Nuclear Engineering and Technology

Korean Nuclear Society (한국원자력학회)
권호 표지
DOI QR코드

DOI QR Code

Effects of microalloying element addition on mechanical properties of SA508 Gr.1A low-alloy steels

  • Se-mi Hyun (Korea University, Department of Materials Science and Engineering) ;
  • Min-Chul Kim (Korea Atomic Energy Research Institute, Materials Safety Technology Research Division) ;
  • Seokmin Hong (Korea Atomic Energy Research Institute, Materials Safety Technology Research Division) ;
  • Jongmin Kim (Korea Atomic Energy Research Institute, Materials Safety Technology Research Division) ;
  • Seok Su Sohn (Korea University, Department of Materials Science and Engineering)
  • Received : 2023.11.28
  • Accepted : 2024.03.31
  • Published : 2024.09.25
Download PDF
⟨ Previous Next ⟩

Abstract

SA508 Gr.1A low-alloy steel is being considered as a candidate material for main steam line piping in nuclear power plants. Therefore, improving its strength and toughness is essential for enhancing the leak-before-break (LBB) margin. In this study, six types of model alloys were fabricated by varying the contents of microalloying elements (C, Cu, B, Ti, and Nb) to enhance the mechanical properties of the specimens. The addition of a few ppm of B led to the formation of a fine-grained low-temperature transformation microstructure, resulting in the highest strength among the model alloys. However, the addition of Nb and Ti increased the formation of coarse ferrite, significantly decreasing the strength of the alloys. Reducing the C content while adding a small amount of B simultaneously maintained strength and enhanced toughness. Furthermore, the LBB margins of model alloys and commercial steel were evaluated to validate the influence of varying microalloying content. The model alloys exhibited a substantial increase in yield strength and fracture resistance, resulting in a more than 10% increase in the LBB margin. Notably, the LBB margin of the alloy with 15 ppm B was 1.39, approximately 25% higher than that of commercial steels.

Keywords

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT) (No. RS-2022000144399).

References

  1. Y.S. Chang, M.J. Jung, B.S. Lee, H.S. Kim, N.S. Huh, Structural integrity of nuclear components, Hanshouse (2013) 30-32.
  2. S. Hong, K.D. Min, S.M. Hyun, J.M. Kim, Y.S. Lee, H.D. Kim, M.C. Kim, Effect of cooling rate on mechanical properties of SA508 Gr.1A steels for main steam line piping in nuclear power plants, Int. J. Pres. Ves. Pip. 191 (2021) 104359, https://doi.org/10.1016/j.ijpvp.2021.104359.
  3. M.W. Kim, Y.S. Lee, I.W. Shin, J.S. Yang, H.D. Kim, Leak-before-break assessment margin analysis of improved SA508-Gr.1a pipe material, Trans. of the KPVP. 16 (2020) 42-48, https://doi.org/10.20466/KPVP.2020.16.1.042.
  4. P. Dillstrom, W. Zang, ProLBB-A Probabilistic Approach to LeakBefore Break Demonstration, SKI Report 2007:43, Swedish Nuclear Inspection Authority (SKI), Stockholm, 2007, p. 183.
  5. B.S. Lee, M.C. Kim, J.H. Yoon, J.H. Hong, Characterization of high strength and high toughness Ni-Mo-Cr low alloy steels for nuclear application, Int. J. Pres. Ves. Pip. 87 (2010) 74-80, https://doi.org/10.1016/j.ijpvp.2009.11.001.
  6. K.H. Lee, S.G. Park, M.C. Kim, B.S. Lee, D.M. Wee, Characterization of transition behavior in SA508 Gr.4N Ni-Cr-Mo low alloy steels with microstructural alteration by Ni and Cr contents, Mater. Sci. Eng. 529 (2011) 156-163, https://doi.org/10.1016/j.msea.2011.09.012.
  7. M.C. Kim, S.G. Park, K.H. Lee, B.S. Lee, Comparison of fracture properties in SA508 Gr.3 and Gr.4N high strength low alloy steels for advanced pressure vessel materials, Int. J. Pres. Ves. Pip. 131 (2015) 60-66, https://doi.org/10.1016/j.ijpvp.2015.04.010.
  8. K.H. Lee, M.C. Kim, W.J. Yang, B.S. Lee, Evaluation of microstructural parameters controlling cleavage fracture toughness in Mn-Mo-Ni low alloy steels, Mater. Sci. Eng. 565 (2013) 158-164, https://doi.org/10.1016/j.msea.2012.12.024.
  9. M.C. Kim, B.S. Lee, W.J. Yang, J.H. Hong, Determination of the key microstructural parameter for the cleavage fracture toughness of reactor pressure vessel steels in the transition region, Key Eng. Mater. 297-300 (2005) 1672-1677. https://doi.org/10.4028/www.scientific.net/KEM.297-300.1672.
  10. S. Hong, C.L. Lee, M.C. Kim, B.S. Lee, Effects of microstructure variation on tensile and Charpy impact properties in heavy-section SA508 Gr.3 low alloy steels for commercial reactor pressure vessel, Korean J. Met. Mater 55 (2017) 752-759, https://doi.org/10.3365/KJMM.2017.55.11.752.
  11. S.M. Hyun, S.M. Hong, M.C. Kim, J.M. Kim, S.S. Sohn, Effect of intercritical heat treatment on J-R fracture resistance of SA508 Gr.1A low-alloy steels, Met. Mater. Int. 28 (2022) 2907-2918, https://doi.org/10.1007/s12540-022-01188-7.
  12. ASTM A508/A508M-16. Standard Specification for Quenched and Tempered Vacuum-Treated Carbon and Alloy Steel Forgings for Pressure Vessels, ASTM International, West Conshohocken, PA, 2016.
  13. H.C. Lee, K. SShin, S.H. Lee, B.J. Lee, Development of Advanced Low Alloy Steel for Nuclear RPV, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of), 2000, pp. 1-159. KAERI/CM-378/99.
  14. H.C. Lee, S.H. Lee, Y.M. Ku, B.J. Lee, Strength and Toughness Improvement of Low-Alloy Steel for Nuclear Applications, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of), 2002, pp. 1-127. KAERI/CM-537/2001.
  15. S.M. Hong, S.M. Hyun, J.M. Kim, Y.S. Lee, M.C. Kim, Effect of Mo and V addition on microstructure and mechanical properties of SA508 Gr.1A steel for pipeline in nuclear power plants, Metall. Mater. Trans. 53A (2022) 1499-1511, https://doi.org/10.1007/s11661-022-06616-2.
  16. S.M. Hyun, S.M. Hong, M.C. Kim, J.M. Kim, S.S. Sohn, S.I. Hong, Microstructural changes by controlling austenitizing and tempering conditions on the J-R fracture resistance of SA508 Gr. 1A low alloy steels, Mater. Sci. Eng. 811 (2021) 141069, https://doi.org/10.1016/j.msea.2021.141069.
  17. J.H. Hong, Neutron irradiation effect and integrity of nuclear reactor pressure vessel, kor, J. Mater. Res. 33 (1993) 393-404.
  18. S.L. Lee, et al., The estimation of neutron fluence in nuclear reactor vessel materials by the analysis of ultrasonic characteristics, J. Korean Soc. Nondestruc. Test. 21 (2001) 307-312.
  19. B.C. Hwang, Continuous cooling transformation, microstructure and mechanical properties of high-strength low-alloy steels containing B and Cu, Kor. J. Mater. Res. 23 (2013) 525-530.
  20. ASTM A370-23. Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM International, West Conshohocken, PA, 2023.
  21. ASTM E23-23a. Standard Test Methods for Notched Bar Impact Testing of Metallic Materials, ASTM International, West Conshohocken, PA, 2023.
  22. W. Oldfield, ASTM Stand. News 3 (1975) 24.
  23. ASTM E1820-23b. Standard Test Method for Measurement of Fracture Toughness, ASTM International, West Conshohocken, PA, 2023.
  24. S.M. Hong, S.Y. Shin, J.H. Lee, C.H. Lee, S.H. Lee, Effect of phosphorous and boron addition on microstructural evolution and Charpy impact properties of high-phosphorous-containing plain carbon steels, Mater. Sci. Eng. 564 (2013) 461-472, https://doi.org/10.1016/j.msea.2012.11.102.
  25. S.M. Hong, J.H. Lee, K.S. Park, S.H. Lee, Effects of boron addition on tensile and Charpy impact properties in high-phosphorous steels, Mater. Sci. Eng. 589 (2014) 165-173, https://doi.org/10.1016/j.msea.2013.09.095.
  26. X.L. He, Y.Y. Chu, J.J. Jonas, The grain boundary segregation of boron during isothermal holding, Acta Metall. 37 (1989) 2905-2916.
  27. X.L. He, Y.Y. Chu, J.J. Jonas, Grain boundary segregation of boron during continuous cooling, Acta Metall. 37 (1989) 147-161.
  28. B. Hwang, C. Lee, T.-H. Lee, Correlation of microstructure and mechanical properties of thermomechanically processed low-carbon steels containing boron and copper, Metall. Mater. Trans. 41A (2010) 85-96, https://doi.org/10.1007/s11661-009-0070-4.
  29. J.B. Seol, N.S. Lim, B.H. Lee, L. Renaud, C.G. Park, Atom probe tomography and nano secondary ion mass spectroscopy investigation of the segregation of boron at austenite grain boundaries in 0.5 wt.% carbon steels, Met. Mater. Int. 17 (2011) 413-416, https://doi.org/10.1007/s12540-011-0617-y.
  30. S.I. Kim, Y. Lee, Influence of cooling rate and boron content on the microstructure and mechanical properties of hot-rolled high strength interstitial-free steels, Met. Mater. Int. 18 (2012) 735-744, https://doi.org/10.1007/s12540-012-5001-z.
  31. Z.H. Zhao, W.C. Chen, H. Yuan, Y. D, Li, Effect of Boron on Grain Size of Low Carbon Steel, vol. 3, 2006, pp. 67-70.
  32. Jieyi Wang, Thermal-Physical Simulation of Q345E Large H-Section Steel Treated with Boron and Boron Nickel, Master's thesis Shandong University, 2010.
  33. Xuejing Fu, Chun Xu, Continuous-cooling-transformation diagrams for boron-low carbon micro alloy hot rolled enamel steel, J. Phys.: Conf. Ser. 2435 (2023) 012014, https://doi.org/10.1088/1742-6596/2435/1/012014.
  34. S.S. Babu, G.M. Goodwin, R.J. Rohde, B. Sielen, Effect of boron on the microstructure of low-carbon steel resistance seam welds, Weld. Res. Suppl. 77 (1998) 249-253.
  35. H.K.D.H. Bhadeshia, L.E. Svensson, Model for boron effects in steel welds, in: Int. Conf. Model. Control Join. Process, 1993, pp. 153-160.
  36. S.Y. Lee, J.Y. Kim, B.C. Hwang, Recrystallization behavior in the two-phase (α+γ) region of micro-alloyed steels, Korean J. Mater. Res. 26 (2016) 583-589, https://doi.org/10.3740/MRSK.2016.26.11.583.
  37. U.Y. Huh, Y.S. Rho, M.S. Choi, Y.H. Kim, S.Y. Lee, Study on the effect of austenite grain size and Mn content on hardenability in boron-added low carbon alloys steels, J. of the Korean Society for Heat Treatment 3 (1990) 23-40.
  38. J.Y. Son, B.C. Park, H. Sung, Y.S. Kim, The effect of microstructure and mechanical property with heat treatment condition in boron-treated low carbon low alloy steel, Proc. of Trans. Mater. Process. 10a (2007) 146-149.
  39. H.K.D.H. Bhadeshia, R.W.K. Honeycombe, Steels: Microstructure and Properties, third ed., Elsevier Ltd., 2006.
  40. T.W. Hong, S.I. Lee, J.H. Shim, J.H. Lee, M.G. Lee, B.C. Hwang, Effect of microstructural factors on the strength and deformability of ferrite-pearlite steels with different Mn and V contents, Korean J. Mater. 28 (2018) 570-577, https://doi.org/10.3740/MRSK.2018.28.10.570.
  41. S.C. Wang, P.W. Kao, The effect of alloying elements on the structure and mechanical properties of ultra low carbon bainitic steels, J. Mater. Sci. 28 (1993) 5169-5175, https://doi.org/10.1007/BF00570058.
  42. R. Rodriguez-Galeano, Karol Felipe Rodriguez-Baracaldo, A. Mestra-Rodriguez, J. J. Cabrera-Marrero, Jose Maria Olaya-Florez, Influence of boron content on the fracture toughness and fatigue crack propagation kinetics of bainitic steels, Theor. Appl. Fract. Mech. 86 (2016) 351-360. https://doi:10.1016/j.tafmec.2016.09.0104.
  43. R.J. Klassen, M.N. Bassim, M.R. Bayoumi, H.G.F. Wilsdorf, Characterization of the effect of alloying elements on the fracture toughness of high strength, low alloy steels, Mater. Sci. 80 (1986) 25-35, https://doi.org/10.1016/0025-5416(86)90299-5.
  44. V. Kumar, Elastic-Plastic Fracture Analysis of through-Wall and Surfaces Flaw in Cylinders, Electric Power Research Institute (EPRI), 1988.
  45. K.D. Bae, H.W. Ryu, Y.J. Kim, J.W. Kim, J.S. Kim, Y.J. Oh, Determination method of ramberg-osgood constants for leak before break evaluation, Trans. Korean Soc. Mech. Eng. A 39 (2015) 645-652, https://doi.org/10.3795/KSMEA.2015.39.7.645.
  46. Y.J. Kim, N.S. Huh, Y.J. Kim, Y.H. Choi, J.S. Yang, On relevant ramberg-osgood fit to engineering non-linear fracture mechanics analysis, Trans. Korean Soc. Mech. Eng. A 27 (2003) 1571-1578.
  47. D.M. Norris, B. Chexal, PICEP: Pipe Crack Evaluation Program (Revision 1): Special Report: EPRI-NP-3596-SR-Rev. 1[R], EPRI, Palo Alto, 1987.
  48. J.G. Park, N.S. Huh, Y.J. Kim, S.M. Lee, Development of elastic-plastic fracture mechanics evaluation program for leak-before-break analysis of nuclear piping, Trans. of the KPVP. 16 (2020) 35-46, https://doi.org/10.20466/KPVP.2020.16.2.035.
  49. S. Hong, J. Kim, M.W. Kim, H.D. Kim, B.S. Lee, M.C. Kim, Evaluation of LBB characteristics of candidate materials for main steam line piping in Korea nuclear power plants, Int. J. Pres. Ves. Pip. 188 (2020) 104226, https://doi.org/10.1016/j.ijpvp.2020.104226.