Volume 67, Issue 4

Kurzfassung Seit mehr als 25 Jahren werden in Wärmebehandlungsbetrieben standardisierte Qualitätssicherungsnormen angewendet. Die Bedeutung dieser Maßnahmen wird von den Wärmebehandlungsbetrieben und deren internen und externen Auftraggebern gleichermaßen als sehr wichtig eingestuft. Dennoch existieren noch immer sehr unterschiedliche Auffassungen darüber, welche Voraussetzungen für eine sachgerechte Wärmebehandlung erforderlich sind und wer dafür die Verantwortung trägt. Es werden konkrete Beispiele angeführt, die diesen Konflikt deutlich machen. Schließlich wird eine Empfehlung ausgesprochen, die AWT möge Kriterien für einen Fachauditor Wärmebehandlung erarbeiten.

Typically, highly stressed gears are heat treated to satisfy operational demands. Case hardening is a common heat treatment associated with power train components. In the heat treatment process complex distortion takes place, which has been studied in these examinations. Object of the actual investigations were spur wheels with small module. The case hardening was realized utilizing low pressure carburization with subsequent high pressure gas quenching in a heat treatment furnace of industrial proportion. The systematic analysis was guided using design of experiment methods. In strategic focus were the three contributing heat treatment steps heating, carburization and quenching. Heating related factors were the batch design and the preheating temperature. During carburization the temperature, carburization depth and surface carbon content were altered. Finally no quenching related variations were performed. The influences of the different parameters on the size and shape changes of the gear wheels were evaluated statistically. The identified main factors on size as well as on shape changes of the base body and the toothing will be presented and discussed.

The substitution of expensive alloying elements like Mo and Ni by cheaper ones, e. g. Mn or B-Ti, was studied on the Q&T steel 42CrMo4 and the case-hardening steel 18CrNiMo7-6 based on equal hardenability. The alternative alloying concepts met the requirements for hardenability and mechanical properties in both steel types. The total substitution of Mo by Mn in the Q&T steel caused a loss in low temperature impact toughness. Residual elements (P, As, etc.) seem to promote this kind of temper embrittlement, so for temperature-critical cases the Mo content must be adapted. In the case-hardening steel the substitution of a part of Mo and Ni by Mn or B-Ti resp. lead to a tolerably reduced impact toughness and tooth impact bending force. Nb addition improved the impact toughness. The presented concepts of substitution offer a considerable potential for saving costs for alloy additions.

The combination of different metallic materials enables the design of lightweight structures with tailor-made properties. In contrast to conventional joining methods, for example fusion welding, by co-extrusion no degradation occurs in the materials structure in the form of heat affected zones or pore formation. Therefore, co-extrusion exhibits an attractive alternative for joining aluminium and titanium based alloys. The performed extrusion experiments were focused on the co-extrusion of aluminium (EN AW-6082) and titanium (TiAl6V4), where titanium is the reinforcing element that is inserted in aluminium profiles. During co-extruding an intermetallic layer with a thickness of 1 to 3 µm arises in the bonding zone between aluminium and titanium. In this layer an enrichment of elements of the aluminium alloy, such as silicon, was observed. The formation of the intermetallic layer and the strength of the compounds were examined at various positions after the co-extrusion and after subsequent heat treatment. The investigation of the intermetallic layer was performed with light optical microscope, scanning electron microscope and electro probe micro analysis. The mechanical properties were determined by tensile tests. The heat treatment led to the intended hardening of the aluminium alloy. However, the layer thickness did not change. The tensile tests specimen showed different failure locations. The heat treatment led to increased tensile strength values, but also to a decreased yield strength level.

Metalworking fluids (MWF) are used routinely throughout the world as cooling and lubricating agent for metal-cutting processes. They are important components to maintain the quality and precision of the metal-cutting but are slowly consumed within this process. Hence, monitoring of ageing of the MWFs before depletion is important for economical, ecological and security reasons. A method is presented, which enables to estimate the ageing of tools by measuring the microbial volatile outcome (MVOC) of the MWF. Measurements are done by headspace sorptive extraction combined to thermal desorption in a gas chromatography setup with mass selective detector (HSSE-TDS-GCMS). It could be shown that ageing of tools correlates to emission of ketonic and alcoholic MVOCs (namely 2-Heptanone, 2-Octanone, 1-Octanol, 2-Nonanone and 2-Decanone). Analysis of these components can be used as “ageing marker” for the investigated MWF solutions. The obtained information can further be used to calibrate electronic nose sensors for high-throughput and rapid analysis in future projects. Hence, it can be concluded that headspace analysis of volatile microbial metabolites by HSSE in combination with TDS-GC-MS is a suitable monitoring technique for the ageing of metalworking fluids.