An Investigation Into Fully Melting a Maraging Steel Using Direct Metal Laser Sintering (Dmls)

2238 Words Feb 17th, 2012 9 Pages
AN INVESTIGATION INTO FULLY MELTING A MARAGING STEEL USING DIRECT METAL
LASER SINTERING (DMLS)

Mark. Stanford, Kevin. Kibble, Matthew. Lindop, Diane. Mynors and Colin. Durnall

Department of Engineering and Technology

University of Wolverhampton

Shifnal Road, Priorslee

Telford, UK
TF2 9NT

ABSTRACT

This paper reports on the relative capability of the EOS M250 Extended platform to fully melt an 18Ni (‘300’ grade) maraging tool steel from sub-20 µm powder. The work describes the investigation of scanning routines necessary to achieve satisfactory metallurgical integrity and shape manufacturing capabilities of the process. Solidification was observed to take place by cellular and cellular-dendritic growth mechanisms in
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One material developed for the M270 platform is a ‘300’ grade maraging steel (EOS grade MS1). This material is capable of being sintered in layers of 40 µm with relatively low internal stress levels. However, unlike other commercially available steel powders this material can be manipulated in a soft condition as-sintered and machined conventionally. The steel can then be age- hardened to 50-55 Rc, thereby matching tool steels alloyed with relatively high levels of chromium (>5%).
The mechanical properties required of dies for plastics injection moulding and metal die-casting are a high hardness and a high tensile strength. For high volume production runs tool steels are preferred, with a hardness exceeding 500 HV (>50 Rc). If conformal water-cooled channels are also incorporated into the dies then some measure of corrosion resistance will also be required of the tooling. Typical tool steels contain relatively high carbon and high chromium contents. Although chromium offers some corrosion resistance the presence of a relatively high carbon will result in carbides being present in the microstructure that can promote corrosion. Fe-Cr based tool steels are austenitised, quenched and tempered to produce a tempered martensite matrix containing Fe-Cr carbides. In quenching these alloys significant distortion can occur, as there is a volume expansion associated with the transformation to high

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