Study of creep crack growth in a modified 9Cr–1Mo steel weld metal and heat affected zone

Kumar, Yatindra; Venugopal, S.; Sasikala, G.; Albert, Shaju K.; Bhaduri, A.K.

doi:10.1016/j.msea.2015.12.053

Cited by 28 publications

(15 citation statements)

References 25 publications

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“…The authors also confirmed a good correlation between the creep crack growth rates in the P91 parent metal and the cross-weld specimens for a given contour-integral (C*) [17], in which the crack growth rate was 10 times higher in the cross-welded CT specimens than those of the parent metal. Using the same type of specimens, Kumar et al [18] reported similar conclusions, adding the idea that the HAZ enables the faster generation and growth of cracks to the detriment of the parent material and melted zone, creating the best conditions for the deviation of crack paths from those zones to the HAZ. In addition, using CT specimens of P91 steel welded and non-welded, Venugopol et al [19] reached similar conclusions, using the fracture mechanics parameter C*.…”

Section: Introductionmentioning

confidence: 75%

Evaluation of Welded Joints in P91 Steel under Different Heat-Treatment Conditions

Silva

Pinho

Péreira

et al. 2020

Metals

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P91 steel has been of interest to many researchers over the past two decades. This interest is because this steel has very interesting characteristics for application in power plants, where it is common to have pipes that need to support steam at temperatures between 570 and 600 °C, and at pressures in the range of 170 to 230 bar. These working conditions are quite severe for most common steels, requiring increased high-temperature mechanical strength as well as high creep resistance. The manufacture of these pipes normally includes welding operations, which must preserve the main characteristics of this type of steel. This justifies the concern of the researchers to ensure the best welding conditions so that the preservation of the properties of these steels becomes possible. The present work intends to depict the best results obtained varying the heat-treatment conditions applied to weldments made on heat-resistant steel P91. This steel usually takes the designation SA 213 T91 (seamless tube) or SA 335 P91 (seamless pipe), according to ASME II, as well as the designation X10CrMOVNb9-1 according to EN 10216-2. The purpose of this study is to compare the behavior of pipe welding under different post-welding heat-treatment (PWHT) conditions. One of them is performed with thermal cycles (preheating, post-heating, and the post-weld heat treatment) in agreement with most construction codes and standard rules. The second one is performed without any thermal cycle before and after welding. Both welds were made by the same process, TIG (Tungsten Inert Gas, or GTAW—Gas Tungsten Arc Welding) in the horizontal position (2G according to ASME IX) and the same welding parameters. In order to evaluate the results obtained in the welds, microstructure analyses, hardness measurements, bending tests, and tensile tests at room and high temperature (600 °C) have been performed. Other tests were also carried out according to the quality procedures, such as visual, penetrant dye, and X-ray tests. Regarding the different strategies used in the heat treatments, the best results have been obtained using a strategy similar to the one currently in use and recommended by construction codes and steel manufacturers but excluding the phases’ transformation time, and it was possible to observe that the tensile strength is impaired by about 2% to 9% at room and elevated temperatures, respectively; the elongation is reduced by 39% at room temperature but keeps a good performance at elevated temperature; the hardness profile is very similar at both temperatures; the microstructure presented is compatible with the requirements; and no cracking trend has been reported. Thus, a new strategy for the welding heat treatment of grade 91 steels was drawn, saving energy and processing time.

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Section: Introductionmentioning

confidence: 75%

Evaluation of Welded Joints in P91 Steel under Different Heat-Treatment Conditions

Silva

Pinho

Péreira

et al. 2020

Metals

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“…Specifically, on the one hand, a crack may traverse (or grow along) the grain boundary, where the weakest atomic bonds are present. This may be attributed to stress concentration at the grain boundary, since the existence of the stress gradient results in the convergence of vacancies [12,13], and in particular, the vacancies at the grain boundary provide favourable conditions for diffusion creep [10,50]. In this case, the crack along the grain boundary gradually accumulates, and then reaches the next triple point, where the opportunity for re-direction is provided.…”

Section: Crack Propagationmentioning

confidence: 99%

“…Specifically, the weakest zone shows an intensified state, which is normally caused by defects. These include vacancies, which are beneficial to diffusion creep [10,50], and microcracks, which aggravate the concentration of stress and hence provide favourable conditions for diffusion. These defect-related effects may also change the direction of crack growth.…”

mentioning

confidence: 99%

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Liú

Pons

2018

Metals

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Background-Creep-fatigue damage is generally identified as the combined effect of fatigue and creep. This behaviour is macroscopically described by crack growth, wherein fatigue and creep follow different principles. Need-Although the literature contains many studies that explore the crack-growth path, there is a lack of clear models to link these disparate findings and to explain the possible mechanisms at a grain-based level for crack growth from crack initiation, through the steady stage (this is particularly challenging), ending in structural failure. Method-Finite element (FE) methods were used to provide a quantitative validation of the grain-size effect and the failure principles for fatigue and creep. Thereafter, a microstructural conceptual framework for the three stages of crack growth was developed by integrating existing crack-growth microstructural observations for fatigue and creep. Specifically, the crack propagation is based on existing mechanisms of plastic blunting and diffusion creep. Results-Fatigue and creep effects are treated separately due to their different damage principles. The possible grain-boundary behaviours, such as the mismatch behaviour at grain boundary due to creep deformation, are included. The framework illustrates the possible situations for crack propagation at a grain-based level, particularly the situation in which the crack encounters the grain boundary. Originality-The framework is consistent with the various creep and fatigue microstructure observations in the literature, but goes further by integrating these together into a logically consistent framework that describes the overall failure process at the microstructural level.

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“…Creep voids formation was controlled by the vacancy diffusion. A high stress triaxiality would stimulate vacancies to diffuse from the region of low stress constraint [48]. Nix [49] assumed that high stress concentration at grain boundary particles may cause decohesion and joining of voids and lead to crack opening at triple points.…”

Section: Materials Propertiesmentioning

confidence: 99%

Predicting failure modes in creep and creep-fatigue crack growth using a random grain/grain boundary idealised microstructure meshing system

Zhao

Nikbin

2017

Materials Science and Engineering: A

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An idealised microstructure mesh model combined with a novel creep and creepfatigue damage accumulation model was employed to simulate crack growth behaviour under creep/fatigue conditions for a modified 9Cr-1Mo steel. The influence of microstructures on the crack growth behaviour was studied using a random grains separated by idealised grain boundaries. For accurately representing the damage accumulation in creep-fatigue regime, a non-linear damage model was employed. In this case, creep damage was determined by multiaxial ductility exhaustion approach and fatigue damage was reliant on maximum stress and plastic range ahead of crack tip per loading cycle. When creep dominated, cracks mainly propagated along grain boundaries in steady crack growth stage. As an exception, the crack growth in the tertiary crack growth stage gradually changed from intergranular to mixed model and finally transgranular fracture. In contrast, in creep-fatigue regime, the crack growth behaviour was greatly reliant on the dwell time. For short duration period, the crack mainly propagated in a transgranular manner. But as the dwell time increased to greater than 600s, the creep intergranular fracture dominated once again. Furthermore, the grain size gradient had little influence on the crack growth model and only affected the fracture life in creep and creep-fatigue regimes.

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Study of creep crack growth in a modified 9Cr–1Mo steel weld metal and heat affected zone

Cited by 28 publications

References 25 publications

Evaluation of Welded Joints in P91 Steel under Different Heat-Treatment Conditions

Evaluation of Welded Joints in P91 Steel under Different Heat-Treatment Conditions

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Predicting failure modes in creep and creep-fatigue crack growth using a random grain/grain boundary idealised microstructure meshing system

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