 pm

I've read a little bit about this. From what I've seen, titanium is stronger than some of the softest steels. So in marketing they can say that it is stronger than steel and lighter than steel, but in reality it's not as great as it sounds.

I think the strong points of titanium are it's weight/density, corrosion resistance, and other unique properties.
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Postby npueppke » Tue Dec 28, 2010 10:23 pm

Hmm. I just read an article about watches, and, coincidentally, they also talk about titanium vs steel, saying that "titanium has a hardness exceeding that of most steels". One reference I found (http://www.keytometals.com) says that a typical titanium alloy has a rockwell C hardness of around 34. I couldn't find any reputable source for steel hardness values but I still find it a bit hard to believe that most steels are below 34.

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Postby 2cha » Wed Dec 29, 2010 12:17 pm

npueppke wrote:Hmm. I just read an article about watches, and, coincidentally, they also talk about titanium vs steel, saying that "titanium has a hardness exceeding that of most steels". One reference I found (http://www.keytometals.com) says that a typical titanium alloy has a rockwell C hardness of around 34. I couldn't find any reputable source for steel hardness values but I still find it a bit hard to believe that most steels are below 34.
Steel before heat treatment or after? Steel with alloying metals or without?
I have a titanium Panerai watch. It seems to scratch more easily than my stainless watches. It could also be that my Ti watch is much thicker than my SS watches so that it is in position to get banged up more often.

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Postby npueppke » Wed Dec 29, 2010 1:10 pm

It said "harder than most alloy steels" so I'm assuming something like a low alloy/mild steel but I don't know. For sure knife steels are harder than TI.

I don't know how steels are classified but the sites that I did find with info about steels gave their hardness in Vickers not RC.

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Postby Piet.S » Wed Dec 29, 2010 2:05 pm

It's just marketing.
Most people nowadays never worked with metals so they will believe anything.
And people love to hear that they are buying something very special.

Ti has its place in the aerospace industry but for many other applications it is a bit of a hype.
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Postby bh49 » Thu Dec 30, 2010 1:22 pm

npueppke wrote: I just read an article about watches, and, coincidentally, they also talk about titanium vs steel, saying that "titanium has a hardness exceeding that of most steels". One reference I found (http://www.keytometals.com) says that a typical titanium alloy has a rockwell C hardness of around 34. I couldn't find any reputable source for steel hardness values but I still find it a bit hard to believe that most steels are below 34.
Piet.S wrote:It's just marketing.
+1

IMHO this is just marketing. You cannot speak about steel hardness in general. Range is too wide. Most of us heard about harden tool steels in HRc 60+ range, but there are steels, which do not have much carbon and cannot be hardened. Their hardness below Rockwell scale. Couple times I checked hardness on A2 tool steel prior to hardening, it was also below HRc scale. I am working for company, which does a lot of machining. Mostly steel, also aluminum and 6Al-4v titanium. Currently all material received prior to hardening. HRc for titanium usually in mid 40th, steel lower than this. But quite a few steel can reach much higher hardness after heat treatment. I have no exprience about titanium alloys other than 6Al-4v
npueppke wrote:
I don't know how steels are classified but the sites that I did find with info about steels gave their hardness in Vickers not RC.
Vicker is using 10 kg load (C scale is 150 kg)testing performed when harden material is very thin. Also can be used for case harden steels.
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Postby Donut » Thu Dec 30, 2010 4:06 pm

RYP on bladeforums announced the other day that there are some new titanium alloys that can achieve 60 HRC.

Not sure how accurate this info is.

Reference link.
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Postby Tsujigiri » Sat Jan 01, 2011 2:56 am

In my experience, titanium in watches scratches much more easily than stainless steel. So titanium is softer than at least some steel.. since knife steel is intended to be hard I'm sure it's harder than titanium.

On a side note, does anyone know why there aren't any knives made of tungsten carbide?

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Postby SQSAR » Sat Jan 01, 2011 7:17 am

Tungsten usually has a RC of about 74-80, making it awesome for edge retention, and its ability to cut through a boat load of stuff. The catch comes with the fact that it is brittle and susceptible to chipping and cracking much more than high performance steel alloys used in the knife business. This is why a lot, if not most, applications that use tungsten as the cutting surface, only use 'carbine tipped' blades. Lateral stresses will do them in., and tungsten is pretty binary, it's either straight and cutting well, or it bends slightly and cracks all the way through. But I'm sure there has to be a number of guys here who can offer a more technical answer.

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Postby jimbo@stn24 » Mon Jan 03, 2011 10:36 am

Piet.S wrote:It's just marketing.
Most people nowadays never worked with metals so they will believe anything.
And people love to hear that they are buying something very special.

Ti has its place in the aerospace industry but for many other applications it is a bit of a hype.
Thanks for the honesty Piet, don't think I've ever heard it said so plainly. It has it's place, and it has an "ooh" factor, but it isn't magical.

One of my favorite examples is bicycles and titanium. Titanium chainrings (the rings on the crankset) are almost non-existant due to the fact a well made aluminum ring is stiffer, cheaper, and the nearly the same wieght, with acceptable wear resistance. Also, the first titanium bicycles were almost unrideable due to titaniums low stiffness/weight ratio. Once it was alloyed properly and treated correctly, the titanium frameset came into it's own.

When you start to see titanium edition camper trailers and Columbia titanium jackets, you know the word is being played purely for the hype it seems to generate.
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Postby SQSAR » Mon Jan 03, 2011 12:43 pm

Jimbo@stn24: Good point. Also notice, in the bicycle world, how Ti pedal spindles also have weight limits? Ti is great stuff for the applications it's suited for, but it isn't a metallurgical panacea that the hype would lead one to believe.

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Postby jzmtl » Mon Jan 03, 2011 1:15 pm

Yeah Ti is getting hyped to the extreme nowadays. Although Ti watch is nice in one regard, they feel almost as light as plastic on on wrist (thou much more $$$) and look better.


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