Influence of the carbon content on the phase composition and mechanical properties of P92-type steel

The deformation behavior and the microstructure evolution under the creep of 10Kh9V2MFBR steel (Russian analog of the P92 steel) (in wt %, Fe-8.9% Cr-0.05% Si-0.2% Mn-1.9% W-0.5% Mo-0.25% V-0.07Nb-0.08% N-0.01% B) with the standard (0.1%) and lowered (0.018%) carbon contents have been investigated. After the heat treatment, which included normalizing at 1050A degrees C and tempering at 720-750A degrees C, carbides M (23) C (6) and carbonitrides M(C,N) are formed in the 10Kh9V2MFBR steel, while in the 02Kh9V2MFBR steel (modified P92 steel), carbides M (23) C (6), nitrides M N-2, and carbonitrides M(C,N) as well as delta-ferrite (23%) were found. The measurements of hardness and tensile tests at room and elevated temper-atures did not reveal substantial distinctions in the short-term mechanical properties of both steels. The hardness of steels after tempering was 220 HB. At the same time, the creep characteristics of the steels were found to be different. A decrease in the carbon content leads to an increase in the long-term creep strength and creep limit at 650A degrees C for short-term tests with time-to-fracture shorter than 10(3) h. The time to fracture of steels with various carbon contents is almost the same in long-term creep tests. Factor responsible for such effect of carbon on the creep strength are discussed.