Crack resistance of rotor Cr-Ni-Mo-V steel with a bainitic structure

1. A highly tempered bainitic structure clearly affects fracture toughness KIc and the threshold value for stress intensity factor ΔKth of large forgings for rotors of high-power turbogenerators made of Cr-Ni-Mo-V steel. 2. The fracture toughness KIc of rotor Cr-Ni-Mo-V steel of commercial purity deoxidized with silicon with a structure of highly tempered upper bainite is considerably lower than for steel with a structure of highly tempered lower bainite. 3. A highly tempered structure of upper bainite has a positive effect on fatigue failure resistance in the threshold region. 4. Deoxidation with carbon in a vacuum for silicon-free Cr-Ni-Mo-V steel and comprehensive refining with respect to phosphorus and sulfur leads to marked weakening of the embrittling effect of highly tempered upper bainite and coarsening of the original austenite grain size.