The main process variables to produce galvanized dual phase (DP) steel sheets in continuous galvanizing lines are time and temperature of intercritical austenitizing (tIA and TIA), cooling rate (CR1) after intercritical austenitizing, holding time at the galvanizing temperature (tG) and finally the cooling rate (CR2) to room temperature. In this research work, the effects of CR1, tG and CR2 on the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of cold rolled low carbon steel were investigated by applying an experimental central composite design and a multivariate regression model. A multi-objective optimization and the Pareto Front were used for the optimization of the continuous galvanizing heat treatments. Typical thermal cycles applied for the production of continuous galvanized AHSS-DP strips were simulated in a quenching dilatometer using miniature tensile specimens. The experimental results of UTS, YS and EL were used to fit the multivariate regression model for the prediction of these mechanical properties from the processing parameters (CR1, tG and CR2). In general, the results show that the proposed multivariate model correctly predicts the mechanical properties of UTS, YS and %EL for DP steels processed under continuous galvanizing conditions. Furthermore, it is demonstrated that the phase transformations that take place during the optimized tG (galvanizing time) play a dominant role in determining the values of the mechanical properties of the DP steel. The production of hot-dip galvanized DP steels with a minimum tensile strength of 1100 MPa is possible by applying the proposed methodology. The results provide important scientific and technological knowledge about the annealing/galvanizing thermal cycle effects on the microstructure and mechanical properties of DP steels.
predicted by the phase diagram, by simply considering the composition of the material. Among them, liquid phase may The microstructural evolution during sintering of form which in uences the sintering mechanisms and the 10% bronzes obtained by mixing elemental powders dimensional behaviour. 4 ± 6 Therefore, the study of the copperwas studied, in order to investigate the mechanisms tin interaction does not have a simple microstructural responsible for microstructural homogenisation, coninterest only, but has a noticeable impact on the process solidation of the green compacts, and dimensional design and control and on the technological properties of variation. The eVect of the copper powder was also the components. studied using an electrolytic and an atomised com-The present study investigates the transformations which mercial powder. As a consequence of the diVerent occur during sintering of 10% Sn bronzes obtained by mixes surface area and surface chemistry, and of the presence of elemental copper and tin powders and the in uence of of internal pores and microcavities in the atomised the copper powder. In fact, two diVerent copper powders copper powder, the two mixes display signi cantly were used, one electrolytic and the other water atomised, diVerent dimensional behaviour but, under speci c time the latter having been speci cally developed as an alternative and temperature conditions, they give rise to the same to the former for the production of bearings. Dilatometry dimensional variation and the same microstructural was used as the experimental technique to sinter green parts characteristics.P M /0962 because of its sensitivity to phase transformations involving speci c volume changes, such as the formation of the liquid Dr M enapace, D r Zadra, and Professor M olinari phases. 7, 8 A detailed microstructural characterisation was
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