29«6y (2009. 12) 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, 406-840, Korea *Inha University, Incheon, 402-751, Korea **Castec Korea Co., Ltd, Busan, 617-843, 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 E-mail : 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.
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 3.45 4.0 0.5~0.7 Grade C 0.4~0.6 2. 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 4.2 0.8wt% 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 1 3.40 4.15 0.20 0.55 0.01 0.04 Heat 2 3.35 4.37 0.20 0.81 0.01 0.03 Heat 3 3.30 4.35 0.20 1.05 0.01 0.03 Heat 4 3.40 4.73 0.21 0.52 0.01 0.04 bal. Heat 5 3.35 4.70 0.20 0.81 0.01 0.03 Heat 6 3.37 4.80 0.20 1.05 0.01 0.03
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 4.2 4.8wt% Fe-Mo k. œ 2.0wt% š þƒ wì w 1,173K 1.0wt%, z ü w š
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
29«6y (2009. 12) 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.
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 13.0 ~ 14.2 10-6, 573 ~ 773 Fig. 10. Variation of lattice parameter of ferrite matrix varying with Si and Mo contents. 14.2 ~ 15.0 10-6, š 773 ~ 973K 15.0 ~ 16.2 10-6 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.
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 =7.6 10-6 ( )) 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. 9 10 ƒƒ y x z y Ì y ³ w w ùkü. y w y (š³ + 1023K) 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
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