Long-term strength of heat-resistant steels under creep conditions

Conclusions

• 1. Changes in the structure that occur in the process of creep are similar in steels 12Kh1MF, 15Kh1M1F, 12Kh2M1, and 14Kh1GMF at 540–565°.

• 2. The service life and consistency of the properties in the course of operation depend mainly on the structure in the original condition. With the optimal bainitic-ferritic structure in the condition as-received the steam pipes of these steels are fairly reliable in operation up to 100,000 h and longer.

• 3. The possibility of steam pipes of Cr-Mo-V and Cr-Mo steels operating for more than 100,000 h depends on the rate of softening processes, which depends on the consistency of the composition of the solid solution, carbide reactions, and the processes of pore formation and rebuilding of dislocation arrays. Each of these factors may have the decisive effect on the accumulation of damage in different stages of creep.

• 4. The condition of the metal before failure is characterized by the mean size of carbides, the distance between them, and the lattice constant of the α solid solution.