Assessment of 10CrMo9-10 Power Engineering Steel Degradation State by Using Small Punch Test

Degradation of power engineering steel structures requires constant monitoring of their mechanical properties to estimate remaining service life. Therefore, the current study aimed to develop a methodology that will enable for accurate determination of changes in mechanical properties of 10CrMo9-10 steel after long-term exploitation involving the Small Punch Test (SPT). Firstly, the as-received 10CrMo9-10 steel was annealed at 770 °C for different periods (1.5, 6 and 24 h) to deteriorate its strength to a level similar to its exploited counterpart. Then, mechanical properties were characterized by uniaxial tensile tests and the SPT method using miniaturized discs with a diameter of 8 mm and a thickness of 0.5 mm as recommended by the EN 10371:2021 standard. It allowed to determine a formula correlating the SPT results (i.e., elastic-plastic transition force and maximum force) with the yield and ultimate tensile strength. The β_Rp0.2 and β_Rm correlation factors were equal to 0.437 and 0.255, respectively. Finally, the exploited 10CrMo9-10 steel was tested by the SPT method. Based on the SPT results, the values of R_p0.2 = 236 ± 27 MPa and R_m = 459 ± 17 MPa were estimated, which were close to those assessed during the uniaxial tensile tests (R_p0.2 = 218 ± 3 MPa and R_m = 454 ± 4 MPa). It was shown that the application of such a relatively simple method is a promising way for determining the changes in mechanical properties of structural steels after long-term service at elevated temperature.