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Physics Procedia 12 (2011) 255–263
LiM 2011
Microstructure and mechanical properties of Selective Laser Melted 18Ni-300 steel. a
a
b
a
K.Kempen *, E.Yasa , L.Thijs , J.-P. Kruth , J.Van Humbeeck
b
a Department of Mechanical engineering, Katholieke Universiteit Leuven, Leuven, Belgium b Department of Metallurgy and Materials engineering,, Katholieke Universiteit Leuven, Leuven, Belgium
Abstract Selective Laser Melting (SLM) is an Additive Manufacturing process in which a part is built in a layer by layer manner. A laser source selectively scans the powder bed according to the CAD data of the part to be produced. The high intensity laser beam makes it possible to completely melt the metal powder particles to obtain almost fully dense parts. In this work, the influence of process parameters in SLM (e.g. scan speed and layer thickness) and various age hardening treatments on the microstructure and mechanical properties of 18Ni-300 steel is investigated. It is shown that almost fully dense parts with mechanical properties comparable to those of conventionally produced maraging steel 300 can be produced by SLM. Keywords: Selective Laser Melting; Maraging steel 300; Additive Manufacturing; Microstructure
1. Introduction Selective laser melting, SLM, is a powder-based additive manufacturing process that allows the production of functional three-dimensional parts directly from a CAD-model. During the process, successive layers of metal powder particles are molten and consolidated on top of each other by the energy of a high intensity laser beam. Consequently, almost fully dense parts without need for any post-processing other than surface finishing are produced. Customized medical parts, tooling inserts with conformal cooling channels and functional components with high geometrical complexity are good examples to reveal the scope of the application areas of this process [1, 2].
* Corresponding author. Tel.: +32 16322552. E-mail address:
[email protected].
1875-3892 © 2011 Published by Elsevier Ltd. doi:10.1016/j.phpro.2011.03.033
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K.Kempen et al. / Physics Procedia 12 (2011) 255–263
Figure 1.A schematic view of the SLM process
Laser processing of materials is generally accompanied with high cooling rates due to the short interaction time and high thermal gradients. The high cooling rates during SLM may result in the formation of non-equilibrium phases, quasi-crystalline phases and new crystal phases with extended composition ranges [2]. Finer structures may be observed in the microstructure at sufficiently high cooling rates compared to the conventional manufacturing methods [3]. Moreover, during the SLM process, gas bubbles and oxide inclusions can become entrapped in the material during solidification due to various causes such as decrease in the solubility of the dissolved elements in the melt pool during cooling and solidification, chemical reaction or trapped gas. Therefore, the mechanical and material properties obtained after SLM may be different than the properties of materials produced by conventional production techniques. In this study, the influence of the SLM-process parameters on the density, the microstructure and the mechanical properties was investigated. Moreover, the effect of temperature and duration of the hardening (aging) heat treatment on the obtained hardness was studied. 2. Background Maraging steels are well known for combining good material properties like high strength, high toughness, good weldability and dimensional stability during aging heat treatment. Mainly maraging steels are used for two application areas: the aircraft and aerospace industry in which superior mechanical properties and weldability of maraging steels are the most important features, and secondly in tooling applications which require superior machinability [4]. The nominal composition of maraging steel, grade 300, is given in Table 1. Table 1.Chemical composition of 18Ni-300 steel [5,6] Alloying element
Fe
Ni
Co
Mo
wt %
rest
17-19
8.5-9.5
4.5-5.2
Ti
Al
0.6-0.8 0.05-0.15
Cr
C
Mn,Si
P,S
