Identify unknown steel

[MechDesign105]

Hi guys,
We have a project in which the refurbishment of a servomotor was given to an external company.
This equipment will only be installed for another 10 years, before a larger project will replace all the equipment in the substation.

Therefore, the company was told that no changes to the original design must be made.
The original piston removed could not be recycled and needs to be replaced by a new one.
We have asked the exact same material be used to machine the new piston.
The company therefore proceeded to the chemical composition analysis : it was determined that the original material was AISI 1040.

What other tests must be done in order to identity the original material (its state, its mechanical properties, etc)?
The equipment is installed inside, Tamb is above 10C at all times.

Thanks for your help

 

[tbuelna]

If you have established that the material is 1040 carbon steel, the only other thing you need to know is the heat treat used for the part. Cut the piston in half and do a hardness check from the surface to the core of the part. This will tell you if the part was case hardened, thru hardened, or used in some other condition.

 

[MechDesign105]

Hi tbuelna ,
Thanks for your reply,
I am under the impression that solely measuring the hardness at the center and at the surface will not be enough to determine the heat treatment...
For example, this will give no indication as to the yield strength...

 

[jbeckhou]

send to a lab for analysis.

Petrotrim Services, LLC

http://www.petrotrim.com

 

[redpicker]

The hardness values will tell you the hardness of the pat. As tbuelna states, if taken from surface to core (not just at the surface and at the core) this will tell you if the part was case hardened, through hardened, or some other condition. The hardness (and heat treat condition) will give an indication of the yield strength, but will not tell you precisely what the yield strength actually is. To determine the actual yield strength, you will have to perform a tensile test.

Even if you perform a tensile test, however, you will not know what the original design specification was. It is quite possible that the actual yield strength determined by your test met the original design specification (often, the design will specify a yield range and all you will know is a single value). It is also possible that the actual yield did not meet the design specification, but was accepted by the manufacturer on a deviation (say, the manufacturer knew the minimum specified yield was 5 times what was necessary for this specific assembly). The actual yield strength will not tell you any of this.

What you do know is the material chemistry and, if you perform a hardness profile on a cross-section, you will have a good idea if the material was in the annealed, hardened, or case-hardened condition. At that point, you may need to perform additional tests (microstructure, for example) to fully define the processing used.

With this information, however, you will still not know what the original design was, only what material and processing will produce an acceptable part (assuming the original part gave acceptable performance).

rp

 

[mrfailure]

I would actually perform a surface microhardness profile, to establish whether a surface hardening treatment had been performed and, if it had, what case depth you had. Since you would make a mount for this anyway, you should also go ahead and etch for structure as a sanity check.