The hardness of metal materials is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.
The hardness of metal materials
Hardness refers to the ability of a material to resist local deformation, especially plastic deformation, indentation or scratch. It is an indicator to measure the hardness and softness of a material. According to different test methods, hardness is divided into three types.
① Scratch hardness. It is mainly used to compare the hardness and softness of different minerals. The method is to select a rod with one end hard and the other end soft, and scratch the material to be tested along the rod. The hardness and softness of the material to be tested are determined according to the position of the scratch. Qualitatively speaking, the scratch made by a hard object is long, and the scratch made by a soft object is short.
②Indentation hardness. Mainly used for metal materials, the method is to use a certain load to press the specified indenter into the material to be tested, and compare the softness and hardness of the material to be tested by the size of the local plastic deformation on the surface of the material. Due to the differences in the indenter, load and load duration, there are many types of indentation hardness, mainly Brinell hardness, Rockwell hardness, Vickers hardness and microhardness.
③Rebound hardness. Mainly used for metal materials, the method is to make a special small hammer fall freely from a certain height to impact the sample of the material to be tested, and determine the hardness of the material by the amount of strain energy stored (and then released) by the sample during the impact (determined by the rebound height of the small hammer).
The most common Brinell hardness, Rockwell hardness and Vickers hardness of metal materials belong to indentation hardness. The hardness value indicates the ability of the material surface to resist plastic deformation caused by another object pressing into it. The rebound method (Shore and Leeb) measures hardness, and the hardness value represents the size of the metal's elastic deformation function.
Brinell Hardness
Use a hardened steel ball or carbide ball with a diameter of D as an indenter, press it into the surface of the specimen with the corresponding test force F, and after the specified holding time, remove the test force to obtain an indentation with a diameter of d. Divide the test force by the surface area of the indentation, and the value obtained is the Brinell hardness value, represented by the symbol HBS or HBW.
The difference between HBS and HBW is the difference in the indenter. 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 made of carbide and is used to measure materials with a Brinell hardness value below 650.
For the same test block, when other test conditions are exactly the same, the two test results are different, and the HBW value is often greater than the HBS value, and there is no quantitative rule to follow.
After 2003, my country has equivalently adopted international standards, canceled the steel ball indenter, and all used carbide ball heads. Therefore, HBS is no longer used, and HBW is used to represent the Brinell hardness symbol. In many cases, Brinell hardness is only represented by HB, which refers to HBW. However, HBS is still seen in literature papers.
The Brinell hardness measurement method is suitable for cast iron, non-ferrous alloys, various annealed and tempered steels, and is not suitable for measuring samples or workpieces that are too hard, too small, too thin, and do not allow large indentations on the surface.
Rockwell Hardness
A diamond cone with a 120° apex angle or a Ø1.588mm and Ø3.176mm hardened steel ball is used as an indenter and load. The sample is pressed into the test piece under the action of an initial load of 10kgf and a total load of 60, 100 or 150kgf (i.e., initial load plus main load). After the total load is applied, the hardness is expressed by the difference between the indentation depth when the main load is removed but the main load is retained and the indentation depth under the action of the initial load.
The Rockwell hardness test uses three test forces and three indenters, which have a total of 9 combinations, corresponding to the 9 scales of Rockwell hardness. The application of these 9 scales covers almost all commonly used metal materials. The commonly used ones are HRA, HRB and HRC, among which HRC is the most widely used.
Common Rockwell hardness test specification table
| Hardness symbol | Indenter type | Total test force F/N (kgf) | Hardness range | Application examples |
| HRA | 120° diamond cone | 588.4(60) | 20~88 | Carbide, carbide, shallow surface hardening steel, etc. |
| HRB | Ø1.588mm hardened steel ball | 980.7(100) | 20~100 | Annealed, normalized steel, aluminum alloy, copper alloy, cast iron |
| HRC | 120° diamond cone | 1471(150) | 20~70 | Quenched steel, quenched and tempered steel, deep surface hardened steel |
HRC scale is used in the range of 20~70HRC. When the hardness value is less than 20HRC, because the conical part of the indenter is pressed too much, the sensitivity decreases, and the HRB scale should be used instead; when the hardness of the sample is greater than 67HRC, the pressure on the tip of the indenter is too large, the diamond is easily damaged, and the life of the indenter will be greatly shortened, so the HRA scale should generally be used instead.
The Rockwell hardness test is easy to operate, quick, and has a small indentation. It can test the surface of finished products and harder and thinner workpieces. Due to the small indentation, the hardness value fluctuates greatly for materials with uneven structure and hardness, and the accuracy is not as high as Brinell hardness. Rockwell hardness is used to measure the hardness of steel, non-ferrous metals, cemented carbide, etc.
Vickers Hardness Vickers Hardness
The measurement principle of Vickers hardness is similar to that of Brinell hardness. A diamond square pyramid indenter with a relative angle of 136° is used to press into the surface of the material with a specified test force F. After maintaining the test force for a specified time, the test force is removed, and the hardness value is expressed by the average pressure per unit surface area of the square pyramid indentation, and the symbol is HV.
The Vickers hardness measurement range is large, and it can measure materials with a hardness range of 10~1000HV. It has a small indentation and is generally used to measure thinner materials and surface hardening layers such as carburizing and nitriding.
Leeb Hardness
Use a certain mass of impact body with tungsten carbide ball head to impact the surface of the test piece under a certain force, and then rebound. Due to the different hardness of the material, the rebound speed after the impact is also different. Permanent magnetic material is installed on the impact device. When the impactWhen the body moves up and down, its outer coil will induce an electromagnetic signal proportional to the speed, which is then converted into the Leeb hardness value through the electronic circuit, and the symbol is HL.
The Leeb hardness tester does not need a workbench. Its hardness sensor is as small as a pen and can be directly operated by hand. It can easily detect large and heavy workpieces or workpieces with complex geometric dimensions.
Another advantage of the Leeb hardness tester is that it causes little damage to the surface of the product, and can sometimes be used as a non-destructive test; it is unique in testing the hardness of all directions, narrow spaces and special parts.
Common HV=HB=HRC hardness comparison table
| Tensile strength
（N/mm2） |
Vickers hardness
HRC | ||
| 255 | 80 | 76.0 | — |
| 270 | 85 | 80.7 | — |
| 285 | 90 | 85.2 | — |
| 305 | 95 | 90.2 | — |
| 320 | 100 | 95.0 | — |
| 335 | 105 | 99.8 | — |
| 350 | 110 | 105 | — |
| 370 | 115 | 109 | — |
| 380 | 120 | 114 | — |
| 400 | 125 | 119 | — |
| 415 | 130 | 124 | — |
| 430 | 135 | 128 | — |
| 465 | 145 | 138 | — |
| 480 | 150 | 143 | — |
| 490 | 155 | 147 | — |
| 510 | 160 | 152 | — |
| 530 | 165 | 156 | — |
| 545 | 170 | 162 | — |
| 560 | 175 | 166 | — |
| 575 | 180 | 171 | — |
| 595 | 185 | 176 | — |
| 610 | 190 | 181 | — |
| 625 | 195 | 185 | — |
| 640 | 200 | 190 | — |
| 660 | 205 | 195 | — |
| 675 | 210 | 199 | — |
| 690 | 215 | 204 | — |
| 705 | 220 | 209 | — |
| 720 | 225 | 214 | — |
| 740 | 230 | 219 | — |
| 755 | 235 | 223 | — |
| 770 | 240 | 228 | 20.3 |
| 785 | 245 | 233 | 21.3 |
| 800 | 250 | 238 | 22.2 |
| 820 | 255 | 242 | 23.1 |
| 835 | 260 | 247 | 24.0 |
| 850 | 265 | 252 | 24.8 |
| 865 | 270 | 257 | 25.6 |
| 880 | 275 | 261 | 26.4 |
| 900 | 280 | 27.1 | |
| 915 | 285 | 271 | 27.8 |
| 930 | 290 | 276 | 28.5 |
| 950 | 295 | 280 | 29.2 |
| 965 | 300 | 285 | 29.8 |
| 995 | 310 | 295 | 31.0 |
| 1030 | 320 | 304 | 32.2 |
| 1060 | 330 | 314 | 33.3 |
| 1095 | 340 | 323 | 34.4 |
| 1125 | 350 | 333 | 35.5 |
| 1115 | 360 | 342 | 36.6 |
| 1190 | 370 | 352 | 37.7 |
| 1220 | 380 | 361 | 38.8 |
| 1255 | 390 | 371 | 39.8 |
| 1290 | 400 | 380 | 40.8 |
| 1320 | 410 | 390 | 41.8 |
| 1350 | 420 | 399 | 42.7 |
| 1385 | 430 | 409 | 43.6 |
| 1420 | 440 | 418 | 44.5 |
| 1455 | 450 | 428 | 45.3 |
| 1485 | 460 | 437 | 46.1 |
| 1520 | 470 | 447 | 46.9 |
| 1555 | 480 | (456) | 47.7 |
| 1595 | 490 | (466) | 48.4 |
| 1630 | 500 | (475) | 49.1 |
| 1665 | 510 | (485) | 49.8 |
| 1700 | 520 | (494) | 50.5 |
| 1740 | 530 | (504) | 51.1 |
| 1775 | 540 | (513) | 51.7 |
| 1810 | 550 | (523) | 52.3 |
| 1845 | 560 | (532) | 53.0 |
| 1880 | 570 | (542) | 53.6 |
| 1920 | 580 | (551) | 54.1 |
| 1955 | 590 | (561) | 54.7 |
| 1995 | 600 | (570) | 55.2 |
| 2030 | 610 | (580) | 55.7 |
| 2070 | 620 | (589) | 56.3 |
| 2105 | 630 | (599) | 56.8 |
| 2145 | 640 | (608) | 57.3 |
| 2180 | 650 | (618) | 57.8 |
| 660 | 58.3 | ||
| 670 | 58.8 | ||
| 680 | 59.2 | ||
| 690 | 59.7 | ||
| 700 | 60.1 | ||
| 720 | 61.0 | ||
| 740 | 61.8 | ||
| 760 | 62.5 | ||
| 780 | 63.3 | ||
| 800 | 64.0 | ||
| 820 | 64.7 | ||
| 840 | 65.3 | ||
| 860 | 65.9 | ||
| 880 | 66.4 | ||
| 900 | 67.0 | ||
| 920 | 67.5 | ||
| 940 | 68.0 |
The data in this table are from German standard DIN50150。