Most engineers and buyers never run this test themselves. They read HV numbers on a mill certificate and have to trust what those numbers mean. That's a problem when the difference between "acceptable" and "reject" comes down to a diagonal measurement under a microscope.
This guide breaks down how Vickers microhardness testing works, when it's used, how to interpret the results, and which standards govern the process.
Key Takeaways
- Vickers testing uses a single 136-degree diamond indenter across both micro and macro load ranges
- Smaller loads (under 1 kgf) fall under "micro" Vickers, per ASTM E384's 1-1000 gf range
- ASTM E92, E384, and ISO 6507 govern reporting; conversions to other scales (per ASTM E140) are approximate only
- Hardness data is one piece of a traceable material certification package, not a standalone checkbox
What Is Vickers Microhardness Testing?
Vickers hardness testing presses a diamond pyramid indenter into a material's surface under a controlled load, then measures the resulting indentation to calculate a hardness value. The harder the material, the smaller the indent left behind.
The indenter itself never changes shape: a square-based pyramid with a 136-degree angle between opposite faces. What changes is the load.
Micro vs. macro Vickers comes down to force:
- Micro Vickers: loads from 1 to 1000 gf, per ASTM E384-22
- Macro Vickers: loads up to 120 kgf, per ASTM E92-23
Both use the same indenter geometry. Only the applied force differs.
Struers uses 1 kgf as the practical dividing line between the two ranges. Most labs use that number in conversation, even though ASTM states the micro ceiling as 1000 gf rather than 1 kgf.
Why Vickers Beats Rockwell or Brinell for Range
Rockwell and Brinell each work well in a narrow band of hardness and part size. Vickers doesn't have that limitation. One indenter geometry covers everything from soft aluminum to hardened tool steel, and from bulk sections down to thin case-hardened layers or individual weld passes. Research labs, quality audits, and failure investigations rely on that range when other methods fall short.
How the Vickers Test Is Performed
Getting a trustworthy HV number starts long before the indenter touches the part.
Sample Preparation
The surface needs to be flat, clean, and usually polished. Optical measurement of a microscopic indentation doesn't forgive surface flaws:
- Scratches
- Oxide layers
- Uneven surface finish
Any of these can throw off the diagonal reading and skew the result.
The Test Sequence
- Position the sample under the diamond indenter using the tester's stage
- Apply the load: a controlled force held for a dwell time, commonly 10 to 15 seconds (per ZwickRoell and Buehler technical documentation)
- Remove the load, leaving a square indentation on the surface
- Measure both diagonals of the indentation under magnification
- Average the two diagonal measurements and calculate HV using the applied force
Equipment Involved
- Load application system (dead-weight or motorized)
- Optical or CCD measurement system for diagonal reading
- Positioning stage, often motorized in automated systems
Manual systems still exist, but automated setups with autofocus and motorized positioning reduce the variability that comes from different operators reading the same indent differently. That matters when a certification depends on a single number holding up under audit.
Why Vickers Testing Matters for Metal Buyers and Fabricators
A hardness number on a cert is evidence that a forging or heat-treated bar actually reached the mechanical condition the spec called for.
Where Vickers testing earns its keep:
- Confirming heat-treated alloy steel meets mechanical property requirements for gears, bearings, or shafts
- Verifying case-hardened layers on carburized or nitrided parts only a few thousandths of an inch deep
- Checking weld zones where heat input can locally soften or embrittle surrounding material
- Spot-checking hardness consistency across a heat-treatment lot
For context on what heat treatment can do to hardness: one peer-reviewed study on a C250 aero-engine forging alloy found average microhardness rose from roughly 320 HV in the as-forged state to about 550 HV after solid-solution aging — an increase of more than 70%. That's the kind of swing a Vickers test is built to catch, and it's exactly why hardness verification follows heat treatment rather than skipping it.
Traceable documentation is non-negotiable once material reaches aerospace or defense supply chains. A hardness result on its own doesn't mean much without the applicable standard, load, dwell time, and specimen identification attached to it.
Aero-Vac Alloys & Forge, an ISO 9001 and AS9100 certified distributor of alloy steels and forging stock, works within these documentation expectations every day. Grades such as 4140, 4340, and 9310V for gear or bearing work only move on schedule when the cert package matches the material.
Vickers vs. Other Hardness Testing Methods
Not every hardness test measures the same thing the same way.
| Method | How it measures | Best fit |
|---|---|---|
| Vickers | Optical diagonal measurement of a diamond pyramid indent | Wide hardness range, thin sections, localized features, welds |
| Rockwell | Depth of penetration | Fast production-floor checks on bulk material |
| Brinell | Large ball indenter, indentation diameter | Rough or coarse-grained materials, castings |
Rockwell is quick and depth-based — great for a production line running the same part repeatedly. Brinell's large ball indenter works well on coarse or inhomogeneous material where a tiny Vickers indent might land on an unrepresentative spot.
Vickers wins out for research, quality audits, and any part too thin or small for a Rockwell or Brinell indenter to sit on properly. The same 1 kgf boundary mentioned earlier splits the "micro" territory (thin sections, coatings, case depth) from "macro" (bulk material checks).
Standards and Reporting for Vickers Hardness Tests
Three standards govern most Vickers work in North America:
- ASTM E92 — macro Vickers and Knoop hardness of metallic materials, covering loads from 1 gf up to 120 kgf
- ASTM E384 — microindentation hardness, covering the 1 to 1000 gf range
- ISO 6507-1:2023 — the international equivalent, specifying Vickers test methods across three force ranges
What a Test Report Should Include
A complete Vickers report goes beyond the final HV number. Look for:
- Applied load and dwell time
- Individual diagonal measurements and their average
- Calculated HV value
- Reference to the governing standard (and edition)
- Specimen or heat/lot identification
A Note on Conversions
Hardness conversion tables, like those in ASTM E140, let you estimate an HRC value from an HV number or vice versa. These conversions are approximate.
ASTM states they can be inaccurate for a given application and should only be used when direct testing under the specified method isn't possible. If a spec calls for HV, don't substitute a converted Rockwell reading and call it equivalent.
FAQ
What is Vickers hardness testing and how is it performed?
Vickers hardness testing measures a material’s resistance to plastic deformation. A diamond pyramid indenter is pressed into the surface under a controlled load, held for a dwell time (commonly 10–15 seconds), then removed. The two diagonals of the square indentation are measured and averaged to calculate the HV value.
What is the difference between micro Vickers and Vickers hardness testing?
"Micro" refers to loads below roughly 1 kgf (per ASTM E384, 1–1000 gf), while standard Vickers covers loads from about 1 kgf up to 120 kgf per ASTM E92. Both use the same 136-degree diamond pyramid indenter—only the load range differs.
What kind of equipment is used for Vickers hardness testing?
Vickers testers combine a load application system, an optical or CCD measurement system for reading indentation diagonals, and a positioning stage. Automated systems add motorized stages and autofocus to reduce measurement variability.
Which indenter is used in a Vickers hardness test?
A diamond ground into a square-based pyramid shape, with a 136-degree angle between opposite faces. This same indenter geometry is used across both micro and macro load ranges.
What is the ASTM standard for Vickers hardness testing?
ASTM E92 covers macro Vickers testing (about 1 kgf to 120 kgf), while ASTM E384 covers microindentation hardness (1 to 1000 gf). ISO 6507 is the international equivalent standard.
What is a Vickers hardness test report?
A complete report includes the applied load, dwell time, individual diagonal measurements, the calculated HV value, and a reference to the governing standard and edition used, along with specimen identification for traceability.
