Hot-Dip Aluminizing of Flow-formed AISI 4140 Steel A. Karakaş1,2,∗, M. Baydoğan2 1 Repkon Machine and Tool Industry, Istanbul 34980, Türkiye 2 Department of Metallurgical and Materials Engineering, Istanbul Technical University, Istanbul 34469, Türkiye ∗ aptullah.karakas@repkon.com.tr Keywords: Hot-dip aluminizing, Flow forming, Microstructure Flow forming is a cold deformation technique for the manufacturing of axisymmetric components. During the flow forming, a rotating initial tube (preform) is pushed by rollers through the thickness direction of the tube. After the process, the tube elongates along the flow forming direction with a corresponding reduction in its thickness. Cold plastic deformations recognizably cause increasing lattice imperfections such as point defects and dislocations in the structure, which could then have an effect on diffusion characteristics of the material [1-2]. In order to explore such an effect of flow forming, a flow formed AISI 4140 steel and an annealed 4140 steel were subjected to the HDA process in a molten Al7020 bath at 750◦ C for 4 minutes, and a subsequent diffusion annealing was performed at 800◦C, and their coating characteristics such as coating thickness and hardness were compared. The results indicated that the coating thickness of the flow formed samples was higher (80 µm) than that of the annealed sample (µm) after the HDA process. Diffusion annealing increased the coating thickness of both samples five times, reaching 400 µm and 250 µmfor the flow formed and the annealed samples, respectively. Comparing the measured thickness of the coatings revealed that flow forming accelerates diffusion during the HDA process, probably due to the defect structure induced by the flow forming. On the other hand, the coating hardness was in between 1000-1100 HV for both samples, implying that the initial condition of the sample does not have a remarkable effect on hardness after the HDA process. References [1] Karakaş, A., Fenercioğlu, T.O., Yalçinkaya, T. (2021), The influence of flow forming on the precipitation characteristics of Al2024 alloys, Materials Letters, Vol. 299, 130066. [2] Yürektürk, Y. and Baydoğan, M. (2018), Characterization of ferritic ductile iron subjected to successive aluminizing and austempering, Surface and Coatings Technology, Vol. 347, Pages 142-149. 29
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