Minimization of banded structure in spring steels by the optimization of continuous casting machine parameters

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2019
Akpınar, Mehmet
Leaf springs are one of the important components of suspension systems especially of light and heavy commercial vehicles. The plate products produced by spring steel qualities such as 51CrV4, 55Cr3, and 52CrMoV4 are often preferred by the leaf spring manufacturers. In continuous casting steelmaking, the segregation of the alloying elements such as C, Mn, Si into inter-dendritic regions during solidification causes different chemical composition in these regions compared to others. Depending on the chemical composition of the steel, different phases may form in these regions which are elongated parallel to the rolling direction after hot rolling. This phenomenon is called microstructural banding. The martensite bands with high hardness in 52CrMoV4 steel negatively impact the cold sawing and drilling of materials. Consequently, production rate and tool life decrease during cutting and hole-making operations in the leaf spring manufacturing process. This thesis investigates the effects of secondary cooling intensity and electro-magnetic stirring on the distribution of alloying elements in billet, and the martensite band intensity in the hot rolled product. As a result, by the optimization of continuous casting parameters, the area ratio of martensite bands was reduced to about 15% from 40% without any additional operation and cost. Accordingly, the center hardness of the products was decreased by 15 HRC. Also, it was provided that the tool life of band saws used in cutting operation was increased by about 2.5 times and that of drilling heads used in the hole-making operation was doubled.
Citation Formats
M. Akpınar, “Minimization of banded structure in spring steels by the optimization of continuous casting machine parameters,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Metallurgical and Materials Engineering., Middle East Technical University, 2019.