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Revista Latinoamericana de Metalurgia y Materiales
Print version ISSN 0255-6952
Abstract
GONZALEZ, Juan Carlos and LUIGGI, Ney. Characterization of low-alloy steels by means of different techniques. Rev. LatinAm. Metal. Mater. [online]. 2013, vol.33, n.1, pp.147-155. ISSN 0255-6952.
Two low carbon steels with different concentrations of carbon, one with manganese as its principal alloy component, were studied using electrical resistivity, Differential Scanning Calorimetry (DSC), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) as experimental techniques to study the kinetic of phase changes occurring during a non-isothermal heating in normalized and austenized microstructures. The measurements of electrical resistivity were used to test the austenization process at 1100ºC, showing how sensitive this method is to the concentration of solute in the samples. The resistivity being slightly larger at the onset, possibly due to the precipitation of carbides, and becoming slightly erratic and diminished as the aging time increases. For DSC, measurements were taken at different heating rates, which demonstrated different exothermic and endothermic transformations, indicative of the initial microstructure of the samples. Austenization introduces a new endothermic reaction, not present in the normalized samples, very localized and basically associated with the dissolution of martensite. Optical and scanning electron microscopy allowed us to visualize the granular state of the samples and follow the sequence of evolution of phases present in these steels, the normalized state showing a matrix rich in ferrite and pearlite, and all the treated samples showing a matrix rich in martensite, product of rapid tempering. The activation energies, for the endothermic reactions corresponding to the allotropic transformations α - α + γ and α + γ - γ., calculated by isoconversión methods are in the neighborhood of 22.2 y 26.7 Kcal/mol for the first and second endothermic processes, respectively.
Keywords : Low-Alloy Steels; DSC; SEM; Activation Energy.
