guidelines to hardness testing
TRANSCRIPT
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 1/22
Home | Contact | Sitemap | Imprint
Suche
ProductsUniversal testing machines
Static testing machinesDynamic testing machinesSpecial testing machinesModernisation of universal testing machinesTesting softwareApplicationsAccessories for universal testing machines
Furniture testing machinesTesting of seating furniture, upholstered furniture, tables, cabinetsTesting of drawers, drawer guidings and functional fittingsTesting of beds, mattresses, slatted frames, cushion framesAccessories furniture testing
Special testing plantShock testingReverse bend testing machinesFriction test standsMechanical creep behaviour testing equipmentTorsion test stand
Hardness testing machinesBasic hardness testersHardness test benchesModernisation of Hardness TestersHardness testing softwareAccessories for hardness testers
Length measurement technologyMagnescale digital gaugeSony digital measuring technologyMeasurement equipmentModernisation of machine tools
Testing machines for AutomationAutomated testing system with universal testing machine and robotorAutomated hardness testing system with robotor
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 2/22
ServicesInstallation and instructionAdviceCustomer serviceMaintenance of testing machinesDAkkS calibrationTraining and workshopsContract testing
The CompanyPortraitCustomers and partnersCertifications
News and PressLatest newsDatesPress and publicationsWilly presentsJobs
Interesting factsGuidelines to hardness testingGlossar
Contact and SpecialsContact
Contact us formularGermanyInternational
ServiceServiceFormMagnescale Product Information ToolSitemapSearchImprint
Interesting facts » Guidelines to hardness testing
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 3/22
Contents:
1. General notes on hardness testing 2. The Rockwell procedure 2.1 Standard Rockwell 2.2 Superficial Rockwell 2.3 Fields of application with different Rockwell scales 2.4 Tests on cylindric and spherical surfaces 2.5 Pros and cons of the Rockwell procedure 2.6 Variations of the Rockwell procedure
3. The Brinell method 3.1 The labelling of Brinell tests 3.2 Different applications of Brinell tests 3.3 Pros and cons of the Brinell procedure 3.4 Rockwell tests with Brinell loads and Brinell penetrators
4. The Vickers method 4.1 Applications of different Vickers test loads 4.2 Pros and cons of the Vickers procedure
5. Other hardness testing procedures 5.1 The Shore procedure (for metals) 5.2 The Knoop method
6. Revaluation tables and hardness comparison plates 6.1 The use of revaluation tables 6.2 The use of hardness comparison plates
1. General Notes on Hardness Testing
Among the different kinds of measurements that are carried out in a laboratory, hardness testing is one of the mostcomplex ones. On the one hand, there are different measurement procedures; on the other hand, it is necessary to measure large, small,hard, soft, thin or thick metal parts.Considering the different procedures and the large number of scales, it is understandable that even very experiencedpersons can be challenged by hardness testing tasks.
As in so many other areas of application, electronic development has led to a significant simplification of hardness testing.With computeraided hardness testers, a higher precision during result readout, data storage and the possibility of dataprocessing to statistics, graphic representations, documentation, etc. have become a matter of course.
However, electronics are still only used for results readout (and, if necessary, automation of the measuring / drive), whilethe different mechanic testing results are still applicable.
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 4/22
Although later we will be talking about definitions, advantages and disadvantages of the Rockwell, Brinell, and Vickersprocedures, it is still beneficial to deal briefly with the most important features that should be considered before buyingsuch a device, here in the introduction: 1) the total test load; 2) the hardness range; 3) accuracy, 4) the flexibility of thedevice with regard to forms and dimensions of specimens, and 5) economic aspects.
1. Total test load
On the one hand, there is the general rule to use a test load as high as possible. This allows for higher accuracy(because the measurement is less sensitive to the surface texture with a higher test load).
On the other hand, the indentation should not be deeper than 1/10 of the thickness of the specimen or thehardened surface.
The degree of homogeneity of the material is also an important criterion: a typical example is cast iron, which isusually only tested with a high total load, except in the ranges where it has been induction hardened, e.g. machinetool bases.
2. Hardness rangeAbove a hardness of approximately 650 HB/30, a diamond penetrator should be used; below that value it is alsopossible to use a penetrator made of steel or hard metal.
The Brinell method, which does not allow diamond penetrators, cannot be used for hardened steel.
The Rockwell method is more universal, because it allows for the used of diamond cone and steel ballpenetrators.
The Vickers method, which only allows for a diamond pyramid penetrator, can be employed in the entire hardnessrange. However, it is most suitable for tests in laboratories compared to tests in workshops.
3. AccuracyThe precision of the measurement is heavily dependent on the accuracy employed by the operator. This alsoincludes wellground surfaces, sufficient measurement periods and frequent revisions of the testing device withreliable test plates. If possible, the use of static systems should be preferred to dynamic systems. Using very low testing loads is a particular restriction to the precision of the measurements
4. Flexibility of the device with regard to forms and dimensions of specimensThe specimen can be put on the device, or the device can be put on the specimen. The first case describesstationary devices, which have enough capacity to hold the specimen. Stationary devices are, thus, primarilysuitable for tests on small and mediumsized specimens.
Portable devices can be clamped to the specimens (clamping jaw, chain, etc) or – when testing large or bulkyspecimens – just put on the specimens.
Portable devices can only be dynamic when using high testing loads. When the testing loads are smaller, they canalso be static. It is possible to find customerspecific solutions for special cases.
5. Economic aspectsThis includes the following elements: the purchase price of the device, the universalism of the application, the measurement period, and the qualification needed to operate the device.
The first two aspects are important when specimens of different forms and with different surface treatments are
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 5/22
tested. This is usually the case in technical companies and in smallscale industries.
In companies that do their tests serially the quickness of the measurements and the possibility to employ unskilledstaff are very important. Here, such devices are preferred that do not need special clamping equipment.
Top Content
2. The Rockwell method
For a better understanding, the sequence of the Rockwell method, which is described below, is also shown in thenumbered images below (figure 1). The meter, which is connected to the penetrator and displays the penetrators shifts ona larger scale, is also included in the figure.
1. The tested surface is exposed to the penetrator and the first test load Fo (preload) is applied. A small indentation
appears. At this point, the meter is set to zero.
2. Slowly and without shocks the load F1 is applied additionally. Together with the preload this is defined as total testload F. With this load the penetrator enters the material more or less deep, depending on the hardness of thematerial. This position needs to be kept to reach the final penetration (when testing hard materials the penetration isalmost immediate; with soft materials it is necessary to wait for a number of seconds). The penetration procedurecan also be observed on the indicator of the meter.
3. When the indicator of the meter finally stops moving, the additional load F1 is removed until the preload is applied
respectively. This way, the penetrator remains in the imprint and all elastic deformations, which were caused by theapplication of the total test load, are eliminated; thus, the meter only shows the remaining penetration depth (asdifference between preload and total test load).
The penetrator, preloads, test loads, and the units are standardised in the Rockwell method and can be divided into twogroups: standard Rockwell (method N) and superficial Rockwell (method T).
Top Content
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 6/22
2.1 Standard Rockwell
The standard Rockwell procedure is intended for the use of one single diamond cone penetrator of 120° with a rounded offpeak of 0.2 mm radius (see figure 2), or different ball penetrators made from hard metal with diameters of 1/16"; 1/8"; 1/4";1/2" (inch).
Figure 2 profile of the Rockwell penetrator with diamond cone
The preload is unchanging: 98.07 N.The total test loads are (preload + additional load): 588.4 N; 980.7 N; 1,471 N.Themeasuring unit in standard Rockwell corresponds to 0.002 mm penetration.The hardness value increases with the hardnessof the material, but at the same time the penetration difference between the preload and the total testing load decreases theharder the material is. Thus, Rockwell hardness values are calculated by subtracting the penetration depth (per 0.002 mm)from 100 (when using the diamond penetrator) or from 130 (when using any ball penetrator).
Example: with a diamond penetrator and a penetration depth of 0.082mm this makes 100 – 0.082/0.002 = 59 Rockwell; the same penetration depth measured with a ball penetrator makes 130 – 0.082/0.002 = 89 Rockwell
When using analogue devices with dial gauges, which usually have 100 partitions (one rotation = 0.2 mm), the Rockwellvalues can be read directly from the dial. The dial then usually has 2 series of numbers: the black ones are for diamondpenetrators and the red numbers are made for ball penetrators. For the zero position always use the black 0 (or the red30). When using a digital device, the data are displayed after the complete measuring cycle was run through. Due to thedifferent combinations of penetrators and test loads, there is a great number of scales, which are labelled with differentletters (see Table 1).
HR SCALE
Penetrator:
DiamondCone
Ball 1/16" 1,5875mm
Ball 1/8" 3,175mm
Ball 1/4 *
Ball 1/2" *
Numbers:
black
red
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 7/22
F=1471N
C
G
K
P
V
F=980,7N
D
B
E
M
S
F=588,4N
A
F
H
L
R
Table 2 – superficial Rockwell scales, F=total test load (Newton)*) W, X, Y are not standardised
The ERNST devices NR3SR, AT130ASR and AT130DSR all work with the superficial Rockwell procedure.
Top Content
2.2 Superficial Rockwell
Although the superficial Rockwell method uses the same penetrators as the standard Rockwell procedure, the methodrequires a more precisely shaped diamond cone penetrator. This regards not only the conicity of the 120° cone peak, butalso its rounding off of 0.2 mm. With this method, smaller total loads are used to create smaller indentations, so that thesmallest shape defects on the peak would falsify the measuring results.The preload is unchanging: 29.42 NThe total testloads are (preload + additional load): 147.1N; 294.2N; 441.3 NThe measuring unit in superficial Rockwell corresponds to0.001 mm penetration depth. In contrast to standard Rockwell, the zero point is set to 100 (0 on the dial gauge) in thesuperficial Rockwell procedure (both with the diamond penetrator and with the ball penetrator). The dial only has one seriesof numbers and 100 partitions. One rotation of the index equals 0.1 mm.
Example:With a diamond or ball penetrator and a penetration depth of 0.082mm this makes 100 – 0.082/0.001 = 18 superficialRockwell. Due to the different combinations of penetrators and test loads, there is a great number of superficial Rockwellscales, which are labelled with different letters. The respective letter is also preceded by a number which indicates the totalload used in the test (see Table 2).
HR Scale
Penetrator
DiamondCone
Ball 1/16" 1,5875mm
Ball 1/8" *
Ball 1/4" *
Ball 1/2" *
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 8/22
F=441,3N 45 N 45 T 45 W 45 X 45 Y
F=294,2N
30 N
30 T
30 W
30 X
30 Y
F=147,1N
15 N
15 T
15 W
15 X
15 Y
superficial Rockwell scales, F=total test load (Newton)*) W, X, Y are not standardised
The ERNST devices NR3SR, AT130ASR and AT130DSR all work with the superficial Rockwell procedure.
Top Content
2.3 Fields of application with different Rockwell scales
As we have seen, there is a considerable number of Rockwellscales. Which scale to choose is a question depending on thehardness of the material, and the thickness of the specimen or hardened surface (in cases where there have been surfacetreatments such as carburisation, nitriding etc.).The hardness of the material determines the choice of the penetrator:diamond cone or ball.
The diamond cone is solely used for tempered or hardened steel and hard metal. It is not recommendable for steel with asolidity below 785 N/mm2 (20 HRC, 230 HB/30).
The steel ball penetrator is used for softer materials. The softer the material, the larger should be the diameter of the ball and/ or the smaller should be the total test load. For instance, the materials that can be tested with the HRB scale (ball 1/16" –total test load 980.7N) are harder than the materials tested with the HRL scale (ball 1/4 " total test load 588.4N).
The large balls are solely used for the testing of plastics and materials alike. Flowing plastics can be measured as well, ifcertain steps are taken, with the help of the total test load.
Again, we would like to mention that the HR hardness testing also requires a minimum thickness of the sample. However,there is no hard rule for this minimum thickness. It is usually estimated by calculating 10 x the penetration depth (see Table3). This principle is also valid for hardened surfaces (carburisation etc.), which are usually measured with the smallest totaltest load (scale HRA).
F
HRC
20
30
40
50
60
70
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 9/22
147,1N
0.41
0.33
0.26
0.19
0.14
0.09
294,2N
0.69
0.58
0.47
0.36
0.26
0.17
441,3N
0.91
0.77
0.63
0.50
0.37
0.25
588,4N
1.0
0.9
0.8
0.7
0.6
0.5
1471N
1.8
1.6
1.4
1.2
1.0
0.8
Table 3 measurable minimum thickness for Rockwell tests with diamond penetrators
Most frequently used are the following Rockwell scales:
1. HRC (diamond cone 1471N)HRC is the most characteristical Rockwell scale for testing hardened, tempered and carburised samples.When talking about "Rockwell hardness" in general, this usually means the HRC scale. This might cause a certain confusion,because sometimes a hardness of the HRC scale is ordered, although the small dimensions of the sample make tests with atotal test load of 1471 N impossible. In such cases, other Rockwell scales or other measuring procedures are used todetermine the hardness, which is then revalued to HRC with the help of charts.As we will see later, those revaluation tables can only give approximated values. That is why it is recommended to use onlyhardness values that can be measured in reality when entering them into drafts, orders, etc.
2. HRA (diamond cone – 588.4N)Mainly used for carburised materials and hard metals, whose high carbide hardness might damage the diamond.
3. HRB (ball 1/6" – 980.7N)In Europe, this scale is usually used for copper alloys (brass, bronze etc.); in the U.S., it is also used for steel up to approx.686 N/mm².
4. Rockwell N and T (superficial Rockwell)The scales HR 15N, HR 30N, HR 45N (diamond cone) are used for samples with thin carburisation; the scales HR 15T,HR 30T, HR 45T (ball 1/16") are used for thin metal sheets. The general notes concerning the choice of the total test loadalways have to be attended to.
Top Content
2.4 Tests on cylindric and spherical surfaces
It is clear that the conditions for hardness measurements on cylindric or spherical surfaces are
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 10/22
different from those on flat surfaces. The differences are not as crucial with larger diametersbecause then the bending of the surface is small and approximates a flat.
When working with smaller diameters (with higher bending) it is necessary to keep in mind thatthe penetrations get an oval shape (for cylinders) when viewed from above and that the verticalprofile of the penetrated area has different thicknesses. That is why the tester has to add correctionvalues to the results, which depend on the hardness and the diameter of the sample (see Table 4).
Cylindric sample surfaces
Hardness scales andread off hardness
Cylinder diameter d in mm
3
6,5
9,5
11
12,5
16
19
HardnessHRACDdiamondcone
80
0,5
0,5
0,5
0
0
0
0
70
1,0
0,5
0,5
0,5
0,5
0
0
60
1,5
1,0
0,5
1,0
0,5
0
0
50
2,5
1,5
1,0
1,5
0,5
0,5
0,5
40
2,0
1,0
2,0
1,0
0,5
0,5
30
2,5
1,5
2,5
1,0
1,0
0,5
20
2,0
3,5
1,5
1,0
1,0
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 11/22
Hardness scales and read off hardness Cylinder diameter d in mm
3
5
6,5
8
9,5
11
12
Hardness HRB F GBall penetrator
90
4,0
3,0
2,0
1,5
1,5
1,5
1,0
80
5,0
3,5
2,5
2,0
1,5
1,5
1,5
70
4,0
3,0
2,5
2,0
2,0
1,5
60
5,0
3,5
3,0
2,5
2,0
2,0
50
4,0
3,5
3,0
2,5
2,0
40
4,5
4,0
3,0
2,5
2,5
Spherical sample surfaces
Hardness scales and read offhardness
Ball diameter d in mm
4
6,5
8
9,5
11
15
25
Hardness HRCDiamond cone
65
5,2
3,2
2,6
2,2
1,9
1,4
0,8
60
5,8
3,6
2,9
2,4
2,1
1,5
0,9
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 12/22
55
6,4
3,9
3,2
2,7
2,3
1,7
1,0
The correctional value deltaH, which needs to be added to themeasured value, can be calculated with the values from thistable and the following formula:
Table 4 – correctional values for Rockwell measurements on cylindric and spherical surfaces with diamond and ballpenetrators. (The correctional values must be added to the values on the display or the dial gauge.)
Top Content
2.5 Pros and cons of the Rockwell procedure
Among the known hardness testing procedures Rockwell is the only one that allows for the direct reading of thehardness value without optical measuring. Thus, this procedure is not only quicker, it is also the only hardness testingprocedure that can be automated completely. Hardness testing devices that work according to the Rockwell procedure are the most widespread. The mostimportant advantages are: deviations due to personal estimations are avoided; it is less sensitive to rough surfaces(even though the standard says that surfaces have to be flat and carefully abraded). The most important limits of the application range are the possible total test loads. The minimum is 147.1N (HR15N/ HR15T) and the maximum is 1,471N. However, workshops or foundries often require test loads of 10N or less, orof up to 30,000N. There is no Rockwell scale for tests on cast iron, nor is there one for steel sheets thinner than0.15mm. In order to close this gap, there are devices that work with the Rockwell procedure (with pre and totaltest loads), but with much larger (or smaller) and thus nonstandardised test loads. While there are many scales, a different solution has been established for some materials (e.g. untreated steel). Theyare usually tested with a Rockwell device, which is equipped with a Brinell penetrator and uses Brinell testing loads(in this regard refer to chapter 3.4).
Top Content
2.6 Variations of the Rockwell procedure
A profound disadvantage of the traditional Rockwell devices is that the accuracy of the measurement is mainly based on theperfect contact between the test specimen and the contact surface.
When using the Rockwell procedure (Fig. 1, point 3; removal of additional test loads and return to preload), the only
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 13/22
deformation displayed on the dial gauge should be the indentation itself.
However, this is only the case if the specimen is supported perfectly. If the supporting surface is polluted with an oil film,grease or other contaminants, there is a plastic deformation when the test load is applied and the result of the indentationmeasurement is falsified. This is an obvious limitation for workshops and hardening shops, because, of course, they cannotguarantee to work under ideal conditions for those devices.
In order to solve this problem, new devices have been developed that work according to the Rockwell procedure. Theirpenetrators are surrounded by a ferrule which allows for another contact with the specimen’s surface as the reference forthe measurement (see Fig. 3). Thus, a possible resilience of the specimen, the spindle or other moveable parts of the standcannot influence the result. In this regard, the advantages are the same as if one would use the Brinell or Vickers procedures(as we will see later).
Figure 3 – variation of the Rockwell procedure (ferrule
0: exchange of specimens: in rest position, the point of the penetrator (a) pokes out of the ferrule (b). 1: Both the penetrator and the ferrule lower down on the specimen and the penetrator recedes because of theapplied load. The zero position is set automatically. 2: The total test load is applied. 3: The total test load is released and the displacement (intrusion) of (a) compared to (b) is determined.
If the specimen yields, the relation between (a) and (b) stays unchanging and the possibility of the typical Rockwell error iseliminated. This procedure can also be applied with superficial Rockwell tests.
Some ERNSThardness testers include a third element which should not be confused with the ferrule (b). This element iscalled clamping hood and it can be found in devices with a stand. It is used to clamp specimens so that no extra tools arenecessary to fix the specimens. It is also very easy to remove that clamping hood if it is not needed for tests.
Portable devices also have an element similar to this, which is called measuring foot. It can be exchanged and helps to getan optimum contact.
Top Content
3. The Brinell method
The Brinell method involves ball penetrators of different diameters (always in mm, in contrast to the Rockwell dimensions ininch), which are pressed with a certain load onto a smooth and even surface for a certain amount of time (10 to 15seconds).
The emerging indentation, which has the shape of a spherical cup, is measured with optical devices (microscope orprojector).
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 14/22
Figure 4 hardness testing according to Brinell
The Brinell hardness (HBW) is determined by the relation between the applied testing load and the surface of the sphericalcup. This is the formula:
where F is the test load in N , D is the diameter of the ball penetrator in mm and d is the diameter of the indentation inmm.In practice, tables are used that give the Brinell hardness values subject to the test load, ball diameter and the diameterof the indentation.Usually, the Brinell method uses the following standardised ball penetrators:
Ball diameter: 10mm 5mm 2,5mm 1mm
The standard test loads are:
AbbreviationHBW 10
Ball diameter
Test load(N)
AbbreviationHBW 5
Ball diameter
Test load(N)
HBW 10/3000
10 mm
29420 HBW 5/750
5 mm
7335
HBW 10/1500
10 mm
14710 HBW 5/250
5 mm
2452
HBW 10/1000
10 mm
9807 HBW 5/125
5 mm
1226
HBW 10/500
10 mm
4903 HBW 5/62,5
5 mm
612,9
HBW 10/250 2452 HBW 5/25 245,2
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 15/22
10 mm 5 mm
HBW 10/100
10 mm
980,7
AbbreviationHBW2.5
Balldiameter
Testload(N)
AbbreviationHBW 1
Balldiameter
Testload(N)
HBW 2,5/187,5
2,5 mm
1839 HBW 1/30
1 mm
294,2
HBW 2,5/62,5
2,5 mm
612,9 HBW 1/10
1 mm
98,07
HBW 2,5/31,25
2,5 mm
306,5 HBW 1/5
1 mm
49,03
HBW 2,5/15,625
2,5 mm
153,2 HBW 1/2,5
1 mm
24,52
HBW 2,5/6,25
2,5 mm
61,29 HBW 1/1
1 mm
9,807
Table 5 – Brinell abbreviations, ball diameter and test loads (see ISO 65061)
The following points have to be considered for the Brinell method:
1. The standard (EN ISO 65061) requires the diameter of the indentation to be between 0.24 and 0.6 of the diameterof the ball penetrator.In order to meet this requirement there has to be a certain degree of loading. If a small ball penetrator is pressed on asoft material with a high load, the indentation will be to deep, of course. Then again, if a larger ball penetrator ispressed on a hard material with a small load, the indentation might be smaller than 0.24 of the ball diameter. It is thus,almost illegible and not admissible.
2. For the Brinellmethod there is a basic formula to determine the degree of loading: 1.02 F/D² between test load (N)and diameter (mm) of the ball penetrator squared. The harder the material, the higher must the degree of loading be.
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 16/22
Degree of loading: 1.02 F / D²
30
15*
10
5
2,5
1
Table 6 – degree of loading *) The degree 15 is only standardised for HBW10/1500, all the other degrees of loading can be used for all tests
The degree of loading 1.02F/D² is important because there are different results depending on which degree of loading wasused. For example: a Brinell hardness value determined with a 10 mm ball and 9,807N (degree of loading 10) for a materialis different from the hardness value determined with a 10 mm ball and 4,903N (degree of loading 5). However, if the samematerial is measured with a 2.5 mm ball and a total test load of 612,9N (degree of loading 10) the resulting hardness valueis the same as in the first measurement because the degree of loading is the same (provided that the material ishomogeneous and has no layers of different hardnesses).
Top Content
3.1 The labelling of Brinell tests
The abbreviation HBW stands for Brinell hardness. The Brinell hardness stands before the abbreviation and is followed bythe ball diameter in mm, the test load according to the table and the testing time in seconds, if it differs from the standardtime (1015 seconds).
Example: 305 HBW 2.5 / 187.5: Brinell hardness 305, determined with ball penetrator 2.5mm, 1,839N test load and 1015 seconds load application time Example: 305 HBW 2.5 / 187.5 / 20: Brinell hardness 305, determined with ball penetrator 2.5mm, 1,839N test load and20 seconds load application time
Top Content
3.2 Different applications of Brinell tests
As mentioned before, it is the hardness of the material which determines the degree of loading that is applied. When themost suitable degree is chosen, the test load is chosen according to the following elements:
1. the thickness of the tested specimen; because the considerations mentioned in the Rockwell chapter, which say thatthe minimum thickness should be 10x the depth of the indentation, also apply for Brinell tests (see table 7).
BallD inmm
Centered indentation diameter
0,5
1,0
1,5
2,0
3,0
4,0
5,0
6,0
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 17/22
1
0,54
2
0,25
1,07
2,5
0,83
2,00
5
0,92
1,67
4,00
10
1,84
3,34
5,36
8,00
Table 7 measurable minimum thickness for Brinell tests (see ISO 65061)
2. the homogeneity of the material; because for less homogeneous materials it is recommended to use high test loads.
3. convenience of the readout; because the determination (either with a microscope or projector) of the indentation’sdiameter is easier with large indentations.
For the following materials there are standard Brinell tests:
Steel: almost always HBW x | 3000 (x=ball diameter).For steel, the Brinell method is very important because there is a constant, quite accurate relation between the Brinellhardness and the tensile strength (with a ratio of 3.53 for carbon steel, chromium steel and chromiummanganese steel; forchromiumnickel steel it is 3.33).
Example: 225 HBW x | 3000 à 225 x 3.53 = 794.3 N/mm² (see DIN 50150)
This is the only possibility to determine the tensile strength of steel nondestructively.However, the Brinell method cannot beused for hardened steel. As there is no diamond penetrator intended for the Brinell procedure, tests on treated steel withmore than 1765 N/mm² are not possible. Soft iron is usually tested with HB x | 3000, although the indentation diameterexceeds 0.6 of the ball diameter.
Cast iron: always use HBW x | 3000. Due to the smaller homogeneity, it is recommended to use the highest total test loadof 29,420 N.
Light metal: usually HBW x | 10 or HBW x | 5; for very soft alloys it is also possible to use HBW x | 2.5. The fact that itis possible to use different degrees of loading for medium hardness values might easily cause confusion. Thus, it is importantto indicate the kind of test exactly (opposed to ferrous alloys, for which HBW x | 30 is always used).
Copper alloys: For bronze use HBW x | 10 (if it is very hard, use HBW x | 30), and HBW x | 10 or HBW x | 5 for brass.Apart from that, also consider the principles mentioned for light metals.
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 18/22
Top Content
3.3 Pros and cons of the Brinell procedure
The main advantage of the Brinell method is that it uses very high test loads generated by relatively simple and robustdevices. Furthermore, the indentation can be measured with the help of a simple microscope or even with a measuringmagnifier. Measurements can also be carried out when the conditions are not ideal, because (contrary to the Rockwell method)a possible drawback of the specimen does not influence the result. The Brinell value can be multiplied with a certain coefficient, which is specific for every material, to determine thematerial’s tensile strength. One of the most serious disadvantages of the Brinell method is the fact that the indentation is measured optically,which includes the danger for measuring errors. Modern, automatic image evaluation computer systems reduce thissource of errors significantly. Although high test loads are used, the surface must be well prepared in order to achieve the high accuracy needed forthe measurement of the indentation. Thus, Brinell testing is not a quick task and not suitable for routine tests. To avoid this disadvantage, the Rockwellmethod is often used with Brinell penetrators and Brinell test loads (see next chapter). Tests on cylindrical surfaces are not possible. If such specimens need to be testes, the surface must be prepared sothat an even area is produced for the measurement (10).
Top Content
3.4 Rockwell tests with Brinell loads and Brinell penetrators
In order to avoid the different disadvantages and to find as much applications for the Rockwell devices as possible, thesedevices are often used with Brinell penetrators and test loads.
Most of these devices also offer the loads 612.9, 1226 and 1839 N, apart from the usual Rockwell loads. Thus, they aresuitable for Brinell tests. But they measure hardness according to the Rockwell method, with the depth of the indentationand not by measuring the diameter.The result can be read off a Rockwell dial gauge or displayed immediately. With the help of tables this result can then beconverted to the Brinell value.However, this relatively quick method cannot be considered a genuine Brinell test.
As a matter of fact, the converted results are not the same for each material (for instance, the conversion for steel is not thesame as that for cast iron). This method should be preferred for routine tests or when there is no possibility for opticalmeasurements. It also offers the advantage that the surface must not be prepared as well as for optical analysis. And thetensile strength for steel can be measured reliably.
To achieve better accuracy during routine tests, the ERNSTdevices offer the possibility to calibrate the Brinell scalebeforehand with an optical test measurement.
Top Content
4. The Vickers method
(NOTE! Some of the details in this chapter are out of date! It is being revised.)This method is similar to the Brinell method,but it uses a diamond penetrator in the shape of a pyramid with a square base and an angle of 136°. Thus, the indentationlooks like a concave (negative) pyramid with a square base. The length of the two diagonals of the indentation is measured
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 19/22
(mean value).
Figure 5 principle of hardness testing according to Vickers (see ISO 65071, 2, 3)
Similar to the Brinell method, the Vickers hardness value HV is determined by the ratio between the applied test load andthe surface of the indentation.The test loads most often used are: 9.81, 19.62, 49.05, 98.10, 294.30 N. It is also possibleto use test loads below 9.81 N, which means entering the domain of micro hardness and applications in metallographicallaboratories.The Vickers hardness is calculated with the following formula, whereas d is the mean value of the indentation’sdiagonals (accuracy: +/ 0.002 mm):
The labelling for Vickers tests is HV (H= hardness, V = Vickers), then the test load and the test time. The test load isindicated in the usual kp numerical values. That is why the actual test load must be divided by 9.81 to get the Vickers label(e.g. HV50: 50 = 490.5N / 9.81). Thus, a Vickers hardness value might look as follows:
210 HV50/30 Vickers hardness 210, test load 490.5N, test time 30 seconds
Usually, the test load is applied within 15 seconds and effective for another 30 seconds. Soft materials require longer testtimes, steel with a hardness of 140 HV or more requires only 10 seconds.
Top Content
4.1 Applications of different Vickers test loads
The values obtained with different test loads are comparable because the Vickers method allows for only one penetratorand the Vickers value is the specific test load per mm² of the surface.For instance, when a material is tested with a test loadof 294.30N and then a second time with 9.81N the results are the same (of course, only if the material is homogeneous andwithout layers of different hardness values).The Vickers method is also suitable for materials with different layers. Increasingtest loads are applied subsequently to determine the thickness of certain surface layers, e.g. after nitration hardening.Apartfrom that, all the rules mentioned above for the other methods (minimum thickness = 10 x indentation depth) also apply toVickers. In other words, the diagonal must not be longer than 2/3 of the specimen thickness.The Vickers method isespecially suitable for tests of small and thin parts or components with any kind of surface treatment, i.e. for tests with lowtest loads.However, the Vickers method should not be used for inhomogeneous materials, like cast iron.
Top Content
4.2 Pros and cons of the Vickers procedure
The biggest advantage of Vickers is its scale, which comprises the smallest and the highest hardness values in onescale. It is thus very suitable for laboratory tests. Most of the disadvantages of Vickers are based on the long duration of the whole procedure because the indentationmust be measured optically (with the help of a miscroscope or projector). This, of course, also is a source formeasuring errors. However, modern, automatic image evaluation computer systems reduce this source of errorssignificantly.The surface must be well prepared and the penetrator must be applied evenly. Otherwise, the smallest inclination
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 20/22
would cause irregularities in the indentation. Thus, the Vickers procedure is not suitable for routine tests. The indentation is not well readable on some materials because of the irregular distribution of the load (more load onthe edges than on the sides of the pyramid).
To put it in a nutshell, the Vickers procedure is more suitable for applications in laboraties than in workshops.ERNSTdevices offer possibilities to read Vickers hardness values quicker and more direct so that some of these limitations can beovercome.
Top Content
5. Other hardness testing procedures
5.1 The Shore procedure (for metals)
This methods is based on the principle that a ball (or a shaft with ball point) is dropped on the specimen and rebounds moreor less, dependingon the hardness of the material and the drop height. However, this method is used seldomly because theprecision of the results is very much depending on the mass of the specimen and on the perfectly vertical falling axis. Thehardness values are then given in Shore points and are only standardised for big, dressed to size cylinders (calenders).
Top Content
5.2 The Knoop method
This procedure is similar to Vickers, with a pyramidshaped diamond penetrator and a rhombical base area (diagonals at aratio of 1 : 7.), and it is only used in laboratories with a few grammes as total test load.
Top Content
6. Umwertungstabellen und Härtevergleichsplatten
6.1 The use of revaluation tables
As there is no mathematical interrelationship between the different hardness scales, the revaluation tables had to becompiled with the help of empirical tests. There are different tables which might have considerable differences. Usually, thetables also offer the tensile strength in N/mm² for steel.The values taken from the revaluation tables must be considered anorientation; they are not absolute.
Top Content
6.2 The use of hardness comparison plates
Usually, the equipment of a hardness tester includes one or more hardness comparison plate. They must be made from veryhomogeneous and appropriately treated materials. To achieve the highest possible accuracy they should only be evaluatedon one side. It is very important to test the hardness testing device regularly with the help of the comparison plates to ensurethat it works properly.
The distance between two indentations on one plate is measured between the middle of each indentation or between themiddle of an indentation and the edge of the specimen. It should be no less than the following:
for Rockwell tests: min. 4 x the indentation’s diameter; not less than 2 mm
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 21/22
(edge distance: min. 2.5 x the indentation’s diameter; not less than 1 mm) for Brinell: min. 3 x the indentation’s diameter(edge distance: min. 2,5 x the indentation’s diameter for Vickers: min. 3 x the indentation’s diameter(edge distance: min. 3 x the indentation’s diameter
When there are so many indentations that the surface is covered with them, do not grind them to reuse the plate. Thestructures of the layers below the indentations (approximately 8x the indentation depth) are usually altered because of theload application and thus, measuring results would not be accurate.
Top Content
ContactContact us formularGermanyInternational
ServiceServiceFormMagnescale Product Information ToolSitemapSearchImprint
ProductsUniversal testing machinesFurniture testing machinesSpecial testing plantHardness testing machinesLength measurement technologyTesting machines for Automation
ServicesInstallation and instructionAdviceCustomer serviceMaintenance of testing machinesDAkkS calibrationTraining and workshopsContract testing
The CompanyPortraitCustomers and partnersCertifications
News and PressLatest newsDatesPress and publications
10/28/2015 Guidelines to hardness testing
http://www.hegewaldpeschke.com/interestingfacts/guidelinestohardnesstesting.html#c274 22/22
Willy presentsJobs
Interesting factsGuidelines to hardness testingGlossar
Contact and SpecialsContactService
XINGYouTubeDE