Table 3 Mechanical properties of T91 welded joints Table 5 Mechanical properties of T91 welded joints at room temperature at increasing temperatures Tensile strength, ob, MPa Yield strength, oo.2, MPa Tensile Sample no·1ⅡAwg6 Test Test GB 5310 Data fr temperature,C results specification(a) Metre MPa 708.5 1234 693.5 450 712 741.0 525 728.0 T9I specification ≥585 20 200 056000 Table 4 Bending test results of T91 welded joints 300 376 Bending style Test condition Sample no Results 371 Face bending 358 D=3T,a=50° 123451234 Qualified 3050805 60 D, denotes the bending diameter; T, denotes the material thickness; a denotes the bending angle 5350 China(Ref 40), yield strengths(oo.2)of the joints were all qualified with increase of temperatures. Also, corresponding data of the T91 welded joints with same welding wire and process from Metrode Products Ltd. (Ref 41) were listed in the table and the figure. Meanwhile, the tensile strengths of our (a) This GB 5310 specification is just for T91 base material joints at these increasing temperatures were displayed as well tion Figure 3(a) displays the metallographic microstructure of the haz after welding, which consisted of sorbite with finer t data from metrod laths than that of t91 base material. Further detailedly, by means of TEM, it could be obviously observed that coarsened rod-like carbides of M2C, had ripened and precipitated on the 2 5004 grain boundaries in the HAZ, marked with arrows in Fig. 4(a) Especially in some triangular grain boundaries, the carbides were even larger, marked in Fig. 4(b). In contrast, the weld as also martensite just like the t91 base material but der laths of about 3 um, seen in Fig 3(b). Moreover subgrains existed within the dislocation martensite ig 4c), and nearly no coarsened M23C6 carbides had boundaries(Fig. 4d) According to the metallographic microstructures and the 500600700 TEM micrographs, compared with the weld seam, HAZ of the Ter joints displayed fine sorbitic microstructure with coarsened M23C6 carbides on the grain boundaries. This could be ascribed Fig 2 Mechanical properties of T91 welded joints at increasing to the heat effect from the weld seam during the welding process, thus the initial martensites decomposed into finer sorbite. Meanwhile, since carbide as M23 C6 on the grai boundaries for boundaries precipitates prior to MC within the grains(Ref 42 ), turned to be coarsened under he the M23C6 carbides that originally existed on the grain the haZ decreased and made it Journal of Materials Engineering and Performance Volume 21(7) July 2012--1315China (Ref 40), yield strengths (r0.2) of the joints were all qualified with increase of temperatures. Also, corresponding data of the T91 welded joints with same welding wire and process from Metrode Products Ltd. (Ref 41) were listed in the table and the figure. Meanwhile, the tensile strengths of our joints at these increasing temperatures were displayed as well. 3.2 Metallographic Microstructures Inspection Figure 3(a) displays the metallographic microstructure of the HAZ after welding, which consisted of sorbites with finer laths than that of T91 base material. Further detailedly, by means of TEM, it could be obviously observed that coarsened rod-like carbides of M23C6 had ripened and precipitated on the grain boundaries in the HAZ, marked with arrows in Fig. 4(a). Especially in some triangular grain boundaries, the carbides were even larger, marked in Fig. 4(b). In contrast, the weld seam was also martensite just like the T91 base material but with wider laths of about 3 lm, seen in Fig. 3(b). Moreover, tangling subgrains existed within the dislocation martensite laths (Fig. 4c), and nearly no coarsened M23C6 carbides had precipitated on the grain boundaries (Fig. 4d). According to the metallographic microstructures and the TEM micrographs, compared with the weld seam, HAZ of the joints displayed fine sorbitic microstructure with coarsened M23C6 carbides on the grain boundaries. This could be ascribed to the heat effect from the weld seam during the welding process, thus the initial martensites decomposed into finer sorbites. Meanwhile, since carbide as M23C6 on the grain boundaries precipitates prior to MC within the grains (Ref 42), the M23C6 carbides that originally existed on the grain boundaries for purpose of pinning strengthening ripened and turned to be coarsened under heat too. As a result, strength of the HAZ decreased and made it the weak region of the whole Table 3 Mechanical properties of T91 welded joints at room temperature Sample no. Tensile strength, rb, MPa Elongation, I II Avg. d5, % 1 706 711 708.5 18 2 693 694 693.5 3 707 712 709.5 4 730 752 741.0 5 735 721 728.0 T91 specification ‡585 ‡20 Table 4 Bending test results of T91 welded joints Bending style Test condition Sample no. Results Face bending 1 2 3 4 D = 3T, a = 50 5 Qualified Back bending 1 2 3 4 5 D, denotes the bending diameter; T, denotes the material thickness; a, denotes the bending angle Table 5 Mechanical properties of T91 welded joints at increasing temperatures Test temperature, C Yield strength, r0.2, MPa Tensile strength, rb, MPa Test results GB 5310 specification(a) Data from Metrode 50 450 660 100 470 384 580 525 650 150 475 378 590 500 595 200 377 565 580 250 377 560 560 300 376 535 530 350 371 535 535 400 358 510 515 450 337 480 485 500 380 306 460 385 455 515 490 540 550 350 260 395 365 410 575 350 375 330 375 600 280 198 335 290 345 625 275 310 290 315 650 250 265 245 280 (a) This GB 5310 specification is just for T91 base material Fig. 2 Mechanical properties of T91 welded joints at increasing temperatures Journal of Materials Engineering and Performance Volume 21(7) July 2012—1315