Effects of Powder Preheating on The Processing of Selective Laser Melted Tool Steels

摘要

This paper presents results of powder bed preheating on fabrication of hot work tool steel grades G1, G2 and G3 for the selective laser melting process. The effect of powder bed preheating on microstructure and residual stresses is analysed. The experiments show that an elevated preheating temperature is necessary to reduce the temperature gradient between the substrate-plate and the laser-molten steel powder. The optical measurements indicate a low risk of defects and a low level of residual stresses at elevated temperatures. Consequently, alloys with higher carbon content 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 processing properties are determined for these powder materials. A homogeneous microstructure is achieved by optimisation of the powder bed preheating temperature. Metallographic examinations illustrate that adapted parameters lead to a minimum level of porosity, limited number of defects and a modification of the microstructure.