Hardness testing measures a material's resistance to permanent deformation under a localised force — pressing a hardened indenter into the surface and measuring either the depth of the impression (Rockwell) or the size of the impression left behind (Brinell, Vickers, Knoop). The number that comes out tells you something practical: whether a heat treatment worked, whether a bolt is the grade it claims to be, whether a casting will resist wear, whether a tool steel insert will hold its edge, and whether a weld zone has been embrittled. This guide covers the four main test methods, when to use each, how the scales convert between one another, the published hardness ranges for common engineering steels and Australian-standard bolts, the file-test workshop reality, portable Leeb and UCI options for field inspection, and the AS 1815/1816/1817 standards framework that governs hardness testing in Australia.
AIMS supplies precision measurement equipment including the Mitutoyo range — calipers, micrometers, dial indicators, gauge blocks, surface plates and the Hardmatic portable hardness tester. Benchtop hardness testers are capital equipment and we work with our supply partners to quote and source. For pricing, application advice, demonstration arrangements and quote requests on benchtop or portable hardness testing equipment, contact our team on (02) 9773 0122 or via aimsindustrial.com.au/contact-us.
What is hardness — and why every workshop should care
Hardness is the resistance of a material to permanent indentation under a controlled load. It's not a fundamental physical property like density or melting point — it's a derived property that correlates strongly with other practical mechanical properties: tensile strength, wear resistance, fatigue strength, and machinability. A higher hardness number generally means a stronger, more wear-resistant, more brittle, and harder-to-machine material. The relationship isn't linear and varies by alloy, but the correlation is reliable enough that hardness testing has become the single most common mechanical test performed in metalworking — faster, cheaper and more portable than tensile testing, and almost always non-destructive on a finished part.
The practical reasons every workshop should care about hardness testing fall into five buckets:
- Heat-treat verification. Did the quench-and-temper actually produce the hardness you specified? A 4140 shaft heat-treated to 30 HRC for fatigue strength is a different part from the same shaft at 50 HRC for wear resistance. Hardness testing is how you confirm.
- Fastener and component quality. A Grade 8.8 bolt sits in a defined HRC range (22-32 per AS 4291). A reading outside that range indicates wrong grade, wrong heat treatment, or counterfeit product. Hardness is the quickest screening test for "is this bolt what the box says it is".
- Wear and tool life prediction. An HSS tool at Rc 64 lasts longer than the same geometry at Rc 60. A casting at 220 HB wears faster than the same casting at 280 HB. Hardness is a direct predictor.
- Weld zone evaluation. Welds and heat-affected zones change hardness — sometimes dramatically. A pressure vessel weld over 350 HV in the HAZ is at risk of hydrogen cracking. Hardness traverse across welds is mandatory for many AS 1210 and AS 3992 applications.
- Material identification. When stock material isn't labelled, hardness gives you a first cut on what it might be. A mystery bar at 18-22 HRC is probably mild steel; at 40-45 HRC it's probably hardened tool steel.
The four main hardness test methods at a glance
Four indentation methods dominate metallic hardness testing. Each was developed for different applications, and each survives because the trade-offs between speed, sample size, indentation size and accuracy still match different workshop needs. The shorthand table:
| Method | Indenter | Load | What's measured | Best for | AU Standard |
|---|---|---|---|---|---|
| Rockwell (HR) | Diamond cone (HRC) or steel/carbide ball (HRB and softer scales) | 60, 100 or 150 kgf major load, plus 10 kgf minor preload | Depth of indentation | Production QC, heat-treat verification, fast direct readout, no microscope | AS 1815 |
| Brinell (HB / BHN) | 10 mm tungsten carbide ball (most common; 5 mm and 2.5 mm balls used for smaller samples) | 3000 kgf (steels); 500-1500 kgf (softer alloys) | Diameter of indentation under microscope | Castings, forgings, weld HAZ, coarse-grained materials, large samples | AS 1816 |
| Vickers (HV) | Diamond pyramid, 136° angle between opposite faces | 5-120 kgf (macro); 0.01-1 kgf (micro) | Diagonal length of indentation under microscope | Thin sections, case-hardened layers, individual phases, microhardness across welds, hardened tool steels | AS 1817 |
| Knoop (HK) | Rhombohedral diamond (elongated pyramid) | 0.01-1 kgf (microhardness) | Long diagonal length under microscope | Brittle materials, thin coatings, hardness traverses on very thin sections, ceramics | ISO 4545 (no direct AS equivalent) |
Rockwell dominates production environments because it gives a direct digital readout in seconds with no microscope. Brinell dominates foundries and weld-shop inspection because the large indentation averages out local inconsistencies in coarse-grained materials. Vickers dominates inspection labs because the diamond pyramid gives one continuous scale across the entire range from soft aluminium to hardened tool steel. Knoop is a specialty for brittle thin-section work.
The Rockwell hardness test (HR) — how it works
The Rockwell method, patented in 1914 by Stanley P. Rockwell, became the production standard because it's fast, simple, and gives a direct numerical readout without measurement of the indentation. The procedure has four steps:
- Preload (minor load) application. A 10 kgf minor load is applied to the indenter — diamond cone (Rockwell C) or steel ball (Rockwell B). This seats the indenter through any surface debris or oxide and establishes a zero reference.
- Major load application. A larger load (60, 100 or 150 kgf depending on scale) is added on top of the minor load. The total force drives the indenter deeper into the material.
- Major load release. The major load is removed, leaving only the 10 kgf minor load. The indenter rebounds slightly as the elastic deformation recovers, but the plastic indentation depth remains.
- Depth measurement. The increased indentation depth (final position minus the initial minor-load position) is measured. This depth is converted to a hardness number by the formula HR = N - (d/s), where N is a scale constant (130 for ball indenter scales, 100 for diamond cone scales), d is the indentation depth, and s is the scale increment (0.002 mm per Rockwell point on most scales).
The depth-based measurement is what makes Rockwell fast — modern testers display the hardness number on a digital readout within seconds, no operator measurement required, no microscope, no skilled judgment. The trade-off is that depth-based measurement is more sensitive to surface preparation, sample backing, and small inhomogeneities than the area-based Brinell or Vickers methods. A Rockwell tester on a worn anvil, a thin sample, or a poorly-prepared surface produces scattered readings.
The standardised procedure is defined in AS 1815 (which is ISO 6508-3 MOD) and ASTM E18 internationally. Both require:
- Sample surface roughness Ra better than 0.4 µm (smoother on harder materials)
- Sample thickness at least 10× the indentation depth (otherwise the anvil reads through)
- Spacing between indentations at least 4× the indentation diameter
- Edge distance at least 2.5× the indentation diameter
- Test temperature 23 ± 5 °C for routine testing
Rockwell scales decoded — HRC, HRB, HRA and the rest
The Rockwell method isn't a single scale — it's a family of about 30 scales, each combining a specific indenter and load for a specific hardness range. The two that dominate everyday workshop practice are HRC and HRB. The others handle the materials those two can't measure accurately.
| Scale | Indenter | Total load | Typical range | Best for |
|---|---|---|---|---|
| HRA | 120° diamond cone (Brale) | 60 kgf | 20-88 HRA | Cemented carbide, hard thin steel, shallow case-hardened |
| HRB | 1/16" steel ball | 100 kgf | 20-100 HRB | Soft steels, copper alloys, brass, aluminium alloys, malleable iron |
| HRC | 120° diamond cone (Brale) | 150 kgf | 20-70 HRC | Hardened steels (tool steel, hardened structural, bolts grade 8.8+, bearings) |
| HRD | 120° diamond cone | 100 kgf | 40-77 HRD | Thin steel, hardened cast iron, case-hardened steel |
| HRE | 1/8" steel ball | 100 kgf | 70-100 HRE | Cast iron, aluminium, magnesium, bearing metals |
| HRF | 1/16" steel ball | 60 kgf | 40-100 HRF | Annealed copper, very soft steel sheet |
| HRG | 1/16" steel ball | 150 kgf | 30-94 HRG | Phosphor bronze, beryllium copper, malleable iron |
| HRN scales (15N, 30N, 45N) | 120° diamond cone (Brale) | 15, 30 or 45 kgf | Shallow case-hardened, thin sheet, surface treatments | Superficial Rockwell — for thin material where standard HRC would punch through |
| HRT scales (15T, 30T, 45T) | 1/16" steel ball | 15, 30 or 45 kgf | Soft thin sheet | Superficial Rockwell on soft materials |
The two key decision points: use HRC if your material is over 20 HRC equivalent (most hardened steels, bolts, bearings, tool steel), and use HRB if your material is under 100 HRB equivalent (mild steel, copper, brass, aluminium). If your reading falls below 20 HRC, switch to HRB. If it exceeds 100 HRB, switch to HRC. Readings near the bottom or top of any scale are unreliable.
The superficial Rockwell scales (HR15N, HR30N, HR45N for hard materials; HR15T, HR30T, HR45T for soft) come in when you're testing thin sheet or shallow case-hardening and a standard 150 kgf load would either punch through or read the anvil. They use the same indenters as the standard scales but with reduced loads and shallower indentations.
The Brinell hardness test (HB / BHN) — how it works
The Brinell test is the oldest of the four major methods — developed by Johan August Brinell in 1900. It pre-dates Rockwell by 14 years and survives because nothing else handles coarse-grained, inhomogeneous materials as well. The procedure:
- A hardened tungsten carbide ball — typically 10 mm diameter — is pressed into the test sample under a steady load (usually 3000 kgf for steel; lower loads of 500-1500 kgf for softer alloys like brass or aluminium).
- The load is held for 10-15 seconds (steels) or longer for softer materials (10-30 seconds).
- The load is released and the diameter of the indentation is measured optically — under a microscope or with a calibrated optical scale — in two perpendicular directions, and averaged.
- The Brinell hardness number (HB or BHN) is calculated by dividing the applied load (in kgf) by the curved surface area of the indentation (in mm²). The formula:
HB = 2F / (πD × (D − √(D² − d²)))
...where F is the applied load in kgf, D is the ball diameter, and d is the average indentation diameter. In practice, the diameter is looked up in a Brinell hardness conversion table rather than calculated manually.
The 10 mm ball at 3000 kgf produces an indentation typically 3-6 mm across — much larger than Rockwell's <1 mm or Vickers' <0.5 mm. The large indentation is exactly what makes Brinell valuable for certain materials:
- Castings — grey iron, ductile iron, cast steel. Coarse grain structure means small indentations land randomly on hard or soft phases; large indentations average across them.
- Forgings — similar coarse grain structure logic.
- Weld heat-affected zones — material varies across short distances, large indentation gives a meaningful average.
- Plate and large sections — where local hardness scatter from rolling is real.
- Sample identification — coarse but reliable hardness check on unknown stock material.
The trade-off is that Brinell needs a robust sample (3000 kgf is significant force), a fairly smooth surface (better than 0.4 µm Ra), enough thickness to absorb the indentation (typically 10 mm minimum), and an operator with a microscope and calibrated optical scale. It's slow compared to Rockwell — 30+ seconds per measurement plus optical read time — and it's destructive on cosmetically critical surfaces because the indentation is visible to the naked eye.
The procedure is standardised in AS 1816 (ISO 6506-1 MOD) and ASTM E10.
The Vickers hardness test (HV) — how it works
The Vickers test was developed by Robert L. Smith and George E. Sandland at Vickers Ltd in 1921 specifically to address Brinell's main weakness: the 10 mm ball begins to deform plastically on materials over ~600 HB, making the test useless on hard tool steels. The Vickers solution was to use a diamond pyramid indenter — diamond doesn't deform plastically at any practical hardness — and to measure the indentation diagonals rather than the depth. The procedure:
- A square-based diamond pyramid with an apex angle of 136° between opposite faces is pressed into the sample under a controlled load (5-120 kgf for macrohardness; 0.01-1 kgf for microhardness).
- The load is held for 10-15 seconds.
- The load is released and the two diagonals of the square indentation are measured under a microscope and averaged.
- The Vickers hardness number (HV) is calculated as:
HV = 1.854 × F / d²
...where F is the applied load in kgf and d is the average diagonal length in mm. The 1.854 constant comes from the geometry of the 136° pyramid.
Vickers' practical advantages over both Rockwell and Brinell:
- One continuous scale — Vickers numbers run from about 5 HV (very soft pure metals) to 2400 HV (diamond itself). You don't have to switch scales between hardened steel and pure aluminium; the same HV number is comparable across the whole materials range.
- Small indentations — typically 0.1-0.5 mm across at macrohardness loads. Allows testing on thin sections, individual features, and around the edge of small parts.
- Microhardness capability — at loads of 10-1000 gf (0.01-1 kgf), Vickers indentations are 10-100 µm across. This lets you measure hardness of individual grains, case-hardened layers (case depth profiling), thin coatings (PVD, electroless nickel, etched chrome), weld HAZ traverses, and prior-austenite grain hardness on quenched steels.
- Diamond indenter never wears or deforms — calibration drift is minimal compared to Rockwell's diamond Brale (which does wear) or Brinell's carbide ball (which deforms on hard materials).
The trade-offs are speed (slower than Rockwell because it requires microscope measurement of the diagonals), cost of the equipment (Vickers microhardness testers with motorised stages and image analysis can be major capex), and operator skill (the diamond pyramid leaves a square indentation, and accurate measurement of the diagonals requires consistent technique).
Standardised in AS 1817 (ISO 6507-1 MOD), ASTM E92 (macrohardness), and ASTM E384 (microhardness).
The Knoop hardness test (HK) — when to use it
The Knoop test was developed at the US National Bureau of Standards in 1939 as a microhardness method optimised for brittle materials and thin sections that Vickers can crack or punch through. The indenter is a rhombohedral diamond — an elongated diamond pyramid with one long diagonal seven times the length of the short diagonal. The procedure mirrors Vickers but with this elongated indenter and microhardness loads (10-1000 gf).
The Knoop hardness number (HK) is calculated from the long diagonal of the indentation. The elongated geometry gives:
- Shallower indentation than Vickers at the same load — allows testing of thin coatings, brittle surface layers, and friable materials
- Less risk of cracking — important on ceramics, hardened glass, and very brittle metals
- Better resolution for hardness traverses — the long diagonal lets you place indentations closer together for a finer hardness profile across a case-hardened layer or coating
Knoop is essentially a specialist microhardness method — it's not used for routine production hardness testing on bulk metals (Rockwell handles that). It comes into play for ceramics, thin-film coatings (TiN on cutting tools, hard chrome on shafts), case-depth profiling, and academic metallurgy. Most workshops don't need Knoop. Inspection labs and university metallurgy departments use it routinely.
Standardised in ISO 4545 and ASTM E384 (which covers both Vickers and Knoop microhardness).
Shore and other elastomer hardness scales
The four indentation methods above cover metallic hardness. Shore hardness is a separate family of scales developed for non-metallic materials — rubber, plastics, elastomers — where the indentation methods above don't work because the material recovers elastically and either gives near-zero readings or destroys itself under the load.
Shore testers use a spring-loaded indenter with a defined tip geometry and a defined spring force. The depth of penetration is read off a dial calibrated 0-100. There are two main scales for workshop use:
- Shore A — for soft rubbers and elastomers (NBR, EPDM, silicone, soft polyurethane, neoprene). Typical workshop range 30A (very soft) to 95A (hard). A rubber drive belt is around 65-75A; a tyre tread compound is around 60-65A; a soft O-ring seal is around 70-80A.
- Shore D — for hard plastics and hard elastomers (PVC, Delrin, polycarbonate, hard polyurethane, nylon). Typical range 40D to 90D. Above 95A the Shore A scale becomes inaccurate and you switch to Shore D.
Shore hardness is a separate audience from this guide — rubber compounders, O-ring specifiers, mould-makers selecting elastomer formulations. For comprehensive elastomer hardness coverage, see our O-Ring Guide, which covers Shore A material grades for NBR, Viton, EPDM and silicone seal selection.
Shore hardness is governed by ASTM D2240 (the international workshop standard) and ISO 7619. It is not directly convertible to Rockwell, Brinell or Vickers — the underlying physics differs (rubber elasticity vs metallic plasticity), so any "conversion chart" between Shore and metallic scales is approximate at best and misleading at worst.
Choosing the right test method — decision matrix
Method selection is driven by material, sample geometry, required accuracy, and whether the test must be non-destructive on a finished part. The practical decision matrix:
| Scenario | Best method | Why |
|---|---|---|
| Heat-treated steel parts, production QC | Rockwell HRC | Fast, direct readout, no microscope, AS 1815 standard, every metallurgist understands HRC numbers |
| Soft steel sheet, copper alloys, brass, aluminium | Rockwell HRB | Steel ball indenter handles soft metals where HRC diamond would punch through |
| Iron castings, ductile iron, weld HAZ, large forgings | Brinell HB | 10 mm indentation averages across coarse grain structure |
| Hardened tool steel over 65 HRC, cemented carbide | Vickers HV or HRA | Brinell ball deforms above ~600 HB; Vickers diamond doesn't; HRA uses diamond Brale at reduced load |
| Thin sections under 1 mm | Vickers HV at reduced load, or superficial Rockwell (15N/30N/45N) | Small indentation depth, sample-thickness rule satisfied |
| Case-hardened layer, surface hardness profile | Vickers HV microhardness at 100-500 gf | Indentations spaced 0.05-0.2 mm apart map the case-depth profile |
| Welds — hardness traverse across base metal / HAZ / weld metal | Vickers HV typically at 1-10 kgf | One scale, fine spatial resolution, AS 3992 reference method |
| Thin coatings (PVD, electroless nickel, hard chrome) | Knoop HK at 10-50 gf | Shallow indentation, minimal substrate effect |
| Brittle materials — ceramics, sintered carbide, hardened glass | Knoop HK or low-load Vickers | Elongated Knoop indenter reduces cracking risk |
| Rubber, plastics, elastomers | Shore A or D | Indentation methods don't work on elastic materials |
| Field inspection — installed welds, large fabrications, in-place machinery | Leeb (rebound) or UCI portable | Benchtop testers can't reach the work; portables sacrifice some accuracy for accessibility |
| Workshop go/no-go on heat-treated parts (no tester available) | Hardness test files | RC 40-65 file set, ±3-5 HRC accuracy, adequate for most general engineering verification |
Sample preparation — the step most people skip
Hardness test results are only as good as the sample preparation. Forum-validated reality across Practical Machinist, Hobby-Machinist and inspection-lab sources: more bad hardness readings come from poor surface preparation than from any other single cause. The four practical requirements:
- Surface roughness. For Rockwell, surface roughness should be better than Ra 0.4 µm — the equivalent of a smooth machined or fine-ground finish. For Vickers and Brinell, finer finishes (Ra 0.2 µm or better) are required because the indentation diameter is measured optically. As-cast, as-forged, as-welded surfaces give scattered readings; grinding to 240-400 grit minimum is standard prep.
- Sample thickness. The 10× rule — sample thickness must be at least 10 times the indentation depth, otherwise the anvil reads through the sample and you're measuring the support material. For HRC indentations on hardened steel, that means roughly 1.5 mm minimum thickness; for HRB on soft steel, 3 mm minimum. Below those thresholds, switch to superficial Rockwell (15N/30N or 15T/30T) or to low-load Vickers.
- Sample backing. Hardness testers have an anvil that supports the sample under the indenter load. The anvil must contact the sample firmly — no air gaps, no debris, no oil — or the sample flexes under load and gives a low reading. Thin samples sometimes need to be supported on a flat, hardened steel block of known hardness.
- Indentation spacing. Indentations placed too close together interact — the plastic deformation from one impression affects the next. AS 1815 minimum: at least 4× the indentation diameter between centres, and 2.5× the indentation diameter from any edge. Practical rule on HRC: spacing ≥ 3 mm, edge ≥ 2 mm.
The "I tested it five times and got five different readings" complaint, common in workshops without a metallurgical background, almost always traces to one of these four causes — usually surface roughness or sample backing.
Hardness conversion between scales — ASTM E140 framework
Engineers and inspectors regularly need to convert hardness readings between scales — a drawing specifies "55 HRC minimum" but the only available tester is a Vickers; a foundry quotes "240 HB" but the receiving inspector reports HRC. ASTM E140 is the international reference standard for hardness conversion, published as conversion tables for specific material families (low-carbon steels, austenitic stainless, nickel alloys, etc.).
The reality of conversion: it's approximate, not exact. Hardness scales measure related but different mechanical responses, and the relationships between them depend on the specific alloy and microstructure. ASTM E140 conversions are accurate to roughly ±5% for plain carbon and low-alloy steels in the 20-60 HRC range; outside that range and for non-ferrous materials, the error grows. The practical hardness conversion reference for common workshop use:
| HRC | HRB | HV (Vickers) | HB (Brinell, 3000 kgf) | Approx. tensile strength (steel, MPa) |
|---|---|---|---|---|
| — | 50 | 89 | 89 | 320 |
| — | 70 | 125 | 125 | 460 |
| — | 90 | 180 | 180 | 630 |
| — | 100 | 240 | 240 | 820 |
| 20 | — | 238 | 226 | 770 |
| 25 | — | 266 | 253 | 855 |
| 30 | — | 301 | 286 | 965 |
| 35 | — | 345 | 327 | 1100 |
| 40 | — | 392 | 371 | 1255 |
| 45 | — | 446 | 421 | 1430 |
| 50 | — | 513 | 481 | 1635 |
| 55 | — | 595 | 560 | — |
| 60 | — | 697 | 654 | — |
| 65 | — | 832 | — | — |
| 68 | — | 940 | — | — |
The tensile-strength column reflects the well-established "500-rule" for plain carbon and low-alloy steels. Three important caveats on conversion:
- Do not convert across material families. The HRC↔HB↔HV conversion for plain carbon steel does NOT apply to austenitic stainless (work-hardens under indentation), aluminium alloys, brass, copper, or any non-ferrous metal. Use ASTM E140 tables specific to the material family.
- Brinell ball deforms above ~600 HB. The standard 10 mm tungsten carbide ball begins to plastically deform on materials harder than about 600 HB, so Brinell readings above that threshold are unreliable. For hardened tool steel, use Vickers or Rockwell HRC, not converted Brinell.
- Conversion accuracy degrades at scale endpoints. Conversions in the middle of the working range of each scale are most accurate; conversions near the bottom or top of any scale carry larger errors.
Hardness and tensile strength — the 500-rule and its limits
For plain carbon and low-alloy steels, there's a well-established empirical relationship between Brinell hardness and ultimate tensile strength (UTS):
UTS (psi) ≈ 500 × HB
...or in metric units:
UTS (MPa) ≈ 3.45 × HB
The rule was originally established by Bethlehem Steel in the 1930s and has been validated extensively since. It works best in the 150-400 HB range — the bulk of structural and tool steel applications. So a steel at 250 HB has an approximate UTS of 125,000 psi (860 MPa). Above 400 HB, the relationship flattens because hardness keeps rising but tensile strength saturates as the steel becomes too brittle to sustain elongation under tension.
The rule does NOT apply to:
- Austenitic stainless steel (304, 316) — work-hardens during indentation, gives misleadingly high hardness for the actual UTS
- Aluminium alloys
- Brass, copper, and copper-based alloys
- Cast iron (different multiplier — closer to 350-400 × HB)
- Very high-hardness tool steels above 400 HB (rule saturates)
The rule's value in practice: it lets you estimate the tensile strength of an unknown steel sample from a hardness test alone, without destructive tensile testing. For acceptance testing on plain carbon and low-alloy steels in the 150-400 HB range, the estimate is within ±10% of the true UTS — adequate for most engineering decisions.
Hardness of common engineering steels — reference table
The following hardness ranges cover the most common engineering steels in AU industrial supply. Specific heat-treat conditions, manufacturer tolerances and AU mill standards (AS 1444 for tool steel, AS 1450 for stainless) vary the exact numbers; the table is a practical reference for material identification, acceptance screening and selection conversations.
| Material | Typical condition | HRC | HRB | HB (3000 kgf) |
|---|---|---|---|---|
| Mild steel (AS 1442 grade 1020, low-carbon) | Hot-rolled annealed | — | 55-75 | 120-160 |
| Medium-carbon steel (1040, 1045) | Normalised | — | 85-95 | 170-220 |
| 4140 alloy steel (chrome-moly) | Annealed | — | 92-100 | 200-235 |
| 4140 alloy steel | Quenched and tempered (T condition) | 28-35 | — | 285-345 |
| 4340 alloy steel | Quenched and tempered | 30-42 | — | 302-401 |
| O1 tool steel (oil-hardening) | Hardened and tempered | 57-62 | — | 620-720 |
| D2 tool steel (high-chrome) | Hardened and tempered | 58-62 | — | 650-720 |
| A2 tool steel (air-hardening) | Hardened and tempered | 57-62 | — | 620-720 |
| M2 high-speed steel (HSS) | Hardened and tempered (drill bits, end mills, taps) | 62-66 | — | — |
| M42 high-speed steel (8% cobalt HSS, premium tooling) | Hardened and tempered | 67-69 | — | — |
| 304 austenitic stainless | Annealed | — | 70-90 | 140-180 |
| 304 austenitic stainless | Work-hardened (cold-drawn) | 20-30 | — | 240-300 |
| 316 austenitic stainless | Annealed | — | 75-90 | 150-180 |
| 17-4 PH precipitation-hardening stainless | H900 condition | 40-45 | — | 380-440 |
| Grey cast iron (AS 1830 grade T220) | As-cast | — | — | 200-260 |
| Ductile iron (AS 1831 grade 500-7) | As-cast | — | — | 170-240 |
| Hardened bearing steel (52100 / EN31) | Through-hardened | 60-67 | — | — |
| Cemented tungsten carbide insert | As-sintered | — | — | 1300-1700 HV (off-scale on HB) |
Bolt grade hardness ranges — AS 4291 reference
One of the most frequent questions asked of hardness testing — "is this bolt actually the grade it claims to be" — is directly answerable from AS 4291.1 (the AU standard for mechanical properties of carbon-steel and alloy-steel bolts, screws and studs, which is ISO 898-1 MOD). The standard specifies hardness ranges for each property class, and out-of-range hardness is one of the strongest indicators of incorrect grade or counterfeit product:
| Bolt grade (property class) | HRC range | HV range | HB range (10 mm ball, 3000 kgf) | Typical UTS (MPa) |
|---|---|---|---|---|
| Grade 4.6 (mild steel, M5-M39) | — | 120-220 HV | 114-209 | 400 (min) |
| Grade 4.8 | — | 130-250 HV | 124-238 | 420 (min) |
| Grade 5.6 | — | 155-220 HV | 147-209 | 500 (min) |
| Grade 5.8 | — | 160-250 HV | 152-238 | 520 (min) |
| Grade 6.8 | — | 190-250 HV | 181-238 | 600 (min) |
| Grade 8.8 (high-tensile, M16+ alloy steel) | 22-32 HRC | 250-336 HV | 238-319 | 800 (min) |
| Grade 10.9 (high-tensile alloy steel) | 32-39 HRC | 320-380 HV | 304-361 | 1040 (min) |
| Grade 12.9 (highest standard grade, alloy steel) | 39-44 HRC | 385-435 HV | 366-414 | 1220 (min) |
| Grade 14.9 | 44-49 HRC | 435-490 HV | — | 1400 (min) |
Practical use: a workshop receiving a batch of Grade 8.8 bolts can sample-test for hardness. A reading of 25-30 HRC confirms the grade; a reading of 18 HRC or 40 HRC indicates wrong grade, wrong heat treatment, or counterfeit product. For comprehensive coverage of AU bolt grades, head markings, identification and torque specifications, see our Bolt Grade Chart Guide.
The file test — practical workshop method and accuracy
Most general-engineering AU workshops don't own a hardness tester — and most don't need to. The reality across Practical Machinist, Hobby-Machinist and AU trade forum threads is that hardness test files are the practical workshop method for verifying heat treatment, screening unknown stock, and confirming tool hardness. The technique:
- A hardness test file set contains 6-8 files, each precision-hardened to a known HRC value — typically 40, 45, 50, 55, 60, 63 and 65 HRC.
- The procedure: starting with the lowest-hardness file, draw the file across the test surface with light pressure. If the file "bites" (removes material), the test sample is softer than the file. Step up to the next-hardest file and repeat. The sample's hardness is approximately equal to the hardest file that bites — or one HRC below the softest file that just skates over the surface.
- Accuracy is typically ±3-5 HRC — adequate for go/no-go heat-treat verification, unknown-stock screening, and tool hardness confirmation. Not adequate for production QC where hard tolerance limits matter, but more than sufficient for general engineering decision-making.
Quality hardness test files (Bahco, Pferd, Nicholson, Eclipse) typically last for years of normal use. Storing them in a sealed case prevents corrosion of the precision-hardened surface. They're the right tool for the workshop that needs occasional hardness verification but doesn't justify a benchtop tester.
For workshops that do need quantitative readings — toolrooms, mould-makers, gear shops, knife-makers, fastener QC — a benchtop Rockwell tester is the next step up. Contact our team for advice on entry-level vs production-grade benchtop testers and current Mitutoyo HR-series availability.
Portable hardness testers — Leeb and UCI for field inspection
Benchtop hardness testers handle samples that fit on the anvil. Field inspection — installed welds, large fabrications, mining equipment in-situ, pressure vessel inspection, mill rolls, large gears, machinery overhauls — needs a tester that comes to the work. Two portable technologies dominate this space:
Leeb (rebound) hardness testers
Mitutoyo Hardmatic HH-411 is the benchmark portable Leeb tester in AU industrial supply. The technology, developed by Dietmar Leeb in 1975 (ASTM A956), works by firing a spring-loaded impact body (D-type, 11 g, with a tungsten carbide ball tip) at the test surface, and measuring the ratio of rebound velocity to impact velocity. A harder surface rebounds more vigorously than a soft one. The result is reported as a Leeb hardness value (HL) and converted internally to HRC, HRB, HB, HV or tensile strength.
HH-411 specifications and practical reality:
- Hardness range: 100-940 HLD (covers most engineering steels and alloys)
- Accuracy: ±12 HL at 800 HL reference (Mitutoyo specification); field reality typically ±20-30 HL on real workpieces
- Test direction: automatic compensation for impact direction (vertical down, horizontal, vertical up) — the unit detects gravity orientation
- Sample requirements: minimum 5 mm from any edge, minimum 3 mm between test points, minimum sample weight 5 kg (or rigidly clamped to a larger mass), minimum thickness 5 mm
- Surface preparation: Ra better than 1.6 µm typically required; rougher surfaces give low/scattered readings
- Limitations: degraded accuracy on thin sections (<5 mm), small parts (<5 kg without clamping), curved surfaces (correction tables required for cylindrical/spherical), and very soft materials (under ~80 HB)
Leeb is well-suited to large fabrications, weld HAZ inspection on pressure vessels, in-situ machinery hardness checks, and incoming inspection on large forgings and rolled plate. It's not a substitute for benchtop accuracy where tolerances are tight — most field-quality Leeb readings are ±2-3 HRC in real conditions, which is adequate for go/no-go decisions but not for tight production QC.
UCI (Ultrasonic Contact Impedance) testers
UCI, governed by ASTM A1038, uses a Vickers diamond bonded to the end of a vibrating rod. The rod's resonant frequency shifts when the diamond is pressed into the test surface — the shift is proportional to the diamond's contact area and therefore to hardness. UCI advantages over Leeb:
- Better accuracy on thin sections — works on samples down to 1-2 mm with no minimum mass requirement
- Better on curved and small surfaces — gear teeth, small shafts, weld bead profiles
- Smaller indentation — visually less invasive on finished surfaces
- Direct Vickers calibration — no conversion needed if HV is the target scale
UCI trade-offs: slower per measurement than Leeb (UCI requires the operator to apply controlled hand pressure for 1-2 seconds vs Leeb's instant impact), more dependent on operator technique, and surface preparation must be better (Ra 0.8 µm or smoother).
Both Leeb and UCI are field-grade instruments — they sacrifice some absolute accuracy for portability and accessibility. For acceptance testing or specification-critical decisions, a benchtop tester remains the right tool. For field screening, weld inspection, and in-place machinery assessment where the work won't come to a lab, portable testers are the only practical option.
For pricing, application demonstration, and current availability on the Mitutoyo Hardmatic HH-411 portable Leeb tester, or on benchtop Rockwell, Brinell or Vickers equipment from the Mitutoyo HR/HM/HV series, contact our team on (02) 9773 0122 or via aimsindustrial.com.au/contact-us.
Australian Standards — AS 1815/1816/1817 framework
Australian hardness testing is governed by three primary AS standards, each closely aligned with the equivalent ISO standard (the ISO standards are adopted with modifications, designated MOD in AS publications). The framework:
| AU Standard | ISO equivalent | ASTM equivalent | Scope |
|---|---|---|---|
| AS 1815.1 | ISO 6508-1 MOD | ASTM E18 | Rockwell hardness test — test method |
| AS 1815.2 | ISO 6508-2 MOD | — | Rockwell — verification and calibration of testing machines |
| AS 1815.3 | ISO 6508-3 MOD | — | Rockwell — calibration of reference blocks |
| AS 1816.1 | ISO 6506-1 MOD | ASTM E10 | Brinell hardness test — test method |
| AS 1816.2 | ISO 6506-2 MOD | — | Brinell — verification and calibration of testing machines |
| AS 1816.3 | ISO 6506-3 MOD | — | Brinell — calibration of reference blocks |
| AS 1816.4 | — | — | Brinell — table of hardness values |
| AS 1817.1 | ISO 6507-1 MOD | ASTM E92, E384 | Vickers hardness test — test method |
| AS 1817.2 | ISO 6507-2 MOD | — | Vickers — verification and calibration of testing machines |
| AS 1817.3 | ISO 6507-3 MOD | — | Vickers — calibration of reference blocks |
| AS 4291.1 | ISO 898-1 MOD | — | Mechanical properties of fasteners (incl. specified hardness ranges for property classes 4.6 through 12.9) |
| — | — | ASTM A956 | Leeb rebound portable hardness testing (no AS equivalent; international reference) |
| — | — | ASTM A1038 | Ultrasonic Contact Impedance (UCI) hardness testing (no AS equivalent) |
| — | — | ASTM E140 | Hardness conversion between scales (international reference) |
| — | ISO 4545 | ASTM E384 | Knoop hardness test |
| — | ISO 7619, ISO 868 | ASTM D2240 | Shore hardness (rubber and plastics) — separate audience |
For routine production hardness testing in Australia, AS 1815 (Rockwell) covers the vast majority of work. AS 1816 (Brinell) and AS 1817 (Vickers) come in for foundry/forging inspection, weld qualification work, and metallurgical lab applications. AS 4291 is the bolt-grade hardness reference — every fastener inspector should know the HRC ranges for 8.8, 10.9 and 12.9 by memory.
NATA-certified hardness testing in Australia
For specification-critical hardness testing (pressure vessels under AS 1210, structural steel under AS 4100, weld procedure qualification under AS 3992, aerospace components, and any test result needed for legal or contractual purposes), the test should be performed by or witnessed by a NATA-accredited laboratory. NATA (National Association of Testing Authorities) accredits metallurgical labs against ISO/IEC 17025 — the international standard for testing and calibration laboratory competence.
Major NATA-accredited testing labs that perform hardness testing in Australia include Bureau Veritas, SGS, Bisalloy Steels laboratory, and university metallurgy departments at most major Australian universities. Typical turnaround for routine hardness testing is 3-5 business days; rush service is available at premium pricing. For a single specimen, expect to budget for sample preparation, the hardness test itself, and a NATA-endorsed certificate — significantly more cost-effective than a benchtop tester for occasional critical testing, significantly less cost-effective for ongoing production QC.
AIMS hardness testing equipment — capital equipment and consumables
AIMS Industrial supplies the precision measurement equipment that complements hardness testing infrastructure — including the Mitutoyo range. For workshops investing in or expanding hardness testing capability, our team works with our supply partners to quote, demonstrate and source:
- Mitutoyo HR-series benchtop Rockwell testers — HR-110 (entry-level manual), HR-210/320 (workshop-grade), HR-430 (production QC), HR-500 (automated). Mitutoyo Absolute encoder technology, AS 1815-compliant, full range of Rockwell scales including superficial.
- Mitutoyo HM-series Vickers micro-hardness testers — HM-100/200 series, motorised stages, image analysis, case-depth profiling, weld HAZ traverses. AS 1817 / ASTM E384 compliant.
- Mitutoyo HV-100 Vickers macro-hardness tester — 1-100 kgf loads, weld qualification, large component inspection.
- Mitutoyo Hardmatic HH-411 portable Leeb tester — field inspection, weld HAZ, in-situ machinery, large fabrications. D-type carbide impactor per ASTM A956.
- Hardness reference test blocks — NATA-calibrated reference blocks for HRC, HRB, HV and HB scales. Required for daily verification of any benchtop tester under AS 1815/1816/1817.
- Hardness test files — RC 40-65 file sets for workshop go/no-go heat-treat verification, the practical alternative for workshops that don't justify a benchtop tester.
- Sample preparation consumables — surface plates (AS 4054 reference work), gauge blocks (AS 1217 / ISO 3650 grades), precision indicators, micrometers and calipers (all stocked at AIMS) — the supporting metrology infrastructure that quality hardness testing depends on.
AIMS is bringing the Mitutoyo precision measurement range into stock as a regular supply line. Benchtop hardness testers are capital equipment and we work with our supply partners on a quoted basis — pricing, application advice, demonstration arrangements and quote requests handled by our team.
For pricing, application advice, demonstration arrangements and quote requests, contact our team on (02) 9773 0122 or via aimsindustrial.com.au/contact-us.
For supporting precision measurement infrastructure that AIMS stocks directly, see our guides on Micrometers, Digital Calipers, Dial Indicators, Gauge Blocks and Surface Plates.
Frequently Asked Questions
What is hardness in materials testing?
Hardness is the resistance of a material to permanent indentation under a controlled load. It correlates strongly with tensile strength, wear resistance, fatigue strength and machinability, making it the most common mechanical test performed in metalworking. Hardness is measured by pressing a hardened indenter (diamond cone, steel ball or diamond pyramid) into the test surface and measuring either the depth of the impression (Rockwell) or the size of the impression (Brinell, Vickers, Knoop) — the four primary indentation methods governed by AS 1815, AS 1816 and AS 1817.
How is hardness measured?
Hardness is measured by indentation — pressing a hardened indenter into the test surface under a controlled load, then measuring either the depth (Rockwell) or the size (Brinell, Vickers, Knoop) of the resulting indentation. Rockwell testers convert the depth directly to a hardness number on a digital readout. Brinell, Vickers and Knoop require optical measurement of the indentation dimensions under a microscope. The hardness number is calculated from the load and the indentation geometry by standard formulas defined in AS 1815/1816/1817 and ASTM E18/E10/E92.
What is the difference between Rockwell, Brinell, Vickers and Knoop hardness tests?
All four are indentation methods that measure resistance to permanent deformation, but they use different indenters, loads and measurement principles. Rockwell uses a diamond cone (HRC) or steel ball (HRB) with a 60-150 kgf load and measures indentation depth — fast, direct digital readout, dominant in production QC. Brinell uses a 10 mm tungsten carbide ball under 3000 kgf and measures the diameter of a large indentation — best for castings, forgings and weld zones where coarse grain structure requires large-area averaging. Vickers uses a diamond pyramid (136° angle) under 5-120 kgf for macrohardness or 0.01-1 kgf for microhardness — best for thin sections, hardened tool steels, case-depth profiling and weld traverses. Knoop uses an elongated diamond pyramid for microhardness on brittle materials, thin coatings and ceramics.
What does HRC mean?
HRC stands for Hardness Rockwell C — the most widely used scale for hardened steel. It uses a 120° diamond cone indenter (called a Brale) under a 150 kgf total load (with 10 kgf preload). The HRC scale runs from 20 (mild hardened steel) to about 70 (hardened tool steel, M42 high-speed steel). Below 20 HRC, switch to HRB (Rockwell B, steel ball at 100 kgf); above 70 HRC, accuracy degrades and Vickers or HRA become more reliable. A typical 4140 quench-and-tempered shaft sits around 28-35 HRC; hardened bearing steel sits around 60-67 HRC; an HSS drill bit sits around 62-66 HRC; a tungsten carbide insert is far above HRC (uses HV directly).
What is the difference between HRC and HRB?
HRC and HRB are two Rockwell scales for different hardness ranges. HRC uses a 120° diamond cone indenter under 150 kgf and is the standard for hardened steel (range 20-70 HRC). HRB uses a 1/16-inch steel ball indenter under 100 kgf and is the standard for soft steels, copper alloys, brass, malleable iron and aluminium (range 20-100 HRB). A material reading below 20 HRC is too soft for the HRC scale — re-test on HRB. A material reading above 100 HRB is too hard for the HRB scale — re-test on HRC. The two scales overlap in the medium-hardness range (roughly 100 HRB ≈ 22 HRC) but they're not directly equivalent in the overlap region; conversion is approximate per ASTM E140.
Which hardness test should I use for my application?
Rockwell HRC for hardened steel parts in production QC and heat-treat verification (fast, direct, AS 1815 standard). Rockwell HRB for soft steels, copper alloys and aluminium. Brinell HB for castings, forgings, weld HAZ and large rough samples where coarse grain structure needs large-area averaging (AS 1816). Vickers HV for thin sections, hardened tool steel above ~600 HB, case-depth profiling, microhardness of individual phases, and weld traverses (AS 1817). Knoop HK for brittle materials, thin coatings and microhardness work on samples that Vickers might crack. Shore A or D for rubber and plastics. Portable Leeb or UCI for field inspection of installed welds, large fabrications and in-place machinery.
How do I convert HRC to Brinell or Vickers?
Use the ASTM E140 conversion tables, which are widely published and built into modern digital hardness testers. As a quick reference: 30 HRC ≈ 286 HB ≈ 301 HV; 40 HRC ≈ 371 HB ≈ 392 HV; 50 HRC ≈ 481 HB ≈ 513 HV; 60 HRC ≈ 654 HB ≈ 697 HV. Above 60 HRC, Brinell becomes unreliable because the 10 mm carbide ball begins to deform. The conversions are accurate to roughly ±5% for plain carbon and low-alloy steels in the 20-60 HRC range. Do not convert across material families — the conversion for plain carbon steel does NOT apply to austenitic stainless, aluminium, brass or non-ferrous metals; use ASTM E140 tables specific to the material.
What is the hardness range for Grade 8.8, 10.9 and 12.9 bolts under AS 4291?
AS 4291.1 (ISO 898-1 MOD) specifies these HRC ranges for the high-tensile fastener property classes: Grade 8.8 = 22-32 HRC; Grade 10.9 = 32-39 HRC; Grade 12.9 = 39-44 HRC. A hardness reading outside the specified range for the marked grade indicates wrong heat treatment, wrong material, or counterfeit product — and is one of the strongest quick screening tests for fastener quality. For Grade 4.6, 4.8, 5.6, 5.8 and 6.8 bolts, the standard specifies Vickers (HV) ranges rather than HRC because the hardness is below the practical HRC range. See our Bolt Grade Chart Guide for full coverage.
Can I test hardness with a file?
Yes — hardness test files are the practical workshop method for verifying heat treatment when a benchtop tester isn't available. A file set contains 6-8 precision-hardened files at known HRC values (typically 40, 45, 50, 55, 60, 63 and 65 HRC). Starting with the lowest, draw each file across the test surface with light pressure. The sample's hardness is approximately equal to the hardest file that bites (cuts into the material) or one HRC below the softest file that skates over the surface. Accuracy is ±3-5 HRC — adequate for go/no-go heat-treat verification, unknown stock screening and tool hardness confirmation. Not adequate for production QC with tight tolerance limits, but more than sufficient for general engineering verification.
What's the sample thickness rule for hardness testing?
The sample must be at least 10 times thicker than the indentation depth — otherwise the anvil reads through the sample and you measure the support material rather than the sample. For HRC indentations on hardened steel, this means roughly 1.5 mm minimum thickness; for HRB on soft steel, around 3 mm minimum. Below these thresholds, switch to superficial Rockwell (HR15N, HR30N or HR15T, HR30T) or to low-load Vickers (1-10 kgf). For Brinell, the rule is the same but the indentations are larger — minimum sample thickness of 10 mm is typical for 3000 kgf Brinell on steel.
Why does my hardness reading vary across the same sample?
Four common causes, listed by frequency. First, surface roughness — Rockwell needs Ra better than 0.4 µm; Vickers and Brinell need Ra 0.2 µm or better. As-cast, as-forged or as-welded surfaces give scattered readings. Second, sample backing — flex of a thin or poorly-seated sample under the indenter load gives low readings; ensure firm, flat contact with the anvil. Third, indentation spacing — indentations placed too close interact via plastic deformation; maintain at least 4× the indentation diameter spacing and 2.5× the indentation diameter from any edge. Fourth, genuine inhomogeneity — cast structures, weld HAZs, decarburised surfaces and case-hardened layers do have real hardness variation across short distances, which is why Brinell's large indentation is preferred for these applications.
How accurate is a portable Leeb hardness tester?
Mitutoyo's published accuracy specification for the Hardmatic HH-411 is ±12 HL at 800 HL reference (about ±0.5 HRC equivalent). Field reality on real workpieces is typically ±20-30 HL (±2-3 HRC), because real-world samples have surface roughness, thickness limits, curvature and small mass that degrade the published specification. Leeb portable testers are best suited to large fabrications, weld HAZ inspection, in-situ machinery and large forgings — applications where benchtop accuracy isn't achievable because the work won't come to a lab. For tight tolerance production QC or specification-critical acceptance testing, a benchtop Rockwell tester or NATA-certified lab is the right choice; for field go/no-go screening, portable Leeb is adequate and often the only option.
What's the difference between Leeb (rebound) and UCI (ultrasonic) portable hardness testers?
Both are field-grade portable methods that sacrifice some absolute accuracy for portability. Leeb (ASTM A956) fires a spring-loaded impact body with a carbide ball at the surface and measures rebound velocity — fast, single-impact, works on large mass samples but degraded accuracy on thin sections, small parts and curved surfaces. UCI (ASTM A1038) uses a vibrating diamond pyramid and measures resonant frequency shift under hand pressure — slower per measurement, more operator-dependent, but better accuracy on thin sections, small parts, curved surfaces and gear teeth. Leeb suits welds, large forgings and in-situ machinery. UCI suits small or curved samples where Leeb's mass requirement isn't met. Both are field-grade — neither replaces a benchtop tester for tight-tolerance work.
Does hardness predict tensile strength?
For plain carbon and low-alloy steels in the 150-400 HB range, yes — the empirical "500-rule" gives tensile strength in psi as approximately 500 × Brinell number, or 3.45 × HB in MPa. So a steel at 250 HB has an approximate ultimate tensile strength of 125,000 psi (860 MPa). The rule is accurate to roughly ±10% in the validity range. It does NOT apply to austenitic stainless steel (work-hardens during indentation), aluminium alloys, brass, copper, cast iron (different multiplier), or very high-hardness tool steels above 400 HB (rule saturates). For acceptance testing of plain steel where destructive tensile testing isn't practical, hardness gives a useful tensile estimate.
Where can I get a sample hardness tested in Australia?
For specification-critical hardness testing — pressure vessels under AS 1210, structural steel under AS 4100, weld procedure qualification under AS 3992, aerospace components, contractual or legal test results — use a NATA-accredited metallurgical laboratory. Major NATA-accredited testing labs in Australia include Bureau Veritas, SGS, Bisalloy Steels laboratory, and university metallurgy departments at most major Australian universities. Typical turnaround is 3-5 business days; rush service is available. For routine workshop go/no-go verification, hardness test files give ±3-5 HRC accuracy at a fraction of lab cost. For ongoing production QC, a benchtop tester is more cost-effective than lab testing — contact our team for pricing and demonstration arrangements on Mitutoyo HR-series benchtop testers.
Quote requests and application advice on hardness testing equipment. AIMS Industrial works with our Mitutoyo supply partners to quote benchtop and portable hardness testing equipment, reference blocks, hardness test files and the supporting precision measurement infrastructure. Call our team on (02) 9773 0122 or contact us via aimsindustrial.com.au/contact-us for current availability, lead times and demonstration arrangements.
