Effect of Cu Addition on Precipitation and Growth Behavior of MnS in Silicon Steel Sheets
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UCTION
THE influences of MnS in steels on microstructure and mechanical behavior have been widely investigated.[1–3] MnS is known to have a deleterious effect on the formability of steels,[4] but this can be minimized or eliminated by controlling the morphology of MnS. MnS has been shown to be initiation sites of pitting corrosion.[5–7] In contrast, MnS can be utilized to control the microstructure of steels.[3,8] It is well known that HAZ toughness is improved by the intragranular ferrite produced as a result of MnS addition. The orientation of silicon steel can also be controlled by utilizing MnS. Thus, to control the material properties, it is important to be well-informed with regard to MnS precipitation behavior and changes in the morphology of MnS. The growth of MnS during deformation was investigated by Sun et al.[9] They found that the growth behavior of MnS precipitates follows a parabolic law and the law of Ostwald ripening at the early stage and later stage, respectively. The composition dependence of the morphology of MnS and its precipitation has been investigated as well. Oikawa et al.[10] investigated the
NOBUFUMI UESHIMA and KATSUNARI OIKAWA are with the Department of Metallurgy, Tohoku University, Sendai, Japan. Contact e-mail: [email protected] TAKUYA MAEDA is with the Department of Metallurgy, Tohoku University, and also with the Toyota Industries Corporation, Kariya, Japan. Manuscript submitted November 8, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
effect of additional elements on morphology of MnS in cast Fe-Mn-S steel and found that the morphology can be classified and explained on the basis of stable and metastable phase diagrams. The effect of S content on MnS precipitation has been investigated by Wakoh et al.[11] They found that MnS precipitates on the oxides when S content is higher than 100 ppm. While Mishra and Kumar[12] reported on the complex sulfide of copper precipitated in silicon steel containing approximately 0.02 pct copper, the exact chemical composition and atomic structure of the sulfide was not clarified. Ishiguro et al.[13] reported that Cu8S5 was precipitated in ultra-low carbon steel containing a residual amount of copper. The effect of Cu addition on MnS precipitation and growth behavior, however, has not yet been investigated. The purpose of this study is to elucidate the influence of Cu addition on the behavior of precipitation and growth of MnS in steels.
II.
EXPERIMENTAL METHODOLOGY
Firstly, Fe-2.88Si-0.1Mn-xCu (x = 0, 0.25) weighing about 300 g were melted in an induction melting furnace in an alumina crucible under an Ar atmosphere using high-purity iron, silicon, manganese, and copper. After melting, C and FeS were added, and the alloy was kept in the molten state for several minutes before the molten metal was poured into an SUS304 mold to obtain an ingot 20 mm in diameter and 90 mm in height. 5 mm from either edge of the cylindrical specimens were cut off, and the diameter was reduced to 18 mm by lathing
to remove the segregated region. The cylin
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