Advanced Pressure Boundary Materials

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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
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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

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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-0.05
  N, wt
• P911 A387 Gr 911
• Fe-0.1C-0.4Mn-0.3Si-9Cr-1Mo-0.1Ni-0.2V-0.08Nb-0.06
  N-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

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

• A1 defines upper limit for post weld heat
  treatment

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For complex systems temperatures can be estimated
using Computational Thermodynamics

• CT is a powerful tool for thermodynamic
  calculations in multicomponent (gt 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

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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
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Predicted A1 ranges for 9Cr steels
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Predicted A1 range for 12Cr-2W steel
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Thermo-based estimates of A1 may have important
implications for Cr-Mo steel component fabrication

• In homogenized wrought material, A1 is uniquely
  defined by alloy chemistry
• A1 is most often estimated from measurements on a
  limited number of alloys - AC1
• AC1 is not a unique temperature
• It increases with heating rate during measurement
• Using AC1s to specify PWHT temperatures
  increases the probability of exceeding A1s
• PWHT limit of 800C for 9Crs adopted by ASME
  BPV Code is based on AC1 data
• It may be prudent to reconsider Code specified
  limits

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Continuing work

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

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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

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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

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HAZ behavior of new steel is significantly
different from more conventional 9Cr steel
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Two explanations are proposed for the unique
behavior of the NIMS steels

• Austenite memory effect
• With retained austenite, heating to Ts 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

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Transformation behavior is being examined using
the Advanced Photon Source

• The Advanced Photon Source (APS) at Argonne
  National Laboratory is a national
  synchrotron-radiation light source research
  facility funded by the U.S. Department of Energy,
  Office of Science, Office of Basic Energy
  Sciences.
• High flux, high brilliance x-ray beams are
  available for basic and applied research
• Flux brilliance 1 second per diffraction
  pattern

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Ferrite/austenite transformation was tracked
through HAZ heating cycles

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

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

• Result 14 overtempered ??, 21 regrown ?, 61.5
  ??, 3.5 ?

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Austenite transformation is much more sluggish in
HAZ of N130B

• Result 54 overtempered ??, 23 regrown ?, 22.5
  ??, 0.5 ?

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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

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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

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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
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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

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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