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Title: The novel quenching and partitioning heat treatment of steel
Author: Al Malki, Uthman Mosfer
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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The recently proposed and novel steel heat treatment process known as quenching and partitioning (Q&P) is studied, in particular, the partitioning stage. Characterization of the partially quenched microstructure prior to the partitioning stage is enabled by using a base composition containing a higher Mn concentration than for conventional Q&P steels, such that quenching to room temperature produces only partial decomposition of austenite to martensite. Increasing the carbon concentration of this base composition also enabled a study of the effect of steel carbon content, although at the higher carbon contents refrigeration was required to achieve marten site because of the reduced Ms temperatures. Increased carbon also allowed the effect of martensite morphology to be examined. Intercritical annealing of a conventional TRIP steel composition provided an alternative route towards increasing the carbon concentration of austenite prior to partitioning. Light optical microscopy, scanning electron microscopy, X-ray and neutron diffraction were used to characterise the evolution of microstructure. In particular, in-situ examination of the Q&P heat-treatment process, enabled by introducing a furnace into the neutron beam-line, gave real -time observations and analyses of partitioning. Lattice parameter measurements enabled calculation of the carbon content of retained austenite, providing evidence of carbon partitioning from martensite to untransformed austenite during the partitioning stage. Thus, the partitioning process was shown to be effective in thermal and mechanical stabilization of retained austenite. In addition, evidence was found for substantial carbon enrichment of the austenite phase, which might be expected to provide opportunity for new Q&P steel grades with enhanced properties
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available