Restoration of the Properties of Heat-Resistant Steel after Long-Term Operation in a Steam Turbine

We analyze the specific features of fracture, structure, and mechanical properties of 25Kh2\M1F heat-resistant steel after 21 center dot 10(4) h of operation under severe temperature-and-force service conditions of the fastening elements of high-pressure cylinder bodies of steam turbines of the thermal power plants (TPP). We optimized the mode of repeated thermal treatment of exploited steel, demonstrated the possibility of restoration of the parameters of hardness, strength, and plasticity to the regulated levels and, which is most important, attained a significant increase in the impact toughness of steel. Hence, we proved the possibility of restoration of the mechanical properties and extension of the lifetime of studs after long-term operation. We plot the correlation dependence between the impact toughness and grain sizes and proposed to use this dependence for the diagnostics of changes in the current engineering state of the metal in the course of operation.

Automated summary

The study reveals that by optimizing the thermal treatment mode, it is possible to restore the hardness, strength, and plasticity parameters of the steel and significantly increase its impact toughness; There is a correlation between the impact toughness of the steel and grain size, which can be used for diagnosing changes in the metal's engineering state during operation.