Causes of Failure of Weld Joint During Long Time Creep Testing (original) (raw)
Related papers
Behaviour of dissimilar weld joint of steels FB2 and F during long-term creep test
IOP Conference Series: Materials Science and Engineering
Creep test to the rupture of both the dissimilar weld joint made of FB2 and F martensitic steels and the base materials was carried out at temperatures ranging from 550 °C to 650 °C in the stress range from 70 to 220 MPa. Creep rupture strengths of the weld joint and the base materials were evaluated using Larson-Miller parameter. Assessment of microstructure development and changes of hardness was correlated with the creep strength. Critical zones of creep damage were determined. At lower temperatures and higher stresses the weld joint ruptured in the base material of F steel unaffected by welding, while at higher temperatures and lower stresses rupture occurred in the intercritical heated and fine-grained parts of heat affected zone of steel F. During creep at temperatures above 575 °C Laves phase precipitated in all parts of the weld joint and especially in the heat affected zones. Coarse Laves phase particles and their clusters with chromium carbides served as nucleation centres for cavities. As the fine grained heat affected zone of F steel was the softest part of the weld joint, many cavities originated and initiated causing failure of samples.
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.
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.
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.
Creep Crack Growth Behavior of a P91 Steel Weld
Procedia Engineering, 2014
Modified 9Cr-1Mo steel (P91) weld joints operating at elevated temperatures are well known to be prone to premature failure due to cracking in the heat affected zone because of the gradients in microstructure, popularly referred to as Type IV cracking. A campaign was undertaken to study the creep crack growth behaviour of modified 9Cr-1Mo weld joints. Creep crack growth (CCG) tests were carried out on compact tension (CT) specimens machined from P91 weld joints prepared using multipass shielded manual metal arc welding procedure. Specimens with two notch locations have been employed, (i) within the weld metal, between the centreline and the fusion line and (ii) in the heat affected zone. Constant load CCG tests were carried out at different applied loads at 798 and 898 K. The C*-da/dt correlations (da/dt =A C *m) were established for both notch locations. At 898 K, a higher A (0.064) and lower m (0.533) for the case with notch placed in the HAZ, compared to those for the case of notch in the weld (0.0399 and 0.75 respectively) were observed indicating the higher creep crack growth in HAZ, confirming type IV cracking. The difference increases at lower C* levels which correspond to long term behaviour. Heavy creep damage was observed in the HAZ region even for the sample with notch in the weld, whereas the weld metal regions showed relatively less damage. As the crack grew, a change in its course to follow the HAZ region was observed.
Metallurgical and Materials Transactions A, 2001
The evaluation of the creep deformation and fracture behavior of a 2.25Cr-1Mo steel base metal, a 2.25Cr-1Mo/2.25Cr-1Mo similar weld joint, and a 2.25Cr-1Mo/Alloy 800 dissimilar weld joint at 823 K over a stress range of 90 to 250 MPa has been carried out. The specimens for creep testing were taken from single-V weld pads fabricated by a shielded metal arc-welding process using 2.25Cr-1Mo steel (for similar-joint) and INCONEL 182 (for dissimilar-joint) electrodes. The weld pads were subsequently given a postweld heat treatment (PWHT) of 973 K for 1 hour. The microstructure and microhardness of the weld joints were evaluated in the as-welded, postweld heat-treated, and creeptested conditions. The heat-affected zone (HAZ) of similar weld joint consisted of bainite in the coarse-prior-austenitic-grain (CPAG) region near the fusion line, followed by bainite in the fine-prioraustenitic-grain (FPAG) and intercritical regions merging with the unaffected base metal. In addition to the HAZ structures in the 2.25Cr-1Mo steel, the dissimilar weld joint displayed a definite INCONEL/ 2.25Cr-1Mo weld interface structure present either as a sharp line or as a diffuse region. A hardness trough was observed in the intercritical region of the HAZ in both weld joints, while a maxima in hardness was seen at the weld interface of the dissimilar weld joint. Both weld joints exhibited significantly lower rupture lives compared to the 2.25Cr-1Mo base metal. The dissimilar weld joint exhibited poor rupture life compared to the similar weld joint, at applied stresses lower than 130 MPa. In both weld joints, the strain distribution across the specimen gage length during creep testing varied significantly. During creep testing, localization of deformation occurred in the intercritical HAZ. In the similar weld joint, at all stress levels investigated, and in the dissimilar weld joint, at stresses Ն150 MPa, the creep failure occurred in the intercritical HAZ. The fracture occurred by transgranular mode with a large number of dimples. At stresses below 150 MPa, the failure in the dissimilar weld joint occurred in the CPAG HAZ near to the weld interface. The failure occurred by extensive intergranular creep cavity formation.
Metallurgical and Materials Transactions A, 2012
Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.
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.
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 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.