Einfluss der bainitischen Umwandlung auf die mechanischen Eigenschaften von Warmarbeitsstählen

Hot-work tool steels are used in engineering applications especially as tool material for hot-pressing, extrusion and forging, offering high strength, high toughness and a good tempering resistance. This is achieved by using materials which have a high microcleanliness and homogeneity over the entire cross-section, usually with a martensitic microstructure. However, due to the rising demand for increasing tool dimensions the cooling rate during quenching can become a major problem. For instance, depending on the alloy composition dies made by classical hot-work tool steels show an increase of bainite attributed to the temperature gradient between the centre and the surface of large components. This change in microstructure is accompanied by the formation of different precipitates, which in turn affect the mechanical properties. Their characterisation was conducted by means of mechanical tests such as tensile tests, fracture toughness tests and instrumented impact tests in order to obtain the strength, deformation behaviour, impact toughness, and plane strain fracture toughness of the engineering material. The results revealed that the mechanical properties degrade with decreasing cooling rates. These degradations are related to the presence of the bainitic microstructure connected with M₇C₃ carbides, which are present at former austenite grain boundaries as well as martensite and bainite lath boundaries.     

Einfluss des pH Wertes auf die Korrosion von Zn-Al-Mg feuerverzinkten Stahlbändern in Chlorid enthaltenden Umgebungen

Previous studies of our group showed that Zn-Al-Mg hot-dip galvanized steel sheets have a superior corrosion resistance compared to conventional hot-dip galvanized steel sheets. This work focuses especially on the stability of this material at different pH values and the formation of corrosion products. Therefore experiments based on the normal salt spray test according to DIN EN ISO 9227 were conducted. During those tests the solution was adjusted to different pH values from acidic to alkaline. All other parameters were left untouched. The samples were compared to conventional hot-dip galvanized steel sheets of the same coating thickness. The results showed that the corrosion resistance is severely influenced by the pH value of the testing medium. Also the amount and the type of corrosion products formed in the course of the tests varies greatly. While in severely acidic conditions mainly Simonkolleite is formed. In mildly acidic to neutral conditions, Simonkolleite and Hydrozincite are formed, while, in strongly basic conditions, Simonkolleite and ZnO are formed. Corrosion products were analyzed by SEM, EDX, XRD, IR, and RAMAN spectroscopy. A cross section analysis in SEM showed that the severity of the attack of the coating is very much dependent on the pH value of the testing solution. The corrosion products could be identified as Simonkolleite and Hydrozincite. In alkaline conditions the formation of Zincoxide and Zn-Al-Hydrotalcite was also observed.     

Bauvorhaben im alpinen Bereich: Beurteilung von Georisiken und Maßnahmenplanung im Zuge der Genehmigungsverfahren – Fallbeispiele

The rockfall hazard is denoted as a “classic” georisk in construction projects in the Alpine area. For the assessment of this threat, currently the national rule ONR 24810:2013 (Technical protection against rockfall – terms and definitions, effects of actions, design, monitoring and maintenance) is in use. This ONR (ON Rule) specifies normative principles for technical protection against stone-chipping. It applies to primary measures (e.g. anchorage) and also secondary measures (e.g. nets, embankments). The geological and geotechnical processing based on this ON Rule is described in a case study. Another georisk is less known in our immediate environment, however, this georisk can occur in all landforms respectively outside the Alpine area depending on the geological conditions: building hazards caused by gypsum karst. The necessary measures in connection with planned construction by appropriate ground investigations are presented in a case study.     

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BHM Verbandsnachrichten

Aus der Industrie – Neues von der Montanuniversit?t – Neues von der ASMET – Personalnachrichten – Tagungsankündigungen – Hinweise auf Neuerscheinungen     

Aus der Industrie – Neues von der Montanuniversität – Personalnachrichten – Tagungsankündigungen – Neues von der ASMET – Hinweise auf Neuerscheinungen

BHM Verbandsnachrichten

Aus der Industrie – Neues von der Montanuniversit?t – Personalnachrichten – Tagungsankündigungen – Neues von der ASMET – Hinweise auf Neuerscheinungen     

Einfluss der Mikrolegierung (Nb,Al, N) auf die Feinkornbeständigkeit von Einsatzstählen vom Typ 18CrNiMo7−6

The case-hardening steel 18CrNiMo7???6 is used for large gear wheels in wind turbines. To achieve the requirements for a wear resistant and tough material, the steel is carburized and case hardened at 980?°C for 80 h. During this heat treatment, grain growth occurs, which should be avoided by micro-alloying the steel with aluminium and niobium. These elements pin the grain boundaries in form of carbides and nitrides to reduce the grain growth. In this work the grain size stability of several micro-alloyed variants of the case-hardening steel 18CrNiMo7???6 under different heat treatment conditions was examined. For the microstructural characterization, light microscopy, scanning, and transmission electron microscopy as well as atom probe tomography were applied.     

Mikrostrukturielle Charakterisierung von ultra-hochfesten Schweißgütern

Welded steel structures are a crucial part of lightweight constructions in several industrial segments. The filler metal plays a vital role in optimizing the properties of welded joints. In this study different methods were used to characterize the microstructure of ultra-high strength all-weld metal samples with different chemical compositions. It was evaluated which method can be used to link the grain size of a sample to its toughness.     

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BHM Verbandsnachrichten

Aus der Industrie – Neues von der Montanuniversit?t – Personalnachrichten – Tagungsankündigungen – Hinweise auf Neuerscheinungen