Effect of Precipitation Hardening on Elastic Modulus

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SUMMARY

The discussion centers on the evaluation of spring rings made from Inconel 718 that were delivered in an annealed state instead of the required heat-treated condition. The hardness of the delivered parts is HRB 92, approximately 14 HRC, while the specification demands a hardness greater than 36.0 HRC. Participants confirm that the elastic modulus of Inconel 718, typically around 200 GPa, remains largely unaffected by changes in hardness, indicating that the primary concern should be the material's yield strength rather than its elastic properties.

PREREQUISITES
  • Understanding of Inconel 718 properties
  • Knowledge of hardness scales (HRC and HRB)
  • Familiarity with elastic modulus concepts
  • Basic principles of material yield strength
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  • Research the heat treatment processes for Inconel 718
  • Learn about the relationship between hardness and yield strength in metals
  • Investigate methods for testing the yield strength of annealed materials
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Materials engineers, mechanical engineers, and quality assurance professionals involved in the evaluation and application of high-performance alloys like Inconel 718.

minger
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Hey guys, we have ordered some spring rings made out of Inconel 718. For some reason the company didn't finish the heat treat and the parts are just annealed, in the "dead-soft" condition.

I need to evaluate if these things are usable (they are actually supposed to be soft and were designed to be as soft as possible). Unfortunately I'm not a materials guy and cannot find any info on an "as-annealed" state of this stuff. Given a properly heat-treated piece, is there anything I can deduce about the elastic modulus from simply the hardess, or at least make a guess?

FYI, The spec calls for >36.0 HRC, and we have HRB 92, which ~14 HRC

Any help? Thanks,
 
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Forgive me if this comment is too basic, but elastic modulus is relatively insensitive to changes in microstructure such as precipitate size or density. (Hardness is a measure of resistance to permanent deformation, while elastic modulus is a measure of resistance to elastic deformation.) For example, steels are generally far harder than iron, their main constituent, but have approximately equal stiffness. Is there a reason you think that your specific samples would vary far from the general Inconel elastic modulus of ~200 GPa?
 
Hi minger. I agree with Mapes. I've seen a lot of data and never seen anything that indicates a change in modulus due to change in hardness.

If the springs are annealed, I'd be much more concerned with the material yielding when put into use.
 
OK, so the hardening pretty much only increases hardness and strength? Then, I only need to analyze whether or not these things will fail?

gotcha, thanks a bunch.
 

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