Experimental Study On Creep Strength Of The Weld Joints Of 9%Cr Heat Resistant Steels Experimental Study On Creep Strength Of The Weld Joints Of 9%Cr Heat Resistant Steels (original) (raw)
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Experimental Study On Creep Strength Of The Weld Joints Of 9%Cr Heat Resistant Steels
2016
The aim of this study is optimizing the creep properties of T91 weld joints at high temperature and pressure. After welding, tube portions were subjected to different cycles of post welding heat treatment, than creep tests at 650°C and a range of pressure values. Crept specimens were exterminated in order to determine the weakest zones in the joint. It was found that the rupture occurs in the base metal at high pressures and in the heat affected zone at low ones. The creep rupture time of weld joint is lower than those of the base metal.Microstructure after creep is compared to the original one, to better understand the impact of creep exposure on microstructure evolution and to evaluate the strength of weld joints.
Creep resistance of similar and dissimilar weld joints of P91 steel
Materials at High Temperatures, 2006
Two experimental weld joints, a similar weld joint of 9Cr-1Mo steel and a dissimilar weld joint of 9Cr-1Mo and 2.25Cr-1Mo steels, were fabricated by the TIG þ E method and post-weld heating was applied. Creep testing was carried out at temperatures ranging from 525 to 625 C in the stress range 40-240 MPa. Creep rupture strength was evaluated using the Larson-Miller parameter. Extended metallography including transmission electron microscopy was performed and critical zones were indicated where fractures were concentrated during the creep exposure. At high temperatures rupture of the dissimilar weldment occurred in the heat affected zone (HAZ) of the weld metal while rupture of the similar weldment was located in the HAZ of the parent material. The processes of recovery seem to be the main causes of decrease in creep rupture strength of both weld joints in comparison to the parent materials.
The Impact of Weld Metal Creep Strength on the Overall Creep Strength of 9% Cr Steel Weldments
Journal of Engineering Materials and Technology, 2011
In this work, three joints of a X11CrMoWVNb9-1-1 (P911) pipe were welded with three filler metals by conventional arc welding. The filler metals varied in creep strength level, so that one overmatched, one undermatched, and one matched the creep strength of the P911 grade pipe base material. The long-term objective of this work was to study the influence of weld metal creep strength on the overall creep behavior of the welded joints and their failure mechanism. Uniaxial creep tests at 600°C and stresses ranging from 70 MPa to 150 MPa were performed on the cross-weld samples of all three welds. A total creep testing time of more than 470,000 h was accumulated. The longest running sample achieved a time-to-rupture of more than 45,000 h. Creep testing revealed that the use of undermatching weld metal led to a premature fracture in the weld metal at higher stress levels. Compared with undermatching weld metal, the use of matching and overmatching filler materials increased the time-to-r...
Creep behavior of P91B steel in the presence of a weld joint
Materials Science and Engineering: A, 2015
The paper presents creep test data on standard P91B steel specimens made from two distinct regions of a welded plate over a range of stresses (50-190 MPa) and temperatures (600-650°C). The analysis of test data revealed that the samples having a weld zone within the gage length (cross-weld samples) have lower long term rupture strength than the samples made of the base metal. Estimated weld strength factors (WSF) of this steel were found to be higher than those reported for P91 steel. The study also showed that the effect of welding on loss of rupture ductility is much more prominent than its effect on the reduction in rupture strength. In presence of welded zone the extent of local deformation in ruptured samples was not as prominent as in the samples without weld. Creep damage tolerance factors (λ) were estimated from the creep strain versus time plots. This also showed that the magnitude of λ is significantly reduced in the presence of welding. Examination of microstructure and measurement of density revealed that this difference is primarily due to the formation of cavities in the heat affected zones of welded specimens. In the lower stress regime a few test specimens without any welded region did not fail even after very long creep exposure. Diameters of these specimens were found to have increased in spite of measureable increase in length due to creep. This unusual effect has been attributed to oxide scale growth. It shows up when the increase in diameter due to the growth of oxide scale becomes greater than the decrease in diameter due to the accumulation of creep strain.
Creep strength and microstructure of a modified P911-type steel weld joint
IOP Conference Series: Materials Science and Engineering, 2021
The creep strength and microstructure of the weld joint of the modified P911-type steel has been studied. The creep rupture time of the welded joint at 650° of 1375 h is close to that of the base metal. The heat affected zone-is found to be the weakest area due to the increased size and relatively high coarsening rate of precipitates. The increased boron content in the weld steel effectively stabilizes the M23(C,B)6 particles and is beneficial for the creep strength of the weld joint in the fusion zone.
Effect of welding on creep damage evolution in P91B steel
Journal of Nuclear Materials, 2017
Study of creep behavior of base metal (without weld) and welded specimens P91B steel over a range of temperature (600-650 °C) and stress (50-180 MPa) showed similar values of minimum creep-rates for both specimens at higher stress regime (> 100 MPa) whilst, significantly higher creep rates of welded specimens at lower stress regime Considering that welded specimen comprised of two distinct structural regimes, i.e. weld affected zone and base metal, a method was proposed for estimating the material parameters describing creep behavior of those regimes. Stress-strain distribution across welded specimen predicted from finite element analysis based on material parameters revealed preferential accumulation of stress and creep strain at the interface between weld zone and base metal. This is in-line with the experimental finding that creep rupture preferentially occurs at inter-critical heat affected zone in welded specimens owing to ferrite-martensite structure with coarse Cr 23 C 6 particles.
A Comparison of Creep Rupture Behaviour of 2.25Cr-1Mo and 9Cr-1Mo Steels and Their Weld Joints
High Temperature Materials and Processes, 2000
Creep rupture behaviour of 2.25Cr-lMo and 9Cr-lMo base metals and weld joints has been studied at 823 Κ over a stress range of 100-250 MPa. In the stress range examined, 2.25Cr-lMo steel showed better creep rupture strength compared to 9Cr-lMo steel. Both the weld joints displayed a creep rupture strength inferior to those of their respective base metals. Failure occurred in the respective intercritical region of the heat affected zone (HAZ) in both the steel weld joints. At a given applied stress, the difference in rupture life of base and weld joint was more pronounced in 2.25Cr-lMo steel than in 9Cr-lMo steel and this difference increased with decrease in applied stress. As the presence of Mo 2 C precipitate imparts creep resistance to 2.25Cr-lMo steel, its absence in the intercritical HAZ region of the joint is held responsible for its poor creep life. On the other hand, 9Cr-lMo steel which is strengthened by solid solution hardening and dislocation substructure, is less prone to degradation in the intercritical region. Also, the presence of δ-ferrite in the coarse grain region of HAZ of 9Cr-lMo steel reduces its grain growth tendency and also its susceptibility to intergranular creep cavitation compared to 2.25Cr-lMo steel.
There has been a constant search for new materials for high temperature applications, such as for parts of steam generators, parts of thermal power plants, piping of liquid metal reactors, which are likely to be exposed to temperature 5500c and above. Good strength and ductility values possessed by special steels make them the first choice of designers for applications mentioned. Modified 9Cr-1Mo steel has been in use for such applications since a decade. For any given material, along with the mechanical properties, there is a need to determine the creep property if the material is the choice for high temperature service applications. Further, as it has been experienced that the welds are likely zones of failure, under extreme conditions of load and temperature, probing the creep property of the welded joints of a given material becomes an important aspect of research.Hence it is proposed to probe into the creep resistance aspect of the welded joints of 9Cr-1Mo steel under different conditions of load and temperature. It is also proposed to age the samples of 9Cr-1Mo steel under different conditions so that variation of creep properties in both the parent and the weld metal can be studied adopting the indentation creep test methodology. Experiments will be designed to extract all possible information regarding structural disintegration of the material. Additionally, scanning electron microscopy is planned to be adopted to observe micro-structural changes and correlation will be attempted to link them to observed creep behaviour.
Creep deformation and failure of E911/E911 and P92/P92 similar weld-joints
Engineering Failure Analysis, 2009
This paper deals with characterisation of microstructure and creep behaviour of similar weld-joints of advanced 9% Cr ferritic steels, namely E911 and P92. The microstructures of the investigated weld-joints exhibit significant variability in different weld-joint regions such as weld metal (WM), heat-affected zone (HAZ), and base metal (BM). The cross-weld creep tests were carried out at 625°C with initial applied stresses of 100 and 120 MPa. Both weld-joints ruptured by the ''type IV cracking failure mode" in their fine-grained heataffected zones (FG-HAZ). The creep fracture location with the smallest precipitation density corresponds well with its smallest measured cross-weld hardness. The welds of P92 steel exhibit better creep resistance than those of E911 steel. Whereas the microstructure of P92 weld after creep still contains laths, the microstructure of E911 weld is clearly recrystallized. The creep stress exponents are 14.5 and 8 for E911 and P92 weld-joints, respectively. These n-values indicate the ''power-law creep" with dislocation-controlled deformation mechanism for both investigated weld-joints.
Analysis of the Creep Behavior of P92 Steel Welded Joint
Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.