Knowledge Hardness testing according to Vickers | Brinell | Rockwell
Definition of the hardness of a material
Definition: Hardness is the mechanical resistance that a material offers to the mechanical penetration of another body.
During hardness testing, the material is compressed to the maximum by a synthetic diamond or a hard metal ball under the application of a defined test force. ductile, easily formable materials It is important to adhere to the test force exposure time specified in the standards, since these medium-hard/soft metals still undergo deformation (flow) even after several seconds.
Hardness Testing in compliance with the Test force holding time: seconds (+ tolerances)
- Vickers: 10 - 14 seconds
- Brinell: 10 - 14 seconds
- Rockwell: Preload: 3 seconds, main load 5 seconds, unloading 4 seconds
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Hardness testing as a quality feature of materials
Hardness testing determines one of the most important material parameters in modern quality assurance and is an indispensable test. For example, the components of a ball bearing must be extremely hard in order to withstand billions of revolutions without damage. The high hardness (ball bearings approx. 60 HRC) is the basis for low wear behavior.
On the other hand, there are requirements where the hardness of a material must be low. For example, when forming material: it would break or cracks would appear as a result of the forming process. Likewise, the hardness of a component must not be too high if it is to be subjected to mechanical stress. If the material were too hard (and therefore too brittle), cracks would appear prematurely. Hardness testing at various process stages is essential for safeguarding the manufacturing process in every manufacturing process.
Increasing the hardness of a material generally serves to protect against wear. However, as hardness increases, toughness decreases - the material becomes more brittle.
FAQ: When do I use which? Comparison of hardness testing methods Vickers | Brinell | Rockwell
Vickers hardness tester
- universal- hardness tester Vickers Brinell Rockwell tabletop instruments <250 kpf
- Universal hardness tester (HV, HB, HR) with (HV1 – HV120)
- Low-force hardness testing machine HV 0,3 – HV10
- Vickers hardness testing machine HV 0,3 – HV 30
- Micro hardness testing machine HV0,01 – HV1 (HV2)
- Nano-Vickers hardness testing machine HV0,001 – HV1
Typical material
- extremely hard materials / metals (+ ceramics)
- homogeneous materials, homogeneous structure
- cast steel / hardened materials
- Vickers: Typical for hardness curves CHD (EHT) SD (NHT) RHT
Advantages and disadvantages
+ standardized hardness test method according to DIN EN ISO 6507-1 and ASTM
+ Preliminary assessment of the test position due to optical method
+ most universal process from very soft to extremely hard
+ exact positioning possible due to optical method (measuring microscope)
+ only (exact) method for hardness depth determination CHD, SD, RHT
– not suitable for porous material (e.g. gray cast iron)
– homogeneous material / structure required
Brinell hardness tester
- universal hardness tester
- Stand-alone devices with clamping cap
- swiveling radial drill stand with test head
- mobile test clamp + measuring magnifier | VideoMagnifier: large, heavy test pieces
Typical stuff
- cast steel
- Non-ferrous metals
- Soft metals
- Gray cast iron
- inhomogeneous materials
- sintered metals (unsintered)
Advantages and disadvantages
+ standardized hardness test method according to DIN EN ISO 6506-1 and ASTM
+ porous, inhomogeneous materials Grey cast iron can be tested
+ well suited for soft materials
+ optical method: easy positioning
– not suitable for high / very high hardness
– Preparation of test site required (minor grinding)
– more complex than Rockwell hardness testing
Rockwell hardness tester
- Simple Rockwell hardness tester dial gauge analog / digital
- Universal hardness testing machines tabletop devices
- Universal hardness testing machines, floor-standing devices
- High-quality Rockwell hardness tester load cell
- Simple Super Rockwell Hardness Testers
Typical material
- hard to very hard materials (HRC)
- medium-hard / soft metals (Rockwell ball)
- plastics (ball penetration depth)
- carbon (ball penetration depth)
Advantages and disadvantages
+ standardized hardness test method according to DIN EN ISO 6508-1 and ASTM
+ most common measurement method / most well-known (Rockwell-C)
+ quick check
+ inexpensive device type
+ simple series testing (also automatic in the robot testing system)
– Support table must be kept very clean
– The underside of the test piece must be very smooth
– no exact positioning possible
