ENGINEERING REFERENCE CHART
Material Hardness Chart
A material hardness chart converts and compares hardness values across Brinell (HB), Rockwell (HRC, HRB, HRA), and Vickers (HV) scales, helping engineers read drawing specifications and compare measurements from different hardness tests.
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HB / HRC / HRB / HV Conversion
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ASTM E140 & ISO 18265 Reference
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CNC Material Selection Support
Hardness Scales
Common engineering measurement systems
HB
Brinell
HRC
Rockwell C
HRB
Rockwell B
HV
Vickers
Hardness Conversion Reference
HB ↔ HRC ↔ HRB ↔ HV
MATERIAL SCIENCE
What Is Material Hardness?
Material hardness measures a material’s resistance to permanent surface indentation or scratching. It is determined through standardized hardness tests using different indenters, loads, and measurement methods.
Hardness is not a single physical property. The measured value depends on the testing method, which is why the hardness scale designation is important when comparing engineering materials.
Brinell (HB)
A tungsten-carbide ball is pressed into the material surface under a defined load. The indentation diameter is measured, making Brinell suitable for castings, forgings, and softer metals.
Rockwell (HRC, HRB, HRA)
Rockwell testing measures the permanent depth of penetration under a defined load. It provides fast direct readings and is widely used for production quality control.
Vickers (HV)
Vickers testing uses a diamond pyramid indenter and measures indentation diagonals. It works across a wide hardness range from soft metals to hardened tool steels and coatings.
HARDNESS REFERENCE DATA
Material Hardness Chart: HB, HRC, HRB & HV Conversion
Compare hardness values across common engineering scales using reference conversion tables based on ASTM E140 and ISO 18265.
Hardness conversions are approximate material-specific correlations. Values should be used for reference comparison and not treated as exact equivalents.
| Rockwell C (HRC) | Brinell (HB) | Vickers (HV) | Rockwell B (HRB) | Rockwell A (HRA) |
|---|---|---|---|---|
| 68 | 739 | 940 | — | 85.6 |
| 60 | 654 | 697 | — | 82.2 |
| 50 | 477 | 513 | — | 78.0 |
| 40 | 371 | 392 | — | 71.0 |
| 30 | 286 | 302 | — | 62.5 |
| 20 | 226 | 238 | 95 | 53.5 |
| 10 | 165 | 177 | 84 | — |
ASTM E140 & ISO 18265
Conversion tables follow recognized engineering standards for comparing hardness measurements across different testing scales.
Material-Specific Conversion
Steel conversion values should not be applied directly to aluminum, brass, copper, or other alloy families because hardness relationships differ.
READING GUIDE
How to Read a Material Hardness Chart
Follow three steps to identify hardness values, compare different scales, and understand material conditions used in CNC manufacturing.
01
Identify the Scale
Confirm the hardness scale before comparing values. A number without the scale letter has no engineering meaning, such as HRC, HRB, HB, or HV.
02
Find the Value
Locate the measured hardness value in the conversion table and identify the corresponding row for comparison.
03
Read Across
Read across the table to find approximate equivalent values on other hardness scales.
Example: HRC 34 Conversion
A material test report shows HRC 34 and requires an equivalent Brinell value. The conversion chart places HRC 34 between HRC 35 and HRC 32 values.
HRC 35
≈ 327 HB
HRC 34
≈ 314 HB
HRC 32
≈ 301 HB
MATERIAL REFERENCE
Material Hardness by Material (Common Machined Alloys)
Typical hardness values for common CNC machined alloys. Actual hardness depends on material condition, heat treatment, and production variation.
| Material | Grade | Condition | HB | HRB | HRC | HV |
|---|---|---|---|---|---|---|
| Aluminum | 6061-T6 | Aged | 95 | 60 | — | 107 |
| Aluminum | 7075-T6 | Aged | 150 | 87 | — | 175 |
| Carbon Steel | 1018 | Hot Rolled | 126 | 71 | — | 131 |
| Alloy Steel | 4140 | Hardened & Tempered | 321 | — | 34 | 340 |
| Stainless Steel | 304 | Annealed | 201 | 92 | — | 210 |
| Tool Steel | D2 | Hardened | — | — | 58–64 | 650–800 |
| Titanium | Ti-6Al-4V | Annealed | 334 | — | 36 | 350 |
| Nickel Alloy | Inconel 718 | Annealed/Aged | 331 | — | 36 | 350 |
Which Hardness Scale Should You Use?
Whether you are choosing from this material hardness chart or from a drawing, pick the scale that matches your material and its hardness range. Using the wrong scale produces invalid, unrepeatable readings.
| Scale | Indenter | Typical range | Best for |
|---|---|---|---|
| Brinell (HB) | 10 mm tungsten-carbide ball | 16–600 HBW | Castings, forgings, aluminum, brass; the large ball averages out microstructure |
| Rockwell B (HRB) | 1/16 in steel ball | 0–100 HRB | Soft metals: aluminum, brass, annealed and mild steel |
| Rockwell C (HRC) | Diamond cone | 20–70 HRC | Hardened and heat-treated steels, tool steels, titanium, fasteners |
| Rockwell A (HRA) | Diamond cone | 60–85 HRA | Very hard thin surfaces: carbides, case-hardened layers |
| Vickers (HV) | Diamond pyramid | 5–2,000+ HV | Thin sections, coatings, hardness gradients, and any material across a wide range |
As a rule of thumb, use HRB for materials softer than about 100 HRB, and HRC for materials harder than about 20 HRC. If a reading lands near the top or bottom of a scale, switch scales; end-of-range readings are unreliable. When the part is thin, coated, or case-hardened, use HV, because only the Vickers pyramid keeps its geometry across such a wide range of loads.
CNC MACHINING APPLICATION
Hardness and CNC Machinability
Material hardness directly affects machining strategy, tooling selection, cutting speed, surface finish, and achievable tolerances.
Hardness is the single most important property for machining strategy. A harder workpiece resists chip formation, cuts slower, wears tools faster, and requires tougher tooling during CNC machining.
Below 35 HRC
Standard Machining Range
Conventional high-speed steel and standard carbide tooling work well. This covers most machined metals including aluminum, brass, copper, annealed steels, 304 and 316 stainless, and titanium grades.
35–45 HRC
Hardened Material Range
Carbide tooling cuts reliably with lower speeds and more careful chip control. This range includes hardened 4140/4340, 17-4 PH at H900, and Ti-6Al-4V.
Above 45 HRC
High Hardness Range
Requires carbide or ceramic tooling, reduced cutting speeds, and often grinding or EDM machining for final geometry. Tool steels such as A2 and D2 fall within this range.
Hardness Effects on Surface Finish and Tolerance
Harder materials can maintain better surface finish because they deflect less under the cutting edge, but they also generate higher cutting forces that can push thin-walled parts out of tolerance. Engineers balance these factors when reviewing CAD files to achieve precision results.
±0.001″
CNC Tolerance Capability
CMM
Inspection Process
Surface Finish
Quality Control
Material Hardness Questions
Material Hardness FAQ
HRC and HRB are two different Rockwell scales. HRC uses a diamond cone indenter under a 150 kgf major load and is for hard materials such as hardened steels and tool steels. HRB uses a 1/16-inch steel ball under a 100 kgf load and is for soft metals like aluminum, brass, and annealed steel. The scale letter is never optional: 64 HRC and 64 HRB describe wildly different materials.
No. Hardness conversions are approximate empirical correlations, not mathematical equivalences, because each test uses a different indenter and load. Per ASTM E140 and ISO 18265, converted values are estimates and may be inaccurate for a specific application. When a specification requires a value on a particular scale, always test on that scale.
Typical values: mild steel (1018) is about 71 HRB; 304 stainless steel is about 92 HRB; 6061-T6 aluminum is about 60 HRB; hardened 4140 alloy steel is about 34 HRC. Hardened tool steels like A2 and D2 range from 57 to 64 HRC. These are typical values for the stated condition; always verify against the material test report.
Yes, with heat treatment. Annealing softens a part for easier machining, while hardening and tempering raise hardness afterward. For this reason, the drawing’s hardness requirement is applied to the final condition. Some finished parts are also surface-hardened by case carburizing or nitriding. Plan the sequence with your supplier so the machined part is not distorted by a later heat-treat step.
Directly. Harder materials resist cutting, so they need lower speeds, tougher tooling, and more careful chip control. Most machined alloys fall between 80 HRB and 35 HRC; above about 45 HRC you typically need carbide or ceramic tooling, or grinding and EDM for final geometry. Hardness also influences achievable surface finish and tolerance.
Use the scale specified on the drawing; do not substitute. If you are choosing, use HRB for soft metals, HRC for hardened steels, and HV for thin sections, coatings, or a wide hardness range. For a typical CNC job in aluminum or stainless steel, HRB and HRC cover nearly every case. When in doubt, ask the machinist: they will test on the scale your print requires.
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