The Effect of Long‐Term Ageing on Microstructural Properties and Laves Phase Precipitation of Welded P91 and P92 Steels

Junek, Michal; Svobodová, Marie; Horváth, Jakub; Mára, Vladimír

doi:10.1002/srin.202100311

Cited by 5 publications

(4 citation statements)

References 19 publications

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“…In numerous published works [7][8][9][10][11][12][13][14], the degradation of mechanical properties (especially creep strength and impact toughness) of P/T92 steel was primarily ascribed to the Laves phase precipitation and coarsening. Detailed microstructural analyses, e.g., in [10][11][12][13][14][15][16], confirmed that the Laves phase very often precipitates on the Cr 23 C 6 -based carbides, which serve as preferential sites for the Laves phase nucleation. Some authors, e.g., [17][18][19][20], revealed positive effects of fine Laves phase particles on creep resistance of high-chromium boiler steels in the early stages of their high-temperature exposure.…”

Section: Introductionmentioning

confidence: 88%

“…In order to differentiate between coarse Cr 23 C 6 -based carbides and Fe 2 W-based Laves phase, SEM visualizations were performed using back-scattered electrons (BSEs) contrast, which is highly sensitive on the average atomic number of a phase. This SEM/BSE technique has also been widely used by several other authors, e.g., [16][17][18][19], in order to identify reliably the Laves phase precipitates in 9 wt.% Cr steels. The corresponding SEM micrographs are shown in Figures 3b, 4b, and 5b.…”

Section: Experimental Materials and Methodsmentioning

confidence: 99%

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The Effects of Various Conditions of Short-Term Rejuvenation Heat Treatment on Room-Temperature Mechanical Properties of Thermally Aged P92 Boiler Steel

et al. 2021

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In this work, the effects of various conditions of short-term rejuvenation heat treatment on room-temperature mechanical properties of long-term aged P92 boiler steel were investigated. Normalized and tempered P92 steel pipe was thermally exposed at 600 °C for time durations up to 5000 h in order to simulate high-temperature material degradation, as also occurring in service conditions. Thus, thermally embrittled material states of P92 steel were prepared, showing tempered martensitic microstructures with coarsened secondary phase precipitates of Cr23C6-based carbides and Fe2W-based Laves phase. Compared with the initial normalized and tempered material condition, thermally aged materials exhibited a slight decrease in strength properties (i.e., yield stress and ultimate tensile strength) and deformation properties (i.e., total elongation and reduction of area). The hardness values were almost unaffected, whereas the impact toughness values showed a steep decrease after long-term ageing. An idea for designing the rejuvenation heat treatments for restoration of impact toughness was based on tuning the material properties by short-term annealing effects at various selected temperatures somewhat above the long-term ageing temperature of P92 material. Specifically, the proposed heat treatments were performed within the temperature range between 680 °C and 740 °C, employing variable heating up and cooling down conditions. It was revealed that short-term annealing at 740 °C for 1 h with subsequent rapid cooling into water represents the most efficient rejuvenation heat treatment procedure of thermally aged P92 steel for full restoration of impact toughness up to original values of normalized and tempered material state. Microstructural observations clearly indicated partial dissolution of the Laves phase precipitates to be the crucial phenomenon that played a key role in restoring the impact toughness.

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Section: Introductionmentioning

confidence: 88%

Section: Experimental Materials and Methodsmentioning

confidence: 99%

The Effects of Various Conditions of Short-Term Rejuvenation Heat Treatment on Room-Temperature Mechanical Properties of Thermally Aged P92 Boiler Steel

et al. 2021

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“…During long-term creep, the microstructure of the material will change, and new phases, such as the Laves phase (Fe, Cr) 2 (W, Mo), primarily precipitate at the boundaries of primary austenite grains, subgrains and martensite laths [2][3][4][5]. The finely dispersed Laves phase has a precipitation-strengthening effect on the matrix, which can prevent the recovery of martensitic slats and dislocations [6][7][8]. However, Abe et al [9,10] found that the precipitation of the Laves phase led to a decrease in the creep rate, but when the size of the Laves phase began to increase significantly, the creep rate increased after reaching the minimum creep rate.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Characterization Method of Laves Phase in 9Cr Martensitic Heat-Resistant Steel and Creep Life Prediction

Yuan,

Li,

Guo

et al. 2023

Crystals

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The Laves phase formed during the long-term creep of 9% Cr heat-resistant steels plays an important role in their high-temperature mechanical properties. Detecting and quantifying the Laves phase is one of the main problems in predicting the creep residual life. This study detects and quantifies the Laves phase in various 9% Cr heat-resistant steel samples by anodic polarization. Both T92/P92 samples after creep and 9Cr ferritic martensitic samples after thermal ageing precipitate Laves phase particles, and the content of the Laves phase increases with the service time. Comparing the results obtained by the electrochemical method with those obtained by the traditional SEM observation method, it can be found that there is a similar two-stage linear relationship between the two results in all materials, which is related to the diameter change of Laves phase particles during service. According to the correlation between the Laves phase content and creep time, an extrapolation method for the prediction of the residual creep life is proposed. The results show that the creep life of P92 can be predicted by using the dissolved charge density of the Laves phase with high prediction accuracy. This method has the potential to evaluate the service states of materials and predict the long-term creep life in the industrial field.

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“…Weldments of P92 steel offer poor mechanical properties at room temperature due to the formation of brittle fresh martensite in the weld fusion zone (WFZ). Other factors, including heterogeneous microstructure formation along weldments, the evolution of residual stresses along weldments, the formation of soft δ ferrite patches, the presence of diffusible hydrogen and the hardening of coarse-grained HAZ are also considered major causes of failure in P92 weldments [16,[19][20][21][22][23][24][25]. Heterogeneity in the microstructure as a result of high heat input mainly leads to variation in mechanical properties, i.e., hardness and impact toughness.…”

Section: Introductionmentioning

confidence: 99%

Influence of PWHT Parameters on the Mechanical Properties and Microstructural Behavior of Multi-Pass GTAW Joints of P92 Steel

et al. 2022

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The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

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The Effect of Long‐Term Ageing on Microstructural Properties and Laves Phase Precipitation of Welded P91 and P92 Steels

Cited by 5 publications

References 19 publications

The Effects of Various Conditions of Short-Term Rejuvenation Heat Treatment on Room-Temperature Mechanical Properties of Thermally Aged P92 Boiler Steel

The Effects of Various Conditions of Short-Term Rejuvenation Heat Treatment on Room-Temperature Mechanical Properties of Thermally Aged P92 Boiler Steel

Electrochemical Characterization Method of Laves Phase in 9Cr Martensitic Heat-Resistant Steel and Creep Life Prediction

Influence of PWHT Parameters on the Mechanical Properties and Microstructural Behavior of Multi-Pass GTAW Joints of P92 Steel

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