Material hardness is one of the key parameters when choosing the right materials in the metal product design, But do you know what is the hardness of material? And how to measure it. In this article, as a low-volume manufacturing factory for metal parts, KUSLA will share a guide with you about the hardness of the material.
What is the hardness of the material?
Hardness is the ability of a material to resist localized plastic deformation. In most cases, local deformation is caused by mechanical indentation or wear. Therefore, this property usually includes many meanings, such as the material’s ability to resist scratching, cutting, abrasion, indentation, penetration, etc. In other words, hardness is the ability of one metal to cut another metal. Harder metals can usually cut softer metals or can make indentations on softer metal surfaces.
What are the different types of material hardness?
Scratch Hardness
It is mainly used to compare the softness and hardness of different objects. The method is to select a rod with one end hard and one soft end, scratch the material to be tested along the rod, and determine the softness and hardness of the material being tested according to the location of the scratch. The scratches made by hard objects are long, and the scratches made by soft objects are short. Common scratch hardness tests include Mohs hardness and Vickers hardness.
Indentation hardness
Mainly used for metal materials, the method is to use a certain load to press a specified indenter into the material to be tested and compare the softness and hardness of the material to be tested based on the local plastic deformation of the material surface. Due to differences in indenter, load, and load duration, common indentation hardness tests include Brinell hardness, Rockwell hardness, and Shore hardness.
Rebound hardness
Mainly used for metal materials, the method is to make a special hammer drop freely from a certain height to impact the sample of the material being tested and determine the hardness of the material based on the rebound height of the hammer during the impact process. Common rebound hardness tests include Shore hardness and Leeb hardness.
How to measure the hardness of a material?
Brinell hardness test
Brinell hardness test uses a quenched steel ball or cemented carbide ball with diameter D as the indenter and presses it into the surface of the specimen with the corresponding test force F. After the specified holding time, remove the test force to obtain an indentation with a diameter d. Divide the test force by the indentation surface area, and the resulting value is the Brinell hardness value, and the symbol is represented by HBS or HBW. The unit is kilogram-force/mm2 (N/mm2).
The difference between HBS and HBW is the difference in pressure head. HBS means that the indenter is a hardened steel ball, which is used to measure materials with a Brinell hardness value below 450, such as mild steel, gray cast iron, and non-ferrous metals. HBW indicates that the indenter is carbide and is used to measure materials with a Brinell hardness value below 650.
Rockwell hardness test
This test uses a diamond cone with a cone angle of 120° or Ø1.588mm and Ø3.176mm quenched steel balls as the pressure head and load. Under the initial load of 10kgf and the total force load of 60, 100, or 150kgf, The specimen is pressed into the specimen under successive loads. After the total load is applied, the hardness is expressed by the difference between the indentation depth when the main load is removed and the main load is retained and the indentation depth under the initial load.
The Rockwell hardness test uses three test forces and three indenters. There are 9 combinations of them, corresponding to the 9 types of Rockwell hardness. The applications of these 9 types cover almost all commonly used metal materials. There are three commonly used types: HRA, HRB, and HRC, here is a table to explain these three types of differences.
| HardnessSymbol | Indenter type | Total test force F/N（kgf） | Hardness Value | Application |
|---|---|---|---|---|
| HRA | 120°Diamond cone | 588.4(60) | 20~88 | Carbide, carbide, Shallow surface hardened steel |
| HRB | Ø1.588mmQuenched steel balls | 980.7(100) | 20~100 | Annealed steel, aluminum alloy, copper alloy, cast iron |
| HRC | 120°diamond cone | 1471(150) | 20~70 | Quenched and tempered steel, deep surface hardened steel |
Vickers hardness test
Vickers hardness test uses a diamond square pyramid indenter with an included angle of 136° between opposite faces to press into the surface of the material with the specified test force F. After maintaining the specified time, remove the test force. The average pressure per unit surface area of the square pyramid indentation is used to express the hardness. Value, marked with the symbol “HV”.
Leeb Hardness test
Leeb Hardness test involves an impact body equipped with a tungsten carbide ball head of a certain mass that is used to impact the surface of the specimen under a certain force and then rebound. Due to the different hardness of the materials, the rebound speed after impact is also different. A permanent magnet material is installed on the impact device. When the impact body moves up and down, its peripheral coil induces an electromagnetic signal proportional to the speed, which is then converted into a Leeb hardness value through the electronic circuit, with the symbol “HL”.
Pros and Cons of Different Types of Harness Tests
Each hardness test method has its pros and cons as below:
| PROS | CONS | |
|---|---|---|
| Brinell hardness | The indentation area is large, which can reflect the average performance of the material in a large area. The test data is stable and has good repeatability. | The indentation area is large and it is not suitable to test on the finished product; different materials need to replace the indenter ball with different diameters and change the test force; the indenter ball itself is easily deformed |
| Rockwell hardness | The indentation is small and the finished product can be inspected; the operation is simple and fast; different scales can be used to measure the hardness of various samples; due to the addition of preload, the influence of slight surface unevenness on the test results can be eliminated. | The indentation is small, it is sensitive to the inhomogeneity of the material structure, the test data is scattered, and the repeatability is poor. Hardness values measured with different scales cannot be unified and cannot be directly compared. |
| Vickers hardness | The indentation is square, and the diagonal length is easy to accurately measure; the measurement range is wide, and both soft and hard materials can be tested. | The hardness value needs to be calculated (or looked up in a table) by measuring the diagonal, which is inefficient. |
Comparison of Different Hardness unit values
Different hardness test methods will result in different hardness values with different units, here is a table to compare different hardness units with corresponding values.
| Types of hardness test | tensile strength/mm2 | |||
| Rockwell | Vickers | Brinell | ||
| HRC | HRA | HV | HB | |
| 25 | — | 255 | 251 | 835 |
| 26 | — | 261 | 257 | 860 |
| 27 | — | 268 | 263 | 880 |
| 28 | — | 274 | 269 | 900 |
| 29 | — | 281 | 276 | 920 |
| 30 | — | 289 | 283 | 950 |
| 31 | — | 296 | 291 | 970 |
| 32 | — | 304 | 298 | 995 |
| 33 | — | 312 | 306 | 1020 |
| 34 | — | 320 | 314 | 1050 |
| 35 | — | 329 | 323 | 1080 |
| 36 | — | 338 | 332 | 1110 |
| 37 | — | 347 | 341 | 1140 |
| 38 | — | 357 | 350 | 1175 |
| 39 | 70 | 367 | 360 | 1210 |
| 40 | 70.8 | 382 | 375 | 1260 |
| 41 | 71.1 | 388 | 380 | 1280 |
| 42 | 71.6 | 399 | 391 | 1320 |
| 43 | 72.1 | 411 | 401 | 1360 |
| 44 | 72.6 | 423 | 413 | 1405 |
| 45 | 73.2 | 436 | 424 | 1450 |
| 46 | 73.7 | 449 | 436 | 1500 |
| 47 | 74.2 | 463 | 449 | 1550 |
| 48 | 74.7 | 478 | 461 | 1605 |
| 49 | 75.3 | 493 | 474 | 1660 |
| 50 | 75.8 | 509 | 488 | 1720 |
Common metal Material hardness chart
The below table shows the value range of the common metal materials used in our daily life, you will see a basic hardness level of these metal materials.
| TYPE | Brinell Hardness (HB) | |
| Aluminum alloys | 1 series | 15-30 |
| Aluminum alloys | 2 series | 60-150 |
| Aluminum alloys | 5 series | 40-120 |
| Aluminum alloys | 6 series | 60-160 |
| Aluminum alloys | 7 series | 80-170 |
| Stainless steel | 304 | 70-90 |
| Stainless steel | 316 | 70-90 |
| Stainless steel | 410 | 160 |
| Steel | Low-carbon steel | 60-80 |
| Steel | High-carbon steel | 100-170 |
| Steel | alloy steel | 150-300 |
| Copper | Copper 101 | 40 |
| Copper | Copper C110 | 65-95 |
| TITANIUM | 120-360 |
Guideline for different material hardness test
Different materials can be suitable for different material hardness test methods, below table shows different materials can be tested with different hardness test methods. This could be a guideline for you when you need to test a product with different materials.
| material | Vickers hardness | Rockwell hardness | Brinell hardness | Shore hardness | Leeb hardness |
| Super carbide, ceramic | YES | YES | |||
| Metal | YES | YES | YES | YES | YES |
| Plastic | YES | ||||
| Rubber | YES |
Standards of material hardness test
Here, we list a summary of the national standards for the material hardness tests which you can check in more detail in these standards.
- ASTM E 18-2012 Test methods for Rockwell hardness and Rockwell surface hardness of metallic materials
- ASTM E l0-2012 Brinell hardness test method for metallic materials
- ASTM E 92-82 (2003) Vickers hardness test method for metallic materials
- ASTM E 103-84 (2002) Rapid indentation hardness test method for metallic materials
- ASTM E 110-82 (2002) Test method for determination of indentation hardness of metallic materials using a portable hardness tester
- ASTM E 384-2006e1 Test method for micro indentation hardness of materials
Conclusion
A material hardness test is needed when your product has the requirement of material hardness, There are various ways to test for the hardness of your material. Contact us to know which is a good method to test your product. KUSLA offers cost-effective metal prototypes and metal parts production, we promise to provide the most cost-effective quotations within 12 hours with DFM for your products.
FAQ
What material has good hardness?
Diamond, cubic boron nitride (c-BN), carbon nitrides, and ternary compounds such as B-N-C, are the common materials that have good hardness.
Which material has the highest hardness?
The material with the highest hardness is the diamond we can find on Earth. On the Mohs scale of mineral hardness, diamond ranks as a 10, making it the hardest naturally occurring substance. Other materials, such as cubic boron nitride and some synthetic materials, can also achieve very high hardness levels, but diamond is the highest one.
