on 16 Mar 2021 11:37 AM
  • hardness

For Hard materials with hardness greater than 30 HRC or 300 Vickers or 286 HB it is necessary to pre-broach the slot for the Clins and the broaching tool is recommended.

It is also important to understand that there are so many different hardness test methods in common use that it is easy to get confused. 

Example:
-    AL 7075 has 87HRB what corresponds to 172 hardness Vickers, so no broaching tool is required.
-    An extremely hard steel might have a hardness of 64 HRC and the broaching tool is recommended, while a fairly soft steel might have a hardness of 70 HRB and not broaching tool required.

It should be also noted that Hardness is very important for producing rough metal castings, heat treatment and machining process. Rockwell Hardness (HRC and HRB) and Brinell Hardness (HB or BHN) are most commonly used for steel and iron castings.

How can you convert hardness units?

Formula 1 - Convert HRC into HB

Rockwell C Hardness (HRC)

Brinell Hardness (HB)

From 21 to 30

HB = 5.970 * HRC + 104.7

From 31 to 40

HB = 8.570 * HRC + 27.6

From 41 to 50

HB = 11.158 * HRC - 79.6

From 51 to 60

HB = 17.515 * HRC - 401

Formula 2 - Convert HRB into HB

Rockwell B Hardness (HRB)

Brinell Hardness (HB)

From 55 to 69

HB = 1.646 * HRB + 8.7

From 70 to 79

HB = 2.394 * HRB - 42.7

From 80 to 89

HB = 3.297 * HRB - 114

From 90 to 100

HB = 5.582 * HRB - 319

With the help of the comparisons between hardness :

Table 1 - HRC to HB, HV, Rm

HRC Hardness

HB Hardness

HV Hardness

Rm Tensile Strength

Diamond penetrator

Brinell 3000 Kgf

Vickers 30

N / mm2 MPa

20

226

238

760

21

231

243

770

22

237

248

790

23

243

254

810

24

247

260

820

25

253

266

850

26

258

272

860

27

264

279

880

28

271

286

900

29

279

294

930

30

286

302

950

31

294

310

970

32

301

318

1010

33

311

327

1030

34

319

336

1050

35

327

345

1080

36

336

354

1110

37

344

363

1140

38

353

372

1180

39

362

382

1220

40

371

392

1250

41

381

402

1300

42

390

412

1340

43

400

423

1390

44

409

434

1430

45

421

446

1480

46

432

458

1520

47

442

471

1580

48

455

484

1640

49

468

498

1700

50

482

513

1760

51

496

528

1820

52

512

544

1880

53

525

560

1950

54

543

577

2010

55

560

595

2070

56

577

613

2160

57

595

633

2240

58

615

653

2330

59

634

674

2420

60

654

697

 -

61

670

720

 -

62

688

746

 -

63

706

772

 -

64

722

800

 - 

65

739

832

 -

66

 -

865

 -

67

 -

900

 -

68

 -

940

 -

 

What tests can I use for hardness?

The Rockwell hardness test is the most used hardness test method and is generally easier to perform than other types of hardness testing methods.
The Rockwell test method is used on all metals, except in conditions where the test metal structure or surface conditions would introduce too many variations; where the indentations would be too large for the application; or where the sample size or sample shape prohibits its use. 

The Brinell hardness test method as used to determine Brinell hardness is defined in ASTM E10. Most commonly it is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method