Manganese sulfide precipitation in low-carbon resulfurized free-machining steel
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REFERENCES 1. A. Inoue, Y. Kojima, T. Minemura, and T. Masumoto: Trans. Japan. Inst. Metals, 1979, vol. 20, p. 418. 2. A. Inoue, Y. Kojima, T. Minemura, and T. Masumoto: Metall. Trans. A, 1981, vol. 12A, p. 1245. 3. K.H. Han and W. K. Choo: Metall. Trans. A, 1983, vol. 14A, p. 973. 4. D.C. Joy and D. M. Maher: J. Microscopy, 1981, vol. 124, p. 37. 5. Introduction to Analytical Electron Microscopy, J.J. Hren, J.I. Goldstein, and D. C. Joy, eds., Plenum Press, New York, NY, 1979. 6. Metals Databook, ed. by Japan Inst. Metals, Maruzen, Tokyo, 1983, p. 24. 7. J. Friberg, L.E. Toendahl, and M. Hillert: Jernkont, Annal., 1969, vol. 153, p. 263. 8. A. Inoue, Y. Kojima, T. Minemura, and T. Masumoto: Trans. Iron, Steel Inst. Japan, 1981, vol. 2l, p. 656. 9. A. Inoue, H. Tomioka, and T. Masumoto: Metall. Trans. A, 1983, vol. 14A, p. 1367. 10. O. lzumi: Bulletin Japan Inst. Metals, 1981, vol. 20, p. 472.
Manganese Sulfide Precipitation in Low-Carbon Resulfurized Free-Machining Steel HIROSHI YAGUCHI It is well known that manganese sulfide precipitates from austenite in various types of steel, including AISI 1215 low-carbon resulfurized free-machining steel containing approximately 0.3 pct sulfur and 1 pct manganese. 1-7 In low-carbon resulfurized free-machining steels, most of the manganese sulfide is formed as inclusions nucleated in the liquid phase. 8 However, it has been shown that the presence of sulfides precipitated from austenite contribute significantly to sulfide inclusion size distribution curves observed in an optical image analysis system. 7 In addition, it has been suggested that they may be important in controlling hot workability. Unfortunately, there has not been any substantial investigation of sulfides precipitated from austenite in low-carbon resulfurized free-machining steels. This paper presents the behavior of manganese sulfide precipitates in laboratory-made, free-machining steel. A 136 kg laboratory heat was cast in a sand mold and air cooled to room temperature. The chemical analysis of the heat is shown in Table I. Several pieces of as-cast heat approximately 75 mm x 75 mm x 25 mm were soaked at 1423 K in an argon atmosphere without any mechanical work. Soaking times were 15 minutes and 4 hours. The samples were quenched in ice-water, and the microstructures at the center of the samples were observed where no decarburization was present. Figure 1 shows typical large manganese sulfide inclusions nucleated from the liquid phase in the as-cast structure. They are more or less globular and of Type I, according to Sims' classification. 8 SEM observation in a deeply etched as-cast sample reveals small particles of HIROSHI YAGUCHI is Staff Research Engineer with Inland Steel Research Laboratories, East Chicago, IN 46312. Manuscript submitted March 21, 1986. 2080--VOLUME 17A. NOVEMBER 1986
Chemical Analysis (Wt Pct)
C
Mn
P
S
Si
0.04
0.89
0.07
0.25
0.003
O total 0.058
0.5 p,m or less in diameter in addition to large inclusions, as shown in Figure 2(a). They are manganese sulfide particles becaus
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