Substantiation of modes of restorative heat treatment of heat-resistant steel of TPP steam pipeline bend

Restorative heat treatment modes were tested to improve the microstructure of operated heat-resistant steel in the stretched bend zone of the main steam pipeline of a thermal power plant. The change in the number of grains of different sizes along the pipe wall thickness after long-term operation and additional heat treatment was studied. The mode, which consisted of double normalization from 1100 and 960 °C followed by tempering at 740 °C, for restoring the 12Kh1MF steel structure was substantiated. After restorative heat treatment, the share of small grains increased to 55%, and of large grains decreased to 10% throughout the thickness of the pipe wall.