Physical metallurgy of laser surface melted plastic mould steels: a case study
DOI:
https://doi.org/10.3989/revmetalm.1998.v34.i2.676Keywords:
Laser surface melting, Tool steel, Microstructure, Retained austenite, TemperingAbstract
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°C) is 100°C higher than after conventional heat treatment (500°C), due to the presence of large amounts of retained austenite. It was observed that this phase only destabilizes above 600°C, 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.
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Published
1998-04-30
How to Cite
Colaço, R., & Vilar, R. (1998). Physical metallurgy of laser surface melted plastic mould steels: a case study. Revista De Metalurgia, 34(2), 135–139. https://doi.org/10.3989/revmetalm.1998.v34.i2.676
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