Processing and Material Properties of Hot Work Tool Steels Manufactured by Selective Laser Melting.

Selective Laser Melting (SLM), an additive manufacturing technology, has established rapidly in recent years to produce metallic prototypes and complex component geometries. At present the commercial production of steel components, using this technology, is limited to steel powder with very low carbon content. The aim of this study is to characterize the selective laser melting process by using a metal powder alloy, which is commonly used for manufacturing hot-working tools. In the future these alloys will be utilised to manufacture moulds and inserts for hot working applications such as forging, press hardening, hot stamping and die-casting processes. In this paper the processing of a hot work tool steel alloy with a powder preheating built-platform for SLM is investigated. The results of this study show that an elevated built-platform temperature of 500 °C is necessary to reduce the temperature gradient between the built-platform and the laser-melted powder. The experiments indicate low risks of defects at higher temperatures. Consequently, alloys with a higher content of carbon show a major influence on residual stresses. These stresses lead to distortions and cracking and consequently to failure of the produced parts. In addition, the physical and mechanical properties are determined for these powder materials. A homogeneous microstructure is
achieved by optimizing the process parameters. Metallographic examinations illustrate that the parameters lead to a minimum level of porosity and a limited number of defects.