Variation in the Type IV cracking behaviour of a high Cr steel weld with post weld heat treatment

Albert, Shaju K.; Matsui, Masanao; Watanabe, Takashi; Hongo, Hiromichi; Kubo, Kiyoshi; Tabuchi, Masaaki

doi:10.1016/s0308-0161(03)00072-3

Cited by 89 publications

(43 citation statements)

References 9 publications

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“…[7][8][9] However, it is apparent that there is no clear evidence for these steels that PAG size has a significant influence on properties, and indeed, where data are available, it appears that creep strength and ductility grain size are not a function of PAG size in tempered martensitic steels. One such example is the lack of evidence for a widespread susceptibility to reheat cracking as is documented for bainitic CrMoV steels.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Thermal Cycles on the Microstructure of Grade 92 Steel

West

Siefert³

et al. 2017

Metall Mater Trans A

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The microstructure in the heat-affected zone (HAZ) of welds made from the 9 wt pct chromium martensitic Grade 92 steel is complex and has not yet been completely understood. There is a lack of systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds as a function of the welding process. In this study, the microstructure in the HAZ of an as-fabricated single-pass bead-on-plate weld on a parent metal of Grade 92 steel was systematically investigated by using an extensive range of electron and ion-microscopy-based techniques. A dilatometer was used to apply controlled thermal cycles to simulate the microstructures in the different regions of the HAZ. A wide range of microstructural properties in the simulated materials were then characterized and compared with the experimental observations from the weld HAZ. It was found that the microstructure in the HAZ of a single-pass Grade 92 steel weld can be categorized as a function of a decreasing peak temperature reached as (1) the completely transformed (CT) region, in which the original matrix is completely reaustenitized with complete dissolution of the pre-existing secondary precipitate particles; (2) the partially transformed (PT) region, where the original matrix is partially reaustenitized along with a partial dissolution of the secondary precipitate particles from the original matrix; and (3) the overtempered (OT) region, where the pre-existing precipitate particles coarsen. The PT region is considered to be the susceptible area for damage in the commonly reported HAZ failures in weldments constructed from these types of steels.

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Section: Introductionmentioning

confidence: 99%

The Influence of Thermal Cycles on the Microstructure of Grade 92 Steel

West

Siefert³

et al. 2017

Metall Mater Trans A

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“…From the figure, it is clear that the average grain size of the parent metal is fairly large, while in the HAZ, it is difficult to clearly identify the prior-austenite boundaries. Further, at a distance of 1 to 2 mm from the fusion line, where a fine-grained structure is observed in the HAZs of other conventional ferritic steels, [14] the size of the grains appears to be large and a clear lath structure is observed.…”

Section: A Variation In the Microstructure And Hardness In The Hazmentioning

confidence: 86%

“…Conventional high-Cr steels, such as P91, P92, and P122, have fine prior-austenite grains in that part of the HAZ heated close Ac 3 and below up to Ac 1 . [14,15] In the weld joints of these new steels with a low nitrogen content and boron addition, however, the microstructure at a location in the HAZ where fine grains are expected, is a mixture of large and small grains, with the latter decorating boundaries of the former (Figure 3). The size of the large grains is comparable to that of the base metal.…”

Section: Discussionmentioning

confidence: 99%

“…This is in contrast with what is normally observed in other ferritic steels, in which the sizes of both the M 23 C 6 and Laves phase are much larger in the FGHAZ (which is at a distance of 1 to 2 mm from the fusion line of a GTAW weld) than those present in the unaffected base metal after creep exposure. [14] Weld-joint specimens after creep fracture were examined for creep damage. No creep cavities were observed in the HAZ of the weld joints, even in those cases where fracture initiated in the weld interface and then propagated to the base metal.…”

Section: Microstructures After Creep Testmentioning

confidence: 99%

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Improving the creep properties of 9Cr-3W-3Co-NbV steels and their weld joints by the addition of boron

Albert

Kondo

Tabuchi

et al. 2005

Metall Mater Trans A

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New ferritic steels with a controlled addition of boron have been developed recently for ultrasupercritical fossil power plants. These steels possess excellent creep resistance compared to conventional steels like P91, P92, P122, etc., and this has been attributed to the delay in coarsening of the carbides during creep owing to partial replacement of carbon by boron in these carbides. However, the susceptibility of the weld joints of the boron-containing ferritic steels to type IV cracking, which significantly brings down the rupture life of the weld joints, has not been investigated so far. In the present work, the creep properties of recently developed 9Cr-3W-3Co-NbV steels with boron contents varying from 47 to 180 ppm and of their weld joints have been studied. Creep tests were carried out at 923 K in the stress range of 140 to 80 MPa. Specimens were examined for particle coarsening using field-emission scanning electron microscopy, and the boron content in the precipitates was estimated using field-emission auger electron spectroscopy (FE-AES). The grain size of the parent metal and the heat-affected zone (HAZ) were estimated using electron backscattered pattern (EBSP) imaging. Results showed that the creep properties of the steels with 90 and 130 ppm boron and of their weld joints are superior to those of the P92 steels and its weld joints. Further, no weld joints exhibited type IV cracking. No significant coarsening of the carbides was observed, not only in the parent metal but also in the HAZ of the steels with Ն90 ppm of boron. In addition to the delay in carbide coarsening, the large prior-austenite grain size of the parent metal and the absence of a conventional fine-grained HAZ (FGHAZ) in the weld joints also seem to have a beneficial effect on improving the creep properties of these steels and their weld joints.

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“…This steel yields a martensite microstructure and is used due to its good creep resistance, its low thermal expansion compared to austenitic steels and its weldability. The welded joints obtained are susceptible to type IV cracking, that mainly occurs in the fine grained heat affected zone (FGHAZ) or inter-critical heat affected zone (ICHAZ) also having fine grains (Albert et al, 2003). One of the main reasons for this susceptibility is the heterogeneity of the microstructure near the FGHAZ / ICHAZ which results in a contrast of mechanical properties and causes a localization of damage and deformation in the area FGHAZ / ICHAZ.…”

Section: Methodsmentioning

confidence: 99%

3d Reconstruction of a Multiscale Microstructure by Anisotropic Tessellation Models

Altendorf

Latourte²,

Jeulin

et al. 2014

Image Anal Stereol

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In the area of tessellation models, there is an intense activity to fully understand the classical models of Voronoi, Laguerre and Johnson-Mehl. Still, these models are all simulations of isotropic growth and are therefore limited to very simple and partly convex cell shapes. The here considered microstructure of martensitic steel has a much more complex and highly non convex cell shape, requiring new tessellation models. This paper presents a new approach for anisotropic tessellation models that resolve to the well-studied cases of Laguerre and Johnson-Mehl for spherical germs. Much better reconstructions can be achieved with these models and thus more realistic microstructure simulations can be produced for materials widely used in industry like martensitic and bainitic steels.

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Variation in the Type IV cracking behaviour of a high Cr steel weld with post weld heat treatment

Cited by 89 publications

References 9 publications

The Influence of Thermal Cycles on the Microstructure of Grade 92 Steel

The Influence of Thermal Cycles on the Microstructure of Grade 92 Steel

Improving the creep properties of 9Cr-3W-3Co-NbV steels and their weld joints by the addition of boron

3d Reconstruction of a Multiscale Microstructure by Anisotropic Tessellation Models

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