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1 29«6y ( ) w œwz 257 š³ š p e ³ w y Á Á½ y *Á **Á y w» w w e lg Effects of Si and Mo on the Temperature-Dependent Properties of High Si High Mo Ductile Cast Irons Kyeong-Hwan Choe, Sang-Mok Lee, Myung-Ho Kim*, Sang-Weon Yun**, and Kyong-Whoan Lee Korea Institute of Industrial Technology, Incheon, , Korea *Inha University, Incheon, , Korea **Castec Korea Co., Ltd, Busan, , Korea Abstract The effects of silicon and molybdenum on the temperature-dependent properties of high silicon and high molybdenum ductile cast iron were investigated. Microstructure was composed of ferrite, cell boundary complex carbide, carbide precipitated in the grain and graphite. The number and size of carbide decreased with the increase of silicon content and increased with the increase of molybdenum content, however, the size of cell boundary carbide increased above 0.81wt%Mo. The room temperature tensile strength increased with the increase of silicon and molybdenum contents. That did not increase with the latter with more than 0.8wt%. Meanwhile the high temperature tensile strength showed the similar trend to that of room temperature one, that of the specimen with 0.55wt%Mo was the highest. The A 1 transformation temperature increased with the silicon and molybdenum contents, and showed similar tendency with the variation of strength. It was discussed due to the solubility limit of Molybdenum in ferrite, of which value was assumed to be in the vicinity of 0.81wt%Mo. The weight after oxidation at 1,173K showed the result caused by the difference in solubility of molybdenum in the matrix. That and the thickness change after oxidation did not show any consistent trend with the silicon and molybdenum contents. Key words: Si-Mo ductile iron, Si and Mo addition, High temperature strength, Oxidation behavior, Thermal expansion. (Received November 10, 2009 ; Accepted December 1, 2009) 1. š³ š ³ w ƒƒ 4.0~6.0, š 0.4~2.0wt% r p ü w. œwz(society of Automotive Engineers) ³ w» ü ³ [1] Si w 4.0wt% ³ wš (Table 1 ). ü ƒ š lù p Ni w ƒ ƒ š š³ š ü w, w ü w w š. w ³ w 4.9wt% ¾ š, ü ù š ü y w j ù ù ƒw w š y [2-4]. š³ š w w tankchoe@kitech.re.kr ü j w e ³ w w w ƒ v w. ü ƒ e ³ w w ƒ [5-11], 1970 z z, 80 z l, 2000 CV w [12]ƒ. ü ü š w š p, ü y w e q p [13].» r p ü t š, w A 1 k w A 1 k e Áq w» ü k ƒ w w. w, t w q y ww v w. š³ š w ü ³ w w ƒƒ p w ƒ w w e ƒ w sƒw.

2 258 š³ š p e ³ w - y et al. Table 1. Chemical compositions of commercial heat resistant cast irons of SAE J2515[4]. Grade C (wt%) Si (wt%) Mo (wt%) Grade A 0.8~1.0 Grade B ~0.7 Grade C 0.4~ x 2.1 r x š š³ š ³ ³ (4.0~4.4wt%) š³ (4.7~ 4.9wt%) wš, w 0.6, 0.8, 1.0wt% y g ƒ x r w., r g, r ƒk 50 kg š q w, ww e k w Y w. 4%Ba-Fe-Si w y w. r yw Table 2 ùkü. r 1203K 3 w 873K¾ þwš w œþw w. w r x» w 2,000 ¾ w z 0.1 µm ù w v w 5% ù k 10 k w z Ÿwx (EPIPHOT 200, Nikon) w w. 2.2» sƒ» p sƒw» w 250 kn x» w x, š x» w v x w. ƒ r Y z l, KS B 0801 ³ 10y r ASTM A 327M-91 ³ w e r» ƒœw w. x KS B 0802 w j x 2 mm/min w. š extensometerƒ š x» (AUTOGRAPH AG-1, SHIMADZU, 250 kn) w 1,083K 15 w xr ³ w w z 0.5 mm j x w. 2.3 q p sƒ q p sƒ w r 6 mm, š ¼ 25 mm mx w š ASTM E831 ³ w dilatometer w xw. x w DIL 402PC (v NETZSCH) š N 2»» w 5K/ min 1,103K¾ j ƒ q d wš q š p w k d w. q p» š w» w ƒ r X- z e (XRD, D8-02/ BRUKER AXS GMBH) w X z ql š Cohen w» w. 2.4 š y p š yp sƒw» w r Y z ƒ, ƒ ƒƒ 10 mm (t 600 mm 2 ) j» w š t 2,000 ¾ w w. r wš 2L/min j 1,023 1,173K 50 w y d wš y w. 5 K/min w š 50 z þ k p sƒw. 3. š 3.1 Fig. 1 sƒ w ƒ r. š³ š r p» ky. ³ w r w. Fig. 2 ³ w ƒƒ wt% r k w z. k w µm j» ky r p w w (Fig. 2(a)), w y w (Fig. 2(b)). š z ky 1µm ü ky y. Fig. 3 e mw k y x y w a t ky, š b t ky. B. Black, w ky Fe, Mo Table 2. Chemical compositions of test specimens. Nominal group Low Si High Si Chemical compositions (wt%) Specimen C Si Mn Mo S P Fe Heat Heat Heat Heat bal. Heat Heat

3 Vol. 29, No. 6, 2009 Journal of the Korean FoundrymenÌs Society 259 Fig. 1. Representative annealed microstructures of nominal groups. Fig. 2. Comparison of as-cast and annealed microstructures in the case of 4.2wt% Si and 0.8wt%Mo: a) as-cast and b) annealed microstructure. Fig. 3. The morphologies of eutectic and precipitate carbide. Si w ky œ š x, ky œ k z x ky š šwš [14]. w ƒw œ ky j» ky ƒw, š³ ky j» ùkû. r p ü ³ w r p» y jš w yv x w š p w j.[15] Fig. 4 Thermo-Calc vp w ³ w Fe-C k œ y. ³ w ƒw, œ k d wš Si. w š ³ ƒ» k ww» [16] w w. œ š ƒwš œ j» w œ ky j» w., w ƒw, œ ƒw. œ š lù p / w š k. œ j w ù w. w ƒw œ š x ky j» ƒw. lù p» š þƒ lù p š ƒ w» š ƒ š k ww ky x w. Fig. 5 ³ w ƒƒ wt% Fe-Mo k. œ 2.0wt% š þƒ wì w 1,173K 1.0wt%, z ü w š

4 260 š³ š p e ³ w - y et al. Fig. 4. Variation of eutectic point in Fe-C phase diagram calculated by the Thermo-Calc software: (a) 4.2wt%Si & 0.55wt%Mo, (b) 4.8wt%Si & 0.55wt%Mo, (c) 4.2wt%Si & 1.05wt%Mo and (d) 4.8wt%Si & 1.05wt%Mo. Fig. 5. Fe-Mo phase diagram calculated by the Thermo-Calc software: (a) 3.0wt%C & 4.2wt%Si and (b) 3.0wt%C and 4.8wt%Si. Fig. 6. Various ambient temperature mechanical properties with the variation of Si and Mo contents; (a) tensile strength, (b) elongation, and (c) impact energy. 0.1wt%. þƒ ky k ƒ y» w» j»ƒ w. w, 1,203K w, w ky» š š w k y w w Fig. 2 ù kü. 3.2» Fig. 6» e ³ w w š. ³ w ƒw ƒwš w. w 0.55wt% ³ w ƒw w, j w. w 0.8wt%¾ w ƒw ƒ

5 29«6y ( ) w œwz 261 Fig. 7. Variation of high temperature tensile strength with Si and Mo contents at 1,083K. ƒw, w. w w ³ w w ùkû. w ƒw w, š³ w ƒ wì w w ³ 0.8wt%¾ j wš s j. ³ w š (1,083K) d Fig. 7. š³ ƒ 0.8wt%¾ ƒw, w, ³ w 0.55wt% ƒ š, w 0.8wt% 1.05wt% š³ û ùkü. ³ r p ü š y z g ƒ j [17]. Bjrkegren x mw ³ w ƒ [18]. r p» w š y z ƒ, 0.5wt% ƒ, ky x [19]. š³ š š y z ky w y z w w š q., y r, Fig. 8. Variation of onset temperature of A 1 transformation with Si and Mo contents. w û j ƒw ƒ 0.81wt% ƒs w. w ƒ ky ƒ j ky j» ƒ j» y z ƒ j w». š w e» p (y, k, d w ), x,,, j» [20]. š³ š» p r p» w ³ š w. A 1 k d 0.81wt% w ƒw w 0.81wt%¾» š ƒw w š y z ùkü, sy š y z» w š. š³ r š, 0.81wt% w w š yz w w ƒ, / ky w y z w ƒ š q. w, ³ r w ƒ û 0.55wt% ƒ ùkü. š w j» j» w r, j, j»ƒ Fig. 9. Variation of thermal expansion coefficient with Si and Mo contents for various temperature range; (a) 373~573K, (b) 573~773K, and (c) 773~973K.

6 262 š³ š p e ³ w - y et al. š ƒw. w 0.55wt% ³ r r w j»ƒ j r. š w ƒw ky j»ƒ ƒw. w w w š ƒ, ³ r š y w ¾ ƒ v w. 3.3 q p Fig. 8 ³ w A 1 k y š. A 1 k w ƒ BCC (r p) FCC ( lù p) ë w, ƒƒ k ƒ k w. ³ š³ w ƒw A 1 k ƒ w ƒ 0.8wt% w. w ³ w ƒw, A 1 k w. Fig. 9 ƒƒ r w q w. q w ƒw 0.8wt% ƒ, w, ³ ƒw š, š ³ w w. w w w ùkû. r, 373 ~ ~ , 573 ~ 773 Fig. 10. Variation of lattice parameter of ferrite matrix varying with Si and Mo contents ~ , š 773 ~ 973K 15.0 ~ ƒ w q ƒ ƒw ùkü. A 1 k q d w 0.81wt% š ƒ, w r p» w š w Fig. 11. Representative cross sections showing the oxidized layers after the high temperature oxidation test; (a) 1,023 and (b) 1,173K.

7 Vol. 29, No. 6, 2009 Journal of the Korean FoundrymenÌs Society 263 Fig. 12. Weight change of specimens after high temperature oxidation test; (a) 1,023 and (b) 1,173K. Fig. 13. Thickness change of specimens after high temperature oxidation test; (a) 1,023 and (b) 1,173K.., q 0.81wt% w w. 0.81wt% w w ƒ wì ky j» ƒ w. š³ š r p, Fe- Si-Mo wky w w. ky q (Mo 2 C α = ( )) r p. w q ƒ ƒw q wš, q ƒ j»ƒ ƒw q ƒw. w w XRD l r p» w ùkù (Fig. 10). 3.4 š y p Fig. 8 1,023 1,173K» 50 w z r w. r 2 yd x, w y d t, wù t üd x. 1,023 1,173K yd s ƒw š, 1023K yd ƒ ùkû. SEM-EDX w yd Fe Si s w, t yd Fe ƒ ùkùš, üd yd Si ƒ w ùkù. Fig ƒƒ y x z y Ì y ³ w w ùkü. y w y (š³ K) w w š, w ƒw wš 0.85wt% ƒ. Ì y ³ w w w.» š w 0.81wt% Fig. 9 y w y d y w. 1,173K y w 0.81wt% yƒ, y» w w y x» w»» ƒ ƒ». 4. š³ š e ³ w w w. 1) š³ š r p, w ky, ü ky. 2) ³ w ƒw ky j» wš w ƒw ƒw, 0.81wt% w ky j»ƒ ƒw. 3) ³ w w

8 264 š³ š p e ³ w - y et al. ƒw ƒw, 0.81wt% w ƒw. š š³ w w, ³ 0.55wt% w ƒ ùkü. 4) A 1 k w ³ w w ƒw w, 0.81wt% w s w. 5) 1,173K y» š» w ùkü. 1,023K y Ì y ³ w w w. š x [1] "High temperature materials for exhaust manifold", SAE Standard J 2515, SAE (1999). [3] H. Tsuda, N. Suzuki, S. Ishuzuka and T. Kurikuma: J. JFS, "Effect of Molybdenum and Vanadium on properties at elevated temperature of high silicon spheroidal graphite cast iron", 76(10) (2004) [4] N. Suzuki, S. Ishizuka, Z. Z. Zhang and N. Akita: J. JSAE, "Development of Vanadium-added heat resistant cast iron for exhaust manifold", 28 (2003) [5] H. I. Park and H. Y. Jeong: J. Kor. Foundrymen's Soc., "High temperature properties of vanadium and molybdenum added high silicon ductile iron", 27(5) (2007) [6] D. L. Sponseller, W. G. Scholz and D. F. Rundle: AFS Trans., "Development of Low-Alloy Ductile Irons for Service at F", 76 (1968) [7] J. Y. Kim and H. Y. Ra: J. Kor. Foundrymen's Soc., "The Effects of Si and Mo on the Structures and Mechanical Properties in High Si Spheroidal Graphite Cast Iron", 10(3) (1990) [8] H. J. Bang: J. Kor. Foundrymen's Soc., "Ductile Cast Irons for Elevated Temperature Service", 12(2) (1992) [9] S. W. Kim, K. D. Woo, S. W. Han, J. K. Kim and D. Y. Kim: J. Kor. Foundrymen's Soc., "The study on high Si and Mo DCI with high temperature oxidation resistance property", 18(2) (1998) [10] S. W. Kim, K. D. Woo, S. W. Han and J. K. Kim: Proc. of KSAE, "A development of high Si DCI with heat resistance and high temperature oxidation resistance properties for automobile parts", (1996) [11] S. H. Park, J. M. Kim, H. J. Kim, S. J. Ko, H. S. Park and J. D. Lim: "Development of a heat resistant cast iron alloy for engine exhaust manifolds", SAE (2005). [12] D. Li and R. Logan: "High Silicon Cast Iron with Mixed Graphite (MG) Shape for Elevated Temperature Applications", SAE (2007). [13] D. Li, R. Perrin, G. Burger, D. McFarlan, B. Black, R. Logan and R. Williams: "Solidification Behavior, Microstructure, Mechanical Properties, Hot Oxidation and Thermal Fatigue Resistance of High Silicon SiMo Nodular Cast Irons", SAE (2004). [14] B. Black, G. Burger, R. Logan, R. Perrin and R. Gundlach: "Microstructure and dimensional stability in Si-Mo ductile irons for elevated temperature applications", SAE (2002). [15] J. D. Mullins: "Ductile Iron Data for Design Engineers", Rio Tinto Iron & Titanium Inc., (1990) [16] K. Ogi, A. Sawamoto and J. Hiwatashi: "Transformation Process and Behavior of Carbon in Austempering Heat Treatment of Spheroidal Graphite Cast Iron", 60(4), (1988) [17] F. B. Pickering and T. Gladmann: ISI Special Report No. 81, (1963), 10. [18] L. -E. Björkegren, H. Hamberg and B. Johannesson: AFS Trans. "Mechanical Properties and Machinability of Si- Solution-Hardened Ferritic Ductile Iron", 104 (1997) [19] American Foundrymen's Society: "Ductile Iron Handbook" (1993), 88. [20] K. Maruyama and H. Nakashima: "Materials Science of High Temperature Strength" (1997), 189.