Girish Shastry - Academia.edu (original) (raw)

Papers by Girish Shastry

Journal of Engineering Materials and Technology, 2003

Residual life analysis of power plant components like boiler tubes, superheater outlet headers, r... more Residual life analysis of power plant components like boiler tubes, superheater outlet headers, reheater headers, steam pipes, etc., is important for life extension and avoidance of catastrophic failure. In this context, fracture toughness is very important. The fracture characteristics after prolonged exposure to high temperatures and pressures are likely to be different from that of the virgin material. 2.25Cr-1Mo reheater header pipe exposed at 813 K for 120,000 h was studied by instrumented impact tests (IIT) to evaluate dynamic fracture toughness and Charpy transition properties. The methods presented in this paper for estimating dynamic fracture toughness from IIT of Charpy specimens give reliably conservative results without the need for precracking. For estimating fracture appearance transition temperature (FATT) from IIT load-time traces, the equation for percent shear fracture, PSF3, gives the best 1:1 correlation with measured values from fracture surfaces. The lower boun...

Journal of Engineering Materials and Technology, 2018

This paper outlines a microstructure-based model relating gamma prime microstructure and grain si... more This paper outlines a microstructure-based model relating gamma prime microstructure and grain size of Ni-base alloys to their creep behavior. The ability of the model to explain creep of multiple superalloys with a single equation and parameter set is demonstrated. The only parameters that are changed from alloy to alloy are related to the gamma prime characteristics and grain size. This model also allows prediction of creep performance as a function of heat treatment and explains some apparently contradictory data from the literature.

Nitrogen-alloyed, low carbon grade of type 316 stainless steel has been developed indigenously in... more Nitrogen-alloyed, low carbon grade of type 316 stainless steel has been developed indigenously in collaboration with Alloy Steel Plant (ASP), Durgapur for the nuclear steam supply system components of Prototype Fast Breeder Reactor. Creep properties of this material have been determined at 923 K at various stress-levels and compared with the creep properties of imported steel of similar chemical composition. Material developed at ASP was found to be comparable to the imported steel with respect to its creep properties at 923 K.

Materials Science and Engineering: A, 2007

... We are extremely thankful to Dr. SK Ray, Head, Materials Technology Division, for useful disc... more ... We are extremely thankful to Dr. SK Ray, Head, Materials Technology Division, for useful discussions. The technical assistance of Ms. Omana Gopalan, Mr. AR Doraiswamy, Mr. R. Thirumurugesan and Mr. D. Natarajan is gratefully acknowledged. References. ...

Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures, 2007

ABSTRACT

Materials Science and Engineering: A, 2008

ABSTRACT

Materials Science and Engineering: A, 2013

Abstract Creep and rafting in Ni-based single crystal Rene N4 is described using reported phenome... more Abstract Creep and rafting in Ni-based single crystal Rene N4 is described using reported phenomenological models after modifying the creep model to represent the rafting induced hardening of the structure against creep and the greater propensity for shearing of γ ′ as the structure rafts and dislocation density in the channels and γ / γ ′ interface builds up. The proposed model can describe the creep strain evolution at 1144 K over the stress range 241–413 MPa. The rafting model is shown to provide an adequate representation of horizontal and vertical channel width evolution at 1144 K and 1255 K. The variation of the physical parameters in the creep model viz., back stress, dislocation density and shear rate is rationalized scientifically thereby substantiating the physical basis of the model. The development of back stress in the channels is explained mechanistically through the deposition of dislocation segments at γ / γ ′ interface by the Orowan loops expanding in the channel and the recovery of the interfacial dislocation networks. The evolution in Orowan stress consequent to rafting and its effect on dislocation activity are elucidated. The evolution of the kinetics for dynamic and static recovery processes which accompany creep strain accumulation has also been explained mechanistically.

International Journal of Pressure Vessels and Piping, 2004

The Voce equation was used to model the tensile flow and work-hardening behaviour of a service-ex... more The Voce equation was used to model the tensile flow and work-hardening behaviour of a service-exposed 2.25Cr-1Mo steel. The applicability of Voce parameters obtained from the fit to experimental true stress-true strain datasets for estimating the validity of the fit was examined. The Voce equation was found to model the stress-strain curve closely. The Voce parameter n v was correlated to the underlying dislocation activities. It was found that the values of Voce parameters at various temperatures and strain rates can be used to infer the operating recovery mechanism during stage III hardening. A low absolute value of n v is indicative of recovery by cross-slip, whereas the high temperature transition to climb or sub-boundary migration driven recovery is accompanied by an increase in the value of n v :

Materials Science and Technology, 2007

Tensile deformation behaviour of AISI 316L(N) stainless steel was investigated over the range 298... more Tensile deformation behaviour of AISI 316L(N) stainless steel was investigated over the range 298 to 1023 K. The yield and tensile strength were found to meet the minimum values mandated by RCC-MR, the French design code for fast reactors. The tensile flow behaviour was modelled using Ludwigson and Voce equation. Ludwigson equation could model the flow behaviour adequately before the onset of saturation at temperatures .823 K. Voce equation could model the flow behaviour between 298 and 1023 K. The physical basis for the variation with respect to strain rate and temperature of the constants obtained by modelling the flow curve using Ludwigson and Voce equation is discussed.

Journal of Engineering Materials and Technology, 2003

Residual life analysis of power plant components like boiler tubes, superheater outlet headers, r... more Residual life analysis of power plant components like boiler tubes, superheater outlet headers, reheater headers, steam pipes, etc., is important for life extension and avoidance of catastrophic failure. In this context, fracture toughness is very important. The fracture characteristics after prolonged exposure to high temperatures and pressures are likely to be different from that of the virgin material. 2.25Cr-1Mo reheater header pipe exposed at 813 K for 120,000 h was studied by instrumented impact tests (IIT) to evaluate dynamic fracture toughness and Charpy transition properties. The methods presented in this paper for estimating dynamic fracture toughness from IIT of Charpy specimens give reliably conservative results without the need for precracking. For estimating fracture appearance transition temperature (FATT) from IIT load-time traces, the equation for percent shear fracture, PSF3, gives the best 1:1 correlation with measured values from fracture surfaces. The lower boun...

Journal of Engineering Materials and Technology, 2018

This paper outlines a microstructure-based model relating gamma prime microstructure and grain si... more This paper outlines a microstructure-based model relating gamma prime microstructure and grain size of Ni-base alloys to their creep behavior. The ability of the model to explain creep of multiple superalloys with a single equation and parameter set is demonstrated. The only parameters that are changed from alloy to alloy are related to the gamma prime characteristics and grain size. This model also allows prediction of creep performance as a function of heat treatment and explains some apparently contradictory data from the literature.

Nitrogen-alloyed, low carbon grade of type 316 stainless steel has been developed indigenously in... more Nitrogen-alloyed, low carbon grade of type 316 stainless steel has been developed indigenously in collaboration with Alloy Steel Plant (ASP), Durgapur for the nuclear steam supply system components of Prototype Fast Breeder Reactor. Creep properties of this material have been determined at 923 K at various stress-levels and compared with the creep properties of imported steel of similar chemical composition. Material developed at ASP was found to be comparable to the imported steel with respect to its creep properties at 923 K.

Materials Science and Engineering: A, 2007

... We are extremely thankful to Dr. SK Ray, Head, Materials Technology Division, for useful disc... more ... We are extremely thankful to Dr. SK Ray, Head, Materials Technology Division, for useful discussions. The technical assistance of Ms. Omana Gopalan, Mr. AR Doraiswamy, Mr. R. Thirumurugesan and Mr. D. Natarajan is gratefully acknowledged. References. ...

Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures, 2007

ABSTRACT

Materials Science and Engineering: A, 2008

ABSTRACT

Materials Science and Engineering: A, 2013

Abstract Creep and rafting in Ni-based single crystal Rene N4 is described using reported phenome... more Abstract Creep and rafting in Ni-based single crystal Rene N4 is described using reported phenomenological models after modifying the creep model to represent the rafting induced hardening of the structure against creep and the greater propensity for shearing of γ ′ as the structure rafts and dislocation density in the channels and γ / γ ′ interface builds up. The proposed model can describe the creep strain evolution at 1144 K over the stress range 241–413 MPa. The rafting model is shown to provide an adequate representation of horizontal and vertical channel width evolution at 1144 K and 1255 K. The variation of the physical parameters in the creep model viz., back stress, dislocation density and shear rate is rationalized scientifically thereby substantiating the physical basis of the model. The development of back stress in the channels is explained mechanistically through the deposition of dislocation segments at γ / γ ′ interface by the Orowan loops expanding in the channel and the recovery of the interfacial dislocation networks. The evolution in Orowan stress consequent to rafting and its effect on dislocation activity are elucidated. The evolution of the kinetics for dynamic and static recovery processes which accompany creep strain accumulation has also been explained mechanistically.

International Journal of Pressure Vessels and Piping, 2004

The Voce equation was used to model the tensile flow and work-hardening behaviour of a service-ex... more The Voce equation was used to model the tensile flow and work-hardening behaviour of a service-exposed 2.25Cr-1Mo steel. The applicability of Voce parameters obtained from the fit to experimental true stress-true strain datasets for estimating the validity of the fit was examined. The Voce equation was found to model the stress-strain curve closely. The Voce parameter n v was correlated to the underlying dislocation activities. It was found that the values of Voce parameters at various temperatures and strain rates can be used to infer the operating recovery mechanism during stage III hardening. A low absolute value of n v is indicative of recovery by cross-slip, whereas the high temperature transition to climb or sub-boundary migration driven recovery is accompanied by an increase in the value of n v :

Materials Science and Technology, 2007

Tensile deformation behaviour of AISI 316L(N) stainless steel was investigated over the range 298... more Tensile deformation behaviour of AISI 316L(N) stainless steel was investigated over the range 298 to 1023 K. The yield and tensile strength were found to meet the minimum values mandated by RCC-MR, the French design code for fast reactors. The tensile flow behaviour was modelled using Ludwigson and Voce equation. Ludwigson equation could model the flow behaviour adequately before the onset of saturation at temperatures .823 K. Voce equation could model the flow behaviour between 298 and 1023 K. The physical basis for the variation with respect to strain rate and temperature of the constants obtained by modelling the flow curve using Ludwigson and Voce equation is discussed.