Short answer
- ASTM E3499 is the test method for indentation plastometry of metallic materials (ASTM Committee E28, 2025 edition). From the shape of an indent, it works out the material's stress-strain curve: yield strength, tensile strength and uniform elongation.
- It is not a hardness standard, nor a standard for portable hardness testers. Leeb hardness follows ASTM A956; UCI follows ASTM A1038; and conversion between scales follows ASTM E140.
- If what you need is the hardness of the part — incoming material checks, verifying a heat treatment, comparing batches, testing installed parts — a portable hardness tester is enough. The QH7, which combines Leeb and UCI, does exactly that.
What indentation plastometry measures
As in a Brinell test, a spherical indenter is pressed into the surface and leaves a permanent indent. The difference is what happens next: instead of measuring only the indent diameter, the method measures its full profile — the shape of the crater and of the pile-up around it.
That profile depends on how the material deforms plastically. Finite element software simulates the same test and adjusts the parameters of the plasticity law until the simulated indent matches the measured one (known as inverse analysis). The result is a stress-strain curve comparable to that of a conventional tensile test.
The advantage over tensile testing is that no specimens need to be cut or machined: you can test specific zones of a part (across a weld, for example), screen many samples, or test components in service.
Source: ASTM E3499-25, Standard Test Method for Indentation Plastometry of Metallic Materials, sections 1 and 5 (scope, significance and use).
Plastometry or hardness: they answer different questions
| Indentation plastometry (ASTM E3499) | Portable Leeb or UCI hardness (ASTM A956, A1038) | |
|---|---|---|
| Result | Stress-strain curve: yield strength, tensile strength, uniform elongation | A hardness value (HL, HV, HB, HRC…) and, on steel, an indicative estimate in N/mm² |
| What is measured | The full indent profile, plus a finite element calculation | The rebound of an impact body (Leeb) or the frequency shift of a loaded probe (UCI) |
| Equipment | Indenter, indent profile measurement and inverse analysis software | Hand-held portable hardness tester |
| Where | Samples or prepared zones of the part | On the part itself, in the workshop or in the field, in seconds per reading |
| What it is for | Replacing or complementing a tensile test when specimens can't be taken | Production control, heat treatment verification, accepting or rejecting material |
Put another way: hardness tells you how well the material resists being indented, and that is enough for most checks. Plastometry tries to reconstruct how the whole material behaves when it yields — something that, until now, only a tensile test could tell you.
Where plastometry doesn't work
The standard itself recognises several limits of the method:
- It doesn't give elongation at fracture. It only goes as far as the onset of necking.
- Brittle materials: it overestimates tensile strength.
- It assumes the material behaves the same in tension and compression. That doesn't hold for cast irons, hexagonal close-packed (HCP) metals with strong crystallographic texture, some nanocrystalline materials or certain nickel-based superalloys.
- Highly anisotropic materials (which behave differently depending on direction): not appropriate.
- Non-monotonic hardening: the recommended plasticity laws only apply to materials that harden steadily as they deform.
To classify cast iron (grey or ductile, percentage of nodularity), which falls outside plastometry, a different principle is used: ultrasonic propagation velocity. We explain it in the guide cast iron nodularity.
When a portable hardness tester is enough, and when it isn't
Measuring hardness is enough if…
- The specification or drawing calls for a hardness value (for example, "220–260 HB" or "58–62 HRC").
- You want to check that a heat treatment came out right, or that two batches of the same material behave the same.
- The part is large, installed, or can't be taken to the lab.
- You need many quick readings to find soft or hard spots.
You need a tensile test or plastometry if…
- You need the yield strength or tensile strength as a design value or for certification.
- The specification calls for tensile properties (Rp0.2, Rm, elongation) rather than a hardness value.
The QH7 converts hardness to N/mm² on steel, but that figure is an indicative estimate, even rougher than conversion between hardness scales. Use it to compare, never to calculate. More on this in the hardness conversion chart.
What tends to go wrong, and why
Asking for "a hardness tester to ASTM E3499"
E3499 is not a hardness tester standard. If your specification cites it, it is asking for indentation plastometry, a different test. If it cites A956 (Leeb) or A1038 (UCI), a portable hardness tester complies.
Treating the hardness-to-strength conversion as a design value
The relationship between hardness and tensile strength is empirical and depends on the material. It is a useful guide on steel; for structural calculations you need a tensile test (or plastometry, where the standard allows it).
Applying the steel table to other materials
Steel hardness and strength conversions don't apply to aluminium, brass, austenitic stainless steels or cast irons. Each material has its own tables, or none.
