Effects of substrate preheating during direct energy deposition on microstructure, hardness, tensile strength, and notch toughness

• Published in: Metals and materials international Vol. 23; no. 6; pp. 1204 - 1215
• Main Authors: Baek, Gyeong Yun, Lee, Ki Yong, Park, Sang Hu, Shim, Do Sik
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Institute of Metals and Materials 01.11.2017; Springer Nature B.V; 대한금속·재료학회
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Cold pressing; Deformation; Dendritic structure; Deposition; Die pressing; Die steels; Dies; Electron microscopy; Engineering Thermodynamics; Fracture toughness; Hard surfacing; Heat and Mass Transfer; Heating; High speed tool steels; Machines; Magnetic Materials; Magnetism; Manufacturing; Materials Science; Mechanical properties; Metallic Materials; Metallurgy; Microstructure; Notch toughness; Processes; Research Paper; Solid Mechanics; Temperature; Temperature gradients; Tool steels; 재료공학; metals; laser-assisted deposition; scanning electron microscopy (SEM); mechanical properties
• ISSN: 1598-9623; 2005-4149
• DOI: 10.1007/s12540-017-7049-2

This study examined the effects of substrate preheating for the hardfacing of cold-press dies using the high-speed tool steel AISI M4. The preheating of the substrate is a widely used technique for reducing the degree of thermal deformation and preventing crack formation. We investigated the changes in the metallurgical and mechanical properties of the high-speed tool steel M4 deposited on an AISI D2 substrate with changes in the substrate preheating temperature. Five preheating temperatures (100-500 °C; interval of 100 °C) were selected, and the changes in the temperature of the substrate during deposition were observed. As the preheating temperature of the substrate was increased, the temperature gradient between the melting layer and the substrate decreased; this prevented the formation of internal cracks, owing to thermal stress relief. Field-emission scanning electron microscopy showed that a dendritic structure was formed at the interface between the deposited layer and the substrate while a cellular microstructure was formed in the deposited layer. As the preheating temperature was increased, the sizes of the cells and precipitated carbides also increased. Furthermore, the hardness increased slightly while the strength and toughness decreased. Moreover, the tensile and impact properties deteriorated rapidly at excessively high preheating temperatures (greater than 500 °C). The results of this study can be used as preheating criteria for achieving the desired mechanical properties during the hardfacing of dies and molds.