What does hardness of a material mean?

Hardness refers to the ability of materials to resist local deformation, especially plastic deformation, indentation or scratch. It is a measure of the hardness and softness of materials.

Contents:

According to the different test methods, the 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 one end soft, and then cross the tested material along the rod, and determine the hardness and softness of the tested material according to the location of the scratch. Qualitatively speaking, hard objects have long scratches and soft objects have short scratches.
② Press in hardness. It is mainly used for metal materials. The method is to press the specified indenter into the tested material with a certain load, and compare the soft and hard of the tested material with the local plastic deformation of the material surface. Because of the difference of indenter, load and load duration, there are many kinds of indentation hardness, such as Brinell hardness, Rockwell hardness, Vickers hardness and microhardness.
③ Rebound hardness. It is mainly used for metal materials. The method is to make a special small hammer drop freely from a certain height to impact the sample of the material to be tested. The hardness of the material is determined by the amount of strain energy stored (and then released) during the impact (measured by the rebound height of the small hammer).
Common HV = HB = HRC hardness comparison table

Comparison table of common hardness of ferrous metals (approximate conversion of strength)
Classification of hardness

Tensile strength

N/mm2

Rockwell Vickers Brinell
HRC HRA HV HB
17 211 211 710
17.5 214 214 715
18 216 216 725
18.5 218 218 730
19 221 220 735
19.5 223 222 745
20 226 225 750
20.5 229 227 760
21 231 229 765
21.5 234 232 775
22 237 234 785
22.5 240 237 790
23 243 240 800
23.5 246 242 810
24 249 245 820
24.5 252 248 830
25 255 251 835
25.5 258 254 850
26 261 257 860
26.5 264 260 870
27 268 263 880
27.5 271 266 890
28 274 269 900
28.5 278 273 910
29 281 276 920
29.5 285 280 935
30 289 283 950
30.5 292 287 960
31 296 291 970
31.5 300 294 980
32 304 298 995
32.5 308 302 1010
33 312 306 1020
33.5 316 310 1035
34 320 314 1050
34.5 324 318 1065
35 329 323 1080
35.5 333 327 1095
36 338 332 1110
36.5 342 336 1125
37 347 341 1140
37.5 352 345 1160
38 357 350 1175
38.5 362 355 1190
39 70 367 360 1210
39.5 70.3 372 365 1225
40 70.8 382 375 1260
40.5 70.5 377 370 1245
41 71.1 388 380 1280
41.5 71.3 393 385 1300
42 71.6 399 391 1320
42.5 71.8 405 396 1340
43 72.1 411 401 1360
43.5 72.4 417 407 1385
44 72.6 423 413 1405
44.5 72.9 429 418 1430
45 73.2 436 424 1450
45.5 73.4 443 430 1475
46 73.7 449 436 1500
46.5 73.9 456 442 1525
47 74.2 463 449 1550
47.5 74.5 470 455 1575
48 74.7 478 461 1605
48.5 75 485 468 1630
49 75.3 493 474 1660
49.5 75.5 501 481 1690
50 75.8 509 488 1720
50.5 76.1 517 494 1750
51 76.3 525 501 1780
51.5 76.6 534 1815
52 76.9 543 1850
52.5 77.1 551 1885
53 77.4 561 1920
53.5 77.7 570 1955
54 77.9 579 1995
54.5 78.2 589 2035
55 78.5 599 2075
55.5 78.7 609 2115
56 79 620 2160
56.5 79.3 631 2205
57 79.5 642 2250
57.5 79.8 653 2295
58 80.1 664 2345
58.5 80.3 676 2395
59 80.6 688 2450
59.5 80.9 700 2500
60 81.2 713 2555
60.5 81.4 726
61 81.7 739
61.5 82 752
62 82.2 766
62.5 82.5 780
63 82.8 795
63.5 83.1 810
64 83.3 825
64.5 83.6 840
65 83.9 856
65.5 84.1 872
66 84.4 889
66.5 84.7 906
67 85 923
67.5 85.2 941
68 85.5 959
68.5 85.8 978
69 86.1 997
69.5 86.3 1017
70 86.6 1037

 

  • HRC / HB approximate conversion tips.
  • The hardness is higher than 20hrc, 1hrc ≈ 10hb.
  • The hardness is lower than 20hrc, 1hrc ≈ 11.5hb.

Note: for machining, it is basically possible to convert 1hrc ≈ 10hb (workpiece material hardness has fluctuation range) 

The most common Brinell hardness, Rockwell hardness and Vickers hardness of metal materials belong to indentation hardness, and the hardness value indicates the ability of the material surface to resist the plastic deformation caused by another object when it is pressed in; the rebound method (shore, Richter) measures the hardness, and the hardness value represents the size of metal elastic deformation function.

Brinell hardness

The quenched steel ball or hard alloy ball with diameter D is used as the indenter, and the corresponding test force F is pressed into the surface of the test piece. After the specified holding time, the test force is removed and an indentation with diameter D is obtained. The Brinell hardness value is obtained by dividing the test force by the surface area of the indentation. The symbol is HBS or HBW.

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The difference between HBS and HBW is that of the indenter. HBS indicates that the indenter is a hardened steel ball, which is used to determine materials with Brinell hardness value below 450, such as mild steel, gray cast iron and non-ferrous metals. HBW indicates that the indenter is hard alloy, which is used to determine materials with Brinell hardness value below 650.
In the same test block, when other test conditions are identical, 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.
Since 2003, China has adopted the international standard equivalently, cancelled the steel ball indenter, and adopted the cemented carbide ball head. Therefore, HBS is not used, and HBW is used to represent Brinell hardness symbol. In many cases, Brinell hardness is only represented by Hb, which refers to HBW. However, in the literature, HBS is still seen from time to time.
Brinell hardness measurement method is applicable to cast iron, non-ferrous alloy, all kinds of annealed and tempered steel. It is not suitable to measure the samples or workpieces which are too hard, too small, too thin and whose surface is not allowed to have large indentation.

Rockwell Hardness

The diamond cone with 120 ° cone top angle or 1.588mm and 3.176mm quenched steel balls are used as indenters and loads. The hardness is expressed by the difference between the indentation depth when the main load is removed and the indentation depth when the main load is retained and the indentation depth when the main load is removed under the action of 10kgf initial load and 60, 100 or 150kgf total load (i.e. initial load plus main load) successively.

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The Rockwell hardness test adopts three test forces and three indenters, which have nine combinations, corresponding to nine scales of Rockwell hardness. The application of these 9 scales covers almost all commonly used metal materials. HRA, HRB and HRC are commonly used, of which HRC is the most widely used.
Table of commonly used Rockwell hardness test specifications

Hardness symbol

 

Head type

Total test force

 F/Nkgf

Hardness range

 

Examples of application

HRA

120° Diamond cone

 

588.4(60)

20~88

Hard alloy, carbide, superficial surface hardening steel, etc

 

HRB

Ø1.588mm

Quenched steel ball

980.7(100)

20~100

Annealed, normalized steel, aluminum alloy, copper alloy, cast iron

 

HRC

120° Diamond cone

 

1471(150)

20~70

Hardened steel, Quenched and tempered steel, deep case hardened steel

 

The use range of HRC scale is 20 ~ 70hrc. When the hardness value is less than 20hrc, because the conical part of the indenter is pressed too much and the sensitivity is reduced, 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 easy to be damaged, and the life of the indenter will be greatly shortened, so the HRA scale should be used instead.
Rockwell hardness test is easy to operate, fast and with small indentation. It can be used to test the surface of finished products and hard and thin workpieces. Because of the small indentation, for the material with uneven structure and hardness, the hardness value fluctuates greatly, and the accuracy is not as high as that of Brinell hardness. Rockwell hardness is used to determine the hardness of steel, non-ferrous metals, cemented carbide, etc.

Vickers Hardness

The principle of Vickers hardness measurement is similar to Brinell hardness. The diamond positive pyramid indenter with an included angle of 136 ° is used to press into the surface of the material with the specified test force F, and the test force is removed after the specified time is maintained. The hardness value is expressed by the average pressure on the unit surface area of the positive pyramid indentation, and the mark symbol is HV.

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Vickers hardness can be measured in the range of 10 ~ 1000hv, with small indentation. It is generally used to measure thin materials, carburizing, nitriding and other surface hardening layers.

Leeb Hardness

A certain mass of the impact body with a tungsten carbide ball head is used to impact the surface of the specimen under a certain force, and then rebound. Because of the different hardness of the material, 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 will induce an electromagnetic signal proportional to the speed, and then it will be converted into a Leeb hardness value through the electronic circuit, with the symbol marked HL.
No worktable is needed for the Leeb hardness tester, and its hardness sensor is as small as a pen, which can be operated directly by hand. It is easy to detect whether it is a large, heavy workpiece or a workpiece with complex geometry size.
Another advantage of Leeb hardness is that the surface damage of products is very light, sometimes it can be used as non-destructive testing; hardness testing of various directions, narrow space and special parts has unique characteristics.

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Application of AFFRI crankshaft hardness tester in SAIC

Source: China Fittings Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published:

What affects the hardness of a metal?

The factors that affect the mechanical properties of metal are varied. For instance, yield strength, hardness, the ductile-brittle transition temperature, and susceptibility to environmental conditions are all affected and can be improved, by altering the grain size.

What is the hardest metal?

Tungsten (1960–2450 MPa)
Tungsten is one of the hardest metals you will find in nature. Also known as Wolfram, the rare chemical element exhibits a high density (19.25 g/cm3) as well as a high melting point (3422 °C/ ​6192 °F). In its rare form, tungsten is hard to work with due to its brittleness which can be changed when turned pure. Tungsten is often utilized to create hard alloys, such as high speed steel to increase protection against abrasion as well as improve electrical conductivity.
Iridium (1670 MPa)
Like Tungsten, Iridium is a chemical element that shows signs of high density and a tolerance of high temperatures. Iridium belongs to the platinum group metals, resembling platinum in its look. However, iridium is hard to work with. Since it is very hard, iridium is also quite brittle which is only aggravated by its very high melting point of over 2,000°C. Iridium ranks among one of the rarest Elements on Earth’s surface as well as one of the most corrosion-resistant elements.
Steel
Steel is an alloy metal made of iron and other elements, such as carbon. It is the most used material in construction, mechanical engineering, and other industries. Due to the many variations and levels of quality steel can adopt, there is no uniform hardness value. There exist many different techniques of tempering steel to improve the wear protection of steel, heat tolerance and protection against abrasion. Borocoat for example optimizes the hardness of steel without making it brittle. Find out more about boronizing and Borocoat.
Osmium (3920–4000 MPa)
Osmium belongs to the platinum group metals and displays a high density. In fact, it is the densest, naturally occurring element on Earth with 22.59 g/cm3. This is also why Osmium does not melt until 3033 °C, a temperature that makes it difficult to work with the metal. When it is alloyed with other platinum group metals (such as iridium, platinum and palladium) it can be used in many different areas where hardness and durability are needed.
Chromium (687-6500 MPa)
Chromium is an element often found in alloys, such as stainless steel. On the Mohs scale, which measures scratch resistance, it is found among the top. Chromium is valued for its high corrosion resistance as well as its hardness. Since it is easier to handle as well as more abundant than platinum group metals, chromium is a popular element used in alloys.
Titanium (716 to 2770 MPa)
Titanium is known for its strength. While it does not quite compare to other any other metal on this list in terms of Brinell Hardness, titanium has an impressive strength to weight ratio. Even in its pure form, titanium is harder than many steel forms. As a refractory metal, it is highly resistant to heat and abrasion which is why titanium is a popular alloy metal. It can be alloyed with iron and carbon.

What determines a material’s hardness?

In the example you mention much of the hardness is due to the nature of the atomic bonding within the material. Before proceeding it is important to point out that diamond and graphite are both made purely of carbon and that the differences in their properties arise mainly from the structure and bonding of the carbon atoms in these materials. These structural differences can explain differences in hardnesses of many materials but often there are other factors that go into determining a materials hardness.
For diamond, each carbon atom binds to four other carbon atoms in a very specific tetrahedral arrangement. When a lot of these carbon atoms bind together an extended network of carbon atoms is created. Essentially, an extended network can be thought of as a single, very large molecule which makes diamond extremely resilient because all of the carbon atoms are in a way, “locked together.”
With graphite, the carbon atoms only bind to three other carbon atoms in a planar, trigonal arrangement. When these carbon atoms bind together they form sheets that sort of stack on top of one each other and are only held together by weak forces between the layers. The fact that the carbon is present as a sheet means that the carbon atoms are not “locked together” as they are in diamond and can slide over one another.

What is hardness and what are the different types of hardness associated with materials?

Hardness refers to the resistance of a material’s surface to indentation or scratching. Different hardness scales include Rockwell C & B (metals), Brinell (ball indenter, metals), Vickers (diamond shaped indenter), Knoop (diamond shaped micro-indenter), Meyer (rarely used), Shore A & D (rubber & softer plastics) and Mohs (minerals). Each is measured by pressing an indenter into the test specimen and determining the depth or width of the resulting impression or by testing the relative scratch resistance when a point is dragged across the surface of the specimen. Some measures can be used to derive an indirect measure of tensile strength based on tabulated data. There are useful tables of hardness equivalence between the different scales. Some scales such as Mohs and Shore are highly non-linear. You may look each one up in Wikipedia for more detailed discussion.

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what does hardness of a material mean - What does hardness of a material mean?
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What does hardness of a material mean?
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Hardness refers to the ability of materials to resist local deformation, especially plastic deformation, indentation or scratch. It is a measure of the hardness and softness of materials.
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