چكيده به لاتين
The present study investigates the effect of heat treatment on the hot deformation behavior and mechanical properties of heat-resistant A335-P91 steel. Initially, the received samples were subjected to a bending process and then underwent heat treatment to eliminate thermomechanical history. The heat treatment process included normalization at 1055°C and tempering at 760°C. The durations for normalization were set at 4, 30, and 51 minutes, while tempering times were 15 minutes, 30 minutes, 1 hour, and 4 hours. Mechanical tests, including hot compression, uniaxial tensile, and rupture stress tests, were conducted on the initial, bent, and heat-treated samples. In the uniaxial tensile test, significant variations in yield stress were observed. The lowest yield stress was observed for the sample normalized for 51 minutes and tempered for 4 hours, with a value of 333 MPa. The highest yield stress was observed for the sample normalized for 30 minutes and tempered for 15 minutes, with a value of 703 MPa. The bent sample exhibited a yield stress of 412 MPa. In the hot compression tests, the highest softening fraction at a strain of 0.35 belonged to the bent sample, with a softening fraction of 33.74%. In contrast, the lowest softening fractions were observed for the samples normalized for 30 minutes and tempered for 15 minutes and 1 hour, with softening fractions of 12.6% and 14%, respectively. The hot compression test indicated that the softening fraction is dependent on heat treatment conditions. Reducing the tempering time from 4 hours to 15 minutes for samples normalized for 51 minutes led to an increase in rupture life from 6 minutes to 37 hours. Microstructural analysis showed that increasing the normalization time resulted in grain growth, although this increase was not significant. Moreover, extending the normalization time led to the dissolution of precipitates. The tempering process had no significant effect on grain size but caused changes in the percentage, fraction, and even type of precipitates. These results can serve as a guide for selecting optimal heat treatment temperatures and durations in industries related to boilers and piping systems.
