%0 Journal Article
%T Physical metallurgy of laser surface melted plastic mould steels: a case study
%A Cola£¿o
%A R.
%A Vilar
%A R.
%J Revista de Metalurgia
%D 1998
%I Consejo Superior de Investigaciones Cient¨ªficas
%X The purpose of this paper is to illustrate the potential of laser surface melting to improve the surface characteristics of plastic mould steels, using a typical plastic mould steel (DIN X43Cr12) as a case study. After laser surface melting the microstructure of this steel is formed by fine dendrites of austenite partially transformed into martensite. Although the equilibrium solidification phase is 8- ferrite, the formation of primary austenite is kinetically favored and this phase tends to predominate at the high solidification speeds used in laser processing. It was observed that the volume fraction of retained austenite depends critically on the laser processing parameters, so that the microstructure can change from almost completely martensitic to almost completely austenitic by changing the laser processing parameters. Laser melted tool steels show remarkable secondary hardening after tempering at suitable temperatures. In DIN X42Cr13 the secondary hardening peak temperature after LSM (600¡ãC) is 100¡ãC higher than after conventional heat treatment (500¡ãC), due to the presence of large amounts of retained austenite. It was observed that this phase only destabilizes above 600¡ãC, due to the precipitation of M7C3 and stress relieving. After destabilization, retained austenite transforms into martensite during cooling. Secondary hardening is due to the transformation of retained austenite into martensite and to the precipitation of M7C3 and M23C6 carbides. El objetivo del presente trabajo es ilustrar el potencial de la fusi¨®n superficial mediante l¨¢ser para la mejora de las caracter¨ªsticas estructurales de los moldes de acero para pl¨¢sticos, centr¨¢ndolo en el caso concreto del acero DIN X42Cr13. Tras el tratamiento de fusi¨®n superficial mediante l¨¢ser, la microestructura del material est¨¢ formada por dendritas finas de austenita parcialmente transformadas en martensita. Aunque la fase en equilibrio ser¨ªa ferrita 8, la formaci¨®n de austenita primaria est¨¢ favorecida cin¨¦ticamente, por lo que esta fase tiende a ser predominante a las altas velocidades de solidificaci¨®n que se consiguen en los tratamientos l¨¢ser. Se ha observado que la fracci¨®n de volumen de austenita retenida depende de manera cr¨ªtica de los par¨¢metros del procesado con l¨¢ser , as¨ª como que la microestructura puede cambiar de martensita a austenita en funci¨®n de dichos par¨¢metros. En la fusi¨®n superficial del acero DIN X42Cr13 se obtiene un pico de endurecimiento secundario despu¨¦s del tratamiento con l¨¢ser a 600¡ãC, mientras que, para los tratamientos t¨¦rmicos convencionales ¨¦ste aparece
%K Laser surface melting
%K Tool steel
%K Microstructure
%K Retained austenite
%K Tempering
%K Fusi¨®n superficial por l¨¢ser
%K Herramientas
%K Aceros
%K Microestructura
%K Austenita retenida
%K Revenido
%U http://revistademetalurgia.revistas.csic.es/index.php/revistademetalurgia/article/view/676/688