NUREG/CR–6275 ANL–94/37 Mechanical Properties of Thermally Aged Cast Stainless Steels from Shippingport Reactor Components Manuscript Completed: July 1994 Date Published: April 1995 Prepared by O. K. Chopra and W. J. Shack Argonne National Laboratory 9700 South Cass Avenue Argonne, Illinois 60439 Prepared for Division of Engineering Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, DC 20555 NRC FIN A2256 NUREG/CR–6275 ii Mechanical Properties of Thermally Aged Cast Stainless Steels from Shippingport Reactor Components by O. K. Chopra and W. J. Shack Abstract Thermal embrittlement of static–cast CF–8 stainless steel components from the decom- missioned Shippingport reactor has been characterized. Cast stainless steel materials were obtained from four cold–leg check valves, three hot–leg main shutoff valves, and two pump volutes. The actual time–at–temperature for the materials was ≈13 y at ≈281°C (538°F) for the hot–leg components and ≈264°C (507°F) for the cold–leg components. Baseline mechanical properties for as–cast material were determined from tests on either recovery–annealed material, i.e., annealed for 1 h at 550°C and then water quenched, or material from the cooler region of the component. The Shippingport materials show modest decreases in fracture toughness and Charpy–impact properties and a small increase in tensile strength because of relatively low service temperatures and ferrite content of the steel. The procedure and correla- tions developed at Argonne National Laboratory for estimating mechanical properties of cast stainless steels predict accurate or slightly lower values for Charpy–impact energy, tensile flow stress, fracture toughness J–R curve, and JIC of the materials. The kinetics of thermal embrit- tlement and degree of embrittlement at saturation, i.e., the minimum impact energy achieved after long–term aging, were established from materials that were aged further in the laboratory. The results were consistent with the estimates. The correlations successfully predicted the mechanical properties of the Ringhals 2 reactor hot– and crossover–leg elbows (CF–8M steel) after service of ≈15 y and the KRB reactor pump cover plate (CF–8) after ≈8 y of service. iii NUREG/CR–6275 NUREG/CR–6275 iv Contents Nomenclature................................................................................................................ ix Executive Summary ....................................................................................................... xi Acknowledgments ......................................................................................................... xiii 1Introduction ................................................................................................................ 1 2Material Characterization ............................................................................................. 2 3Mechanical Properties .................................................................................................. 8 3.1 Baseline Mechanical Properties........................................................................ 9 3.2 Charpy–Impact Energy.................................................................................... 12 3.3 Tensile Properties .......................................................................................... 13 3.4 Fracture Toughness ....................................................................................... 20 4Estimation of Mechanical Properties .............................................................................. 20 4.1 Charpy–Impact Energy.................................................................................... 20 4.2 Fracture Toughness ....................................................................................... 31 4.3 Tensile Properties .......................................................................................... 33 5Ringhals Reactor Elbows............................................................................................... 40 6KRB Reactor Pump Cover Plate..................................................................................... 46 7Conclusions................................................................................................................ 48 References.................................................................................................................... 51 Appendix A: Charpy–Impact Energy ................................................................................. 55 Appendix B: Tensile Properties ........................................................................................ 65 Appendix C: J–R Curve Characterization........................................................................... 67 v NUREG/CR–6275 List of Figures 1. Photographs of check valve, main shutoff valve, and spare pump volute from the Shippingport reactor............................................................................................ 3 2. Microstructure along axial section of Loop A check valve from the Shippingport reactor............................................................................................................... 5 3. Microstructure along axial section of Loop B main shutoff valve from the Shippingport reactor............................................................................................ 6 4. Microstructure along axial section of the spare volute from the Shippingport reactor............................................................................................................... 6 5. Ferrite morphology of cast materials from Loops A, B, and C cold–leg check valves from the Shippingport reactor.............................................................................. 7 6. Ferrite morphology of cast materials from Loops A, B, and C hot–leg main shutoff valves from the Shippingport reactor.................................................................... 7 7. Ferrite morphology of cast materials from the cold–leg and spare pump volutes from the Shippingport reactor.............................................................................. 8 8. Effect of annealing for 1 h at 550°C and then water quenching on Charpy–transition curves for laboratory–aged Heats 69, 68, and 75, and service–aged KRB pump cover plate...................................................................... 10 9. Effect of annealing on Charpy–transition curve of cast material from the hot–leg main shutoff valve............................................................................................... 12 10. Charpy transition curves for Loop A and B cold–leg check valves after 13 y of service at 264°C ................................................................................................. 14 11. Charpy transition curves for Loop A hot–leg main shutoff valve after 13 y of service at 281°C ................................................................................................. 15 12. Charpy transition curves for Loop A pump volute after 13 y of service at 264°C ..... 16 13. Charpy transition curves for materials from the spare pump volute and cooler region of the main shutoff valve before and after aging for 10,000 h at 400°C........ 17 14. Yield and ultimate stresses estimated from Charpy–impact data and obtained from tensile tests for cold–leg check valve and pump volute, and estimated tensile stresses of annealed materials.............................................................................. 18 15. Yield and ultimate stresses estimated from Charpy–impact data and obtained from tensile tests for hot–leg main valve, and estimated tensile stresses of annealed materials ............................................................................................................ 19 NUREG/CR–6275 vi 16. Yield and ultimate stresses estimated from Charpy–impact data and obtained from tensile tests for spare pump volute and hot–leg main valve before and after aging for 10,000 h at 400°C......................................................................................... 21 17. Fracture toughness J–R curves at room temperature and 290°C for annealed, service–aged, and laboratory–aged material from the cold–leg check valve .............. 22 18. Fracture toughness J–R curves at room temperature and 290°C for unaged, service–aged, and laboratory–aged material from the hot–leg main shutoff valve...... 23 19. Fracture toughness J–R curves at room temperature and 290°C for annealed, service–aged, and laboratory–aged material from the cold–leg pump volute............. 24 20. Fracture toughness J–R curves at room temperature and 290°C for unaged and laboratory–aged material from the spare pump volute............................................ 25 21. Flow diagram for estimating mechanical properties of cast materials obtained from the Shippingport reactor...................................................................................... 26 22. Variations of estimated room–temperature Charpy–impact energy with service time for Loop A cold–leg check valve CA4 and pump volute PV...................................... 30 23. Variations of estimated room–temperature Charpy–impact energy with time for materials from cooler region of the hot–leg main valve MA9 and spare pump volute VR...................................................................................................................... 31 24. Variation of estimated room–temperature Charpy–impact energy with service time for Loop A hot–leg main valve MA1....................................................................... 32 25. Estimated and measured fracture toughness J–R curves for the cold–leg check valve in the annealed, 13–y service at 264°C, and fully embrittled or saturation condition............................................................................................................ 34 26. Estimated and measured fracture toughness J–R curves for the hot–leg main shutoff valve in essentially unaged, 13–y service at 281°C, and fully embrittled or saturation condition............................................................................................. 35 27. Estimated and measured fracture toughness J–R curves for the cold–leg pump volute in the annealed, 13–y service at 264°C, and fully embrittled or saturation condition............................................................................................................ 36 28. Estimated and measured fracture toughness J–R curves for the spare pump volute in the unaged and fully embrittled or saturation condition....................................... 37 29. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for the cold–leg check valve after service for ≈13 y at 264°C....................... 41 30. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for the hot–leg main shutoff valve after service for ≈13 y at 281°C.............. 42 vii NUREG/CR–6275 31. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for the cold–leg pump volute after service for ≈13 y at 264°C...................... 43 32. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for material from cooler regions of the hot–leg main shutoff valve in the unaged and fully embrittled or aged condition........................................................ 44 33. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for the spare pump volute in the unaged and fully embrittled or aged condition............................................................................................................ 45 34. Estimated and experimentally observed room–temperature Charpy–impact energy for the Ringhals hot– and crossover–leg elbows..................................................... 46 35. Estimated fracture toughness J–R curves for the Ringhals hot– and crossover–leg elbows in the unaged condition, after service, and at saturation.............................. 47 36. Variation of estimated room–temperature Charpy–impact energy with service time for the KRB pump cover plate............................................................................... 48 37. Estimated and measured tensile stress–vs.–strain curves at room temperature and 290°C for the KRB pump cover plate in the annealed condition and after 8 y of service at 284°C ................................................................................................. 49 38. Estimated and measured fracture toughness J–R curve for the KRB pump cover plate in the annealed or unaged condition, after service, and at saturation............... 50 List of Tables 1. Chemical composition, ferrite morphology, and hardness of cast stainless steel components from the Shippingport, KRB, and Ringhals reactors.............................. 5 2. Values of constants in Eq. 1 for Charpy transition curve of CF–8 cast SSs from the Shippingport reactor and KRB pump cover plate..................................................... 13 3. Measured and estimated Charpy–impact properties of cast stainless steel materials from the Shippingport, KRB, and Ringhals reactors................................................. 29 4. Measured and estimated tensile yield and flow stresses and JIC values for service– and laboratory–aged cast stainless steels.............................................................. 39 NUREG/CR–6275 viii Nomenclature b Uncracked ligament of Charpy–impact specimen (mm). B Thickness of Charpy–impact speciemn (mm). C Coefficient of power–law J–R curve expressed as Jd = C(Δa)n. Creq Chromium equivalent for a material (wt.%). CV Room–temperature “normalized” Charpy–impact energy, i.e., Charpy–impact energy per unit fracture area, at any given service and aging time (J/cm2). Fracture area for a standard Charpy V–notch specimen (ASTM Specification E 23) is 0.8 cm2. Divide the value of impact energy in J by 0.8 to obtain “normalized” impact energy. CVint Initial room–temperature “normalized” Charpy–impact energy of a material, i.e., unaged material (J/cm2). CVsat Room–temperature “normalized” Charpy–impact energy of a material at saturation, i.e., minimum impact energy that would be achieved for the material after long–term service (J/cm2). CMTR Certified material test record. E Modulus of elasiticity (MPa). Jd Deformation J per ASTM Specification E 813-85 or E 1152–87 (kJ/m2). n Exponent of power–law J–R curve. n1 Ramberg–Osgood parameter. Nieq Nickel equivalent for a material (wt.%). P Aging parameter, i.e., log of time of aging at 400°C. Pm Maximum load for instrumented Charpy–impact test (N). Py Yield load for instrumented Charpy–impact test (N). Q Activation energy for process of thermal embrittlement (kJ/mole). Rf Ratio of tensile flow stress of aged and unaged cast stainless steel. Ry Ratio of tensile yield stress of aged and unaged cast stainless steel. t Service or aging time (h). Ts Service or aging temperature (°C). W Width of Charpy–impact specimen (mm). α Shape factor of curve for change in room–temperature Charpy–impact energy with time and temperature of aging. α1 Ramberg–Osgood parameter. β Half the maximum change in room–temperature Charpy–impact energy. δc Ferrite content calculated from chemical composition of a material (%). Δa Crack extension (mm). ix NUREG/CR–6275 ε Engineering strain. εo Reference strain in Ramberg–Osgood equation. Φ Material parameter. θ Aging behavior at 400°C, i.e., log of time to achieve β reduction in impact energy at 400°C. σf Engineering flow stress expressed as average value of yield and ultimate stress, i.e., (σy + σu)/2 (MPa). σo Reference stress in Ramberg–Osgood equation (MPa). σu Engineering ultimate stress (MPa). σy Engineering yield stress (MPa). In this report, all values of impact energy are considered to be for a standard Charpy–V–notch specimen per ASTM Specification E 23, i.e., 10 x 10–mm cross section and 2–mm V notch. Impact energies obtained on subsize specimens should be normalized with respect to the actual cross–sectional area and appropriate correction factors should be applied to account for size effects. Similarly, impact energy from other standards, e.g., U–notch specimen, should be converted to a Charpy–V–notch value by appropriate correlations. SI units of measure have been used in this report. Conversion factors for measurements in British units are as follows: To convert from to multiply by in. mm 25.4 J* ft·lb 0.7376 kJ/m2 in.–lb/in.2 5.71015 kJ/mole kcal/mole 0.239 *When impact energy is expressed in J/cm2, first multiply by 0.8 to obtain impact energy of a standard Charpy V–notch specimen in J. NUREG/CR–6275 x