Papers by Author: Armando Salinas-Rodríguez

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Authors: Alejandro López-Baltazar, Armando Salinas-Rodríguez, Enrique Nava-Vázquez
Abstract: Interrupted cooling in the run-out table after hot rolling is a processing strategy to produce dual phase ferrite-martensite steel strips. The effects of interrupted cooling temperature and time after austenitizing at 1150 °C are investigated. This is done to establish the conditions for austenite to transform into ferrite-martensite microstructures in a Mn-Cr-Mo strip produced from a CSP (Continuous Strip Processing)-type thin slab. The results show that dual phase microstructures can only be obtained when interrupted cooling is performed at 725
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Authors: Enrique Díaz Barriga-Castro, Armando Salinas-Rodríguez, Enrique Nava-Vázquez
Abstract: The aim of the present work is to determine the austenite to ferrite transformation temperatures in a Si-Al non-oriented electrical steel. Critical transformation temperatures on heating and cooling are determined using an in-situ X-ray diffraction technique where the specimen is heated or cooled in a stepwise manner. The transformation temperatures are estimated from changes in the intensities of the (110)α and (111)γ peaks as a function of temperature. The time evolution of the microstructure resulting from isothermal heat treatments at temperatures between 800 and 1000 °C applied after cooling from 1050 °C is followed by quantitative metallography on samples quenched into water. The results show that, on cooling, formation of ferrite starts at about 950 °C and ends at 790 °C, indicating a strong effect of Si and Al on the austenite to ferrite and eutectoid transformations. These results suggest that the low tensile ductility exhibited by this material at temperatures near 1000 °C can be attributed to strain localization in strain-induced ferrite formed at temperatures as high as 1025 °C.
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Authors: Edgar García S., E. Treviño L., Armando Salinas-Rodríguez
Abstract: The hot tensile ductility of solution treated Si-Al electrical steels was investigated at temperatures between 850 and 1150 °C. Samples for mechanical testing were obtained from continuous cast thin slabs and hot rolled strips. A continuous decrease in ductility was observed up to about 1000 °C. After that, the ductility was recovered in strip samples while in slab samples the ductility remained constant at RA<10%. This behavior was associated with the presence of large quantities of undissolved AlN particles formed during slow cooling of the slab. In the case of strip specimens, where the starting slab is not cooled to room temperature, the 1000 °C ductility minimum was attributed to strain localization at grain boundary nucleated ferrite grains. Rapid nucleation and growth of microvoids at AlN particles formed during cooling to test temperatures in the vicinity of Ae3 resulted in intergranular tensile failure by microvoid coalescence.
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Authors: Emmanuel Gutiérrez C., Armando Salinas-Rodríguez, Enrique Nava-Vázquez
Abstract: The effects of heating rate and annealing temperature on the microstructure and mechanical properties of cold rolled Al-Si, low C non-oriented electrical steels are investigated using SEM metallography and uniaxial tensile tests. The experimental results show that short term annealing at temperatures up to 850 °C result in microstructures consisting of recrystallized ferrite grains with sizes similar to those observed in industrial semi-processed strips subjected to long term batch annealing treatments. Within the temperature range investigated, the grain size increases and the 0.2% offset yield strength decreases with increasing temperature. It was observed that the rate of change of grain size with increasing temperature increases when annealing is performed at temperatures greater than Ac1 (~870 °C). This effect is attributed to Fe3C dissolution and rapid C segregation to austenite for annealing temperatures within the ferrite+austenite phase field. This leads to faster ferrite growth and formation of pearlite when the steel is finally cooled to room temperature. The presence of pearlite at room temperature decreases the ductility of samples annealed at T > Ac1.
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Authors: A. Mani-Medrano, Armando Salinas-Rodríguez
Abstract: The effects of tensile deformation on the amount of hcp phase formed during a 3 hour isothermal aging at 800 °C is studied using in-situ X-ray diffraction and scanning electron microscopy. It is shown that the start of the isothermal martensitic transformation during aging of this material is delayed by prior plastic deformation. Nevertheless, the total amount of hcp phase present in the microstructure at the beginning of aging increases at a continuously decreasing rate due to stress-assisted transformation. This behavior is attributed to the relieving of internal stresses produced by plastic deformation prior to aging. Finally, during the last stage of aging, the amount of hcp phase in the microstructure increases as a result of isothermal martensitic transformation. It is suggested that the presence of mechanically-induced hcp phase during aging inhibits the thermally activated nucleation process that leads to the isothermal martensitic transformation.
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Authors: Armando Salinas-Rodríguez, E. Gutiérrez-Castañeda
Abstract: The effects of annealing prior to cold rolling on the microstructure and magnetic properties of a low-C grain non-oriented (GNO) electrical steel strip have been investigated. It is shown that annealing of the hot-rolled strips in the intercritical region, Ac13, causes rapid decarburization and development of large columnar ferrite grains. This microstructure leads, after cold-rolling and a fast annealing treatment at temperatures between 800 and 850 °C, to a polygonal ferrite grain microstructure with magnetic properties superior to those observed typically in the same steel in the industrial fully processed condition. The results are attributed to the {100}-fiber texture developed during the final annealing. Annealing at T<800 °C or T>850 °C results in formation of {111}-fiber texture components due to recristallization or transformation of deformed ferrite leading to a negative effect on the final magnetic properties. The results suggest that annealing prior to cold rolling offers an attractive alternative processing route for the manufacture of fully processed low-C, Si-Al GNO electrical steels strips.
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Authors: Felipe García, Armando Salinas-Rodríguez, Enrique Nava-Vázquez
Abstract: The reaction between solid steel and liquid Al-Zn-Si alloy leads to the formation of a solid intermetallic interfacial layer. In the case of industrial Al-43.5Zn-1.5Si coated steel strips, the thickness of the intermetallic layer is on average 1.35 μm and the kinetics of the reaction is controlled by the effect of Si on Al and Fe diffusivities through the solid intermetallic layer. In this paper it is shown that the thickness of the intermetallic interfacial layer decreases as the Si content in the liquid alloy increases. EDXS microanalysis at the interface of industrial coated steel strips shows that the interfacial intermetallic compounds are chemically similar to those formed in the bulk of Al-43.5Zn-1.5Si liquid baths in continuous coating lines. Differential acid dissolution of the coatings reveals that the intermetallic layer is not planar at the interface with the coating overlay and is formed by grains of different size and chemical composition. Addition of minute quantities of Ti to the Al-Zn-Si liquid alloy causes changes in the morphology of the intermetallic layer and an overall refining of the microstructure.
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