Vickers Hardness Test: Complete Guide to Method, Scale & Applications
What Is the Vickers Hardness Test?
The Vickers hardness test is a microhardness and macrohardness testing method that measures a material’s resistance to localised permanent deformation by pressing a square-based diamond pyramid indenter under a defined load into the specimen surface. The Vickers hardness number (HV) is calculated from the ratio of applied force to the surface area of the residual indentation — providing a hardness measurement that is consistent across all load levels, making it unique among hardness methods.
The Vickers test is governed by ASTM E92 (macro-range loads), ASTM E384 (micro-range loads), and ISO 6507 — and is considered the most versatile and universally applicable hardness test method, covering all materials from the softest bearing metals to the hardest ceramics and coatings.
Principle of Vickers Hardness Testing
A diamond indenter in the shape of a square pyramid with face angles of 136° is pressed into the polished specimen surface under a defined load (F) for a dwell time of 10–15 seconds. After load removal, the two diagonals (d₁, d₂) of the square residual indentation are measured using an optical microscope.
The Vickers hardness number is calculated as:
HV = 1.8544 × F / d²
where F is the applied force in kgf and d is the mean diagonal length in mm. The resulting hardness number is typically followed by the load used and dwell time — for example, 650 HV 0.5/15 = 650 Vickers hardness measured with a 0.5 kgf load for a 15-second dwell.
Load Ranges and Scale Designation
The Vickers test operates across an extraordinarily wide load range — from 1 gf to 120 kgf — enabling hardness measurement on films, coatings, thin sections, case-hardened layers, weld heat-affected zones, individual phases, and massive forgings:
- Micro-Vickers (HV 0.01–0.1 kgf): Individual phases, thin coatings, ion-implanted layers, grain boundary characterisation
- Low-load Vickers (HV 0.1–1 kgf): Case depth profiles, HAZ characterisation, thin sections
- Macro-Vickers (HV 1–120 kgf): General hardness testing, comparable to Brinell and Rockwell
Key Advantages of the Vickers Test
Continuous scale: Unlike Rockwell (multiple scales for different materials), HV is a single continuous scale from ~1 HV (lead, soft materials) to ~3000 HV (diamond, cubic boron nitride). All materials are directly comparable on the same numerical scale.
Geometric similarity: The 136° pyramid angle ensures that the hardness number is independent of load — the same material gives the same HV regardless of load level (within the elastic/plastic deformation regime). This is not true for Brinell or Rockwell testing.
Small indentation: The Vickers indentation is smaller than Brinell and comparable to Rockwell microhardness, enabling testing of thin sections, coatings, and heat-affected zones without substrate influence.
Excellent correlation with mechanical properties: Empirical relationships between HV and UTS (σ_UTS ≈ 3.3 × HV for steels in MPa), wear resistance, and fatigue strength make Vickers hardness a useful predictor of material performance.
Industrial Applications
In the case-hardening industry, Vickers microhardness profiles from the surface to the core measure the effective case depth (depth to the H transition, typically from 700+ HV at the surface to 550 HV at the core boundary for carburised steel). In the weld inspection industry, Vickers hardness surveys across weld cross-sections verify that maximum hardness in the HAZ does not exceed code limits (e.g., 350 HV maximum for sour service per ISO 15156). In the coating industry, the the Vickers hardness of PVD/CVD coatings verifies coating quality and identifies deviations in the deposition process.
Conclusion
The Vickers hardness test — based on indentation with a diamond pyramid and calculation of hardness from load and indentation geometry — provides a highly versatile and accurate method for measuring a material’s resistance to deformation across a wide range of materials and load conditions. Governed by standards such as ASTM E92, ASTM E384, and ISO 6507, it offers a continuous hardness scale, minimal indentation size, and excellent correlation with mechanical properties. Selecting appropriate load levels and test conditions based on material type and application is essential for obtaining reliable results, making the testing methodology as important as the hardness value itself.
Why Choose Infinita Lab for Vickers Hardness Testing?
Infinita Lab provides Vickers macro- and microhardness testing per ASTM E92, ASTM E384, and ISO 6507 — including case-depth profiling and weld HAZ surveys — through our nationwide, accredited mechanical testing laboratory network.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
Why is the Vickers test preferred over Rockwell for thin coatings and case-hardened layers? The very small Vickers indentation at low loads (10–100 gf) avoids substrate influence — meaning the measured hardness reflects the coating or case layer rather than being affected by the underlying softer substrate. The continuous HV scale also enables direct comparison between coating, transition zone, and substrate hardness without scale conversion.
What is the minimum material thickness for Vickers hardness testing? ASTM E384 requires that no deformation appear on the reverse side of the specimen. As a guideline, specimen thickness should be at least 10× the indent diagonal depth. At 300 HV with 0.5 kgf load, the minimum thickness is approximately 0.5 mm. At 1 kgf, approximately 0.8 mm minimum thickness is needed.
What is the diagonal measurement accuracy required for valid Vickers results? ASTM E92 and E384 require that diagonal measurements be made to ±0.5 µm (0.0005 mm) using a calibrated optical measuring system. This requirement becomes increasingly demanding at low loads where diagonals may be only 10–30 µm — requiring carefully calibrated, high-magnification optical systems.
How does surface finish affect Vickers microhardness results? Surface roughness introduces error in diagonal measurement — the indentation boundaries are obscured by surface asperities. ASTM E384 requires a metallographically polished surface (final polish typically 1 µm diamond or colloidal silica) for reliable microhardness testing. Any visible surface roughness at the magnification required to measure the diagonal is unacceptable.
What is the ISO 15156 maximum hardness limit for sour service weld zones? ISO 15156-1 (NACE MR0175) limits maximum hardness in weld heat-affected zones to 250 HV10 for sour oil and gas service (wet H₂S environments) in carbon and low-alloy steel weldments. Exceeding this limit increases susceptibility to hydrogen-induced cracking (HIC) and sulphide stress cracking (SSC) — catastrophic failure modes in sour service environments.
