Characteristics of premature creep failure in over-tempered base metal of grade 91 steel weldment

2021 ◽  
Vol 192 ◽  
pp. 104396
Author(s):  
Yiyu Wang ◽  
Wei Zhang ◽  
Yanli Wang ◽  
Zhili Feng
Keyword(s):  
Base Metal ◽  
Creep Failure ◽  
Steel Weldment ◽  
Grade 91 ◽  
Grade 91 Steel

Creep-Fatigue Life Determination of Grade 91 Steel Using a Strain-Range Separation Method

2009 ◽  
Author(s):  
Wolfgang Hoffelner
Keyword(s):  
Stress Rupture ◽  
Strain Range ◽  
Inelastic Strain ◽  
Fatigue Curve ◽  
Cyclic Softening ◽  
Least Square ◽  
Creep Failure ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Grade 91 Steel

The method of strain range partitioning developed by Manson offers a possibility for treatment of creep-fatigue interactions. It partitions the strain-range of a complex hysteresis loop into four elementary strain range types. Although the method has its merits it is difficult to apply because of lacking experimental data and difficult loop reconstructions. The paper describes an approach which separates the inelastic strain range only into a fatigue portion and a creep portion following both a power law Coffin-Manson relationship. Coefficients and exponents were determined by a simple least square fitting procedure from a set of literature data. The plastic part agreed very well with the experimentally determined fatigue curve. The creep part could, however, only be understood using fatigue-modified stress rupture data accounting for cyclic softening. With this approach it was possible to determine number of cycles to creep failure as a function of the pure creep strain range. This procedure was applied to a set of literature data of grade 91 steel which covered a temperature range of 500°C, 550°C, 600°C with stress controlled and strain controlled hold-times. Life-times were predicted in a range corresponding with the scatter of pure fatigue or creep curves, which means that a very good agreement was obtained. The paper will give a thorough description of the procedure and demonstrate its applicability to design codes.

scholarly journals Microstructure and Mechanical Properties of Intercritically Treated Grade 91 Steel

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 3985
Author(s):  
Yiyu Wang ◽  
Wei Zhang ◽  
Yong Chae Lim ◽  
Yanli Wang ◽  
Zhili Feng
Keyword(s):  
Mechanical Properties ◽  
Base Metal ◽  
Degradation Mechanism ◽  
Local Strain ◽  
Critical Temperatures ◽  
Microstructure And Mechanical Properties ◽  
Heat Treated ◽  
Hardness Increase ◽  
Grade 91 ◽  
Grade 91 Steel

Premature creep failures at the intercritical heat affected zone (ICHAZ) of creep-resistant steel weldments have been frequently reported. However, the creep degradation mechanism of different microstructure constituents in ICHAZ is complicated and needs further clarification. In this work, Grade 91 steel was intercritically heat-treated at a temperature (860 °C) between the critical temperatures AC1 and AC3, and a correlation between microstructure and mechanical properties of the heat-treated specimen was built. The effects of austenitization and tempering resulting from the intercritical treatment (IT) differentiated the local strain energies between the two microstructure constituents: newly transformed martensite (NTM) and over-tempered martensite (OTM). The formation of NTM grains led to a hardness increase from 247 HV0.5 in the base metal to 332 HV0.5 in the IT specimen. The ultimate tensile strength (UTS) increased from 739 MPa in the base metal to 1054 MPa in the IT specimen. Extensive growth of the OTM grains and rapid recovery of NTM grains took place simultaneously in the IT specimen during a typical tempering at 760 °C. These microstructure degradations led to a lowered hardness of 178 HV0.5, a reduced UTS of 596 MPa, and a poor creep resistance with a minimum creep strain rate of 0.49 %/h at 650 °C in an IT + tempering (ITT) specimen.

Evaluation of Stress Rupture Factors for Grade 91 Weldments

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Kazuhiro Kimura ◽  
Masatsugu Yaguchi
Keyword(s):  
Base Metal ◽  
Rupture Strength ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Premature Failure ◽  
Rupture Data ◽  
Grade 91 ◽  
Grade 91 Steel

Abstract Stress rupture factors and weld strength reduction factors for Grade 91 steel weldments in the codes and literatures have been reviewed. Stress rupture factors for weld metals proposed for code case N-47 in the mid 1980's was defined as a ratio of average rupture strength of the deposited filler metal to the average rupture strength of the base metal. Remarkable drop in creep rupture strength of weldments is significant issue of Grade 91, especially in the low-stress and long-term regime. A premature failure of Grade 91 steel weldments in the long-term, however, is caused by type IV failure which takes place in the fine grain heat affected zone (FG-HAZ), rather than fracture in the deposited weld metal. The stress rupture factor of the Grade 91 steel, therefore, was based on the creep rupture strength of cross weld test specimens. Creep rupture data of Grade 91 steel weldments reported in the publication of ASME STP-PT-077 were integrated with the creep rupture data collected in Japan and used for this study. Time- and temperature-dependent stress rupture factors for Grade 91 steel have been evaluated based on the consolidated database as a ratio of average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.

Re-Evaluation of Stress Rupture Factors for Grade 91 Weldments Based on the Extended Database With the Data Collected in Japan

2019 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Masatsugu Yaguchi
Keyword(s):  
Base Metal ◽  
Rupture Strength ◽  
Stress Rupture ◽  
Creep Rupture ◽  
Weld Strength ◽  
Creep Rupture Strength ◽  
Premature Failure ◽  
Grade 91 ◽  
Grade 91 Steel

Abstract Stress rupture factors and weld strength reduction factors for Grade 91 steel weldments in the codes and literatures have been reviewed. Stress rupture factors for weld metals proposed for Code Case N-47 in the mid 1980’s was defined as a ratio of average rupture strength of the deposited filler metal to the average rupture strength of the base metal. Remarkable drop in creep rupture strength of weldments is significant issue of Grade 91, especially in the low-stress and long-term regime. A premature failure of Grade 91 steel weldments in the long-term, however, is caused by Type IV failure which takes place in the fine grain heat affected zone (FG-HAZ), rather than fracture in the deposited weld metal. The stress rupture factor of the Grade 91 steel, therefore, was based on the creep rupture strength of cross weld test specimens. Creep rupture data of Grade 91 steel weldments reported in the publication of ASME STP-PT-077 was incorporated in the creep database collected in Japan which was used for the previous study. Time and temperature dependent stress rupture factors for Grade 91 steel have been re-evaluated based on the extended database as a ratio of average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.

Localized Creep Deformation Evaluation in Grade 91 Steel Weldment

2021 ◽  
Author(s):  
Yiyu Wang ◽  
Wei Zhang ◽  
Yanli Wang ◽  
Zhili Feng
Keyword(s):  
Creep Deformation ◽  
Steel Weldment ◽  
Grade 91 ◽  
Grade 91 Steel

Causes of heat-to-heat variation of creep strength in grade 91 steel

2017 ◽  
Vol 696 ◽  
pp. 104-112 ◽  
Author(s):  
K. Maruyama ◽  
J. Nakamura ◽  
N. Sekido ◽  
K. Yoshimi
Keyword(s):  
Creep Strength ◽  
Grade 91 ◽  
Grade 91 Steel

Influence of Stress on Degradation and Life Prediction of High Strength Ferritic Steels

2004 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Kiyoshi Kubo ◽  
Hideaki Kushima
Keyword(s):  
Yield Stress ◽  
Elastic Limit ◽  
High Strength ◽  
Time To Rupture ◽  
Limit Stress ◽  
Creep Resistant Steels ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

Influence of stress on creep deformation and degradation behavior has been investigated. Corresponding to inflection of stress vs. time to rupture curve, difference in recovery phenomena, that was homogeneous in short-term and inhomogeneous in long-term, was observed. Inflection of stress vs. time to rupture curve took place at the stress condition corresponding to half of 0.2% offset yield stress at the temperature. Elastic limit stress of Grade 91 steel was evaluated to be 150MPa at 600°C and 100MPa at 650°C, by means of stress abrupt change test. These stresses were found to be almost the same as half of 0.2% offset yield stress at the temperatures. Inflection of stress vs. time to rupture curve is caused by transient of applied stress from higher level than elastic limit to within elastic range. It has been concluded that long-term creep strength of ferritic creep resistant steels should be predicted from the selected creep rupture data under the stresses lower than elastic limit by considering half of 0.2% offset yield stress at the temperature, by means of Larson-Miller parameter with a constant of 20.

A Postassessment Test of 100,000 h Creep Rupture Strength of Grade 91 Steel at 600 °C

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
K. Maruyama ◽  
N. Sekido ◽  
K. Yoshimi
Keyword(s):  
Rupture Strength ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Data Points ◽  
Predicted Values ◽  
Grade 91 ◽  
Term Creep ◽  
Term Data ◽  
Grade 91 Steel

Predictions as to 105 h creep rupture strength of grade 91 steel have been made recently. The predicted values are examined with long-term creep rupture data of the steel. Three creep rupture databases were used in the predictions: data of tube products of grade 91 steel reported in National Institute for Materials Science (NIMS) Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an American Society of Mechanical Engineers (ASME) code committee. Short-term creep rupture data points were discarded by the following criteria for minimizing overestimation of the strength: selecting long-term data points with low activation energy (multiregion analysis), selecting data points crept at stresses lower than a half of proof stress (σ0.2/2 criterion), and selecting data points longer than 1000 h (cutoff time of 1000 h). In the case of NIMS T91 database, a time–temperature parameter (TTP) analysis of a dataset selected by multiregion analysis can properly describe the long-term data points and gives the creep rupture strength of 68 MPa at 600 °C. However, TTP analyses of datasets selected by σ0.2/2 criterion and cutoff time of 1000 h from the same database overestimate the data points and predict the strength over 80 MPa. Datasets selected by the same criterion from the three databases provide similar values of the strength. The different criteria for data selection have more substantial effects on predicted values of the strength of the steel than difference of the databases.

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