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1 [ ] w wz DOI: /MRSK Kor. J. Mater. Res. Vol. 19, No. 12 (2009) y INCONEL 718w Gas Tungsten Arc Welding» p sƒ ½»y Á *Á *Á y** ( ) d lj p wœq, *w wœ» q **( ) d lj p t Mechanical Properties Evaluation of Gas Tungsten Arc Welding for INCONEL 718 alloy apply to Cryogenic Condition Kihong Kim, Insang Moon*, Ilyoon Moon* and Byungho Rhee** Vitzrotech Co., Ltd, Kyunggi-Do, , Korea *Korea Aerospace Research Institute, Dae-jeon, , Korea **President of Vitzrotech Co., Ltd, Kyunggi-Do, , Korea ( : : k) Abstracts Inconel 718 alloy has excellent mechanical properties at room temperature, high temperature and cryogenic conditions. UTS of base metal is about 900MPa at room temperature; this is increased up to 1300MPa after heat treatment & aging-hardening. Mechanical properties of Inconel 718 Alloy were similar to those shown in the the results for tensile test; mechanical properties of Inconel 718 alloy's GTAW were similar to those of base metal's properties at room temperature. Mechanical properties at cryogenic conditions were better than those at room temperature. Heat-treated Inconel 718, non- filler metal GTAW on Inconel 718 and GTAW used filler metal on Inconel 718's UTS was 1400MPa at cryogenic condition. As a result, the excellent mechanical properties of Inconel 718 alloy under cryogenic conditions was proved through tensile tests under cryogenic conditions. In addition, weldability of Inconel 718 alloy under cryogenic conditions was superior to that of its base-metal. In this case, UTS of hybrid joint (IS-G) at -100 o C was 900MPa. Consequently, UTS of Inconel 718 alloy is estimated to increase from -100 o C to a specific temperature below -100 o C. Therefore, Inconel 718 alloy is considered a pertinent material for the production of Lox Pipe under cryogenic conditions. Key words INCONEL 718 alloy, cryogenic tensile test, rocket engine, of lox pipe, high strength alloy, gas tungsten arc welding. 1. l rv w f š y ƒ» œ. p y d š k œ,, y ww y w w., f y š k ü y w w. Ni» ü w wù INCONEL 718 ü,, v j v p w. w, š ¾» p w Rocket Motor Casing ù Corresponding author khkim@vitzrotech.com (K. Kim), -253 o C 650 o C¾ š., w öe w w w yw, y z» ƒ wœ,, ywœ ƒ w. 1,2), y w INCONEL 718» p sƒw, y k ³ wš w. 2. x 2.1 x 2mm Ì INCONEL 718 w, yw» p Table 1 Table 692

2 y INCONEL 718w Gas Tungsten Arc Welding» p sƒ 693 Table 1. Chemical composion of INCONEL 718 Alloy.(wt%) C Mn Fe Cr Al Ti Mo Nb Ni»k IN bal ùkü. INCONEL 718 GTAW(Gas Tungsten Arc Welding) w, Shield gas š Ar gas w š, 125 ma, 30 cm/min w. z H 2» Solution Treatment 1060 o CÁ1hour, Aging 720 o CÁ8hour o CÁ8hour z ¾ Air coolingw. 3) (Fig. 1) x (-50 o C, -100 o C) y 5ƒ w w, x Table š 3.1» p INCONEL 718 x Mill Sheet ùkù MPa w ùkü. w y z y z Mill Sheet ùkù 1390MPa û 1290MPa d, x 45% w ù kü.(fig. 2~4) Fig. 4 ƒ x ùkü, z x w y w. Fig. 2. Tensile Strength (UTS) of INCONEL 718 Alloy. Table 2. Mechanical Properties of INCONEL 718. Y.S (MPa) T.S (MPa) E (%) HRB IN S-A *S-A : Solution Treatment + Aged Fig. 3. Yield Strength of INCONEL 718 Alloy. Fig. 1. Heat treatment of INCONEL 718 Alloy. 3) Table 3. Tensile Testing Coupon Condition of INCONEL 718 Sample Name I7-A I7-S I7-G I7-F IS-G Testing Condition INCONEL 718 As-received INCONEL 718 Solution Treatment + Aged INCONEL 718 GTAW-autogenous welding INCONEL 718 GTAW-used of Filler Metal INCONEL STS 316L GTAW-autogenous welding Fig. 4. Elongation of INCONEL 718 Alloy.

3 694 ½»yÁ Á Á y Fig. 5. Tensile Strength of INCONEL 718 Alloy apply to Cryogenic conditions. (a) -50 o C and (b)-100 o C. Fig. 6. Tensile Strength of INCONEL 718 Alloy to Compare Room Temperature wih Cryogenic Conditions. z y w x, z w w, (I7-A) w ƒ 440MPa w, z(i7-s) 200MPa w y w.(fig. 2~3) INCONEL 718 w yw x w, (I7-G) (I7-S) 1310 MPa ùkü š, r q w., ERNiFeCr-2 w(i7-f) r 1220MPa ùkü. INCONEL 718w STS316Lw r STS316L q w. STS316L w ƒ 290MPa, 560MPa x w, w 200MPa w ù, STS316L w ùkü. 3.2» p 1000 INCONEL 718w -50 C o MPa ùkü, 1300MPa ùkü. š -100 C o Fig. 7. Microstructure of INCONEL 718 Alloy. (a) Base Metal(I7-A) and (b)heat Treated(I7-S). r ƒ ƒƒ 1100MPa, 1400MPa ùkü, ƒ w INCONEL 718w ƒw. y INCONEL 718w -50 o C, -100 C yw w o ùkü.

4 y INCONEL 718w Gas Tungsten Arc Welding» p sƒ 695 Fig. 8. EDS analysis of Precipitation phase. (a) Precipitation phase of SEM, (b) Spectrum analysis, (c) Linescaning profile of Ni and (d) Linescaning profile of Nb. -50 o C w ƒ w 1340MPa ùk ü, -100 C o 1400MPa š ùk ü. š, w r w 1400MPa š ùkü, w., r x x k y w š, š p w. INCONEL 718w STS 316Lw w -100 C 900MPa ùkü o 560MPa w j ƒw yw p ùkü. š INCONEL 718w w ƒ w w STS316L ƒ y w, w ww. INCONEL 718w x x w, Fig. 5 ƒ ƒw y w, I7-F r wš -50 C o -100 Cy ƒ j o ƒw. 3.3 w INCONEL 718w z y γ Ni[Al,Ti]) γ" Ni 3 Nb w š z š š. w 1,2) Ti, Cr, Mo wì MC, M 23 C 6, M 6 C xk ky x w yz š š. x w y 4) y w» w SEM EDS w. INCONEL 718w 1060 o C y z 2 z y w w, z s ƒ j w. Nb w NbC ky, w ƒ ƒw NbC ky s ƒ ƒw q., Fig. 8 EDS Ni 76.6 wt%, Nb 20.3 wt%, Ti 2.4 wt%, Al 0.7 wt% w y. Fig. 9 INCONEL 718w STS316L w Fusion Line w Line Scaningw w INCONEL 718 w ky. ƒ peak r, M 23 C 6

5 696 ½»yÁ Á Á y Fig. 9. EDS analysis of IS-G. (a)linescaning profile of C, (b)linescaning profile of Fe, (c)linescaning profile of Cr and (d)linescaning profile of Mo. Fig. 10. Fracture surface of INCONEL 718 Alloy. (a) Base Metal(I7-A) and (b) Heat Treated(I7-S).

6 y INCONEL 718w Gas Tungsten Arc Welding» p sƒ 697 Fig. 11. Picture of Welded INCONEL 718 Alloy. a) Fracture of weld zone (I7-G) and b) Fracture of base metal (I7-F). Fig. 12. Fracture surface of Welded INCONEL 718 Alloy. a)fracture of cleavage & dimple and b) Fracture of dimple in cleavage. xk Cr Feky q, M 6 Cxk Mo ky d peakƒ. STS316L w Cr Fe w q. 3.4 q ƒ r x z q SEM w. INCONEL 718w r r q w, Fig. 10 q q xk ùkü. w r q dimple w x, w. INCONEL 718w r I7-G q w, r q w.(fig. 11) š w I7-F r q w. q w I7-G r q Fig. 12a) q xkƒ w x. š, Fig. 12b) q 2000 y w w dimple., ƒ w», q w, ƒ w. 4. y INCONEL 718 w, w r x SEM EDS mw» p sƒw. 1) y INCONEL 718w ƒ w ƒ ƒw, -100 o C š ùkü. 2)INCONEL 718w» p -100 o C w ¾ ƒ ƒw. 3)INCONEL 718w STS 316L w STS 316L w ùkü yw x w q. 4)INCONEL 718w y NbC ky, z w ky ƒw. 5)I7-G q q xk ùkü

7 698 ½»yÁ Á Á y, dimple., y ü yw, x w, y š y» p yw INCONEL 718w ww q. wz INCONEL 718w w, yw wš, w k y» p ƒw w w. š x 1. J. H. Choi, K. R. Lee, C. Y. Jo and I. B. Kim, J. Kor. Soc. Heat Treat., 5(2), 94 (in Korean) (1992). 2. J. D. Kim, T. G. Han, J. Y. Kang, in proceeding of the Korean Welding and Joining Society, (SHI, Kyongbuk, Korea, Nov. 2005, in Korean), p The Korean Welding and Joining Society, Handbook of Welding and Joining (in Korean), p. 313 (1998). 4. W. F. Smith, Structure and Properties of Engineering Alloys (trans. by B. H. Han, ed. Intervision, in Korean), 2 nd ed., p.505, Intervision, Korea (2003).