# Presentation: 534415

## Advanced Pressure Boundary Materials

*Mike Santella and John Shingledecker*
*Materials Science & Technology Division*
*Oak Ridge National Laboratory*

- June 12, 2006
- 20th Annual Conference on Fossil Energy Materials
- Knoxville, TN

## Purpose is to build fundamental understanding of materials behavior needed to increase operating temperatures

- Activities encompass ferritic steels, austenitic steels and Ni-based alloys
- “*Analysis of Off-Normal Metallurgical Conditions on the Performance of Advanced Cr-Mo Steels,*” CRADA with Alstom Power, Inc.
- “*Joint Research on Properties of Alloy 263 and 263 Weldments,*” joint research agreement for collaboration with Central Research Institute of Electric Power Industry (CRIEPI), Tokyo, Japan
- “*Mechanisms of Type IV Weld Failures in Cr-Mo Steels*,” collaboration with National Institute for Materials Science (NIMS), Tsukuba, Japan
- Involvement with materials issues relating to the ASME Boiler and Pressure Vessel Code (Section II: Materials)
- Technical support for the U.S. DOE/OCDO Ultrasupercritical Steam Boiler Consortium not included in the ORNL Tasks 2 (mechanical properties) and Task 3 (steamside oxidation) work scope

## Critical temperatures for PWHT are being analyzed in collaboration with Alstom

- P91 – A387 Gr 91:
- Fe-0.1C-0.4Mn-0.3Si-9Cr-1Mo-0.1Ni-0.2V-0.08Nb-0.05N, wt%
- P911 – A387 Gr 911:
- Fe-0.1C-0.4Mn-0.3Si-9Cr-1Mo-0.1Ni-0.2V-0.08Nb-0.06N-1W, wt%
- P92 – 9Cr-2W Material:
- Fe-0.1C-0.4Mn-0.3Si-9Cr-0.3Mo-0.1Ni-0.2V-0.07Nb-0.05N-1.8W, wt%
- P122 – 12Cr-2W Material:
- Fe-0.1C-0.4Mn-0.3Si-11Cr-0.4Mo-0.2Ni-0.2V-0.07Nb-0.07N-2W-1Cu, wt%

## Phase diagrams are fundamental roadmaps needed for alloy development, processing, heat treating

- “*A**1*” defines upper limit for post weld heat treatment

## For complex systems temperatures can be estimated using Computational Thermodynamics

- CT is a powerful tool for thermodynamic calculations in multicomponent (> 3) systems
- Calculations are based on expert assessments of thermochemical measurements
- Models are developed for all types of phases (solid solutions, compounds, carbides, oxides, etc)
- Minimum G yields equilibrium; can add constraints
- G described as function of composition, temperature, etc

## 5 base compositions were used for each analysis

- All elements at maximum specified
- All elements at minimum specified
- All elements at mid-range values
- Austenite formers at maximum of range; ferrite formers at minimum of range
- Ferrite formers at maximum range; austenite formers at minimum range

*1800-2100 individual compositions were analyzed for each steel*

## Predicted A1 ranges for 9Cr steels

## Predicted A1 range for 12Cr-2W steel

## Thermo-based estimates of A1 may have important implications for Cr-Mo steel component fabrication

- In homogenized wrought material, *A**1* is uniquely defined by alloy chemistry
*A**1** *is most often estimated from measurements on a limited number of alloys - *A**C1*
*A**C1* is not a unique temperature
- It increases with heating rate during measurement
- Using *A**C1*’s to specify PWHT temperatures increases the probability of exceeding *A**1*’s
- PWHT limit of 800°C for 9Cr’s adopted by ASME B&PV Code is based on *A**C1* data
- It may be prudent to reconsider Code specified limits

## Continuing work

- Base metal alloys at extremes are being made for experimental measurements
- Consideration of *M**S* estimates
- Weld metal compositions – which ones?
- Other Cr-Mo steels?

## Mechanisms of Type IV weld failure are being studied in collaboration with NIMS

- Type IV failure of Cr-Mo steel welds is due to weakened microstructures in HAZs

## Experimental 9Cr steels have improved creep strength and resistance to Type IV failure

- Results from F. Abe et al., National Institute for Materials Science, Japan

## HAZ behavior of new steel is significantly different from more conventional 9Cr steel

*HAZ behavior of new steel is significantly different from more conventional 9Cr steel*

## Two explanations are proposed for the unique behavior of the NIMS steels

-   Austenite memory effect
- With retained austenite, heating to T’s above A1 regenerates the original  grains
-   Martensitic reversed transformation
- Boron may suppress nucleation of  in HAZs during welding
*Previous ORNL work used APS diffraction experiments to verify that austenite was being retained in 9Cr steel welds*
*NIMS expressed interest in collaborating on a set of diffraction experiments with NIMS steel & P92*

## Transformation behavior is being examined using the Advanced Photon Source

- The Advanced Photon Source (APS) at _[Argonne National Laboratory](http://www.anl.gov/)__ is a national synchrotron-radiation light source research facility funded by the __[U.S. Department of Energy](http://www.energy.gov/)__, __[Office of Science](http://www.er.doe.gov/)__, __[Office of Basic Energy Sciences](http://www.er.doe.gov/production/bes/bes.html)__. _
- High flux, high brilliance x-ray beams are available for basic and applied research
- Flux + brilliance = 1 second per diffraction pattern

## Ferrite/austenite transformation was tracked through HAZ heating cycles

*Ferrite/austenite transformation was tracked through HAZ heating cycles*

- Austenite may be retained in both NIMS 130B steel and P92

## Diffraction indicates HAZ of P92 transforms rapidly to high fraction of austenite 

- Result: 14% overtempered , 21% regrown , 61.5% , 3.5% 

## Austenite transformation is much more sluggish in HAZ of N130B

- Result: 54% overtempered , 23% regrown , 22.5% , 0.5% 

## Continuing work

- Microstructure & hardness analysis
- Analysis of effects on creep behavior & Type IV failure
- Transformation kinetics experiments & model
- Effects of individual elements, e.g., B, Co
- P91 base & weld metals

## Efforts to improve strength of Ni-based alloys is being leveraged through collaborative effort with CRIEPI

*Data for Haynes 230 illustrates need for weld strength reduction factors for boilers designed with Ni-based alloys  *

## Joint Research on Properties of Alloy 263 and 263 Weldments

- Purpose is to measure and analyze creep, fatigue, and creep-fatigue properties
- Optimize fabrication processes for base and weld metal
- Manufacture test articles
- Conduct creep tests
- Conduct fatigue and creep-fatigue tests
- Analyze deformation and damage accumulation behaviors

*Status: Technical details are finalized; approvals for export controls, IP, etc., are proceeding*

## Computational Thermodynamics capabilities will be used to consider methods of strengthening alloy 263

- Data for alloy 740 illustrate the dependence of precipitation on alloy composition

## Advanced Pressure Boundary Materials

- Highlights:
- Using computational thermodynamics tools to assist manufacturers in specifying critical temperature limits for tempering and post weld heat treatments
- Making thermodynamic analysis information accessible, available
- Using advanced tools – like APS – to better understand new high strength ferritic steels
- Collaboration with NIMS
- Using testing, analysis, and CT capabilities to strengthen Ni-based alloys
- Collaboration with CRIEPI