Abstract
Austenite-martensite transformation influence on the dimensional stability of a new experimental tool steel alloyed with niobium (0.08% wt.) and vanadium (0.12% wt.) has been studied. The dimensional stability of this new steel was compared with the dimensional stability of commercial steel, after and before two thermal treatments, T1 (860 °C) and T2 (900 °C). The thermal treatments consisted on heating and cooling, at 1 atmosphere of pressure, in N2 atmosphere furnace, fol lowing by heating in a conventional furnace at 180 °C during 1 hour. Initially, the experimental steel composition and Ac1 and Ac3 transformation temperatures were determined by glow-discharge luminescence (GDL) and dilatometric tests, respectively, in order to select the austenization temperatures of T1 and T2 treatments. After hardness measurement, the microstructure of both steels was characterized by X-Ray Diffraction (XRD) and optical metallography, before and after of T1 and T2 thermal treatments. Finally, longitudinal and angular dimensional stability analyses were realized for both commercial and experimental steels. After a contrastive hypothesis analysis, the results showed that the longitudinal relative variation of the experimental steel calculated was around 0.2% and the angular relative variation was not significant
Highlights
Dilatometric tests, respectively, in order to select the austenization temperatures of T1 and T2 treatments
Influence of the austenite-martensite transformation in the dimensional stability of a new tool steel alloyed with niobium (0.08% wt.) and vanadium (0.12% wt.)
Austenite-martensite transformation influence on the dimensional stability of a new experimental tool steel alloyed with niobium (0.08% wt.) and vanadium (0.12% wt.) has been studied
Summary
Los materiales que apenas varían sus dimensiones originales tras ser sometidos a procesos termomecánicos o fuerzas externas durante los procesos de elaboración y de funcionamiento en servicio son estables dimensionalmente. La cantidad de austenita retenida obtenida durante un enfriamiento continuo ha sido estudiada desde hace décadas (Yao et al, 2004; Telher, 2009; Nallathambi et al, 2010) y se ha demostrado que afecta a la inestabilidad dimensional en procesos posteriores de revenido, y su valor da una idea inicial de la capacidad de transformación de la austenita en el acero después de haber realizado un determinado tratamiento térmico. La tendencia al agrietamiento de un acero durante un enfriamiento está relacionada con el contenido en carbono equivalente (Ceq) (Canale y Totten, 2005) que depende de su composición química en porcentaje en peso. La influencia de los elementos de aleación sobre la transformación austenita-martensita está relacionada con el porcentaje de carbono en la composición del acero, como se ha comentado anteriormente. Estos tratamientos térmicos corresponden a la etapa más crítica, desde el punto de vista de la distorsión dimensional, de un tratamiento térmico global que abarca varios tratamientos térmicos, posteriores a los que se van a estudiar, pero que tienen un menor efecto sobre la estabilidad dimensional
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