In many industrial fields, hardness testers are commonly used testing equipment to measure the wear resistance, hardness, and other important physical properties of materials. In recent years, with the advancement of technology, portable hardness testers have been widely used. These devices are lightweight, easy to operate, and can be easily used in a variety of materials and scenarios.
However, when it comes to choosing a portable hardness meter, you need to choose based on your specific application needs. This article analyzes in detail from multiple perspectives such as detection targets, detection technologies, and external interference factors, and matches the corresponding hardness testing solutions for different scenarios, helping you get twice the result with half the effort.
Before deciding on a hardness tester and testing method, the application environment must be analyzed. The main variables present in the test need to be evaluated to determine which hardness tester has the least impact on the test results. In addition, it is important to consider in advance whether electronic documentation is required and the requirements for indentation on the test surface.
In most cases, reliable test results require that the indentation size be evident compared to the microstructure of the material. Therefore, when testing coarse-grained materials, a Leeb hardness tester with a larger indentation should be considered first than a Vickers or Rockwell hardness tester because of their relatively small indentation, which also means that the latter two products are better suited (but not limited to) for testing fine-grained materials and thin parts or metal sheets of varying shapes and sizes.
When inspecting coarse-grained materials typical of forged and cast large parts, Leeb hardness testers produce larger indentations than other instruments, resulting in more consistent results. However, for some applications, such as testing in a small area of the heat-affected zone (HAZ), to determine whether the welding process is correct, a smaller indentation from the Vickers method or the Rockwell penetration measurement principle is required. Here, high hardness peaks are mainly detected, and if the springback method is used, large indentations may be affected by the weld or base metal and therefore may not be detected.
According to the Leeb and Vickers hardness testing methods, the wall thickness and weight of the test object affect the hardness test results.
The relevant standards specify minimum wall thickness and minimum weight, and if these requirements cannot be met, additional measures must be taken, such as coupling or supporting the specimen, or other more appropriate methods.
The Leeb method (impact devices D, DL, DC, E and S) requires that the component weigh at least 5 kg and be at least 25 mm thick in order to prevent the component from yielding or bending under the enormous forces generated by impact.
For the Vickers method, the standard requires a weight of at least 03 kg with a thickness of at least 5 mm or 15 mm (ASTM A1038). For coatings or surface coats, a minimum thickness of at least ten times the depth of the indentation is required.
If these minimum requirements are not met, the object to be measured will enter a state of natural vibration, resulting in biased readings. Specimens with a weight less than the minimum weight for the Leeb test specified in DIN EN ISO 16859 and ASTM A956, or the Vickers minimum weight specified in DIN 50159-1, or specimens weighing sufficiently large but less than the specified minimum thickness, requiring heavy support and/or coupling with a solid object, can be contacted by our colleagues at Screening Eagle for the requirements for the coupled object.
Portable Rockwell hardness testers are different because they are a purely static measurement method. The object cannot swing and the instrument does not cause vibrations. However, a certain thickness must be provided to prevent the object from being punctured, and the minimum thickness must be ten times the depth of the indentation.
The same material can be inspected in multiple ways, but some methods can require a more intensive surface treatment to achieve high accuracy.
Basically, all hardness testing methods require certain surface conditions, and in most cases, surface treatment.
However, some methods are more demanding on surface conditions (roughness), surface preparation can be more time-consuming, and improper handling can lead to common inspection errors. For example, hardness testing with Screening Eagle's portable hardness testers Rockwell or Leeb C requires a finer surface finish than with Leeb G, as the indentation depth of portable RockWell, UCI HV1 or Leeb C is much shallower than Leeb G.
Materials with higher hardness have a lower depth of penetration and require a better surface treatment. Grinding can be done using a grinding wheel, taking care to ensure that the surface of the material does not generate too much heat during the grinding process, as this may alter the hardness gradient.
Currently, there are no formal requirements for training, qualifications, and certification in ISO 9712 or ASNT TC standards, and insufficient qualifications or lack of measurement experience are the two main causes of error.
Of all the portable hardness testing methods, the Vickers hardness tester is the one that is most prone to incorrect measurements. This is due to the inexperience of most operators and their unfamiliarity with hardness testing procedures. For example, when measuring with a Vickers hardness tester, the indenter of the probe must be perpendicular to the test piece, and the angular deviation can only be in the range of + - 5°, because the surface of the diamond indenter is symmetrical pyramidal, which is different from the contact surface of the material; When performing a Vickers test, the probe must be held firmly, the appropriate pressure must be applied to achieve the indentation, and the probe can be released after the measurement is complete.
The smaller measurement error is the Leeb measurement method, which requires the probe's support ring to be in full contact with the surface of the object being measured. The exception is the Richter DL probe (long nose probe), which may introduce some inertia to the measurement process due to the structure of the probe. As a direct indentation method, the portable Rockwell hardness tester is not prone to operating errors, and only needs to be familiar with some measurement methods. Therefore, if you want to get up to speed quickly and have inexperienced operators, a Leeb hardness tester can be the first choice.
A common denominator of the Richter and Vickers test principles is their dependence on the elasticity of the material (Young's modulus, elastic modulus e), which is determined by the nature of the test principle itself.
For example, in the Vickers measurement method, the instrument monitors the resonance frequency and calculates the frequency shift when the desired test load is reached. The frequency shift is a function of the size of the indentation of the indenter defined under the modulus of elasticity e. By default, Vickers hardness testers are typically calibrated on non-low alloy steels with an elastic modulus E of 210 GPA + - 10 GPA. Therefore, to test on different materials, the instrument must be calibrated within the equivalent modulus of elasticity. A similar conclusion can be reached with the Richter method.
The portable Rockwell hardness tester is a direct press-in method that does not have these problems and can be used as a reference method for the above methods, e.g. by HRC scale. The HRC obtained with a portable Rockwell hardness tester can be directly compared with other methods.
Therefore, in the conversion of materials with different properties, the Rockwell hardness tester is more straightforward, and the results are directly read.