In recent years, a design concept for the stabilisation of the microstructure by addition of boron and nitrogen was developed. This so called martensitic boron–nitrogen strengthened steel (MARBN) combines boron strengthening by solid solution with precipitation strengthening by finely dispersed nitrides. Welded joints of MARBN steels showed no formation of a uniform fine grained region in the heat affected zone (HAZ) which is in general highly susceptible to Type IV cracking. In this work, the crossweld creep strength of a newly developed MARBN steel was analysed and the evolution of damage was investigated using synchrotron microtomography supported by electron microscopy. Three-dimensional (3D) reconstructions of the tested samples together with electron backscatter diffraction investigations revealed an intense void formation in a restricted area along small grains at prior austenite grain boundaries in the HAZ as the main reason for premature creep failures in the HAZ of welded joints.
IEA: ‘World energy outlook’; 2008, Paris, OECD Publishing.
2.
DavidSA, SiefertJA and FengZ: ‘Welding and weldability of candidate ferritic alloys for future advanced ultrasupercritical fossil power plants’, Sci. Technol. Weld. Join., 2013, 18, (8), 631–651.
3.
BhadeshiaHKDH: ‘Design of ferritic creep-resistant steels’, 2001, 41, (6), 626–640.
4.
FrancisJA, MazurW and BhadeshiaHKDH: ‘Review type IV cracking in ferritic power plant steels’, Mater. Sci. Technol., 2006, 22, (12), 1387–1395.
5.
CerjakH: ‘The role of welding in the power generation industry’, Proc. IIW Int. Conf. on ‘Safety and reliability of welded components in energy and processing industry’, Graz, Austria, July 2008, IIW, 17–27.
6.
LiuY, TsukamotoS, ShiraneT and AbeF: ‘Formation mechanism of type IV failure in high Cr ferritic heat-resistant steel-welded joint’, Metall. Mater. Trans. A, 2013, 44A, (10), 4626–4633.
7.
AbeF, TabuchiM and TsukamotoS: ‘Mechanisms for boron effect on microstructure and creep strength of ferritic power plant steels’, Energy Mater. Mater. Sci. Eng. Energy Syst., 2012, 4, (4), 166–174.
8.
AbeF: ‘Effect of boron on microstructure and creep strength of advanced ferritic power plant steels’, Proc. Eng., 2011, 10, 94–99.
9.
AbeF, TabuchiM, KondoM and TsukamotoS: ‘Suppression of type IV fracture and improvement of creep strength of 9Cr steel welded joints by boron addition’, Int. J. Press. Vessels Pip., 2007, 84, (1–2), 44–52.
10.
AbeF, TabuchiM, TsukamotoS and ShiraneT: ‘Microstructure evolution in HAZ and suppression of Type IV fracture in advanced ferritic power plant steels’, Int. J. Press. Vessels Pip., 2010, 87, (11), 598–604.
11.
MayrP: ‘Evolution of microstructure and mechanical properties of the heat affected zone in B-containing 9% chromium steels’, PhD thesis, Graz University of Technology, Styria, Austria, 2007.
12.
MayrP, SchlacherC and MitscheS: ‘Critical issues with creep-exposed ferritic-martensitic welded joints for thermal power plants, Proc. IIW Int. Conf. on ‘Global trends in joining, cutting and surfacing technology’, 417–425; 2011, Alpha Science Intl Ltd. Oxford, UK.
13.
AbeF, TabuchiM, SembaH, IgarashiM, YoshizawaM, KomaiN and FujitaA: ‘Feasibility of MARBN steel for application to thick section boiler components in USC power plant at 650°C’, in ‘Advances in materials technology for fossil power plants: Proceedings from the 5th Int. Conf.’, 92–106; 2007, Materials Park, OH, ASM International.
14.
AbeF: ‘Metallurgy for long-term stabilization of ferritic steels for thick section boiler components in USC power plant at 650°C’, in ‘Materials for advanced power engineering 2006: Proceedings of the 8th Liège conference’, 965–980; 2006, Julich, Energy Technology Forschungszentrum Julich.
15.
AbeF: ‘Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants’, Sci. Technol. Adv. Mater., 2008, 9, (1), 013002.
16.
AlbertS, KondoM and TabuchiM: ‘Improving the creep properties of 9Cr-3W-3Co-NbV steels and their weld joints by the addition of boron’, Mater. Trans. A, 2005, 36A, 333–343.
17.
KondoM, TabuchiM, TsukamotoS, YinF and AbeF: ‘Suppressing type IV failure via modification of heat affected zone microstructures using high boron content in 9Cr heat resistant steel welded joints’, Sci. Technol. Weld. Join., 2006, 11, (2), 216–223.
18.
ShiraneT, TsukamotoS, TsuzakiK, AdachiY, HanamuraT, ShimizuM and AbeF: ‘Ferrite to austenite reverse transformation process in B containing 9%Cr heat resistant steel HAZ’, Sci. Technol. Weld. Join., 2009, 14, (8), 698–707.
19.
HoriuchiT, IgarashiM and AbeF: ‘Improved utilization of added B in 9Cr heat-resistant steels containing W’, ISIJ Int., 2002, 42, 67–71.
20.
StockSR: ‘Recent advances in X-ray microtomography applied to materials’, Int. Mater. Rev., 2008, 53, (3), 129–181.
21.
GuptaC, TodaH, SchlacherC, AdachiY, MayrP, SommitschC and UesugiK: ‘Study of creep cavitation behavior in tempered martensitic steel using synchrotron micro-tomography and serial sectioning techniques’, Mater. Sci. Eng. A, 2013, A564, 525–538.
22.
SketF, DzieciolK, IsaacA, BorbélyA and PyzallaAR: ‘Tomographic method for evaluation of apparent activation energy of steady-state creep’, Mater. Sci. Eng. A, 2010, A527, (7–8), 2112–2120.
23.
SchlacherC, SommitschC, GuptaC, TodaH, UesugiK, SuzukiY and MayrP: ‘Creep and damage investigation of improved 9% Cr steel welded joints’, in ‘Trends in welding research 2012: Proceedings of the 9th international conference’, 376–381; 2013, Materials Park, OH, ASM International.
24.
MayrP, HolzerI and Mendez-MartinF: ‘Experience with 9Cr3W3CoVNbBN Base Material and Crosswelds at 650 C for Implementation in USC Power Plants’, Proc. 3rd Symp. on ‘Heat resistant steels and alloys for high efficiency USC power plants’, Tsukuba, Japan, June 2009, National Insititute for Materials Science.
25.
TodaH, TomizatoF, ZeismannF, Motoyashiki-BeselY, UesugiK, TakeuchiA, SuzukiY, KobayashiM and Brueckner-FoitA: ‘High-resolution observation of steel using X-ray tomography technique’, ISIJ Int., 2012, 52, (3), 516–521.
26.
‘NIMS Creep Data sheet no. 48A’, Tsukuba, Japan, 2012.
27.
AbeF, TabuchiM, TsukamotoS and LiuY: ‘Alloy design of tempered martensitic 9Cr-boron steel for A-USC boilers’, in ‘Advances in materials technology for fossil power plants: Proceedings from the Seventh International Conference’, 1127–1138; 2014, Materials Park, OH, ASM International.
28.
SchneiderC, RasbandW and EliceiriK: ‘NIH Image to ImageJ’, Nat. Meth., 2012, 671–675.
29.
HaibelA: ‘μ-Tomography of Engineering Materials’, in ‘Neutrons and synchrotron radiation in engineering materials science’; 2008, Weinheim, Wiley-VCH Verlag GmbH & Co. KGaA.
30.
LyckegaardA: ‘Development of tomographic reconstruction methods in materials science with focus on advanced scanning methods’, Technical University of Denmark, Denmark, 2011.
31.
LyckegaardA, JohnsonG and TafforeauP: ‘Correction of ring artifacts in X-ray tomographic images’, Int. J. Tomogr. Stat., 2010, 18, F11, 1–9.
32.
TsukamotoS, LiuY, ShiraneT, TabuchiM and AbeF: ‘Improvement of microstructure stability during creep in high Cr ferritic heat resistant steel HAZ mechanism of type IV failure’, in ‘Trends in welding research 2012: Proceedings of the 9th international conference’, 1–10; 2013, Materials Park, OH, ASM International.
