Mystery metal 15

[rhodie]

I have a piece of metal in my hand that appears to be bronze. I am confused about this, because the hardness of it is around 54-58 RC, and it is hardened throughout!

The piece is used as a driveshaft transfer coupling, and splines run the length of the ID. This means the part was probably broached, but I can't be for certain. I have been asked to modify the part, but even when grinding with a diamond wheel the work is SLOW. (This isn't a problem, it's just that I am totally impressed with the toughness of the metal.)

The dimensions (for what it's worth) 2" OD, 1.125" ID, threaded 1/4-20 full lentgth, 8 splines run the ID. The piece cost $800 three years ago. (It has an oil trough drilled inside)

I would ask the manufacturer what mat'l it is, but the manufacturer is out of business. I have asked some toolroom guys what it is, and their best guess is some kind of beryllium steel, but I disagree with that because beryllium steel would offer no great advantage over regular steel where the part is used: a non corrosive, dry, cool, clean and dark environment. The shaft that it couples runs continously, with no jumpy, jerky starts or super-high RPMs.

Young's Modulus is extraordinarily high on Beryllium Copper, but is it on beryllium steel as well?

 

[mcguire]

There is no beryllium steel. Maybe they meant to say boron steel. Boron is used to increase the depth of hardening. It's probably alloy steel but to know which one with accuracy you should use a spectrograph.

 

[TVP]

Why do you think it is bronze? Because of the color? I agree with mcguire, it is likely to be an alloy steel, possibly one that has been coated if it looks copperish.

 

[rhodie]

I have been doing some reading, and I think what I am dealing with is actually an Aluminum-Bronze Alloy.

http://microstructure.copper.org/overview/al_bronze.htm

I can't wait to tell those guys back in the shop that there is no such thing as Beryllium Steel. Maybe I should have them order some for me.

 

[mloew]

rhodie,

Can you calculate the density (measure volume and mass)? That might narrow it down significantly.


Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rhodie]

MLoew:

I calculate it at about .293 lb/in^3

I hope that helps you more than it did me.

 

[Metalguy]

Is it magnetic?

 

[rhodie]

I don't think so. If it is ferrous, it is a really low composition.

 

[TVP]

rhodie,

Aluminum bronze alloys are incapable of attaining a hardness of 54-58 HRC. Beryllium copper alloys have the highest hardness when precipitation hardened, with maximum hardness of ~ 42 HRC.

 

[etch]

I would have hazard a guess at aluminum bronze also, but the colours do not match. Aluminum bronze is a pale golden colour, but it certainly is tough. I have made aluminum bronze and couldn't cut with hacksaw, only an industrial hand grinder. It would be slightly magnetic, due to the nickle and iron content (5%).

 

[rhodie]

Thanks for the replies. I'm still not sure of what it is after reading TVP's reply. When I find out for certain, I'll let everyone know.

 

[brad]

Rhodie,
Maybe you've already figured this out, but I'll add this as nobody has commented on it . . .

You state a density of .293 lb/in^3. This equates to 8100 kg/m^3.

Here is a brief listing of some metal densities (in kg/m^3):

Aluminum: 2800
Cast Iron: 7200
Steel: 7850
Brass: 8470
Bronze Manganese: 8800

I think this supports the suggestion of an aluminum bronze.
Brad

 

[mcguire]

Aluminum bronze with 5% aluminum is 8.17 g/cc. Bradh wins the prize.

 

[Maui]

Bradh, the densities that you listed are average values for these groups of materials. The steel grades that we manufacture vary in density from 0.276 lbs/in^3 for 440C to 0.294 lbs/in^3 for M2. The density itself won't tell you that it definitely is or isn't aluminum bronze. Why not save some of the chips and send them to a local college that has an SEM for an EDAX scan? They probably won't charge you a cent for the service, and it would give the students some practice in identifying an unknown.


Maui

 

[rhodie]

Maui

Your suggestion that I send a sample off for analysis is something I did this morning.

I am sending a sample to a lab at Texas A&M. We'll see how quick the aggies can make something of it.

-Just some clarification on the color; it is a pale golden color, competely thru. I apologize if I confused anyone.

I gathered some more (similar) pieces today, and I find that an average of fifty or so Rockwell readings result in an average RC of 52. That said, the particular piece I am curious about has a RC avg. of 56, and it one of four pieces that read this highly.

The given density of .293 lb/in^3 is a good number.

Today I told the machist (that yesterday offered his guess of Beryllium Steel) to order me a 5" x 5' barstock of the material. I emphasized to him that I didn't want Beryllium Copper or Boron treated steel, I wanted Beryllium Steel or nothing at all. He said it should be "no problem, it'll be here in 4 days." I can't wait to see where this situation goes.

 

[CoryPad]

rhodie,

Are you sure your hardness measurements are correct? Are you performing a Rockwell C test, or converting another test to HRC?





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[rhodie]

I am using a Rockwell C hardness tester with a diamond cone indenter. Should I be using a Rockwell B scale or even an A scale?

The instrument could be "off", but I doubt it.

 

[rhodie]

CoryPad:

I see you point. I should only be getting 80-90 RB to 30 RC depending on the particular alloy of aluminum bronze.

 

[brad]

Maui,
I realize that those are average values; I was merely providing information which is relevant in HELPING identify the metal.

As his metal is on the ABSOLUTE high-scale for steels, this would suggest that it is more likely to be an aluminum-bronze alloy than a steel alloy.

Brad

 

[Metalguy]

Sure sounds like al. bronze and an incorrect hardness test.