Chun-Der Cheng, Pin-Yi Chen, Chi-Shun Tu, Cheng-Sao Chen, Kuei-Chih Feng, Hsiao-Yao Yu, Yi-Tsung Lee, R.R. Chien, J. Anthoniappen
This work explores mechanical properties, structural evolution, and mechanism of creep-life enhancement for widely used P9 heat-resistant steel. The 17-year-on-site used P9 alloy exhibit a higher tensile strength and a smaller elongation than the new P9 alloy from room temperature to 700 ◦C. The P9 alloy also displays a typical ductile feature with a significantly necking profile. The P9 alloy shows phase transformation sequences of a-Fe (bcc) Ac1∼→858 ◦C a + y -Fe (bcc + fcc) Ac3∼→894 ◦C y-Fe (fcc) upon heating and y-Fe (fcc) Ms∼→352 ◦C martensite (bct) Mf ∼300 ◦C → martensite (bct) upon cooling. The new P9-alloy tube mainly contains ∼73.5% ferrite phase (a-Fe) and ∼26.5% carbide M3C. However, the used P9-alloy tube shows four crystalline phases including ∼45.9% ferrite, ∼14.5% martensite, ∼37.5% cementite (M3C) and ∼2.7% carbide M23C6. The creep test indicates that the used P9-alloy tube has a longer creep-life (or better anti-creep ability) than the new tube. Activation energies of atomic diffusion for the new and used tubes are respectively 252.45 and 345.87 kJ/mol, indicating a decreased diffusion capability in the used tube. This work suggests that martensite laths, lath boundaries, and precipitates (such as carbides) play important roles to inhibit creep-deformation in the P9-alloy steel. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Department of Mechanical Engineering, Ming Chi University of Technology, New Taipei City, 24301, Taiwan; Department of Physics, Fu Jen Catholic University, New Taipei City, 24205, Taiwan; Department of Mechanical Engineering, Hwa Hsia University of Technology, New Taipei City, 23567, Taiwan; Department of Physics, University of San Carlos, Talamban Campus, Cebu City, 6000, Philippines
