Suchergebnisse

It has been broadly reported that determination of the martensite start temperature in steels, Ms, requires a complete description of their chemical composition. Recently, several neural networks models considering both chemical composition and austenite grain size (AGS) have been developed. Such models predict a moderate dependence of Ms with AGS. The present work examines the validity of existing neural network models, but focusing on fine AGS (below 5 m). ; The authors acknowledge financial support from the European Union through the European Coal and Steel Community program (ECSC-7210-PR-349) and from the Spanish Ministerio de Educacio´n y Ciencia (Special Action MAT 2002-10808-E). ; Peer reviewed

Parallel electron energy loss spectroscopy (PEELS) has allowed to analyse and quantify local variations in the carbon concentration of austenite islands transformed during the intercritical annealing treatment of commercial dual-phase (DP) steels. These changes in the carbon content of different austenite regions are responsible for the different volume fraction of tempered martensite, martensite and retained austenite obtained after intercritical annealing and overaging treatment. This technique reveals how carbon distribution in austenite evolves as the transformation process advances. ; The authors acknowledge financial support from the European Union through the European Coal and Steel Community programme (ECSC-7210-PR-349) and from the Spanish Ministerio de Educacio´n y Ciencia (Special Action MAT 2002-10808-E). A.G.-J. would like to express her gratitude for the financial support in the form of a Ph.D. research contract (FPU programme) from the Spanish Ministerio de Educacio´n y Ciencia. The authors would also like to express their special acknowledgement to Mrs. J. Drillet for her TEM– PEELS assistance and Dr. T. Iung for helpful discussions. ; Peer reviewed

Determining the content of solute elements in cold rolled ferritic steels constitutes an important aspect in metallurgy, since the interstitial elements have a harmful effect on the anisotropy properties (i.e. texture) of the final product, usually steel sheets for automotive applications. Both the carbon and nitrogen contents in solid solution depend on the chemical composition and thermomechanical parameters, such as the coiling temperature (CT) and the cold reduction degree. In the present paper, thermoelectric power measurements technique has been applied to study the relationship between the process variables such as CT and cold rolling reduction, and the amount of interstitial elements in solid solution. It was shown that at high CTs the value of the thermoelectric power only depends on the carbon content in solid solution, meanwhile at low CTs, a second contribution should be considered due to the presence of nitrogen in solid solution ; financial support from the European Union through the European Coal and Steel Community programme (ECSC-7210-PR-368) and from the Spanish Ministerio de Ciencia e Innovación (Special Action MAT 2002-10810-E) ; Peer reviewed

This paper discusses the influence of Particle Stimulated Nucleation (PSN) on the overall process of nucleation and subsequent grain growth in low carbon (LC) steels and proposes a global recrystallisation kinetics model based on fundamental physical metallurgy principles. The model takes into account the cementite content, which depends on the nominal carbon content, and the second phase particle size. The deformation field around cementite particles and its influence on processes is analysed. Finally, experimental evidence is given to show the accuracy of the theoretical predictions. ; The authors acknowledge the financial support from the European Union through the European Coal and Steel Community Programme (ECSC-7210-PR-368) and from the Spanish Ministerio de Educación y Ciencia (Special Action MAT 2002-10810-E). T. De Cock would also like to express his gratitude to the Consejo Superior de Investigaciones Científicas (CSIC) for financial support in the form of a Ph.D. research grant (I3P program). The authorswould like to thank Prof. V. Amigó of the Mechanical Engineering Department of theUniversidad Politécnica de Valencia for his collaboration with the EBSD measurements. The authors are grateful to M. Bögershausen of the Max Planck Institut für Eisenforschung in Dusseldorf (Germany) for his valuable help in the nanohardness experiments. ; Peer reviewed

In situ studies of reaustenitization in a low carbon microalloyed steel have been carried out by dilatometry. A model is proposed for describing the temperature evolution of the austenite volume fraction and its carbon concentration during continuous heating for various heating rates from dilatometric plots. The model results match metallographic measurements very well and may be applied to the reaustenitization of low carbon steels ; financial support from the European Union through the European Coal and Steel Community Programme (ECSC-7210-PR-349 ; Peer reviewed

During continuous heating of a cold rolled low carbon (LC) steel a dilatometric anomaly has been detected previous to the well known ferrite-to-austenite transformation. This anomaly is due to the dislocation annihilation and the texture change that accompany the recrystallization process. ; The authors acknowledge the financial support from the European Union through the European Coal and Steel Community programme (ECSC-7210-PR-368) and from the Spanish Ministerio de Ciencia y Tecnologı´a (Special Action MAT 2002-10810-E). F.G. Caballero would like to thank the Spanish Ministerio de Educacio´n y Ciencia for the financial support in the form of a Ramo´n y Cajal contract (Programa RyC 2002). T. De Cock would also like to express his gratitude to the Consejo Superior de Investigaciones Cientı´ficas (CSIC) for financial support in the form of a Ph.D. research grant (I3P program). ; Peer reviewed

The possibility of obtaining multiphase steels with considerable fractions of retained austenite, which is of key interest for the occurrence of the transformation-induced plasticity (TRIP) effect, is investigated in steels with low amounts of Si and Al. Special emphasis is given to the microstructural observation of this phase, since its volume fraction, distribution and stability, in relation to the carbon content, will determine the efficiency of the TRIP effect and thus of the resulting mechanical properties. Mechanical testing was carried out in order to measure the efficiency of the retained austenite transforming to martensite. ; The authors acknowledge financial support from the European Union through the European Coal and Steel Community programme (ECSC-7210-PR-368) and from the Spanish Ministerio de Educacio´n y Ciencia (Special Action MAT 2002-10810-E). T. De Cock would also like to express his gratitude to the Consejo Superior de Investigaciones Cientı´ficas (CSIC) for financial support in the form of a Ph.D. research grant (I3P program). J.P. Ferrer would also like to thank the MEC for financial support in the form of a Ph.D. research grant (FPI program). ; Peer reviewed