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Deposition Characteristics of High-Thermal-Conductivity Steel in the Direct Energy Deposition Process and its Hardness Properties at High Temperatures

Son Jong-Youn, Shin Gwang-Yong, Lee Ki-Yong, Yoon Hi-Seak, Shim Do-Sik

Archives of Metallurgy and Materials

2020

Vol. 65, iss. 4

1365--1369

Direct energy deposition (DED) is a three-dimensional (3D) deposition technique that uses metallic powder; it is a multi-bead, multi-layered deposition technique. This study investigates the dependence of the defects of the 3D deposition and the process parameters of the DED technique as well as deposition characteristics and the hardness properties of the deposited material. In this study, high-thermal-conductivity steel (HTCS-150) was deposited onto a JIS SKD61 substrate. In single bead deposition experiments, the height and width of the single bead became bigger with increasing the laser power. The powder feeding rate affected only the height, which increased as the powder feeding rate rose. The scanning speed inversely affected the height, unlike the powder feeding rate. The multi-layered deposition was characterized by pores, a lack of fusion, pores formed by evaporated gas, and pores formed by non-molten metal inside the deposited material. The porosity was quantitatively measured in cross-sectionsof the depositions, revealing that the lack of fusion tended to increase as the laser power decreased; however, the powder feeding rate and overlap width increased. The pores formed by evaporated gas and non-molten metal tended to increase with rising the laser power and powder feeding rate; however, the overlap width decreased. Finally, measurement of the hardness of the deposited material at 25°C, 300°C, and 600°C revealed that it had a higher hardness than the conventional annealed SKD61.

Identification of Lack of Fusion and Incomplete Penetration in Butt Weld Joint by Ultrasonic Phased Array Method and X-Ray Method

Koňár R., Mičian M., Boháčik M., Gucwa M.

Archives of Metallurgy and Materials

2019

Vol. 64, iss. 3

1117--1124

The main goal of the article is to identify artificially created defects like lack of fusion and incomplete penetration in buttweld joint using non-destructive volumetric methods. These defects are the most serious defects in welds of steel constructionsfrom the safety point of view. For identification, an ultrasonic phased array technique and a conventional X-ray using digital imaging were used. The theoretical part of the article describes the current state of the given issue and provides basic theoretical knowledge about ultrasonic and X-ray welding tests. In the experimental part, the procedure and results of testing butt weld joint are described by both non-destructive methods. The butt weld joint was made from steel S420MC. Each indication obtained by the ultrasonic and x-ray technique is supplemented by the macrostructure of the weld taken from the indication position. The results of the experimental work mentioned in the article point to the possibility and reliability of the identification of melting defects by selected nondestructive methods in terms of their character and orientation.