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Vijay K Singh - One of the best experts on this subject based on the ideXlab platform.
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effect of thermal aging on ductile brittle transition Temperature of modified 9cr 1mo steel evaluated with Reference Temperature approach under dynamic loading condition
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2013Co-Authors: S Sathyanarayanan, Joysurya Basu, G Sasikala, Vijay K SinghAbstract:The effect of thermal aging on the ductile-brittle transition behavior has been assessed for a modified 9Cr-1Mo steel (P91) using the Reference Temperature approach under dynamic loading condition (T 0 dy ). The steel in normalized and tempered (NT) condition and in different levels of subsequent cold work (CW) was subjected to thermal aging at Temperatures of 873 K and 923 K (600 °C and 650 °C) for 5000 and 10,000 hours. For the NT and all the cold work conditions of the starting material, a drastic increase in T 0 dy has been noticed after aging at 923 K (650 °C) for 10,000 h. A moderate increase was observed for the NT steel aged at 873 K (600 °C) for 5000 hours and for the 10 pct CW steel aged at 873 K (600 °C) for 10,000 h. A detailed transmission electron microscope (TEM) study of the embrittled materials aged at 923 K (650 °C)/10,000 hours and 873 K (600 °C)/10,000 hours has indicated presence of hexagonal Laves phase of Fe2(Mo,Nb) type with different size and spatial distributions. The increase in the T 0 dy is attributed to the embrittling effect of a network of Laves phase precipitates along the grain boundaries.
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evaluation of dynamic fracture toughness based Reference Temperature t0dy of modified 9cr 1mo steel in phosphorus embrittled and cold worked condition
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: S Sathyanarayanan, G Sasikala, K G Samuel, S K Ray, Vijay K SinghAbstract:Abstract In the present study, the DBTT of a high phosphorus bearing modified 9Cr–1Mo steel in normalized and tempered (N&T) condition and also after 5% and 10% cold work, has been evaluated by extending the Reference Temperature ( T 0 ) based Master Curve approach to dynamic loading conditions. The Reference Temperature in dynamic loading condition ( T 0 dy ) thus determined is found to be significantly high for the N&T Mod.9Cr–1Mo steel as compared to plain 9Cr–1Mo steel. Cold-work effect was not found to be significant in T 0 dy evaluation of Mod.9Cr–1Mo steel. The high T 0 dy of the present Mod.9Cr–1Mo steel is attributed to a fracture initiation mechanism predominated by decohesion of prior austenitic grain boundaries at the fatigue pre-crack front. This is attributed to segregation of phosphorus along the prior austenitic grain boundaries causing embrittlement, supported by SEM and Secondary Ion Mass Spectrometry (SIMS) observations.
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ductile brittle transition Temperatures and dynamic fracture toughness of 9cr 1mo steel
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: P R Sreenivasan, S L Mannan, Vijay K SinghAbstract:The ductile-brittle transition Temperature (DBTT) of 9Cr-1Mo steel was characterized by an RT NDT-based K IR curve approach and a Reference Temperature (T 0)-based master curve (MC) approach. The MC was developed at a dynamic loading condition (loading rate of 5.12 m/s), using precracked Charpy V-notch (PCVN) specimens, and the Reference Temperature was termed T 0 dy . The RT NDT and T 0 dy were determined to be −25 °C and −52 °C, respectively. The T 0 dy was also estimated from instrumented CVN tests, using a modified Schindler procedure to evaluate K Jd ; the result shows close agreement with that obtained from the PCVN tests. The ASME K IR -curve approach proves to be too conservative compared to the obtained trend of the fracture toughness with Temperature. The cleavage fracture stress, σ* f , estimated from the critical length, l*, shows good agreement with that estimated from the load-Temperature diagram (2400 to 2450 MPa), which was constructed from the CVN test results. The crack initiation mechanism has been identified as decohesion of the particle-matrix interface, rather than as the fracture of the particles.
P R Sreenivasan - One of the best experts on this subject based on the ideXlab platform.
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application of a cleavage fracture stress model for estimating the astm e 1921 Reference Temperature of ferritic steels from instrumented impact test of cvn specimens without precracking
Procedia Engineering, 2014Co-Authors: P R SreenivasanAbstract:Abstract A recently proposed semi-empirical cleavage fracture stress (CFS) model by the author based on the microscopic cleavage fracture stress, σ f , for estimating the ASTM E-1921 Reference Temperature, T 0 , of ferritic steels from instrumented impact test (IIT) of Charpy V-notch (CVN) specimens without precracking has been demonstrated for steels with room Temperature yield strength in the range 400-750 MPa, including irradiated steels. The estimate of T 0 , based on the CFS model, T Qcfs lies within a ± 20 °C band, being conservative for most of the steels, but less conservative than T QIGC based on the IGC-procedure. CFS model enhances the validity and utility of the CVN IIT by enabling estimation of design-relevant master curve from unprecracked CVN specimens. In this paper, the method is further applied to some steels (both unirradiated and irradiated) reported in the literature most of which have only IIT data and static tensile data available. The method has also been applied to some IIT test results obtained at IGCAR for 9Cr-1Mo steel in various simulated weld-heat affected zone conditions. The results are compared with T QIGC or other estimates like T QBT or T 0 , if available.
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simplicity consistency and conservatism of some recent charpy energy fracture toughness correlations in estimating the astm e 1921 Reference Temperature
Transactions of The Indian Institute of Metals, 2011Co-Authors: P R SreenivasanAbstract:After examining some recent Charpy energy–fracture toughness correlations, a mean-2 procedure (M2P) has been proposed for estimation of Reference Temperature, T 0, from CVN tests alone and has been established through a correlative approach. The T 0 estimate from the M2P is referred as, T Q-M2, and is obtained as the mean value of two different estimates discussed in the text. Simplicity, consistency and assured conservatism of the T QM2 has been demonstrated by comparison with measured T 0 values for some new steels. For the larger conservative estimate, it is suggested to take the larger of the two and this, in most cases happens to be the simple estimate, T Q41b, and is the same as T 41J (the 41 J Charpy energy Temperature). The applicability of the M2P for irradiated steels has been demonstrated. A new two-parameter correlation for estimating fracture toughness from Charpy energy has been derived and this gives encouraging results for the steels discussed in this paper.
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inverse of wallin s relation for the effect of strain rate on the astm e 1921 Reference Temperature and its application to Reference Temperature estimation from charpy tests
Nuclear Engineering and Design, 2011Co-Authors: P R SreenivasanAbstract:Abstract An inverse relation to that of Wallin's strain rate equation has been obtained for predicting the static Reference Temperature from dynamic results. Wallin strain rate equation (WSRE) predicts the Reference Temperature at faster loading rates (expressed as stress intensity factor – SIF-rates) from room Temperature yield strength (RT-YS) and quasi-static Reference Temperature, T 0 . The inverse WSRE (IWSRE) predicts T 0 from T 0 dy , that is, T 0 at dynamic loading rates as obtained in impact and other dynamic tests. For this purpose, the same dataset that was used by Wallin for deriving the original WSRE has been used. It has also been found that the dynamic Reference Temperature obtained by applying the modified Schindler procedure (MSP) to Charpy V-notch (CVN) impact tests, that is, T QSch dy , provides a conservative or close estimate of Reference Temperature corresponding to a loading rate of ∼10 6 MPa √m s −1 . Then using the T QSch dy in the IWSRE along with RT-YS and SIF rate of 10 6 MPa √m s −1 , results in an estimate of quasi-static T 0 , namely, T QMSP-IW , the subscript indicating use of both the MSP and IWSRE. An equation directly correlating T QSch dy to T 0 has also been obtained. The estimates of T 0 from this direct correlation are referred as T QMSP , the subscript indicating the use of MSP. It has been shown that the larger of the two estimates, T QMSP-IW and T QMSP , provides a reasonably accurate, but conservative estimate of T 0 and is termed – T QSchW, to indicate the use of both the MSP and IWSRE procedures. T QSchW is a promising estimate for steels with T QSch dy less than 60 °C – termed T Q-est , to indicate the estimated Reference Temperature value; for steels with T QSch dy > 60 ° C , T Q-est is the larger of the two estimates, namely, T QM2 and T QSchW . The equation reported in the literature correlating the brittleness transition Temperature, T D (obtained from instrumented Charpy V-notch – CVN – impact tests), though has a tendency to accuracy and ease of estimation, is not suitable for making conservative Reference Temperature estimates, because of excessive scatter and lack of robustness in T D estimation. The shifts in T Q-est , namely, Δ T Q-est , are acceptably conservative even for the highly irradiated steel. For the high Reference Temperature steels and low upper shelf inhomogeneous steels, the anomaly of T Q-est being larger than RT NDT indicates that the conservatism of even the RT NDT approach is not much for such steels. A very useful application of the procedures in this paper is that the T Q-est or ( T Q-est – 20 °C) can provide a convenient test Temperature for performing the tests as per ASTM E-1921 test standard for determining T 0 . The whole procedure or methodology detailed in this paper for obtaining the conservatively estimated Reference Temperature, T Q-est , is designated as IGCAR-procedure, IGCAR being the acronym for the author's organization.
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estimation of astm e 1921 Reference Temperature from charpy tests charpy energy fracture toughness correlation method
Engineering Fracture Mechanics, 2008Co-Authors: P R SreenivasanAbstract:Abstract In this paper, some of the older and newer Charpy-fracture toughness correlations have been examined and new correlations have been developed for predicting the ASTM E-1921 standard Reference Temperature, T 0 . The results have been applied to some selected new steels and compared with measured T 0 , where available. It is found that the predicted Reference Temperature from the new procedure gives reliable and acceptably conservative engineering estimate of T 0 . Predicted values of Reference Temperatures under dynamic conditions from these T 0 using Wallin’s strain rate shift equation agree well with measured dynamic values for a few steels giving added support to the new procedure.
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ductile brittle transition Temperatures and dynamic fracture toughness of 9cr 1mo steel
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: P R Sreenivasan, S L Mannan, Vijay K SinghAbstract:The ductile-brittle transition Temperature (DBTT) of 9Cr-1Mo steel was characterized by an RT NDT-based K IR curve approach and a Reference Temperature (T 0)-based master curve (MC) approach. The MC was developed at a dynamic loading condition (loading rate of 5.12 m/s), using precracked Charpy V-notch (PCVN) specimens, and the Reference Temperature was termed T 0 dy . The RT NDT and T 0 dy were determined to be −25 °C and −52 °C, respectively. The T 0 dy was also estimated from instrumented CVN tests, using a modified Schindler procedure to evaluate K Jd ; the result shows close agreement with that obtained from the PCVN tests. The ASME K IR -curve approach proves to be too conservative compared to the obtained trend of the fracture toughness with Temperature. The cleavage fracture stress, σ* f , estimated from the critical length, l*, shows good agreement with that estimated from the load-Temperature diagram (2400 to 2450 MPa), which was constructed from the CVN test results. The crack initiation mechanism has been identified as decohesion of the particle-matrix interface, rather than as the fracture of the particles.
José Carlos Pinto - One of the best experts on this subject based on the ideXlab platform.
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optimum Reference Temperature for reparameterization of the arrhenius equation part 2 problems involving multiple reparameterizations
Chemical Engineering Science, 2008Co-Authors: Marcio Schwaab, Livia Pereira Lemos, José Carlos PintoAbstract:Abstract Existence of high parameter correlations is one of the major problems during parameter estimation. This is particularly true when the mathematical model presents one or more kinetic constants that depend on Temperature, as defined by the Arrhenius equation. In a recent work, Schwaab and Pinto [2007. Optimum Reference Temperature for reparameterization of the Arrhenius equation. Part 1: problems involving one kinetic constant. Chemical Engineering Science 62, 2750–2764] showed that an optimum Reference Temperature can be defined for reparameterization of the Arrhenius equation and elimination of parameter correlation, when the model contains a single kinetic constant. However, when the model contains more than one kinetic constant, the number of parameter correlations is larger than the number of Reference Temperatures that can be defined; consequently, it becomes impossible to eliminate all the parameter correlations simultaneously. For this reason, in this work different norms are defined for the parameter correlation matrix and are used to allow for minimization of the parameter correlations through manipulation of Reference Temperatures. Three parameter estimation problems are used to illustrate the use of the proposed two-step parameter estimation procedure and to show that the minimization of parameter correlations and relative errors are indeed possible through proper manipulation of Reference Temperatures in problems involving multiple model parameters.
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optimum Reference Temperature for reparameterization of the arrhenius equation part 1 problems involving one kinetic constant
Chemical Engineering Science, 2007Co-Authors: Marcio Schwaab, José Carlos PintoAbstract:The Arrhenius equation is one of the most well-known equations in the chemical field and is widely used to describe the Temperature dependence of kinetic constants. This equation contains two parameters, the frequency factor and the activation energy, which are usually estimated from experimental data. However, the correlation between the two parameter estimates is usually very high and in many cases is practically equal to one. This makes the precise identification of the parameter values very difficult. The high parameter correlation can be diminished through reparameterization of the Arrhenius equation and definition of a Reference Temperature. For problems involving a single kinetic constant, it is shown here both analytically and through numerical examples that the proper definition of the Reference Temperature allows for estimation of the parameters of the Arrhenius equation without correlation and with minimum relative error, leading to improvement of the parameter estimation procedure.
S Sathyanarayanan - One of the best experts on this subject based on the ideXlab platform.
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a study of fracture mechanisms in rafm steel in the ductile to brittle transition Temperature regime
Procedia Engineering, 2014Co-Authors: Arup Dasgupta, Rajendra E Kumar, S Saroja, S Sathyanarayanan, G Sasikala, S K Albert, A K Bhaduri, T. JayakumarAbstract:Abstract The fracture behaviour of a Reduced Activation Ferritic Martensitic Steel (RAFM) has been studied within the Ductile to Brittle Transition Temperature (DBTT) regime. The DBTT has been determined by ASTM E 1921 based Reference Temperature approach under dynamic loading condition. The dynamic Reference Temperature (T0dy) was found to be − 33.8 °C. The fracture mechanism has been studied by extracting TEM specimens precisely at the crack initiation sites using focused ion beam (FIB) technique in a high resolution dual beam scanning electron microscope. Detailed analytical TEM studies revealed that the morphology of carbides play a crucial role in the initiation of a crack. The larger ellipsoidal carbides, which were found to be Cr-rich, have been found to be responsible for dislocation piles ups. The shorter edge of these ellipsoidal carbides are areas of high stress concentration and were found to initiate cracks by decohesion of the particle-matrix interface. On the contrary, the iron rich carbides have been found to be smaller, more spherical, and thus less effective in blocking dislocation movement and therefore formation of pile ups. The results, which reveal an important mechanism towards crack initiation in ferritic-martensitic steels, will be presented in detail.
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effect of thermal aging on ductile brittle transition Temperature of modified 9cr 1mo steel evaluated with Reference Temperature approach under dynamic loading condition
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2013Co-Authors: S Sathyanarayanan, Joysurya Basu, G Sasikala, Vijay K SinghAbstract:The effect of thermal aging on the ductile-brittle transition behavior has been assessed for a modified 9Cr-1Mo steel (P91) using the Reference Temperature approach under dynamic loading condition (T 0 dy ). The steel in normalized and tempered (NT) condition and in different levels of subsequent cold work (CW) was subjected to thermal aging at Temperatures of 873 K and 923 K (600 °C and 650 °C) for 5000 and 10,000 hours. For the NT and all the cold work conditions of the starting material, a drastic increase in T 0 dy has been noticed after aging at 923 K (650 °C) for 10,000 h. A moderate increase was observed for the NT steel aged at 873 K (600 °C) for 5000 hours and for the 10 pct CW steel aged at 873 K (600 °C) for 10,000 h. A detailed transmission electron microscope (TEM) study of the embrittled materials aged at 923 K (650 °C)/10,000 hours and 873 K (600 °C)/10,000 hours has indicated presence of hexagonal Laves phase of Fe2(Mo,Nb) type with different size and spatial distributions. The increase in the T 0 dy is attributed to the embrittling effect of a network of Laves phase precipitates along the grain boundaries.
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evaluation of dynamic fracture toughness based Reference Temperature t0dy of modified 9cr 1mo steel in phosphorus embrittled and cold worked condition
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: S Sathyanarayanan, G Sasikala, K G Samuel, S K Ray, Vijay K SinghAbstract:Abstract In the present study, the DBTT of a high phosphorus bearing modified 9Cr–1Mo steel in normalized and tempered (N&T) condition and also after 5% and 10% cold work, has been evaluated by extending the Reference Temperature ( T 0 ) based Master Curve approach to dynamic loading conditions. The Reference Temperature in dynamic loading condition ( T 0 dy ) thus determined is found to be significantly high for the N&T Mod.9Cr–1Mo steel as compared to plain 9Cr–1Mo steel. Cold-work effect was not found to be significant in T 0 dy evaluation of Mod.9Cr–1Mo steel. The high T 0 dy of the present Mod.9Cr–1Mo steel is attributed to a fracture initiation mechanism predominated by decohesion of prior austenitic grain boundaries at the fatigue pre-crack front. This is attributed to segregation of phosphorus along the prior austenitic grain boundaries causing embrittlement, supported by SEM and Secondary Ion Mass Spectrometry (SIMS) observations.
Marcio Schwaab - One of the best experts on this subject based on the ideXlab platform.
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optimum Reference Temperature for reparameterization of the arrhenius equation part 2 problems involving multiple reparameterizations
Chemical Engineering Science, 2008Co-Authors: Marcio Schwaab, Livia Pereira Lemos, José Carlos PintoAbstract:Abstract Existence of high parameter correlations is one of the major problems during parameter estimation. This is particularly true when the mathematical model presents one or more kinetic constants that depend on Temperature, as defined by the Arrhenius equation. In a recent work, Schwaab and Pinto [2007. Optimum Reference Temperature for reparameterization of the Arrhenius equation. Part 1: problems involving one kinetic constant. Chemical Engineering Science 62, 2750–2764] showed that an optimum Reference Temperature can be defined for reparameterization of the Arrhenius equation and elimination of parameter correlation, when the model contains a single kinetic constant. However, when the model contains more than one kinetic constant, the number of parameter correlations is larger than the number of Reference Temperatures that can be defined; consequently, it becomes impossible to eliminate all the parameter correlations simultaneously. For this reason, in this work different norms are defined for the parameter correlation matrix and are used to allow for minimization of the parameter correlations through manipulation of Reference Temperatures. Three parameter estimation problems are used to illustrate the use of the proposed two-step parameter estimation procedure and to show that the minimization of parameter correlations and relative errors are indeed possible through proper manipulation of Reference Temperatures in problems involving multiple model parameters.
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optimum Reference Temperature for reparameterization of the arrhenius equation part 1 problems involving one kinetic constant
Chemical Engineering Science, 2007Co-Authors: Marcio Schwaab, José Carlos PintoAbstract:The Arrhenius equation is one of the most well-known equations in the chemical field and is widely used to describe the Temperature dependence of kinetic constants. This equation contains two parameters, the frequency factor and the activation energy, which are usually estimated from experimental data. However, the correlation between the two parameter estimates is usually very high and in many cases is practically equal to one. This makes the precise identification of the parameter values very difficult. The high parameter correlation can be diminished through reparameterization of the Arrhenius equation and definition of a Reference Temperature. For problems involving a single kinetic constant, it is shown here both analytically and through numerical examples that the proper definition of the Reference Temperature allows for estimation of the parameters of the Arrhenius equation without correlation and with minimum relative error, leading to improvement of the parameter estimation procedure.
