Browsing by Author "Elvira, Roberto"
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Item Different Phenomena Encountered during Dilatometry of Low-density Steels(2021-11-22) Jimbert, Pello; Guraya, Teresa; Kaltzakorta, Idurre; Gutiérrez, Teresa; Elvira, Roberto; Tafaghodi Khajavi, Leili; CIRMETALIn recent decades, highly alloyed low-density steels are being developed to reduce the weight of different automotive parts. Dilatometry can be a very useful experimental technique to understand phase transformations during heating or cooling of new low-density steel alloys. When performing dilatometry measurements some assumptions are made such as the homogeneity of the sample material tested during the experiment. In this study, dilatometry tests were performed for two different low-density steels, and the variations of the composition between the surface and the inner part of the sample were analyzed. The migration of manganese by diffusion from the interior of the samples and finally its evaporation on the surface under vacuum were observed. This compositional gradient generated in the samples may influence the veracity and interpretation of the results obtained in dilatometry when working with high manganese steel alloys. The detachment of surface grains created by this compositional change near the surface of the samples is also investigated.Item Evolution of Microstructure during Isothermal Treatments of a Duplex-Austenitic 0.66C11.4Mn.9.9Al Low-Density Forging Steel and Effect on the Mechanical Properties(Multidisciplinary Digital Publishing Institute (MDPI), 2021-01-26) Kaltzakorta, Idurre; Gutierrez, Teresa; Elvira, Roberto; Jimbert, Pello; Guraya, TeresaIn the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of isothermal treatments at different combinations of time and temperature, aimed to promote kappa carbide precipitation, and improve the mechanical properties obtained with a water quenching treatment. The effects of the different isothermal treatments on the microstructure and on the mechanical properties have been analyzed and compared to those obtained from a quenching heat treatment. We found that isothermal treatments in the range temperature between 550–750 °C promoted the profuse precipitation of coarse kappa carbides at grain boundaries, which dramatically reduced the ductility of the alloy, whereas a traditional quenching treatment resulted in a better combination of ductility and mechanical strength.Item Manufacturing and forging issues encountered while upscaling 1.3C30Mn10Al-austenitic and 0.65C12Mn-duplex low-density steels(2021-07) Kaltzakorta, Idurre; Gutierrez, Teresa; Elvira, Roberto; Jimbert, Pello; Guraya, Teresa; CIRMETALDifficulties found when manufacturing and forging two low density steels in different scales are described in this work. Austenitic and duplex low-density steels have attracted a lot of interest due to their good combination of mechanical properties and density reduction. In this work, the fabrication of 1.3 C30Mn10Al austenitic low-density steel and 0.65 C12Mn10Al duplex low-density steel have been studied. The scaling up of the manufacturing process from 1 Kg to 35 Kg ingots of both materials and the subsequent hot forging of the ingots is described, showing the difficulties encountered during the production and transformation of these steels. Only the small ingots were successfully forged, but not the larger ones, showing the important differences in the forging properties depending on the geometry and dimensions of the final part to be forged, and the homogenization temperatures. The possible causes of this scale dependence are proposed from the experimental results obtained, as well as from the hot axial compression tests and the thermodynamic simulations carried out.