Hardness Testing

Hardness is not a fundamental property of a material, but rather defined as "the resistance the material exhibits to permanent deformation by penetration of another harder material." The principal purpose of the hardness test is to determine the suitability of a material, or the particular treatment to which the material has been subjected. The quantitative value of hardness should always be evaluated in relation to:

  • The type of indenter and its geometry
  • The given load on the indenter
  • A specific loading time profile and a specific load duration

Methods

Rockwell

Hardness Method

Rockwell

Description

Rockwell diagramCalculated by measuring the depth of an indent, after an indenter has been forced into the specimen material at a given load.

HR = N - (h/E), where N = 100, E = 0.002mm and h = permanent depth.

Indenter and Indent Specifications

  • Conical Diamond, complies to EN ISO standard
  • Lasting impression depth (HR) = N - h/E, where N is 100 units, E is 0.002mm, and h is permanent depth

Load Range

15 – 150kgf

Methods & Applications

HRA 60kgf

Cemented carbides, thin steel and shallow case-hardened steel

HRC 150kgf

Steel, hard cast irons, pearlitic malleable iron, titanium, deep cased hardened steel

HRD 100kgf

Thin and medium case-hardened steel and pearlitic malleable iron

HR15N 15kgf

HR30N 30kgf

HR45N 45kgf

Use superficial rockwell scales where regular scales are problematic

Sample Requirements

  • Must not be mounted
  • None or ground

Testing Considerations

  • Geometric correction is available for small diameter cylindrical or ball shaped samples
  • Indentation depth must be less than 10 times the sample thickness

Strengths

  • Rapid test, ~10 seconds
  • Direct read-out - little/no sample preparation
  • Non-destructive

Weaknesses

  • Multiple test scales needed to cover entire hardness range
  • Many conversion tables exist - can be material dependent

SOP

Hardness on Struers DuraJet SOP (PDF, 91.5 KB)

Instruction manual

DuraJet Instruction Manual (PDF, 1.9 MB)

Resources

Knowledge on Rockwell Hardness Testing

Standards; ASTM E18, ASTM D785, EN ISO 6508, EN ISO 2039-2

Troubleshooting

Booking address

*G SEBE ENG Lab Eqpmt KE2.101 Rockwell Hardness Tester

Brinell Depth

Hardness Method

Brinell Depth

Description

Modified Brinell hardness HBT. Residual indentation depth h from test indentation under pre-load measured in mm.

Indenter and Indent Specifications

  • Tungsten Carbide Ball – 1mm dia. Or 5mm dia.

Load Range

5 – 250kgf

Methods & Applications

Plastics Testing

49.03N, 132.9N, 357.9N, 961N

Brinell Depth

HBD 1/5, 1/10, 1/30

HBD 5/125, 5/250

Carbon Testing

HR 5/7, 5/15, 5/20, 5/40, 5/60, 5/100, 5/150

Sample Requirements

  • None or ground

Testing Considerations

  • Conversion of values to other hardness methods is not the same for each material

Strengths

  • Rapid test, ~10 seconds
  • Direct read-out - little/no sample preparation
  • Tensile strength for steel can be measured reliably

Weaknesses

  • Not a genuine Brinell Test
  • Many conversion tables exist - can be material dependent

SOP

Hardness on Struers DuraJet SOP (PDF, 91.5 KB)

Instruction manual

DuraJet Instruction Manual (PDF, 1.9 MB)

Resources

Standards; EN ISO 2039-1

Booking address

*G SEBE ENG Lab Eqpmt KE2.101 Rockwell Hardness Tester

Vickers

Hardness Method

Vickers

Description

Vickers diagramCalculated by measuring the size of diagonal lengths of an indent left by introducing a diamond pyramid indenter with a given load into the sample material.

HV = 18544 (F/d2), where F = the test load in gf, and d = average diagonal length in mm.

Indenter and Indent Specifications

  • Diamond pyramid, face angle 136°, complies with EN ISO standard
  • Depth of indentation = 1/7 of diagonal length

Load Range

10gf - 10kgf (Micro and Macro)

Methods & Applications

HV 0.01, 0.025, 0.05

Small geometrics, thin layers, ceramics

HV 0.01, 0.5, 1

Hardness progressions, CHD/Eht-nHt-RHT

HV 2, 3

Surface Hardness testing

HV 5, 10 Welding Test, Sintered metals
Case Depth Hardness (CHD), Jominy (end quench) testing, weld testing

Sample Requirements

  • Must be reflective
  • Macro testing = ground
  • Micro testing = polished
  • Less than 50kg

Testing Considerations

  • Geometric correction is available for small diameter cylindrical or ball shaped samples.
    Material thickness:
    • ASTM must be ≥ 6-8 times the sample thickness.
    • ISO must be ≥ 1/3 the longer diagonal length.
  • Indentation spacing is dependent upon material:
    • Steel and copper - 3 diagonal widths indent spacing is required
    • Lead, zinc, and aluminium - at least 6 diagonal widths indent spacing is required
  • Inaccuracy is high when diagonal lengths are < 20mm.
  • Difference in length of the two diagonals should be no more than ±5.0%
  • Indentation time = 10 – 15 seconds.

Strengths

  • One scale covers the entire hardness range
  • A wide range of test forces to suit every application
  • Can be non-destructive
  • One indenter for all materials

Weaknesses

  • Requires a highly finished sample surface for accurate measurement, as measured optically
  • Slow - testing can take 30-60 seconds (excluding sample preparation time)

SOP

Hardness on Struers DuraScan SOP (PDF, 91.0 KB)

Instruction manual

DuraScan Instruction Manual.pdf (PDF, 3.1 MB)

Resources

Knowledge on Vickers Hardness testing

Standards;

  • ASTM E384
  • EN ISO 6507
  • JIS Z 2244
  • CHD - EN ISO 2639, EN ISO 3754
  • Jominy - EN-ISO 642, EN-ISO255
  • Welds – EN-ISO 9015

Troubleshooting

Booking address

*G SEBE ENG Lab Eqpmt KE2.101 Vickers Hardness tester

Knoop

Hardness Method

Knoop

Description

Knoop diagramCalculated by measuring the size of the long diagonal of an indent left by introducing an asymmetrical pyramidal diamond with a given load into the sample material.

HK = 14229 (F/L2), where F = test load in gf, and L =  long diagonal length in mm.

Indenter and Indent Specifications

  • Asymmetrical (rhombic) diamond pyramid
  • Depth of indentation = 1/30 of diagonal length
  • Ratio between long and short diagonal 7:1

Load Range

10gf - 1kgf (Micro)

Methods & Applications

HV 0.01, 0.025, 0.05, 0.1, 0.2, 0.3, 0.5, 1 - Brittle materials, thin layers, coatings

Sample Requirements

  • Must be reflective
  • Highly polished
  • Less than 50kg

Testing Considerations

  • Geometric correction is available for small diameter cylindrical or ball shaped samples.
    Material thickness:
    • ASTM must be ≥ 10 times the sample thickness.
    • ISO must be ≥ 1/3 the longer diagonal length
  • Indentation spacing must be ≥ 2.5 diagonal length from the edge and ≥ 3 diagonal length between.
  • Inaccuracy is high when diagonal lengths are < 20µm.
  • Indentation time = 10 – 15 seconds.

Strengths

  • One scale covers the entire hardness range
  • A wide range of test forces to suit every application
  • Testing on very small or thin samples
  • Lower measurement error compared to Vicker's
  • Results are mainly test force independent over 100g

Weaknesses

  • Requires a highly finished sample surface for accurate measurement, as measured optically
  • Slow - testing can take 30-60 seconds (excluding sample preparation time)

SOP

Hardness on Struers DuraScan SOP (PDF, 91.0 KB)

Instruction manual

DuraScan Instruction Manual.pdf (PDF, 3.1 MB)

Resources

Knowledge on Knoop Hardness Testing

Standards;

Troubleshooting

Booking address

*G SEBE ENG Lab Eqpmt KE2.101 Vickers Hardness tester

Factors that influence hardness testing

Instrument

Instrument factors can be categorised by applied load, indentation, indenter and others. The below table shows the different parameters of each factor that can affect hardness testing.

Applied Load

Indentation

Indenter

Others

Accuracy

Repeatability

Speed

Inertia

Angle

Time

Spacing

Lateral movement

Shape deviations

Damage

Material

Anvil, table support

Spindle

Deflection of the sample

Levelling of the machine

Material

  • Heterogeneity of the microstructure
  • Quality of specimen preparation – reflectivity/transparency of the specimen surface
  • Type of material
  • Material treatment
  • Shape of material
  • Mounting resin

Measurement

Measurement factors can be categorised by procedure used, verification system and others. The below table shows the different parameters of each factor that can affect hardness testing.

Procedure Used

Verification system

Others

Applied method (HB, HK, HR, HV)

Feasibility of method

Standard to be followed (ASTM, ISO, JIS)

Calibration of loading system

Magnification of objective lenses

Resolution of objective lenses

Inadequate image quality

Uniformity of illumination

Vibrations

Dirt, dust, debris

Examples of typical sources of error include:

  • Brighter illumination shows an indent to be smaller than it actually is, which leads to higher hardness values.
  • An unfocused image will cause inaccurate measurement of the diagonals, leading to an inaccurate hardness value.

Operator

  • Clamping or fixturing of the sample
  • Judgement of surface preparation
  • Operator bias in indent sizing
  • Judgement of result

Environmental

  • Temperature
  • Humidity
  • Vibrations
  • Illumination

Conversion Tables

There are many conversion tables that exist. Many are material dependent. Care must be taken when using conversion tables to ensure hardness values are being reported accurately.

Resources

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