Vickers

Vickers

BACKGROUND INFORMATION
VICKERS HARDNESS TESTING (DIN EN ISO 6507)

 
 

Based on the ideas of Smith and Sandland, a hardness testing method was developed in 1925 in the English Vickers works, using a diamond pyramid as the indenter. A regular four-sided diamond pyramid with a surface angle of 136° is pressed vertically into the preferably polished surface of the test specimen with a certain test load. After a certain exposure time, the test specimen is removed again and the two diagonals (d1 and d2) of the indentation are measured with a measuring microscope. The average length d is then calculated. The Vickers hardness is then determined according to the given formula.

 

1. Indentation of the diamond pyramid
with test force F into the test specimen 

 

Vickers 1

2. Measurement of the indentation
with diameter d 

 

Vickers 2

CALCULATION OF THE VICKERS HARDNESS

 

Vickers calculation formula:
 
 
Vickers 3
 
 
 

PREREQUISITES FOR STANDARD-COMPLIANT TESTING

 

Various prerequisites need to be fulfilled for standard-compliant testing:

 

Vickers 4

 

 

Test temperature

  • normal requirements: 10°C bis 35°C
  • high requirements: 23°C ± 5°C
Workpiece thickness
  • t ≥ 1.5 * d with t = sample or layer thickness d = average length of the indentation diagonals
Distances between the indentations and from the edge
  • For steels, Cu and Cu alloys
    • a ≥ 2.5  * d
    • b ≥ 3 * d
  • For light metals, Pb, Zn as well as their alloys
    • a ≥ 3 * d
    • b ≥ 6 * d
It is distinguished between the macro, small force and micro hardness range.
 
 

MACRO HARDNESS RANGE

General tests on relatively thick components
 
Recommended test forces
 		 Name of value
980.70 HV 100
490.30 HV 50
294.20 HV 30
196.10 HV 20
98.67 HV 10

49.03

 

HV 5

 

 

SMALL FORCE RANGE

Tests on thin workpieces, thin surface layers and foils
 
Recommended test forces
 		 Name of value
29.42 HV 3
19.6 HV 2
9.807 HV 1
4.903 HV 0.5
2.942 HV 0.3

1.961

 

HV 0.2

 
 

MICRO HARDNESS RANGE

Measurements at individual structure components
 
Recommended test forces
 		 Name of value
0.981 HV 0.1
0.490 HV 0.05
0.245 HV 0.025
0.196 HV 0.02

0.098

 

HV 0.01

 

VICKERS HARDNESS TESTING RESULTS

According to DIN EN ISO 6507-1, the result of a Vickers test is given as follows:
 
700 HV 10 / 20   ⇒   Hardness value as per Vickers
700 HV 10 / 20   ⇒   Abbreviation for Vickers hardness 
700 HV 10 / 20   ⇒   Test force specification: Test force [N] = 9.807 * test force specification
700 HV 10 / 20   ⇒   Application time of the test force (omitted if it is between 1-15 s)
 
 

MEASURING HARDNESS DEPTHS

The Vickers test is also the preferred method for measuring hardness depths. A distinction is primarily made between the depth of hardening after case hardening (CHD), after nitriding (NHD) and after induction hardening (SHD).

DEPTH OF HARDENING AFTER CASE HARDENING (CHD)

 
When testing the case hardening depth (CHD), the hardness in HV1 is measured on the cross-section at regular distances from the surface. In order to comply with the above-mentioned rules of distance between the individual indentations, this is usually done as a 'zig-zag line'. The values are plotted graphically. The CHD is the distance at which the hardness falls below a certain limit. Usually, the limit is GH = 550 HV1 but a deviating value can be determined.



An example of this method is shown in the following image. The case hardening depth (CHD) can also be calculated from the pairs of values.

 

 

Distance from the surface
[mm] ⇒ Hardness [HV1]

 

0.1 ⇒ 717
0.2 ⇒ 718
0.3 ⇒ 705
0.4 ⇒ 675
0.5 ⇒ 645
0.6 ⇒ 610
0.7 ⇒ 580
0.8 ⇒ 550
0.9 ⇒ 520
1.0 ⇒ 490
1.1 ⇒ 465
1.2 ⇒ 450
1.3 ⇒ 440
1.4 ⇒ 430
1.5 ⇒ 425

Vickers 5

CHD = Case Hardening Depth

 

 
 

DEPTH OF HARDENING AFTER NITRIDING

 
When testing the nitriding hardening depth (NHD), the hardness in HV0.5 is measured on the cross-section at regular distances from the surface. In order to comply with the above-mentioned rules of distance between the individual indentations, this is usually done as a 'zig-zag line'. The values are plotted graphically. The NHD is the distance at which the hardness falls below a certain limit. Usually, the limit is defined as GH = core hardness + 50 HV, but a deviating value can be determined.



An example of this method is shown in the following image. The nitriding hardening depth (NHD) can also be calculated from the pairs of values.

 

 

Distance from the surface
[mm] ⇒ Hardness [HV1]

 

0.05 ⇒ 1080
0.1 ⇒ 1050
0.2 ⇒ 350
0.3 ⇒ 257
0.4 ⇒ 250
0.5 ⇒ 250
0.6 ⇒ 250
0.7 ⇒ 250
0.8 ⇒ 250
0.9 ⇒ 250
1.0 ⇒ 250

Vickers 6

NHD = Nitriding Hardening Depth

 

limit hardness GH = core hardness KH + 50 HV

 

DEPTH OF HARDENING AFTER INDUCTION HARDENING

 
When testing the induction hardening depth (SHD), the hardness in HV15 is measured on the cross-section at regular distances from the surface. In order to comply with the above-mentioned rules of distance between the individual indentations, this is usually done as a 'zig-zag line'. The values are plotted graphically. The SHD is the distance at which the hardness falls below a certain limit. Usually, the limit is defined as GH = 85% of the minimum surface hardness, but a deviating value can be determined.



An example of this method is shown in the following image. The induction hardening depth (SHD) can also be calculated from the pairs of values.

 

Distance from the surface
[mm] ⇒ Hardness [HV1]

 

0.1 ⇒ 698
0.2 ⇒ 700
0.3 ⇒ 703
0.4 ⇒ 705
0.5 ⇒ 705
0.6 ⇒ 705
0.7 ⇒ 703
0.8 ⇒ 701
0.9 ⇒ 698
1.0 ⇒ 700
1.1 ⇒ 701
1.2 ⇒ 660
1.3 ⇒ 500
1.4 ⇒ 300
1.5 ⇒ 285
1.6 ⇒ 284
1.7 ⇒ 283
1.8 ⇒ 285
1.9 ⇒ 282
2.0 ⇒ 281

Vickers 7

SHD = Surface Hardening Depth

 

Target 58+4 HRC
≈ 650+100 HV10
⇒ GH 85%(650HV)
⇒ GH = 553 HV

 

 
 
 

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