The most important requirement of the Hanomag Heat Treatment Group is a consistently high product quality. To ensure this, each of our sites has its own fully equipped material testing laboratory. Following heat treatment, all orders are tested by our qualified personnel for compliance with the prescribed specifications.
The hardness test is the most important core element of quality assurance in the sector of heat treatment technology. A wide range of processes are on hand at every site, starting from measuring the surface hardness up to the determination of the hardness-depth progressions. The ideal process is applied for each material and each heat treatment:
Vickers (DIN EN ISO 6507): Universal process for low to very high hardnesses. Measurement of hardness-depth progressions in the low-load range.
Rockwell (DIN EN ISO 6508): The high load levels of the Rockwell process make it particularly suitable for measuring the surface hardness of hardened steel components. Mobile testing equipment is also available for the Rockwell test.
Brinell (DIN EN ISO 6506): A hard metal ball as penetrator and comparatively high load levels make the Brinell process the preferred hardness test method for cast iron aluminium and other wrought alloys.
Leeb (DIN EN ISO 16859): The Leeb process is a dynamic hardness test method in the form of a mobile test device. With it, very large construction parts can be tested, which due to their dimensions cannot be measured with stationary hardness test equipment.
All hardness test equipment is calibrated annually by an accredited external test laboratory. In addition, a standard-compliant check is made every day of all hardness test equipment by a member of the quality assurance staff.
In order to analyse the microstructure and the layer structure of heat-treated components, a metallographic section is prepared. For this, the section of a component or test piece to be analysed is removed, embedded in epoxy resin and then sanded and polished. On such a section, the hardness-depth progressions of surface layer hardened components can then be determined by the Vickers process (CHD, NHD, SHD).
By etching the polished surface with special etching solutions, the microstructure of the material is made visible. In this way it is possible to assess the desired or undesired changes in the microstructure caused by heat treatment and also to identify and evaluate the layers created (for example the compound layer after nitriding) under the microscope.
Tensile testing is used to determine the mechanical characteristics. The samples used are generally loaded under tension until breakage. Defined samples have to be prepared for tensile testing. This type of testing is frequently carried out within the scope of heat treatment of cast aluminium components.
An alternative that is available under certain circumstances an individualised component test, in which a component is loaded under pressure until breakage. Depending on the type of application, this procedure can be a rapid alternative to tensile testing. With the aid of test series during the testing phase (sampling), correlations can be drawn to the mechanical properties from tensile testing.
Generally with us, this non-destructive testing procedure is used to test cast aluminium components. In the dye penetration test, the component is cleaned and then immersed in or sprayed with a penetrant. After rinsing, this penetrant is stuck in the surface openings (e.g. pores, cracks). After treating with a developer and subsequent drying, these surface openings can be displayed with the aid of UV light.
We carry out a fluorescent penetration test. With this test process we discover casting defects that can negatively influence the performance characteristics of the component.
Corrosion testing in artificial atmospheres, the so-called salt spray tests, are carried out as serial tests on nitrocarburized components. In this procedure, a five percent solution of sodium chloride is sprayed in a controlled atmosphere. Changes in appearance of the specimen are assessed throughout the duration of the test.
Both duration and assessment criteria must be agreed upon with the respective customer. The results are not transferable to the corrosion resistance of the components in practice. This procedure is a comparative test for very similar surface properties.
In order to determine the chemical composition of test pieces, different spectrometers are used.
In spark spectrometers, a spark discharge to the test piece is created with a tungsten cathode, which atomises a small part of the sample surface. These excited atoms radiate light at element-specific wavelengths. The chemical composition of the sample surface can be determined very exactly by the wavelength distribution. Spectrometers are used to monitor the carburizing process exactly or to register material mix-ups, for example.
The glow-discharge spectrometer (GDOES) additionally offers the possibility of determining the elemental distribution up to a depth of 100 µm. This is used particularly when analysing nitriding processes.
Regular monitoring of the process media is the key to consistently high product quality. For this reason, all process media are checked at specified intervals and if necessary purified or exchanged.
Amongst others, these include:
- Quenching oils (water content, degree of contamination)
- Hardening salts (cyanide /cyanate content)
- Washing agents (detergent concentration, oil content, contaminants)
There are extensive chemical analytical processes available in Hanomag Heat Treatment Group, which are carried out according to instructions by the laboratory staff at the respective sites. Further, regular analyses are carried out in external laboratories by certified specialist companies.