Study of connection between the value of crack critical opering and the structure of cast heat-resistant steel after 100 thousand hours of operation

Investigation results on connection of the value of crack critical opening with the structure of metal of turbine vessel details made of the 15Kh1M1FL steel are presented after 100 thousand hours of operation at vapor temperature of 540 deg c and pressure of 13 MPa. It transpiers from electron microscopy investigations that a crack is propagated along the zones of favourable accumulation of carbide precipitations. It is established that structure heterogeneity and presence of carbides at a half and more of a grain boundary length are characteristic for a metal not meeting the requirements of crack critical opening. Some signs of local plastic strain accompanying fracture are discovered in a metal meeting the requirements of crack critical opening. A grain boundary state and a degree of structure heterogeneity are the main factors determining local metal ductility, and hence, its tendency to crack formation both in tests on crack critical opening and during operation