Einfluss der Prozessparameter auf die Gefügeentwicklung von Kaltfließpressstählen bei thermomechanischer Umformung

Translated title of the contribution: Influence of processing parameters on the microstructure of cold heading steels during thermomechanical forming

Katharina Käsznar

    Research output: ThesisMaster's Thesis


    Bolts are the most investigated mechanical fastener in steel and mechanical engineering. Common materials for the production of high-strength bolts are quenched and tempered MnB and 1% Cr steels. Increasing demands regarding weight and cost optimization with at least the same quality and functional properties, require permanent improvements of the component and the manufacturing process. Cost-effective material alternatives include thermomechanically rolled steels. With optimized alloy composition and thermomechanical process control, these steels can be used directly in the bolt industry without the cost-intensive soft annealing process. In this master thesis, the influence of different forming parameters on the microstructure development of a new developed cold extrusion steel during thermomechanical treatment was investigated, with the aim to determine forming parameters resulting in a fine-grained ferritic microstructure. For this purpose, the influence of annealing temperature, final forming temperature and cooling rate on the microstructure was investigated in compression tests. The compressed specimens were metallographically prepared and the microstructure was characterized by optical and scanning electron microscopy. In addition, the hardness was measured along the cross-section of the compressed specimens. The results show that regardless of the annealing temperature, the ferrite content decreases with both increasing cooling rate and increasing final forming temperature. Furthermore, the mean ferrite grain size was found to decrease at both annealing temperatures with constant final forming temperature and increasing cooling rate. The dependence of the average ferrite grain size on the final forming temperature shows a sudden decrease, when the final forming temperature is lower than the temperature at which no complete recrystallisation of the microstructure occurs. The evaluation of the hardness measurements revealed that the annealing temperature at high final forming temperatures no longer has any influence on the hardness of the resulting microstructure. Furthermore, a decrease in hardness with decreasing final forming temperature was observed. At the lowest final forming temperature, a new increase in hardness was observed. For the selection of future process parameters, the annealing temperature must be adjusted to the achieved degree of forming. Furthermore, the final forming temperature should be between the Ac3- and Ar3-temperature and the cooling rate must be adjusted to the required grain size as well as the desired phase fractions.
    Translated title of the contributionInfluence of processing parameters on the microstructure of cold heading steels during thermomechanical forming
    Original languageGerman
    Awarding Institution
    • Montanuniversität
    • Monschein, Stefan, Co-Supervisor (internal)
    • Schnitzer, Ronald, Supervisor (internal)
    Award date8 Apr 2022
    Publication statusPublished - 2022

    Bibliographical note

    embargoed until 16-02-2027


    • thermomechanical forming
    • cold heading steels
    • microstructural evolution

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