1. Overview
Hardness: the ability to resist deformation from local indentation or scratch fracture.
Two types of Mohs hardness sequence tables
| Order | Material | Order | Material |
| 1 | baby powder | 1 | baby powder |
| two | taste | two | taste |
| 3 | calcite | 3 | calcite |
| 4 | fluorite | 4 | fluorite |
| 5 | apatite | 5 | apatite |
| 6 | orthoclase | 6 | orthoclase |
| 7 | quartz | 7 | SiO2 glass |
| 8 | topaz | 8 | quartz |
| 9 | Corundum | 9 | topaz |
| 10 | Adamas | 10 | grenade |
| – | 11 | Cast Zirconia | |
| – | 12 | Corundum | |
| – | 13 | silicon carbide | |
| – | 14 | Carbonization shed | |
| – | 15 | Diamond | |
2. Brinell Hardness
(1) Principle
To determine the Brinell hardness of a metallic material, apply a certain load F with a spherical indenter of diameter D to its surface and maintain it for a specific period. This process will result in the formation of a spherical indentation, and the value of the charge per unit area of the indentation is considered as the Brinell hardness of the metallic material.
Measuring the diameter of the indentation
Penetrator material:
- Hard Alloy Ball (HBW) HB=450~650
- Hardened Steel Ball (HBS) HB<450
(2) Representation method
For example: 280HBS10/3000/30
1kgf=9.81N
- 280 – Hardness value
- HBS – Hardness symbol
- 10 – Diameter of the steel ball mm
- 3000 – Load size kgf
- 30 – Charge retention time s
General conditions: 10mm steel ball diameter; Load of 3000kg; 10s pressure retention time i.e. HB280
(3) Testing steps
(4) Selection of F and D (principle of geometric indentation similarity)
When measuring Brinell hardness with indenters of different diameters and loads of different sizes, the principle of geometric similarity must be met to obtain the same HB value, that is, the opening angleφ of the indentation is equal.
Method: The same HB must be measured for samples with the same material but different thicknesses, or materials with different hardness and softness.
When selecting D and F, F/D 2 will be the same.
Principle of geometric indentation similarity: 
It can be seen that as long as F/D remains constant, HB depends only on the pressing angle φ.
F/D 2 ratio: 30,15,10,5,2,5,1,25,1
According to engineering regulations, the F/D 2 ratio is 30, 10 and 2.5, which are selected according to the hardness of the material and the thickness of the sample.
See various test standards and specifications for details.
Fig. 1-21 Application of the similarity principle
Brinell P/D 2 Hardness Test Selection Chart
| Material type | Brinell/HB hardness number | Sample thickness/mm | Relationship between load P and indenter diameter D | Indenter diameter D/nm | Load P/kgf | Charge retention time/s |
| ferrous metal | 140~450 | 6~3 4-2 <2 |
P=30D 2 | 1052.5 | 3,000 750 187.5 |
10 |
| <140 | >6 6~3 <3 |
P=10D 2 | 1052.5 | 1000 250 62.5 |
10 | |
| Non-ferrous metals | >130 | 6~3 4-2 <2 |
P=30D 2 | 1052.5 | 3,000 750 187.5 |
30 |
| 36~130 | 9~3 6~2 <3 |
P=10D 2 | 1052.5 | 1000 250 62.5 |
30 | |
| 8-35 | >6 6~3 <3 |
P=2.5D 2 | 1052.5 | 250 62.5 15.6 |
60 |
Experience shows that HB is stable and comparable when 0.25D
(5) Charge retention time:
If it has an influence on the test, it must be carried out in strict accordance with the regulations, generally 10s and 30s.
(6) Characteristics and Application of Brinell Hardness
This method is suitable for thick or heterogeneous materials due to its large indentation area and high measurement accuracy. However, due to the large size of the indentation, inspection of finished products can be challenging.
It is mainly used to inspect raw materials, and the indenter material is limited to softer materials (HB450~650). Furthermore, the efficiency of indentation measurement is relatively low.
3. Rockwell hardness
Indentation depth can be used to reflect the hardness of materials.
To adapt to different soft and hard materials, many types of hardness testers use different indenters and loads.
A common class is C, HRC, which uses a total charge of 150 kgf and a 120° conical diamond indenter that is charged twice.
Firstly, an initial load of P1=10kgf is applied to ensure adequate contact between the indenter and the material surface. Then, the main load of P2=140kgf is added.
After removing P2, the depth of indentation is measured and used to determine the hardness of the material.
Fig. 3-17 Schematic diagram of the principle and testing process of Rockwell hardness test
(a) Add preload (b) Add main load (c) Unload main load
| Hardness symbol | Used head | Total test force N | Scope of application | Applied Range |
| HR | diamond cone | 588.4 | 20-88 | Carbide, hard alloy, hardened tool steel, surface hardening steel |
| HRB | φ 1.588mm steel ball | 980.7 | 20-100 | Mild steel, copper alloy, aluminum alloy, malleable cast iron |
| CDH | diamond cone | 1471 | 20-70 | Hardened steel, quenched and tempered steel, deep hardened steel |
Indenter: 120 diamond cone or hardened steel ball
Rockwell hardness definition:
The residual indentation depth of 0.002 mm is a unit of Rockwell hardness.
K – constant, 130 for steel ball indenter and 100 for diamond indenter
Table 3-6 Rockwell Hardness Test Specification and Application
| Ruler | Penetrator type | Initial Test Force/N | Main Test Force/N | Total test force/N | K constant | Hardness range | application examples |
| A | Circular Dimension of Diamond | 100 | 500 | 600 | 100 | 60~85 | High hardness and carbide fine parts |
| B | φ1.588mm steel ball | 900 | 1000 | 130 | 25~100 | Non-ferrous metals, malleable cast iron and other materials | |
| W | Circular Dimension of Diamond | 1400 | 1500 | 100 | 20~67 | Heat-treated structural steel and tool steel | |
| D | diamond cone | 900 | 1000 | 100 | 40-77 | Surface hardened steel | |
| AND | φ3.175mm steel ball | 900 | 1000 | 130 | 70~100 | Plastic | |
| F | φ1.588mmm steel ball | 500 | 600 | 130 | 40~100 | Non-ferrous metals | |
| G | φ1.588mm steel ball | 1400 | 1500 | 130 | 31~94 | Pearlitic steel, copper, nickel, zinc alloy | |
| H | φ3.175mm steel ball | 500 | 600 | 130 | – | Annealed copper alloy | |
| K | φ3.175mm steel ball | 1400 | 1500 | 130 | 40~100 | Non-ferrous metals and plasticsSoft metals and soft non-metallic materialsHigh-hardness thin parts and cemented carbidesNon-ferrous metals, malleable cast iron and other materials | |
| I | φ6.350mm steel ball | 500 | 600 | 130 | – | ||
| M | φ6.350mm steel ball | 900 | 1000 | 130 | – | ||
| P | φ6.350mm steel ball | 1400 | 1500 | 130 | – | ||
| R | φ12.70mm steel ball | 500 | 600 | 130 | – | Heat-treated structural steel and tool steel | |
| s | φ12.70mm steel ball | 900 | 1000 | 130 | – | ||
| V | φ12.70mm steel ball | 1400 | 1500 | 130 | – |
Characteristics and application of Rockwell hardness
(1) This method allows direct reading of the hardness value and is highly efficient, making it suitable for batch inspection.
(2) The indentation is small and generally considered “non-destructive”, making it suitable for inspection of finished products.
(3) However, the small indentation size may result in low representativeness and is therefore not suitable for coarse or non-uniform materials.
(4) The Rockwell hardness test is divided into several scales, each with a wide range of applications.
(5) It is important to note that Rockwell hardness values obtained at different scales are not comparable.
4. Vickers hardness
1. Principle
Press a diamond pyramid onto the metal surface with a certain charge F to form a pyramid indentation.
The value of the charge in the unit indentation area is the Vickers hardness of the metallic material.
When the unit of test force F is kgf:
When the unit of test force F is N:
Penetrator material: diamond pyramid with 136° included angle
2. Representation method
For example: 270HV30/20, if the dwell time is 10-15s, it can be recorded as 270HV
- 270 – Hardness value
- 30 – Load size kgf
- 20 – Charge retention time s
3. Microhardness
Vickers hardness with very small load, load is 5-200gf.
Indicated by Hm, it can be used to test single grain or phase hardness.
| Vickers hardness test | Vickers Low Load Test | Micro Vickers Hardness Test | |||
| Hardness symbol | Test force/N | Hardness symbol | Test force/N | Hardness symbol | Test force/N |
| HV5 | 49.03 | HVO.2 | 1961 | HVO.01 | 0.09807 |
| HV10 | 98.07 | HVO.3 | 2,942 | HVO.015 | 0.1471 |
| HV20 | 196.1 | HVO.5 | 4,903 | HVO.02 | 0.1961 |
| HV30 | 294.2 | HV1 | 9,807 | HVO.025 | 0.2452 |
| HV50 | 490.3 | HV2 | 19.61 | HVO.05 | 0.4903 |
| HV100 | 980.7 | HV3 | 29.42 | HVO.1 | 0.9807 |
| Note: 1. Vickers hardness test can use a test force greater than 980.7N;2. Vickers micro test strength is recommended. | |||||
Characteristics and application of Vickers hardness
(1) The geometric shape of the recoil is always similar, although the load can be varied.
(2) The contour of the corner cone indentation is distinct, resulting in high measurement accuracy.
(3) Diamond indenter has a wide range of applications and can provide consistent hardness scales for various materials.
(4) The efficiency of indentation measurement is low, making it unsuitable for on-site batch inspection.
(5) The indentation is small and is not suitable for coarse or heterogeneous materials.
However, metallographic samples can be used to measure the hardness or hardness distribution of various phases.
5. Improvement of hardness-strength relationship and testing method
(1) Characteristics of hardness test
① The voltage state is very smooth (α>2), widely applicable;
Hardness of some materials
| Material | Illness | Hardness/(kgf/ mm² ） | |
| Metallic Materials | 99.5% aluminum | girdling | 20 |
| cold rolling | 40 | ||
| Aluminum alloy (A-Zn Mg Cu)Mild steel (tc = 0.2%) | girdling | 60 | |
| Precipitation hardening | 170 | ||
| Steel Aluminum Alloy for Bearing (A-Zn Mg Cu) | normalizing | 120 | |
| cold rolling | 200 | ||
| Mild steel (tc=0.2%) | normalizing | 200 | |
| Quenching (830 ℃) | 900 | ||
| Quenching (150℃) | 750 | ||
| ceramic materials | Bathroom | agglutination | 1500 ~ 2400 |
| Cermet (Co=6%, WC subsidy) | 20°C | 1500 | |
| 750°C | 1000 | ||
| Al 2 Ó 3 | ~1500 | ||
| B 4 C | 2500~3700 | ||
| Material | Illness | Hardness/(kgf/ mm² ） |
| BN (cubic meter) | 7500 | |
| Diamond | 6,000-10,000 | |
| Glass | ||
| Silica | 700-750 | |
| Glass of lemon soda | 540~580 | |
| optical glass | 550-600 | |
| Polymer | ||
| High pressure polyethylene | 40-70 | |
| Phenolic plastic (filler) | 30 | |
| polystyrene | 17 | |
| organic glass | 16 | |
| polyvinyl chloride | 14~17 | |
| abdomen | 8-10 | |
| polycarbonate | 9-10 | |
| Polyoxymethylene | 10~11 | |
| Polytetraethylene oxide | 10~13 | |
| polysulfone | 10~13 |
Covalent bond ≥ ionic bond> metallic bond> hydrogen bond> Van bond
② The method is simple, non-destructive and suitable for field inspection;
③ The physical meaning is unclear and it is difficult to project quantitatively.
(2) Relationship between hardness and strength
σb≈KH
Steel: K = 0.33 ~ 0.36
Copper alloy, stainless steel, etc.: K = 0.4 ~ 0.55
Relationship between hardness and strength of annealed metals
| Name of metal and alloy | HB | σb/MPa | k（σb/HB） | σ-1/MPa | σ（σ-1/HB） | |
| Non-ferrous metalsFerrous metalsNon-ferrous metals | Copper | 47 | 220h30 | 4.68 | 68.40 | 1.45 |
| aluminum alloy | 138 | 455.70 | 3:30 p.m. | 162.68 | 1.18 | |
| Duralumin | 116 | 454.23 | 3.91 | 144.45 | 1.24 | |
| ferrous metal | Industrial pure iron | 87 | 300.76 | 3.45 | 159.54 | 1.83 |
| 20 steel | 141 | 478.53 | 3.39 | 212.66 | 1.50 | |
| 45 steel | 182 | 637.98 | 3.50 | 278.02 | 1.52 | |
| 18 Steel | 211 | 753.42 | 3.57 | 264.30 | 1.25 | |
| T12 steel | 224 | 792.91 | 3.53 | 338.78 | 1.51 | |
| 1Cr18Ni9 | 175 | 902.28 | 5.15 | 364.56 | 2.08 | |
| 2Ch13 | 194 | 660.81 | 3:40 am | 318.99 | 1.64 | |
Note: Unit of hardness!
(3) Nano indentation test
During the loading process, elastic deformation first occurs on the sample surface. As the load increases, plastic deformation gradually appears and also increases.
The unloading process is mainly the recovery of elastic deformation, while plastic deformation causes the formation of an indentation on the surface of the sample.
Nano Indentation Load Displacement Curve
Nano indentation test principle
- H – Nanohardness;
- S – Contact rigidity;
- A – Contact area;
- β – Constants related to the geometry of the indenter;
- Er – equivalent module
There are important differences between nanohardness and traditional hardness:
Firstly, the two definitions are different.
Nanohardness: the instantaneous force supported by a unit area in the projection of the surface area of the base indentation during the sample indentation process, which is a measure of the sample's ability to withstand the contact load;
Vickers hardness is defined as the average force per unit area on the surface area of the indentation retained after indenter discharge, which reflects the ability of the sample to resist linear residual deformation.
In the hardness measurement process, if plastic deformation dominates the process, the results of the two definitions will be similar. However, if the process is dominated by elastic deformation, the results will be different.
In pure elastic contact, the residual contact area is very small. Therefore, the traditional definition of hardness will produce an infinite value, making it impossible to obtain the true hardness value of the sample.
Furthermore, the measurement ranges of the two methods are different. Traditional hardness measurement is only applicable to large-sized samples, not only due to the limitations of the measuring instrument, but also because the residual indentation cannot accurately reflect the true hardness of the sample on the micro and nano scales.
New measurement techniques and calculation methods are used for nanohardness measurement, which can more accurately reflect the hardness characteristics of the sample on the micro and nano scales.
The main difference between the two methods is the calculation of the setback area. Measuring nanohardness involves measuring the depth of the indentation and then calculating the contact area using an empirical formula, while traditional hardness measurement involves obtaining the surface area of the indentation from photos taken after unloading.
(4) Nanoindentation test method
The basic components of a nanohardness tester can be divided into several parts, including the control system, moving coil system, charging system and indenter.
Diamond indenters, which are typically triangular cones or four-edged dimensions, are commonly used.
During testing, the initial parameters are entered first and the subsequent detection process is fully automated by the microcomputer.
Manipulation of the charging system and the action of the indenter can be achieved by changing the current in the moving coil system.
Measurement and control of the indenter press load is performed by the extensometer, which also provides feedback to the moving coil system for closed-loop control, allowing the test to be completed according to the input parameter settings.
