Search Results (2)

The effects of thermal simulation on the short-term creep fracture of modified 91 (mod. 91) weld metal (WM) were evaluated at elevated temperature. The reheated zones in the WM during multiple passes were simulated by an infrared heater. The simulated WM specimens after post-weld tempering at 1023 K/2 h were loaded with dead weight either at 903 K/120 MPa or 933 K/80 MPa. In this work, the simulated WM specimens after tempering were loaded either at 903 and 933 K during the tests. The loss in creep lives of various specimens at elevated temperature was determined accordingly and further compared with the Gr. 91 steel base metals, which were normalized either at 1213 K or 1333 K and then tempered at 1033 K for 2 h. The coarse, solidified structure of the WM had much better creep resistance than the base metal even that of the base metal normalized at 1333 K. However, the imposed welding thermal cycles would cause a significant decrease in creep resistance of the WM. Creep lives were shortened obviously in the simulated WM samples, especially in the simulated sample that underwent partial transformation. The combination of a fine-grained structure and soft ferrite present in the simulated WM was responsible for their huge decline in creep resistance, as compared with the WM in the as-tempered condition. Full article

The H13-mod steel optimized by composition and heat treatment has reached the performance index of the shield machine hob. The hot deformation behavior of the H13-mod steel was investigated by compression tests in the temperature range from 900 to 1150 °C and the strain rate range from 0.01 to 10 s⁻¹. The true stress-strain curve showed that the rising stress at the beginning of deformation was mainly caused by work hardening. After the peak stress was attained, the curve drop and the flow softening phenomenon became more obvious at low strain rates. The flow behavior of the H13-mod steel was predicted by a strain-compensated Arrhenius-type constitutive equation. The relationship between the material constant in the Arrhenius-type constitutive equation and the true strain was established by a sixth-order polynomial. The correlation coefficient between the experimental value and the predicted value reached 0.987, which indicated that the constitutive equation can accurately estimate the flow stress during the deformation process. A good linear correlation was achieved between the peak stress (strain), critical stress (strain) and the Zener‒Hollomon parameters. The processing maps of the H13-mod steel under different strains were established. The instability region was mainly concentrated in the high-strain-rate region; however, the microstructure did not show any evidence of instability at high temperatures and high strain rates. Combined with the microstructure and electron backscattered diffraction (EBSD) test results under different deformations, the optimum hot working parameters were concluded to be 998–1026 °C and 0.01–0.02 s⁻¹ and 1140–1150 °C and 0.01–0.057 s⁻¹. Full article