49 Õ 5 Ú Vol.49 No.5 2013 5 Ç 576 582 ACTA METALLURGICA SINICA May 2013 pp.576 582 X100 É ¾ ÅÌ Ô «1,2) ß 1,2) Đ Þ 3) Ü 3) 1) Ð ÊË, 721008 2) Ï Ã, 721008 3) Ü µ Ü ÊËÜÃ, 710065 ºº» Ù± (CTOD) À ± X100 Ô Ô Û Ã () Î ³ º, ºÃº SEM Û TEM ± CTOD «Ó µë Î ³. Ä Ì, ± X100 Ô º Ã. Ϋ, ᧙ δ 0.2 Û δ 0.2BL ÖÉ Ø Ã Ñ Ô Í, «º ¼ Ã Ñ Ô, ÞØ «, Ü º Ö. «Ó Í (GB) Û ± Ñ (QF) Í Ñ (BF), Í M A þ ¾ Í Ñ Ç ; Ô «Ó Ñ (AF), M A Ü «,» Ì ; Ã Ó Í ÛÕ Í Ñ, M A ɼ ¾ ÇÛ Ç. ØÎÑ» M A ËĐßÔ Û Ã º «Æ Ñ, µë ¾ ÃÔ Ñ «º. ½ X100, Ô, º, º» Ù± (CTOD) Ñ Ã TG115.5 ºÎÈ A ¹ 0412 1961(2013)05 0576 07 FRACTURE TOUGHNESS OF WELDED JOINTS OF X100 HIGH STRENGTH PIPELINE STEEL BI Zongyue 1,2), YANG Jun 1,2), NIU Jing 3), ZHANG Jianxun 3) 1) National Engineering Technology Research Center for Petroleum and Natural Gas Tubular Goods, Baoji 721008 2) Steel Pipe Research Institute of Baoji Petroleum Steel Pipe Co., Ltd., Baoji 721008 3) School of Materials Science and Engineering, Xi an Jiao Tong University, Xi an 710065 Correspondent: BI Zongyue, professor, Tel: (0917)3398475, E-mail: bsgbzy@cnpc.com.cn Supported by National Science & Technology Pillar Program (No.2011BAE35B01) Manuscript received 2012 11 27, in revised form 2013 02 27 ABSTRACT Fracture toughness of base metal, weld seam and heat affected zone () in X100 high strength pipeline steel welded joints was investigated by three point crack tip opening displacement (CTOD) test. Microstructure and inclusion near fracture zones were observed by means of SEM and TEM. The results indicated that fracture toughness of X100 high strength pipeline steel welded joints was greatly influenced by test temperature. At the same temperature, the numerical values of apparent crack initiation δ, conditional crack initiation δ 0.2 and δ 0.2BL of base metal are higher than that of weld seam and, and low temperature fracture toughness of base metal is better than those of weld seam and. With temperature decreasing, the fracture toughness of base metal, weld seam and decreased. The microstructure of near fracture zones of base metal specimen was composed of granular bainite (GB), a small quasi polygonal ferrite (QF) and lath bainite ferrite (BF), and the fine and equally dispersed M A structure distributed on the grain boundary. The microstructure of near fracture zones of weld seam specimen was composed of acicular ferrite (AF), and the form of M A constituents shows diversity, sharp angled clearly. The microstructure * Đ Å± Æ 2011BAE35B01 Á²Û : 2012 11 27, ÓÁ²Û : 2013 02 27 ± É : Æ,, 1962, Ë, ¼É DOI: 10.3724/SP.J.1037.2012.00703
5 Ú Å : X100 Ó ¹ 577 of near fracture zones of coarse grain was composed of GB and parallel LBF, and the square, wedged and bar M A constituents distributed on the interior of grain, grain boundary and lath boundary. The poor fracture toughness of weld seam and specimen results from large size and cusp type M A structure. While the higher distribution of inclusion in weld seam makes fracture toughness worse. KEY WORDS X100 pipeline steel, welded joint, fracture toughness, crack tip opening displacement (CTOD) Ù ÁÕ«½ Â, ÂÓ À Đ Ð È, Đ Ð Ç À À Ù Ù Ù ±½Ç [1 3]. ĐÀ Î ÃÄ Ê Ø ÅÆ». Ð ² [4,5], Á ĐÀ Å È Ä 7%. À Ù ± ½ ²» ÐĐ ÉÀ «. «Ý½ßÒ À µù» Ð [6 8] Ø Õ ÀÐ, ² ÆÆ ««Ò Ø Þ Ù³ ÜÞ H 2 S [9 11]. лÜÙ».»ÅÀ¾»¹»Ü«2 ÅÁ È.»¹¼ Ú² δ(ctod)»» Õл ÜÌÍ ², ²»Ü»»¹«Ðصܻ Ð [12 15], CTOD Á º ÕÀÀ» Ð. [16] Í,»¹½ «È δ < δ c (δ c»¹¼ Ú² È, Å Á ). ¼ ÏÚ X100 ̲, X100 Õ Õ» Ð, ÕÀµÄ Ð. ̲ X100 ÕÀ À Õ Ü µäæ () ²È, Å Ü ², ÛÏÞ Æ ²» Ð ½½ µ ³ ² Õ Ü» Ð µä, 쵆 µå CTOD Á» Ð, Ìͳ»ĐÎ ß. 1 Í Á» X100 Ù Õ Õ 1219 mm, 15.3 mm, ÞÈ (б, %) : C, Si, Mn 1.95, P 0.011, S 2, Ni 0.39, Cr 0.28, Cu 0.21, Mo, Nb+V+Ti 0.094, Fe ±. Õ Ïµ À ÞÐ 1, Õ Ú» X100 À ÐÕ ÜÕ. ÏÕ Õ Õ Ü CTOD,» Ð BS7448 µ [17] ÈÚ Ò»¹ µ 3., B 12 mm, W 24 mm,  4W 96 mm, a λ¹Â, Ú ²Ð 1a Û È.» 0.08 mm Õ Mo ¹Ì, Ï¹Ì 9 mm »ÀÔÒ Â 3 mm» 1 X100 À Ö Å ßÑ ¼º½ Û³ (CTOD) Ó Table 1 Mechanical properties and size of base metal, weld seam and heat affected zone () crack tip opening displacement (CTOD) samples of X100 pipeline steel Sample, B, mm W, mm R p0.2, MPa R m, MPa A, % R p0.2 /R m 15 12 24 750 845 17 0.89 15 12 24 645 745 0.87 15 12 24 699 805 0.87 Note: test temperature, R p0.2 yield strength, R m tensile strength, A uniform elongation, B thickness, W width 1 ¼ «Û CTOD «º Á Ç Fig.1 Standard three point bending specimen (a) and length measurement of CTOD specimen (b) (a nominal crack length, δ crack tip opening displacement value)
578 Ê Û 49 Õ Ò»¹,» Ï Á Šż¹»¹. Ï Ò»¹ Í, Đà ƻ¹¼ Õг. ³ Û Å»¹Â ± a 0 Ï 0.45W 0.55W º. CTOD Á Ï CSS 88100 Ï, Á Ó S=96mm, Á µ : ϵ (15 ), 10 Ü 30, Å Í ³ F V»Ð Á Ð. F V 2a, ²³ ÙÍÙ ÕÐ Ú² V p «Æ 2a ÛÈ. Í, Ï Đ, Ý µ Ï Ó. 1b ÛÈ ÏÅ¾Ä 9 Å ±»¹Â, Ý Ó È 1%δ ²Ð, ± ½ 0.01 mm. Ʋ»¹Â : a 0 = 1 8 (a 01 +a 09 8 + a 0i ) (1) 2 i=2 Æ, a 0i (i=2, 3, 4,, 8) i Å Å»¹ Â. a = 1 8 (a 1 +a 9 2 + 8 a i ) (2) i=2 Æ, a i (i=2, 3, 4,, 8) i Å»¹» «Â. Æ, a Ö»»¹«±. a = a a 0 (3) ÈÐ ÙÍÙ F ݲ³ V p,» Ʋ Æ Force F O (a) v P A Parallel to OA v e Crack opening displacement V 2 F V Û ÂÇ «Ç Fig.2 Typical F V curve (a) and observation section (b) of near fracture zone (V p plastic component of notch opening displacement, V e theoretical elastic notch opening displacement) V F CTOD : FS δ = [ BW 3/2f(a 0 W )]2 (1 µ2 ) 2R P0.2 E + 0.4(W a 0)V p 0.4W +0.6a 0 +δ z (4) Æ, Possion µ=0.3; Ðϱ E=2.058 10 5 MPa; R p0.2 ; f(a 0 /W) Ý ±, Ð a 0 /W ϵ ÕÀ ; δ z Ú² ² ² Ø ÐÓ È Ó. Ð BS7448 µ, ÈÐ Ð Þ Ü³, Þ Æ ÛÈ: δ = m+l( a) x m, l 0 and 0 x 1 (5) Æ, m, l Ü x Û À. Æ, R m. È δ = 1.87( R m R p0.2 ) a (6)» S4300 É (SEM) Æ Ô,»» EDAX Genesis6.0 Ù (EDS) ² Ì È Ï, Ä» JEM 200CX (TEM) Æ Ô M A,   60 cm, ² 160kV. CTOD» 1/2» Â Õ ¹ ½Ç Ú, 2b ÛÈ, È SEM Ü TEM, SEM» Ü Ð,» 3%( ) ÉÖ Ü Ö + ÆÐ µ, TEM Þ 50 µm, Ï Ñ Æ Ð 10% À Ö +90% Ö ( ) µ Ï Ñ. 2 Í ÏÇ 2.1 Æ Â ÒÄË CTOD л¹» й Þ»¹«, Æ»¹«,»¹¹«± Æ»¹«, Æ R. 3 Ç X100 Ù Õ Õ Ï½ µ Þ Ü³ ³ ÖÆ., δ Ü δ 0.2 Ø»¹«± a= Ü 0.2 mm Û²³ CTOD, Ý Ò ³ µä; δ 0.2BL Ø Ì ³ ( 3 Blunting line ) a Ö Þ a=0.2 mm CTOD, Ý Ë ³ µä. CTOD È»¹«Í ½ Á»¼ Ú², Þ»¹»Ü«. 4 Ç Á µ ² CTOD δ, δ 0.2 Ü δ 0.2BL µä. Ü, µ ³ ² CTOD µä Æ. Õ CTOD δ, δ 0.2 Ü δ 0.2BL Ùµ Î, Õ» ÐÙµ, Í ³ Ê; Ï µ, CTOD Ù,
5 Ú Å : X100 Ó ¹ 579 CTOD, mm CTOD, mm CTOD, mm 0.50 0.45 0.40 0.35 (a) Blunting line Offset line =-30 o C =15 o C =-10 o C = 2.11 a = 0.13313+0.54086 a 0.90931 =231+0.65044 a 0.95853 =094+0.48713 a 0.59674 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a, mm 0.50 0.45 0.40 0.35 (b) Blunting line Offset line = -30 o C = 15 o C = -10 o C = 2.16 a = 39+0.35118 a 0.47268 = 0.01024+0.32977 a 0.34825 = 0.01451+0.35687 a 0.42961 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a, mm 0.50 0.45 (c) = 15 o C = -10 o C 0.40 0.35 Blunting line Offset line = -30 o C = 2.15 a = 0.01945+0.51211 a = 0.07878+0.36425 a 0.66714 = 469+0.41967 a 0.46169 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a, mm 3 Ô Ã Fig.3 Resistance curves of base metal (a), weld seam (b) and (c) ( a average stable crack extension, δ CTOD value, temperature) Ò, Õ Î,» н, ½ Õ. Ò, µ ³ Đ µä X100 Ù Õ Õ ÐÐ, Ùµ. 2.2 ÁÊÓ 2.2.1 Ö CTOD Ý Æ 5 Ç CTOD Æ Ô. ¾ 5 Ð, Á» X100 Ô Î (GB) ± µ² Ò (QF). Ý, Î Ò (BF) Æ, Ƚ, M A Ä BF Ⱦ. M A Ý ÏÒ ²»¹»Ü«ÆµÄ. [18 20] ±, Î Ä È¾ M A, ½ ²Þ²Ô» ³»¹,»Ä»¹«½Ç Ó, Á»¹«Â,»¹, ² Ð. Ì µ» н Õ Ü À±. 2.2.2 ÚÙ CTOD Ý Æ 6 Õ CTOD Æ Ô. ¾ 6 Ð, Õ Ô Ò (AF) ܵ Ý M A. 6a AF ʵ, Ï AF Ò¾ ²«Þ Ô, M A,, AF Ì Ú Ê¾ Â. ¾ 6b M A ݵ, µú ¼, Ä Ò ¾ È. ¼ M A ² Ð Ñ Æ [12,19]. ³ ²», ²ÔÊ ½ Šϼ ²ÈÜ È», ³,»Ù³ ³³Í ¹, È»Á, È»¹Á. ÌÕ µ» Ð À±. 2.2.3 Å CTOD Ý Æ 7 µäæ CTOD Æ Ô. Ʋ Ó ÞÆ Æ, ÝÕÀ µ (>1150 ) À, à Ac 3 Ö µ, ÅÎ Đ Â Ù, Æ, ÀÅ Ù µ. [21 23], Õ ÞÐ ºÆ Õ ÆÜ ÈÆ. ¾ 7a Ð, Æ Ô GB ÜÖ BF, ÀÅÎ È (PAGB), ½ Ö BF ÀÅÎ Âȵ ÅÜ. 7b Ü c, M A Ê µ Ý, ½ Ü BF È, È, ÏÒÄ 2 µm. Ù Ó ½ ¹, M A ¾Ð Å Ç Â ³, ÏÒ Ù, ¼, Ò ½ÇÐ. ÙÏÒ¼ M A ²Þ²Ô», ³,»¹Â ĐÎ. ² Ð Ù Ú. 2.3 CTOD ÙÎ ßÂ. Ô Ð, Ð Ø Õ Ü²Ì Ô ½ Å Ø, Ò Â ÞÈ ÀÅ Ô Ý, Õ Ì, Ý ÞÈ Ü Í ½. Õ Ð, ÏÕ ÞÈ ² ß ¹ ÞÌ Ò Ti Ü Mo Å, È ± Ì ² AF Ú [24,25].
580 Ê Û 49 Õ 0.18 0.16 (a) 0.26 0.24 (b), mm 0.14 0.2, mm 0.22 0.12 0.2BL, mm 0.36 0.33 0.27 (c) -30-20 -10 0 10 20, o C 0.2, mm 0.18 (d) -30-20 -10 0 10 20, o C = -30 o C = -10 o C = 15 o C 0.24 0.21-30 -20-10 0 10 20, o C 4 ± CTOD Ð Ö δ, δ 0.2 Û δ 0.2BL à Fig.4 Effects of test temperature on apparent crack initiation CTOD δ (a), conditional crack initiation CTOD δ 0.2 (b), and δ 0.2BL (δ resistance to crack extension expressed in terms of CTOD at a = mm crack extension including blunting, δ 0.2 resistance to crack extension expressed in terms of CTOD at a= 0.2 mm crack extension including blunting, δ 0.2BL resistance to crack extension expressed in terms of CTOD at a=0.2 mm crack extension offset to the blunting line) 5 CTOD «Ó Fig.5 SEM (a) and TEM (b) images of near fracture zone in the CTOD sample of base metal (GB granular bainite, QF quasi polygonal ferrite, BF bainite ferrite) 8 Õ Ü Ì EDS. 8a Ð, Ï 75 µm 75 µm Æ Ä 100 Å ± Ì, Ý µêå, ÙÎ ½, Õ 0.1µm 1 µm ½Å. Ì Ì È» ÂÙ ²Ð, ϳ ²», ² ³ ³, Ä»¹Ï È Í µ. Å Ì ¹»¹ ÀÜ, ÐÓ È»¹,». Å EDS Ð, Õ Ì Èµ Å Ü, Å Al 2 O 3, MgO, CaS Ü TiO 2 Å. Ì Õ Â, Ï Ù Æ, Ú 1 Å ± Ì, ÊÅ, ÏÒÄ 1 µm. ± Ì ÏÂ Í ÙÙ Î ³, Ù Ì ¾Ó ¹»¹ À
5v M : X100 F EBoFF "- j [ p: X X#!ofF 581 6 CTOD Fig.6 SEM (a) and TEM (b) images of near fracture zone in the CTOD sample of weld seam (AF acicular ferrite) [ 7 (Kh[ CTOD X X#!ofF Fig.7 SEM (a) and TEM (b, c) images of near fracture zone in the CTOD sample of coarse grain (PAGB prior austenite grain boundaries) [ p:wz6 X X# )S342 O445 8 CTOD Fig.8 SEM images showing morphology and distribution of inclusions in the near fracture zones of weld seam (a) and base metal CTOD specimens (b), and the EDS results of inclusion A in Fig.8a (c) and inclusion B in Fig.8b (d) (Arrows in Fig.8a, b represent inclusions, Wm mass fraction, WA atomic fraction)
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