PhD Thesis
Carlos Capdevila Montes
Abstract:Carlos Capdevila Montes
In this work several theoretical models based on sound metallurgical theories describing the nucleation and growth processes of diffusional phase transformations during the isothermal decomposition of austenite in medium carbon microalloyed forging steels are presented. These model have been successfully applied to calculate the evolution of volume fraction of allotriomorphic ferrite, idiomorphic ferrite and pearlite transformed during the isothermal decomposition of austenite as a function of isothermal temperature and holding time. The influence of factors such as isothermal temperature, the austenite grain size, the initial volume fraction of inclusions and the isothermal holding time has been specifically analysed in these models. Their experimental validation has been carried out with excellent results by means of experimental techniques such as high resolution dilatometry and microstructural characterisation. With this aim a wide experimental study of the diffusional phase transformation during the isothermal decomposition processes that occurs in this steel has been done.
On the other hand, and due to the relevance of the dilatometric analysis monitoring the solid-solid phase transformations in steels, dilatometric models that allow us to calculate the relative change in length as a function of time at a fixed isothermal temperature have been developed. These models take into account the effect of lattice parameter as well as the thermal dilatation coefficients of the phases present in the final microstructure. Theses model have been also properly validated by experimental analysis, and therefore allow us to satisfactory predict the dilatometric behaviour of the isothermal decomposition processes of austenite. The excellent agreement between experimental and theoretical results of the dilatometric models presented in this work indirectly validate the phase transformation models for a medium carbon microalloyed steel described in this work.
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On the other hand, and due to the relevance of the dilatometric analysis monitoring the solid-solid phase transformations in steels, dilatometric models that allow us to calculate the relative change in length as a function of time at a fixed isothermal temperature have been developed. These models take into account the effect of lattice parameter as well as the thermal dilatation coefficients of the phases present in the final microstructure. Theses model have been also properly validated by experimental analysis, and therefore allow us to satisfactory predict the dilatometric behaviour of the isothermal decomposition processes of austenite. The excellent agreement between experimental and theoretical results of the dilatometric models presented in this work indirectly validate the phase transformation models for a medium carbon microalloyed steel described in this work.
Download PDF file of chapter
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