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Title: Characterisation of the metallurgical and thermo-mechanical properties of niobium HSLA steel during hot strip rolling
Author: Rickinson, N.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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Abstract:
Predictions of finishing stand loads in the hot strip mill require a precise understanding of the microstructural evolutionary changes occurring during and after deformation. In order to generate this understanding, it is important to use reliable and accurate techniques. Hence, suitable equipment was developed to produce a controlled testing medium. Single and double uni-axial compression testing was carried out on two steels: a niobium-bearing HSLA and a carbon manganese steel. Testing was carried out between 850°C, 950°C and 1050°C at strain rates of 0.01/s to 1/s, with true strain reductions of up to 50%. All testing was completed above the Ar3 temperature and, therefore, in the austenitic phase. The hyperbolic sine relationship was used to predict flow stress levels at yield stress, peak stress and stress at a large strain. Using other relationships, the flow stress evolution between these points was also described. Interrupt compression testing was carried out to investigate the microstructural evolution taking place between two deformations. The results of these experiments were then used with an Avrami type relationship to describe the softening kinetics of the two steels. Further single compression tests, having testing parameters matching those of the first deformations of the interrupt compression tests, were performed and then quenched. Prior austenite grain boundaries were revealed through chemical etching. This provided a link between the observations made during interrupt compression testing and microstructural examinations. The combined relationships were then used to produce off line predictions for finishing stand flow stress under different processing conditions. These predictions were then compared with observations from hot strip mill. The error margin on these comparisons was sufficiently low to demonstrate the usefulness of this technique. Specifically, application of this approach will significantly reduce the trial cost for new steel grade development. Moreover the technique can be used to safe guard the mill from potential damage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.638666  DOI: Not available
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