Type IV Creep Damage Behavior in Gr.91 Steel Welded Joints

Hongo, Hiromichi; Tabuchi, Masaaki; Watanabe, Takashi

doi:10.1007/s11661-011-0967-6

Cited by 63 publications

(32 citation statements)

References 19 publications

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“…Short-time over-tempering causes the recovery of dislocations, break-down of the lath structure, polygonization, and carbide spheroidizing as well as coarsening [9]. Premature failure of 9-12 Cr creep-strength-enhanced ferritic steel welds after long-term service at elevated temperature is known as Type IV cracking [10][11][12][13][14]. The fine-grained HAZ (FGHAZ) has the lowest creep strength among the different regions of a P91 steel weld [15].…”

Section: Introductionmentioning

confidence: 99%

“…The fine-grained HAZ (FGHAZ) has the lowest creep strength among the different regions of a P91 steel weld [15]. In creep tests of a simulated HAZ, the FGHAZ heated to near the A C3 temperature of Gr.91 steel shows the lowest creep rupture strength [11]. The creep crack growth life of the FGHAZ of a Gr.91 weld at 600 • C is about 45% of that the base metal [16].…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Normalizing Temperature on the Short-Term Creep Rupture of the Simulated HAZ in Gr.91 Steel Welds

Shiue

et al. 2018

Metals

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As-received Gr.91 steel tube was normalized at either 940 or 1060 • C for 1 h, followed by Ar-assisted cooling to room temperature, then tempered at 760 • C for 2 h. Those samples were designated as 940NT or 1060NT samples. An infrared heating system was used to simulate HAZ microstructures in the weld, which included over-tempering (OT) and partial transformation (PT) zones. The results of short-term creep tests showed that normalizing at higher temperature improved the creep resistance of the Gr.91 steel. By contrast, welding thermal cycles would shorten the creep life of the Gr.91 steel. Among the tested samples in each group, the PT samples had the shortest life to rupture, especially the 940NT-PT sample. The microstructures of the PT samples comprised of fine lath martensite and ferrite subgrains with carbides decorating the grain and subgrain boundaries. Excessive dislocation recovery, rapid coalescence of refined martensite laths, and growth of ferrite subgrains were responsible for the poorer creep resistance of the PT samples relative to those of the other samples.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Effect of Normalizing Temperature on the Short-Term Creep Rupture of the Simulated HAZ in Gr.91 Steel Welds

Shiue

et al. 2018

Metals

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“…Previous analyses for similar geometries have shown that, upon reaching a steadystate creep rate, the development of the maximum principal stress or triaxiality factor is sustained through the thickness (Ref. 43). Thus, the feature-type cross-weld creep test geometry provided a resulting stress state that was more comparable to component behavior and enhanced the development of damage in the HAZ.…”

Section: Implications Of the Resultsmentioning

confidence: 97%

Cross-Weld Creep Performance in Grade 91 Steel: Macro-Based Assessment

Siefert¹,

Parker²,

Thomson³

2019

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The martensitic 9% Cr creep strength enhanced ferritic (CSEF) steels Grades 91 and 92 (Table 1) are carefully alloyed and processed to develop a distribution of carbonitrides such as M 23 C 6 and MX-type precipitates that pin the martensitic matrix and dislocation substructure. Upon application of a welding thermal cycle, this microstructure is significantly altered and results in local re-gions [e.g., the heat-affected zone (HAZ)] that possess inferior creep properties compared to that of the unaffected base material. In-service performance of fabricated 9% Cr CSEF steel structures will, in many cases, be limited by the multiaxial stress-state response of the HAZ. It is thus important for well-planned and executed cross-weld creep test programs to carefully evaluate and quantify the extent of damage in the HAZ.The complexity of the martensitic microstructure and the evolution of damage necessitates careful evaluation using well-controlled procedures and for multiple length scales as the microstructural features span several orders of magnitude in length scale using the techniques listed in Table 2. The general length scale for the important features in martensitic CSEF steels are summarized below:Prior austenite grain size ~ 10 to 100s m Packet boundary size ~ 1 to 10s m BN and inclusions ~ 1 m AlN, Laves phase, and M 23 C 6~ 100s nm MX ~ 10s nm Dislocations ~ <1 nm Present damage may be manifested as voids (~1 m), microcracks (~ 100s m), or macrocracks (≥ 1 mm) Significant advances have recently been made for welldeveloped technologies regarding the ability to obtain large datasets such as hardness testing (e.g., automated hardness mapping); conventional microscopy (e.g., development of confocal laser microscopy and light-emitting diode (LED) microscopy); and the ease at which advanced electron microscopy can be applied to obtain large, statistically relevant datasets. It is also true that ever more advanced techniques are becoming more commonplace and are now available to researchers to elucidate the specifics regarding the evolution of damage in base material and cross-weld samples. This was recently highlighted in a special feature in Materials Science and Technology, Ref. 1). The complexity of martensitic CSEF steels necessitates the application of these methods to WELDING RESEARCH ABSTRACTMeaningful characterization of the microstructure in metallurgically complex steels is complicated by the diversity of thermal cycles experienced by multipass fusion welds. To overcome the problems of relevant documentation, it is necessary to balance information from macro-, micro-, and nano-evaluation with appropriate analysis. This paper presents details regarding recommended approaches that optimize this characterization.Initially, specific procedures relevant to macroanalysis, including hardness mapping and calculation of the peak temperature through the width of the heat-affected zone (HAZ), are described. Then, assessment of the distribution of creep damage in feature-type, cross-weld creep tests using laser m...

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“…The second was used to determine material properties for the cavitation mechanism. At the time of model development, the only comprehensive set of data of Grade 91 base metal, cross-welds, and simulated HAZ material, all from the same original heat of Grade 91 steel was that of Hongo et al [9]. Evaluation of this data set indicated that the creep deformation resistance of Grade 91 simulated HAZ material is lower than that of the base metal.…”

Section: Heat-affected Zone Materials Descriptionmentioning

confidence: 99%

Application of a Physically-Based Creep Continuum Damage Mechanics Constitutive Model to the Serviceability Assessment of a Large Bore Branch Connection

Pritchard

Perrin

Parker

et al. 2018

ASME 2018 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries

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Premature creep cracking in fabricated large bore branch connections in Grade 91 steel (9Cr-1Mo-VNbN) piping continues to be a commonly observed failure mechanism in high energy applications. Failures have been observed in components fabricated to the requirements of both ASME Section I and B31.1 codes. This paper presents the application of a physically-based creep continuum damage constitutive model developed for Grade 91 steel to the assessment of a large bore fabricated branch connection. For a specific component geometry and operating conditions, model predictions for the expected location and timing of crack initiation as well as for the crack growth behavior have been made. In addition, as validation, trends in the simulated behavior are compared to information from case studies of large bore branch cracking and failure in service. The physically-based continuum damage model is shown to accurately predict both the location and timing of local crack initiation as well as the observed crack growth behavior.

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Type IV Creep Damage Behavior in Gr.91 Steel Welded Joints

Cited by 63 publications

References 19 publications

The Effect of Normalizing Temperature on the Short-Term Creep Rupture of the Simulated HAZ in Gr.91 Steel Welds

The Effect of Normalizing Temperature on the Short-Term Creep Rupture of the Simulated HAZ in Gr.91 Steel Welds

Cross-Weld Creep Performance in Grade 91 Steel: Macro-Based Assessment

Application of a Physically-Based Creep Continuum Damage Mechanics Constitutive Model to the Serviceability Assessment of a Large Bore Branch Connection

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